| 1 | |
| 2 |
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| 3 | #include <kunit/visibility.h>
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| 4 | #include <linux/kernel.h>
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| 5 | #include <linux/irqflags.h>
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| 6 | #include <linux/string.h>
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| 7 | #include <linux/errno.h>
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| 8 | #include <linux/bug.h>
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| 9 | #include "printk_ringbuffer.h"
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| 10 | #include "internal.h"
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| 11 |
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| 12 | |
| 13 | * DOC: printk_ringbuffer overview
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| 14 | *
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| 15 | * Data Structure
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| 16 | * --------------
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| 17 | * The printk_ringbuffer is made up of 2 internal ringbuffers:
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| 18 | *
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| 19 | * desc_ring
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| 20 | * A ring of descriptors and their meta data (such as sequence number,
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| 21 | * timestamp, loglevel, etc.) as well as internal state information about
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| 22 | * the record and logical positions specifying where in the other
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| 23 | * ringbuffer the text strings are located.
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| 24 | *
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| 25 | * text_data_ring
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| 26 | * A ring of data blocks. A data block consists of an unsigned long
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| 27 | * integer (ID) that maps to a desc_ring index followed by the text
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| 28 | * string of the record.
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| 29 | *
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| 30 | * The internal state information of a descriptor is the key element to allow
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| 31 | * readers and writers to locklessly synchronize access to the data.
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| 32 | *
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| 33 | * Implementation
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| 34 | * --------------
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| 35 | *
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| 36 | * Descriptor Ring
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| 37 | * ~~~~~~~~~~~~~~~
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| 38 | * The descriptor ring is an array of descriptors. A descriptor contains
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| 39 | * essential meta data to track the data of a printk record using
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| 40 | * blk_lpos structs pointing to associated text data blocks (see
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| 41 | * "Data Rings" below). Each descriptor is assigned an ID that maps
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| 42 | * directly to index values of the descriptor array and has a state. The ID
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| 43 | * and the state are bitwise combined into a single descriptor field named
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| 44 | * @state_var, allowing ID and state to be synchronously and atomically
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| 45 | * updated.
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| 46 | *
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| 47 | * Descriptors have four states:
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| 48 | *
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| 49 | * reserved
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| 50 | * A writer is modifying the record.
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| 51 | *
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| 52 | * committed
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| 53 | * The record and all its data are written. A writer can reopen the
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| 54 | * descriptor (transitioning it back to reserved), but in the committed
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| 55 | * state the data is consistent.
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| 56 | *
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| 57 | * finalized
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| 58 | * The record and all its data are complete and available for reading. A
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| 59 | * writer cannot reopen the descriptor.
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| 60 | *
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| 61 | * reusable
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| 62 | * The record exists, but its text and/or meta data may no longer be
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| 63 | * available.
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| 64 | *
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| 65 | * Querying the @state_var of a record requires providing the ID of the
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| 66 | * descriptor to query. This can yield a possible fifth (pseudo) state:
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| 67 | *
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| 68 | * miss
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| 69 | * The descriptor being queried has an unexpected ID.
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| 70 | *
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| 71 | * The descriptor ring has a @tail_id that contains the ID of the oldest
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| 72 | * descriptor and @head_id that contains the ID of the newest descriptor.
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| 73 | *
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| 74 | * When a new descriptor should be created (and the ring is full), the tail
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| 75 | * descriptor is invalidated by first transitioning to the reusable state and
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| 76 | * then invalidating all tail data blocks up to and including the data blocks
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| 77 | * associated with the tail descriptor (for the text ring). Then
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| 78 | * @tail_id is advanced, followed by advancing @head_id. And finally the
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| 79 | * @state_var of the new descriptor is initialized to the new ID and reserved
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| 80 | * state.
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| 81 | *
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| 82 | * The @tail_id can only be advanced if the new @tail_id would be in the
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| 83 | * committed or reusable queried state. This makes it possible that a valid
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| 84 | * sequence number of the tail is always available.
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| 85 | *
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| 86 | * Descriptor Finalization
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| 87 | * ~~~~~~~~~~~~~~~~~~~~~~~
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| 88 | * When a writer calls the commit function prb_commit(), record data is
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| 89 | * fully stored and is consistent within the ringbuffer. However, a writer can
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| 90 | * reopen that record, claiming exclusive access (as with prb_reserve()), and
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| 91 | * modify that record. When finished, the writer must again commit the record.
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| 92 | *
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| 93 | * In order for a record to be made available to readers (and also become
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| 94 | * recyclable for writers), it must be finalized. A finalized record cannot be
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| 95 | * reopened and can never become "unfinalized". Record finalization can occur
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| 96 | * in three different scenarios:
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| 97 | *
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| 98 | * 1) A writer can simultaneously commit and finalize its record by calling
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| 99 | * prb_final_commit() instead of prb_commit().
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| 100 | *
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| 101 | * 2) When a new record is reserved and the previous record has been
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| 102 | * committed via prb_commit(), that previous record is automatically
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| 103 | * finalized.
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| 104 | *
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| 105 | * 3) When a record is committed via prb_commit() and a newer record
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| 106 | * already exists, the record being committed is automatically finalized.
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| 107 | *
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| 108 | * Data Ring
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| 109 | * ~~~~~~~~~
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| 110 | * The text data ring is a byte array composed of data blocks. Data blocks are
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| 111 | * referenced by blk_lpos structs that point to the logical position of the
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| 112 | * beginning of a data block and the beginning of the next adjacent data
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| 113 | * block. Logical positions are mapped directly to index values of the byte
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| 114 | * array ringbuffer.
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| 115 | *
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| 116 | * Each data block consists of an ID followed by the writer data. The ID is
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| 117 | * the identifier of a descriptor that is associated with the data block. A
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| 118 | * given data block is considered valid if all of the following conditions
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| 119 | * are met:
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| 120 | *
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| 121 | * 1) The descriptor associated with the data block is in the committed
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| 122 | * or finalized queried state.
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| 123 | *
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| 124 | * 2) The blk_lpos struct within the descriptor associated with the data
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| 125 | * block references back to the same data block.
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| 126 | *
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| 127 | * 3) The data block is within the head/tail logical position range.
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| 128 | *
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| 129 | * If the writer data of a data block would extend beyond the end of the
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| 130 | * byte array, only the ID of the data block is stored at the logical
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| 131 | * position and the full data block (ID and writer data) is stored at the
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| 132 | * beginning of the byte array. The referencing blk_lpos will point to the
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| 133 | * ID before the wrap and the next data block will be at the logical
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| 134 | * position adjacent the full data block after the wrap.
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| 135 | *
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| 136 | * Data rings have a @tail_lpos that points to the beginning of the oldest
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| 137 | * data block and a @head_lpos that points to the logical position of the
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| 138 | * next (not yet existing) data block.
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| 139 | *
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| 140 | * When a new data block should be created (and the ring is full), tail data
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| 141 | * blocks will first be invalidated by putting their associated descriptors
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| 142 | * into the reusable state and then pushing the @tail_lpos forward beyond
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| 143 | * them. Then the @head_lpos is pushed forward and is associated with a new
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| 144 | * descriptor. If a data block is not valid, the @tail_lpos cannot be
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| 145 | * advanced beyond it.
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| 146 | *
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| 147 | * Info Array
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| 148 | * ~~~~~~~~~~
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| 149 | * The general meta data of printk records are stored in printk_info structs,
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| 150 | * stored in an array with the same number of elements as the descriptor ring.
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| 151 | * Each info corresponds to the descriptor of the same index in the
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| 152 | * descriptor ring. Info validity is confirmed by evaluating the corresponding
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| 153 | * descriptor before and after loading the info.
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| 154 | *
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| 155 | * Usage
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| 156 | * -----
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| 157 | * Here are some simple examples demonstrating writers and readers. For the
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| 158 | * examples a global ringbuffer (test_rb) is available (which is not the
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| 159 | * actual ringbuffer used by printk)::
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| 160 | *
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| 161 | * DEFINE_PRINTKRB(test_rb, 15, 5);
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| 162 | *
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| 163 | * This ringbuffer allows up to 32768 records (2 ^ 15) and has a size of
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| 164 | * 1 MiB (2 ^ (15 + 5)) for text data.
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| 165 | *
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| 166 | * Sample writer code::
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| 167 | *
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| 168 | * const char *textstr = "message text";
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| 169 | * struct prb_reserved_entry e;
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| 170 | * struct printk_record r;
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| 171 | *
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| 172 | * // specify how much to allocate
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| 173 | * prb_rec_init_wr(&r, strlen(textstr) + 1);
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| 174 | *
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| 175 | * if (prb_reserve(&e, &test_rb, &r)) {
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| 176 | * snprintf(r.text_buf, r.text_buf_size, "%s", textstr);
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| 177 | *
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| 178 | * r.info->text_len = strlen(textstr);
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| 179 | * r.info->ts_nsec = local_clock();
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| 180 | * r.info->caller_id = printk_caller_id();
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| 181 | *
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| 182 | * // commit and finalize the record
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| 183 | * prb_final_commit(&e);
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| 184 | * }
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| 185 | *
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| 186 | * Note that additional writer functions are available to extend a record
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| 187 | * after it has been committed but not yet finalized. This can be done as
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| 188 | * long as no new records have been reserved and the caller is the same.
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| 189 | *
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| 190 | * Sample writer code (record extending)::
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| 191 | *
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| 192 | * // alternate rest of previous example
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| 193 | *
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| 194 | * r.info->text_len = strlen(textstr);
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| 195 | * r.info->ts_nsec = local_clock();
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| 196 | * r.info->caller_id = printk_caller_id();
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| 197 | *
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| 198 | * // commit the record (but do not finalize yet)
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| 199 | * prb_commit(&e);
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| 200 | * }
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| 201 | *
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| 202 | * ...
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| 203 | *
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| 204 | * // specify additional 5 bytes text space to extend
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| 205 | * prb_rec_init_wr(&r, 5);
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| 206 | *
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| 207 | * // try to extend, but only if it does not exceed 32 bytes
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| 208 | * if (prb_reserve_in_last(&e, &test_rb, &r, printk_caller_id(), 32)) {
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| 209 | * snprintf(&r.text_buf[r.info->text_len],
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| 210 | * r.text_buf_size - r.info->text_len, "hello");
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| 211 | *
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| 212 | * r.info->text_len += 5;
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| 213 | *
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| 214 | * // commit and finalize the record
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| 215 | * prb_final_commit(&e);
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| 216 | * }
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| 217 | *
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| 218 | * Sample reader code::
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| 219 | *
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| 220 | * struct printk_info info;
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| 221 | * struct printk_record r;
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| 222 | * char text_buf[32];
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| 223 | * u64 seq;
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| 224 | *
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| 225 | * prb_rec_init_rd(&r, &info, &text_buf[0], sizeof(text_buf));
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| 226 | *
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| 227 | * prb_for_each_record(0, &test_rb, seq, &r) {
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| 228 | * if (info.seq != seq)
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| 229 | * pr_warn("lost %llu records\n", info.seq - seq);
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| 230 | *
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| 231 | * if (info.text_len > r.text_buf_size) {
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| 232 | * pr_warn("record %llu text truncated\n", info.seq);
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| 233 | * text_buf[r.text_buf_size - 1] = 0;
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| 234 | * }
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| 235 | *
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| 236 | * pr_info("%llu: %llu: %s\n", info.seq, info.ts_nsec,
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| 237 | * &text_buf[0]);
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| 238 | * }
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| 239 | *
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| 240 | * Note that additional less convenient reader functions are available to
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| 241 | * allow complex record access.
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| 242 | *
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| 243 | * ABA Issues
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| 244 | * ~~~~~~~~~~
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| 245 | * To help avoid ABA issues, descriptors are referenced by IDs (array index
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| 246 | * values combined with tagged bits counting array wraps) and data blocks are
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| 247 | * referenced by logical positions (array index values combined with tagged
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| 248 | * bits counting array wraps). However, on 32-bit systems the number of
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| 249 | * tagged bits is relatively small such that an ABA incident is (at least
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| 250 | * theoretically) possible. For example, if 4 million maximally sized (1KiB)
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| 251 | * printk messages were to occur in NMI context on a 32-bit system, the
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| 252 | * interrupted context would not be able to recognize that the 32-bit integer
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| 253 | * completely wrapped and thus represents a different data block than the one
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| 254 | * the interrupted context expects.
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| 255 | *
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| 256 | * To help combat this possibility, additional state checking is performed
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| 257 | * (such as using cmpxchg() even though set() would suffice). These extra
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| 258 | * checks are commented as such and will hopefully catch any ABA issue that
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| 259 | * a 32-bit system might experience.
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| 260 | *
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| 261 | * Memory Barriers
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| 262 | * ~~~~~~~~~~~~~~~
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| 263 | * Multiple memory barriers are used. To simplify proving correctness and
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| 264 | * generating litmus tests, lines of code related to memory barriers
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| 265 | * (loads, stores, and the associated memory barriers) are labeled::
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| 266 | *
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| 267 | * LMM(function:letter)
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| 268 | *
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| 269 | * Comments reference the labels using only the "function:letter" part.
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| 270 | *
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| 271 | * The memory barrier pairs and their ordering are:
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| 272 | *
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| 273 | * desc_reserve:D / desc_reserve:B
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| 274 | * push descriptor tail (id), then push descriptor head (id)
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| 275 | *
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| 276 | * desc_reserve:D / data_push_tail:B
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| 277 | * push data tail (lpos), then set new descriptor reserved (state)
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| 278 | *
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| 279 | * desc_reserve:D / desc_push_tail:C
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| 280 | * push descriptor tail (id), then set new descriptor reserved (state)
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| 281 | *
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| 282 | * desc_reserve:D / prb_first_seq:C
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| 283 | * push descriptor tail (id), then set new descriptor reserved (state)
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| 284 | *
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| 285 | * desc_reserve:F / desc_read:D
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| 286 | * set new descriptor id and reserved (state), then allow writer changes
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| 287 | *
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| 288 | * data_alloc:A (or data_realloc:A) / desc_read:D
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| 289 | * set old descriptor reusable (state), then modify new data block area
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| 290 | *
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| 291 | * data_alloc:A (or data_realloc:A) / data_push_tail:B
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| 292 | * push data tail (lpos), then modify new data block area
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| 293 | *
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| 294 | * _prb_commit:B / desc_read:B
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| 295 | * store writer changes, then set new descriptor committed (state)
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| 296 | *
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| 297 | * desc_reopen_last:A / _prb_commit:B
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| 298 | * set descriptor reserved (state), then read descriptor data
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| 299 | *
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| 300 | * _prb_commit:B / desc_reserve:D
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| 301 | * set new descriptor committed (state), then check descriptor head (id)
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| 302 | *
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| 303 | * data_push_tail:D / data_push_tail:A
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| 304 | * set descriptor reusable (state), then push data tail (lpos)
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| 305 | *
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| 306 | * desc_push_tail:B / desc_reserve:D
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| 307 | * set descriptor reusable (state), then push descriptor tail (id)
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| 308 | *
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| 309 | * desc_update_last_finalized:A / desc_last_finalized_seq:A
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| 310 | * store finalized record, then set new highest finalized sequence number
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| 311 |
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| 312 |
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| 313 | #define DATA_SIZE(data_ring) _DATA_SIZE((data_ring)->size_bits)
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| 314 | #define DATA_SIZE_MASK(data_ring) (DATA_SIZE(data_ring) - 1)
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| 315 |
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| 316 | #define DESCS_COUNT(desc_ring) _DESCS_COUNT((desc_ring)->count_bits)
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| 317 | #define DESCS_COUNT_MASK(desc_ring) (DESCS_COUNT(desc_ring) - 1)
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| 318 |
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| 319 |
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| 320 | #define DATA_INDEX(data_ring, lpos) ((lpos) & DATA_SIZE_MASK(data_ring))
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| 321 |
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| 322 |
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| 323 | #define DESC_INDEX(desc_ring, n) ((n) & DESCS_COUNT_MASK(desc_ring))
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| 324 |
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| 325 |
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| 326 | #define DATA_WRAPS(data_ring, lpos) ((lpos) >> (data_ring)->size_bits)
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| 327 |
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| 328 |
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| 329 | #define LPOS_DATALESS(lpos) ((lpos) & 1UL)
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| 330 | #define BLK_DATALESS(blk) (LPOS_DATALESS((blk)->begin) && \
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| 331 | LPOS_DATALESS((blk)->next))
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| 332 |
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| 333 |
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| 334 | #define DATA_THIS_WRAP_START_LPOS(data_ring, lpos) \
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| 335 | ((lpos) & ~DATA_SIZE_MASK(data_ring))
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| 336 |
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| 337 |
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| 338 | #define DESC_ID_PREV_WRAP(desc_ring, id) \
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| 339 | DESC_ID((id) - DESCS_COUNT(desc_ring))
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| 340 |
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| 341 | |
| 342 | * A data block: mapped directly to the beginning of the data block area
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| 343 | * specified as a logical position within the data ring.
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| 344 | *
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| 345 | * @id: the ID of the associated descriptor
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| 346 | * @data: the writer data
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| 347 | *
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| 348 | * Note that the size of a data block is only known by its associated
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| 349 | * descriptor.
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| 350 |
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| 351 | struct prb_data_block {
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| 352 | unsigned long id;
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| 353 | char data[];
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| 354 | };
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| 355 |
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| 356 | |
| 357 | * Return the descriptor associated with @n. @n can be either a
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| 358 | * descriptor ID or a sequence number.
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| 359 |
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| 360 | static struct prb_desc *to_desc(struct prb_desc_ring *desc_ring, u64 n)
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| 361 | {
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| 362 | return &desc_ring->descs[DESC_INDEX(desc_ring, n)];
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| 363 | }
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| 364 |
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| 365 | |
| 366 | * Return the printk_info associated with @n. @n can be either a
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| 367 | * descriptor ID or a sequence number.
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| 368 |
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| 369 | static struct printk_info *to_info(struct prb_desc_ring *desc_ring, u64 n)
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| 370 | {
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| 371 | return &desc_ring->infos[DESC_INDEX(desc_ring, n)];
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| 372 | }
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| 373 |
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| 374 | static struct prb_data_block *to_block(struct prb_data_ring *data_ring,
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| 375 | unsigned long begin_lpos)
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| 376 | {
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| 377 | return (void *)&data_ring->data[DATA_INDEX(data_ring, begin_lpos)];
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| 378 | }
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| 379 |
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| 380 | |
| 381 | * Increase the data size to account for data block meta data plus any
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| 382 | * padding so that the adjacent data block is aligned on the ID size.
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| 383 |
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| 384 | static unsigned int to_blk_size(unsigned int size)
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| 385 | {
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| 386 | struct prb_data_block *db = NULL;
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| 387 |
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| 388 | size += sizeof(*db);
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| 389 | size = ALIGN(size, sizeof(db->id));
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| 390 | return size;
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| 391 | }
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| 392 |
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| 393 | |
| 394 | * Sanity checker for reserve size. The ringbuffer code assumes that a data
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| 395 | * block does not exceed the maximum possible size that could fit within the
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| 396 | * ringbuffer. This function provides that basic size check so that the
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| 397 | * assumption is safe. In particular, it guarantees that data_push_tail() will
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| 398 | * never attempt to push the tail beyond the head.
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| 399 |
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| 400 | static bool data_check_size(struct prb_data_ring *data_ring, unsigned int size)
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| 401 | {
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| 402 |
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| 403 | if (size == 0)
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| 404 | return true;
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| 405 |
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| 406 | |
| 407 | * If data blocks were allowed to be larger than half the data ring
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| 408 | * size, a wrapping data block could require more space than the full
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| 409 | * ringbuffer.
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| 410 |
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| 411 | return to_blk_size(size) <= DATA_SIZE(data_ring) / 2;
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| 412 | }
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| 413 |
|
| 414 | |
| 415 | * Compare the current and requested logical position and decide
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| 416 | * whether more space is needed.
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| 417 | *
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| 418 | * Return false when @lpos_current is already at or beyond @lpos_target.
|
| 419 | *
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| 420 | * Also return false when the difference between the positions is bigger
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| 421 | * than the size of the data buffer. It might happen only when the caller
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| 422 | * raced with another CPU(s) which already made and used the space.
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| 423 |
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| 424 | static bool need_more_space(struct prb_data_ring *data_ring,
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| 425 | unsigned long lpos_current,
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| 426 | unsigned long lpos_target)
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| 427 | {
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| 428 | return lpos_target - lpos_current - 1 < DATA_SIZE(data_ring);
|
| 429 | }
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| 430 |
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| 431 |
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| 432 | static enum desc_state get_desc_state(unsigned long id,
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| 433 | unsigned long state_val)
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| 434 | {
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| 435 | if (id != DESC_ID(state_val))
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| 436 | return desc_miss;
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| 437 |
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| 438 | return DESC_STATE(state_val);
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| 439 | }
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| 440 |
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| 441 | |
| 442 | * Get a copy of a specified descriptor and return its queried state. If the
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| 443 | * descriptor is in an inconsistent state (miss or reserved), the caller can
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| 444 | * only expect the descriptor's @state_var field to be valid.
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| 445 | *
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| 446 | * The sequence number and caller_id can be optionally retrieved. Like all
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| 447 | * non-state_var data, they are only valid if the descriptor is in a
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| 448 | * consistent state.
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| 449 |
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| 450 | static enum desc_state desc_read(struct prb_desc_ring *desc_ring,
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| 451 | unsigned long id, struct prb_desc *desc_out,
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| 452 | u64 *seq_out, u32 *caller_id_out)
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| 453 | {
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| 454 | struct printk_info *info = to_info(desc_ring, id);
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| 455 | struct prb_desc *desc = to_desc(desc_ring, id);
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| 456 | atomic_long_t *state_var = &desc->state_var;
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| 457 | enum desc_state d_state;
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| 458 | unsigned long state_val;
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| 459 |
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| 460 |
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| 461 | state_val = atomic_long_read(state_var);
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| 462 | d_state = get_desc_state(id, state_val);
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| 463 | if (d_state == desc_miss || d_state == desc_reserved) {
|
| 464 | |
| 465 | * The descriptor is in an inconsistent state. Set at least
|
| 466 | * @state_var so that the caller can see the details of
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| 467 | * the inconsistent state.
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| 468 |
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| 469 | goto out;
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| 470 | }
|
| 471 |
|
| 472 | |
| 473 | * Guarantee the state is loaded before copying the descriptor
|
| 474 | * content. This avoids copying obsolete descriptor content that might
|
| 475 | * not apply to the descriptor state. This pairs with _prb_commit:B.
|
| 476 | *
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| 477 | * Memory barrier involvement:
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| 478 | *
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| 479 | * If desc_read:A reads from _prb_commit:B, then desc_read:C reads
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| 480 | * from _prb_commit:A.
|
| 481 | *
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| 482 | * Relies on:
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| 483 | *
|
| 484 | * WMB from _prb_commit:A to _prb_commit:B
|
| 485 | * matching
|
| 486 | * RMB from desc_read:A to desc_read:C
|
| 487 |
|
| 488 | smp_rmb();
|
| 489 |
|
| 490 | |
| 491 | * Copy the descriptor data. The data is not valid until the
|
| 492 | * state has been re-checked. A memcpy() for all of @desc
|
| 493 | * cannot be used because of the atomic_t @state_var field.
|
| 494 |
|
| 495 | if (desc_out) {
|
| 496 | memcpy(&desc_out->text_blk_lpos, &desc->text_blk_lpos,
|
| 497 | sizeof(desc_out->text_blk_lpos));
|
| 498 | }
|
| 499 | if (seq_out)
|
| 500 | *seq_out = info->seq;
|
| 501 | if (caller_id_out)
|
| 502 | *caller_id_out = info->caller_id;
|
| 503 |
|
| 504 | |
| 505 | * 1. Guarantee the descriptor content is loaded before re-checking
|
| 506 | * the state. This avoids reading an obsolete descriptor state
|
| 507 | * that may not apply to the copied content. This pairs with
|
| 508 | * desc_reserve:F.
|
| 509 | *
|
| 510 | * Memory barrier involvement:
|
| 511 | *
|
| 512 | * If desc_read:C reads from desc_reserve:G, then desc_read:E
|
| 513 | * reads from desc_reserve:F.
|
| 514 | *
|
| 515 | * Relies on:
|
| 516 | *
|
| 517 | * WMB from desc_reserve:F to desc_reserve:G
|
| 518 | * matching
|
| 519 | * RMB from desc_read:C to desc_read:E
|
| 520 | *
|
| 521 | * 2. Guarantee the record data is loaded before re-checking the
|
| 522 | * state. This avoids reading an obsolete descriptor state that may
|
| 523 | * not apply to the copied data. This pairs with data_alloc:A and
|
| 524 | * data_realloc:A.
|
| 525 | *
|
| 526 | * Memory barrier involvement:
|
| 527 | *
|
| 528 | * If copy_data:A reads from data_alloc:B, then desc_read:E
|
| 529 | * reads from desc_make_reusable:A.
|
| 530 | *
|
| 531 | * Relies on:
|
| 532 | *
|
| 533 | * MB from desc_make_reusable:A to data_alloc:B
|
| 534 | * matching
|
| 535 | * RMB from desc_read:C to desc_read:E
|
| 536 | *
|
| 537 | * Note: desc_make_reusable:A and data_alloc:B can be different
|
| 538 | * CPUs. However, the data_alloc:B CPU (which performs the
|
| 539 | * full memory barrier) must have previously seen
|
| 540 | * desc_make_reusable:A.
|
| 541 |
|
| 542 | smp_rmb();
|
| 543 |
|
| 544 | |
| 545 | * The data has been copied. Return the current descriptor state,
|
| 546 | * which may have changed since the load above.
|
| 547 |
|
| 548 | state_val = atomic_long_read(state_var);
|
| 549 | d_state = get_desc_state(id, state_val);
|
| 550 | out:
|
| 551 | if (desc_out)
|
| 552 | atomic_long_set(&desc_out->state_var, state_val);
|
| 553 | return d_state;
|
| 554 | }
|
| 555 |
|
| 556 | |
| 557 | * Take a specified descriptor out of the finalized state by attempting
|
| 558 | * the transition from finalized to reusable. Either this context or some
|
| 559 | * other context will have been successful.
|
| 560 |
|
| 561 | static void desc_make_reusable(struct prb_desc_ring *desc_ring,
|
| 562 | unsigned long id)
|
| 563 | {
|
| 564 | unsigned long val_finalized = DESC_SV(id, desc_finalized);
|
| 565 | unsigned long val_reusable = DESC_SV(id, desc_reusable);
|
| 566 | struct prb_desc *desc = to_desc(desc_ring, id);
|
| 567 | atomic_long_t *state_var = &desc->state_var;
|
| 568 |
|
| 569 | atomic_long_cmpxchg_relaxed(state_var, val_finalized,
|
| 570 | val_reusable);
|
| 571 | }
|
| 572 |
|
| 573 | |
| 574 | * Given the text data ring, put the associated descriptor of each
|
| 575 | * data block from @lpos_begin until @lpos_end into the reusable state.
|
| 576 | *
|
| 577 | * If there is any problem making the associated descriptor reusable, either
|
| 578 | * the descriptor has not yet been finalized or another writer context has
|
| 579 | * already pushed the tail lpos past the problematic data block. Regardless,
|
| 580 | * on error the caller can re-load the tail lpos to determine the situation.
|
| 581 |
|
| 582 | static bool data_make_reusable(struct printk_ringbuffer *rb,
|
| 583 | unsigned long lpos_begin,
|
| 584 | unsigned long lpos_end,
|
| 585 | unsigned long *lpos_out)
|
| 586 | {
|
| 587 |
|
| 588 | struct prb_data_ring *data_ring = &rb->text_data_ring;
|
| 589 | struct prb_desc_ring *desc_ring = &rb->desc_ring;
|
| 590 | struct prb_data_block *blk;
|
| 591 | enum desc_state d_state;
|
| 592 | struct prb_desc desc;
|
| 593 | struct prb_data_blk_lpos *blk_lpos = &desc.text_blk_lpos;
|
| 594 | unsigned long id;
|
| 595 |
|
| 596 |
|
| 597 | while (need_more_space(data_ring, lpos_begin, lpos_end)) {
|
| 598 | blk = to_block(data_ring, lpos_begin);
|
| 599 |
|
| 600 | |
| 601 | * Load the block ID from the data block. This is a data race
|
| 602 | * against a writer that may have newly reserved this data
|
| 603 | * area. If the loaded value matches a valid descriptor ID,
|
| 604 | * the blk_lpos of that descriptor will be checked to make
|
| 605 | * sure it points back to this data block. If the check fails,
|
| 606 | * the data area has been recycled by another writer.
|
| 607 |
|
| 608 | id = blk->id;
|
| 609 |
|
| 610 | d_state = desc_read(desc_ring, id, &desc,
|
| 611 | NULL, NULL);
|
| 612 |
|
| 613 | switch (d_state) {
|
| 614 | case desc_miss:
|
| 615 | case desc_reserved:
|
| 616 | case desc_committed:
|
| 617 | return false;
|
| 618 | case desc_finalized:
|
| 619 | |
| 620 | * This data block is invalid if the descriptor
|
| 621 | * does not point back to it.
|
| 622 |
|
| 623 | if (blk_lpos->begin != lpos_begin)
|
| 624 | return false;
|
| 625 | desc_make_reusable(desc_ring, id);
|
| 626 | break;
|
| 627 | case desc_reusable:
|
| 628 | |
| 629 | * This data block is invalid if the descriptor
|
| 630 | * does not point back to it.
|
| 631 |
|
| 632 | if (blk_lpos->begin != lpos_begin)
|
| 633 | return false;
|
| 634 | break;
|
| 635 | }
|
| 636 |
|
| 637 |
|
| 638 | lpos_begin = blk_lpos->next;
|
| 639 | }
|
| 640 |
|
| 641 | *lpos_out = lpos_begin;
|
| 642 | return true;
|
| 643 | }
|
| 644 |
|
| 645 | |
| 646 | * Advance the data ring tail to at least @lpos. This function puts
|
| 647 | * descriptors into the reusable state if the tail is pushed beyond
|
| 648 | * their associated data block.
|
| 649 |
|
| 650 | static bool data_push_tail(struct printk_ringbuffer *rb, unsigned long lpos)
|
| 651 | {
|
| 652 | struct prb_data_ring *data_ring = &rb->text_data_ring;
|
| 653 | unsigned long tail_lpos_new;
|
| 654 | unsigned long tail_lpos;
|
| 655 | unsigned long next_lpos;
|
| 656 |
|
| 657 |
|
| 658 | if (LPOS_DATALESS(lpos))
|
| 659 | return true;
|
| 660 |
|
| 661 | |
| 662 | * Any descriptor states that have transitioned to reusable due to the
|
| 663 | * data tail being pushed to this loaded value will be visible to this
|
| 664 | * CPU. This pairs with data_push_tail:D.
|
| 665 | *
|
| 666 | * Memory barrier involvement:
|
| 667 | *
|
| 668 | * If data_push_tail:A reads from data_push_tail:D, then this CPU can
|
| 669 | * see desc_make_reusable:A.
|
| 670 | *
|
| 671 | * Relies on:
|
| 672 | *
|
| 673 | * MB from desc_make_reusable:A to data_push_tail:D
|
| 674 | * matches
|
| 675 | * READFROM from data_push_tail:D to data_push_tail:A
|
| 676 | * thus
|
| 677 | * READFROM from desc_make_reusable:A to this CPU
|
| 678 |
|
| 679 | tail_lpos = atomic_long_read(&data_ring->tail_lpos);
|
| 680 |
|
| 681 | |
| 682 | * Loop until the tail lpos is at or beyond @lpos. This condition
|
| 683 | * may already be satisfied, resulting in no full memory barrier
|
| 684 | * from data_push_tail:D being performed. However, since this CPU
|
| 685 | * sees the new tail lpos, any descriptor states that transitioned to
|
| 686 | * the reusable state must already be visible.
|
| 687 |
|
| 688 | while (need_more_space(data_ring, tail_lpos, lpos)) {
|
| 689 | |
| 690 | * Make all descriptors reusable that are associated with
|
| 691 | * data blocks before @lpos.
|
| 692 |
|
| 693 | if (!data_make_reusable(rb, tail_lpos, lpos, &next_lpos)) {
|
| 694 | |
| 695 | * 1. Guarantee the block ID loaded in
|
| 696 | * data_make_reusable() is performed before
|
| 697 | * reloading the tail lpos. The failed
|
| 698 | * data_make_reusable() may be due to a newly
|
| 699 | * recycled data area causing the tail lpos to
|
| 700 | * have been previously pushed. This pairs with
|
| 701 | * data_alloc:A and data_realloc:A.
|
| 702 | *
|
| 703 | * Memory barrier involvement:
|
| 704 | *
|
| 705 | * If data_make_reusable:A reads from data_alloc:B,
|
| 706 | * then data_push_tail:C reads from
|
| 707 | * data_push_tail:D.
|
| 708 | *
|
| 709 | * Relies on:
|
| 710 | *
|
| 711 | * MB from data_push_tail:D to data_alloc:B
|
| 712 | * matching
|
| 713 | * RMB from data_make_reusable:A to
|
| 714 | * data_push_tail:C
|
| 715 | *
|
| 716 | * Note: data_push_tail:D and data_alloc:B can be
|
| 717 | * different CPUs. However, the data_alloc:B
|
| 718 | * CPU (which performs the full memory
|
| 719 | * barrier) must have previously seen
|
| 720 | * data_push_tail:D.
|
| 721 | *
|
| 722 | * 2. Guarantee the descriptor state loaded in
|
| 723 | * data_make_reusable() is performed before
|
| 724 | * reloading the tail lpos. The failed
|
| 725 | * data_make_reusable() may be due to a newly
|
| 726 | * recycled descriptor causing the tail lpos to
|
| 727 | * have been previously pushed. This pairs with
|
| 728 | * desc_reserve:D.
|
| 729 | *
|
| 730 | * Memory barrier involvement:
|
| 731 | *
|
| 732 | * If data_make_reusable:B reads from
|
| 733 | * desc_reserve:F, then data_push_tail:C reads
|
| 734 | * from data_push_tail:D.
|
| 735 | *
|
| 736 | * Relies on:
|
| 737 | *
|
| 738 | * MB from data_push_tail:D to desc_reserve:F
|
| 739 | * matching
|
| 740 | * RMB from data_make_reusable:B to
|
| 741 | * data_push_tail:C
|
| 742 | *
|
| 743 | * Note: data_push_tail:D and desc_reserve:F can
|
| 744 | * be different CPUs. However, the
|
| 745 | * desc_reserve:F CPU (which performs the
|
| 746 | * full memory barrier) must have previously
|
| 747 | * seen data_push_tail:D.
|
| 748 |
|
| 749 | smp_rmb();
|
| 750 |
|
| 751 | tail_lpos_new = atomic_long_read(&data_ring->tail_lpos
|
| 752 | );
|
| 753 | if (tail_lpos_new == tail_lpos)
|
| 754 | return false;
|
| 755 |
|
| 756 |
|
| 757 | tail_lpos = tail_lpos_new;
|
| 758 | continue;
|
| 759 | }
|
| 760 |
|
| 761 | |
| 762 | * Guarantee any descriptor states that have transitioned to
|
| 763 | * reusable are stored before pushing the tail lpos. A full
|
| 764 | * memory barrier is needed since other CPUs may have made
|
| 765 | * the descriptor states reusable. This pairs with
|
| 766 | * data_push_tail:A.
|
| 767 |
|
| 768 | if (atomic_long_try_cmpxchg(&data_ring->tail_lpos, &tail_lpos,
|
| 769 | next_lpos)) {
|
| 770 | break;
|
| 771 | }
|
| 772 | }
|
| 773 |
|
| 774 | return true;
|
| 775 | }
|
| 776 |
|
| 777 | |
| 778 | * Advance the desc ring tail. This function advances the tail by one
|
| 779 | * descriptor, thus invalidating the oldest descriptor. Before advancing
|
| 780 | * the tail, the tail descriptor is made reusable and all data blocks up to
|
| 781 | * and including the descriptor's data block are invalidated (i.e. the data
|
| 782 | * ring tail is pushed past the data block of the descriptor being made
|
| 783 | * reusable).
|
| 784 |
|
| 785 | static bool desc_push_tail(struct printk_ringbuffer *rb,
|
| 786 | unsigned long tail_id)
|
| 787 | {
|
| 788 | struct prb_desc_ring *desc_ring = &rb->desc_ring;
|
| 789 | enum desc_state d_state;
|
| 790 | struct prb_desc desc;
|
| 791 |
|
| 792 | d_state = desc_read(desc_ring, tail_id, &desc, NULL, NULL);
|
| 793 |
|
| 794 | switch (d_state) {
|
| 795 | case desc_miss:
|
| 796 | |
| 797 | * If the ID is exactly 1 wrap behind the expected, it is
|
| 798 | * in the process of being reserved by another writer and
|
| 799 | * must be considered reserved.
|
| 800 |
|
| 801 | if (DESC_ID(atomic_long_read(&desc.state_var)) ==
|
| 802 | DESC_ID_PREV_WRAP(desc_ring, tail_id)) {
|
| 803 | return false;
|
| 804 | }
|
| 805 |
|
| 806 | |
| 807 | * The ID has changed. Another writer must have pushed the
|
| 808 | * tail and recycled the descriptor already. Success is
|
| 809 | * returned because the caller is only interested in the
|
| 810 | * specified tail being pushed, which it was.
|
| 811 |
|
| 812 | return true;
|
| 813 | case desc_reserved:
|
| 814 | case desc_committed:
|
| 815 | return false;
|
| 816 | case desc_finalized:
|
| 817 | desc_make_reusable(desc_ring, tail_id);
|
| 818 | break;
|
| 819 | case desc_reusable:
|
| 820 | break;
|
| 821 | }
|
| 822 |
|
| 823 | |
| 824 | * Data blocks must be invalidated before their associated
|
| 825 | * descriptor can be made available for recycling. Invalidating
|
| 826 | * them later is not possible because there is no way to trust
|
| 827 | * data blocks once their associated descriptor is gone.
|
| 828 |
|
| 829 |
|
| 830 | if (!data_push_tail(rb, desc.text_blk_lpos.next))
|
| 831 | return false;
|
| 832 |
|
| 833 | |
| 834 | * Check the next descriptor after @tail_id before pushing the tail
|
| 835 | * to it because the tail must always be in a finalized or reusable
|
| 836 | * state. The implementation of prb_first_seq() relies on this.
|
| 837 | *
|
| 838 | * A successful read implies that the next descriptor is less than or
|
| 839 | * equal to @head_id so there is no risk of pushing the tail past the
|
| 840 | * head.
|
| 841 |
|
| 842 | d_state = desc_read(desc_ring, DESC_ID(tail_id + 1), &desc,
|
| 843 | NULL, NULL);
|
| 844 |
|
| 845 | if (d_state == desc_finalized || d_state == desc_reusable) {
|
| 846 | |
| 847 | * Guarantee any descriptor states that have transitioned to
|
| 848 | * reusable are stored before pushing the tail ID. This allows
|
| 849 | * verifying the recycled descriptor state. A full memory
|
| 850 | * barrier is needed since other CPUs may have made the
|
| 851 | * descriptor states reusable. This pairs with desc_reserve:D.
|
| 852 |
|
| 853 | atomic_long_cmpxchg(&desc_ring->tail_id, tail_id,
|
| 854 | DESC_ID(tail_id + 1));
|
| 855 | } else {
|
| 856 | |
| 857 | * Guarantee the last state load from desc_read() is before
|
| 858 | * reloading @tail_id in order to see a new tail ID in the
|
| 859 | * case that the descriptor has been recycled. This pairs
|
| 860 | * with desc_reserve:D.
|
| 861 | *
|
| 862 | * Memory barrier involvement:
|
| 863 | *
|
| 864 | * If desc_push_tail:A reads from desc_reserve:F, then
|
| 865 | * desc_push_tail:D reads from desc_push_tail:B.
|
| 866 | *
|
| 867 | * Relies on:
|
| 868 | *
|
| 869 | * MB from desc_push_tail:B to desc_reserve:F
|
| 870 | * matching
|
| 871 | * RMB from desc_push_tail:A to desc_push_tail:D
|
| 872 | *
|
| 873 | * Note: desc_push_tail:B and desc_reserve:F can be different
|
| 874 | * CPUs. However, the desc_reserve:F CPU (which performs
|
| 875 | * the full memory barrier) must have previously seen
|
| 876 | * desc_push_tail:B.
|
| 877 |
|
| 878 | smp_rmb();
|
| 879 |
|
| 880 | |
| 881 | * Re-check the tail ID. The descriptor following @tail_id is
|
| 882 | * not in an allowed tail state. But if the tail has since
|
| 883 | * been moved by another CPU, then it does not matter.
|
| 884 |
|
| 885 | if (atomic_long_read(&desc_ring->tail_id) == tail_id)
|
| 886 | return false;
|
| 887 | }
|
| 888 |
|
| 889 | return true;
|
| 890 | }
|
| 891 |
|
| 892 |
|
| 893 | static bool desc_reserve(struct printk_ringbuffer *rb, unsigned long *id_out)
|
| 894 | {
|
| 895 | struct prb_desc_ring *desc_ring = &rb->desc_ring;
|
| 896 | unsigned long prev_state_val;
|
| 897 | unsigned long id_prev_wrap;
|
| 898 | struct prb_desc *desc;
|
| 899 | unsigned long head_id;
|
| 900 | unsigned long id;
|
| 901 |
|
| 902 | head_id = atomic_long_read(&desc_ring->head_id);
|
| 903 |
|
| 904 | do {
|
| 905 | id = DESC_ID(head_id + 1);
|
| 906 | id_prev_wrap = DESC_ID_PREV_WRAP(desc_ring, id);
|
| 907 |
|
| 908 | |
| 909 | * Guarantee the head ID is read before reading the tail ID.
|
| 910 | * Since the tail ID is updated before the head ID, this
|
| 911 | * guarantees that @id_prev_wrap is never ahead of the tail
|
| 912 | * ID. This pairs with desc_reserve:D.
|
| 913 | *
|
| 914 | * Memory barrier involvement:
|
| 915 | *
|
| 916 | * If desc_reserve:A reads from desc_reserve:D, then
|
| 917 | * desc_reserve:C reads from desc_push_tail:B.
|
| 918 | *
|
| 919 | * Relies on:
|
| 920 | *
|
| 921 | * MB from desc_push_tail:B to desc_reserve:D
|
| 922 | * matching
|
| 923 | * RMB from desc_reserve:A to desc_reserve:C
|
| 924 | *
|
| 925 | * Note: desc_push_tail:B and desc_reserve:D can be different
|
| 926 | * CPUs. However, the desc_reserve:D CPU (which performs
|
| 927 | * the full memory barrier) must have previously seen
|
| 928 | * desc_push_tail:B.
|
| 929 |
|
| 930 | smp_rmb();
|
| 931 |
|
| 932 | if (id_prev_wrap == atomic_long_read(&desc_ring->tail_id
|
| 933 | )) {
|
| 934 | |
| 935 | * Make space for the new descriptor by
|
| 936 | * advancing the tail.
|
| 937 |
|
| 938 | if (!desc_push_tail(rb, id_prev_wrap))
|
| 939 | return false;
|
| 940 | }
|
| 941 |
|
| 942 | |
| 943 | * 1. Guarantee the tail ID is read before validating the
|
| 944 | * recycled descriptor state. A read memory barrier is
|
| 945 | * sufficient for this. This pairs with desc_push_tail:B.
|
| 946 | *
|
| 947 | * Memory barrier involvement:
|
| 948 | *
|
| 949 | * If desc_reserve:C reads from desc_push_tail:B, then
|
| 950 | * desc_reserve:E reads from desc_make_reusable:A.
|
| 951 | *
|
| 952 | * Relies on:
|
| 953 | *
|
| 954 | * MB from desc_make_reusable:A to desc_push_tail:B
|
| 955 | * matching
|
| 956 | * RMB from desc_reserve:C to desc_reserve:E
|
| 957 | *
|
| 958 | * Note: desc_make_reusable:A and desc_push_tail:B can be
|
| 959 | * different CPUs. However, the desc_push_tail:B CPU
|
| 960 | * (which performs the full memory barrier) must have
|
| 961 | * previously seen desc_make_reusable:A.
|
| 962 | *
|
| 963 | * 2. Guarantee the tail ID is stored before storing the head
|
| 964 | * ID. This pairs with desc_reserve:B.
|
| 965 | *
|
| 966 | * 3. Guarantee any data ring tail changes are stored before
|
| 967 | * recycling the descriptor. Data ring tail changes can
|
| 968 | * happen via desc_push_tail()->data_push_tail(). A full
|
| 969 | * memory barrier is needed since another CPU may have
|
| 970 | * pushed the data ring tails. This pairs with
|
| 971 | * data_push_tail:B.
|
| 972 | *
|
| 973 | * 4. Guarantee a new tail ID is stored before recycling the
|
| 974 | * descriptor. A full memory barrier is needed since
|
| 975 | * another CPU may have pushed the tail ID. This pairs
|
| 976 | * with desc_push_tail:C and this also pairs with
|
| 977 | * prb_first_seq:C.
|
| 978 | *
|
| 979 | * 5. Guarantee the head ID is stored before trying to
|
| 980 | * finalize the previous descriptor. This pairs with
|
| 981 | * _prb_commit:B.
|
| 982 |
|
| 983 | } while (!atomic_long_try_cmpxchg(&desc_ring->head_id, &head_id,
|
| 984 | id));
|
| 985 |
|
| 986 | desc = to_desc(desc_ring, id);
|
| 987 |
|
| 988 | |
| 989 | * If the descriptor has been recycled, verify the old state val.
|
| 990 | * See "ABA Issues" about why this verification is performed.
|
| 991 |
|
| 992 | prev_state_val = atomic_long_read(&desc->state_var);
|
| 993 | if (prev_state_val &&
|
| 994 | get_desc_state(id_prev_wrap, prev_state_val) != desc_reusable) {
|
| 995 | WARN_ON_ONCE(1);
|
| 996 | return false;
|
| 997 | }
|
| 998 |
|
| 999 | |
| 1000 | * Assign the descriptor a new ID and set its state to reserved.
|
| 1001 | * See "ABA Issues" about why cmpxchg() instead of set() is used.
|
| 1002 | *
|
| 1003 | * Guarantee the new descriptor ID and state is stored before making
|
| 1004 | * any other changes. A write memory barrier is sufficient for this.
|
| 1005 | * This pairs with desc_read:D.
|
| 1006 |
|
| 1007 | if (!atomic_long_try_cmpxchg(&desc->state_var, &prev_state_val,
|
| 1008 | DESC_SV(id, desc_reserved))) {
|
| 1009 | WARN_ON_ONCE(1);
|
| 1010 | return false;
|
| 1011 | }
|
| 1012 |
|
| 1013 |
|
| 1014 |
|
| 1015 | *id_out = id;
|
| 1016 | return true;
|
| 1017 | }
|
| 1018 |
|
| 1019 | static bool is_blk_wrapped(struct prb_data_ring *data_ring,
|
| 1020 | unsigned long begin_lpos, unsigned long next_lpos)
|
| 1021 | {
|
| 1022 | |
| 1023 | * Subtract one from next_lpos since it's not actually part of this data
|
| 1024 | * block. This allows perfectly fitting records to not wrap.
|
| 1025 |
|
| 1026 | return DATA_WRAPS(data_ring, begin_lpos) !=
|
| 1027 | DATA_WRAPS(data_ring, next_lpos - 1);
|
| 1028 | }
|
| 1029 |
|
| 1030 |
|
| 1031 | static unsigned long get_next_lpos(struct prb_data_ring *data_ring,
|
| 1032 | unsigned long lpos, unsigned int size)
|
| 1033 | {
|
| 1034 | unsigned long begin_lpos;
|
| 1035 | unsigned long next_lpos;
|
| 1036 |
|
| 1037 | begin_lpos = lpos;
|
| 1038 | next_lpos = lpos + size;
|
| 1039 |
|
| 1040 |
|
| 1041 | if (!is_blk_wrapped(data_ring, begin_lpos, next_lpos))
|
| 1042 | return next_lpos;
|
| 1043 |
|
| 1044 |
|
| 1045 | return (DATA_THIS_WRAP_START_LPOS(data_ring, next_lpos) + size);
|
| 1046 | }
|
| 1047 |
|
| 1048 | |
| 1049 | * Allocate a new data block, invalidating the oldest data block(s)
|
| 1050 | * if necessary. This function also associates the data block with
|
| 1051 | * a specified descriptor.
|
| 1052 |
|
| 1053 | static char *data_alloc(struct printk_ringbuffer *rb, unsigned int size,
|
| 1054 | struct prb_data_blk_lpos *blk_lpos, unsigned long id)
|
| 1055 | {
|
| 1056 | struct prb_data_ring *data_ring = &rb->text_data_ring;
|
| 1057 | struct prb_data_block *blk;
|
| 1058 | unsigned long begin_lpos;
|
| 1059 | unsigned long next_lpos;
|
| 1060 |
|
| 1061 | if (size == 0) {
|
| 1062 | |
| 1063 | * Data blocks are not created for empty lines. Instead, the
|
| 1064 | * reader will recognize these special lpos values and handle
|
| 1065 | * it appropriately.
|
| 1066 |
|
| 1067 | blk_lpos->begin = EMPTY_LINE_LPOS;
|
| 1068 | blk_lpos->next = EMPTY_LINE_LPOS;
|
| 1069 | return NULL;
|
| 1070 | }
|
| 1071 |
|
| 1072 | size = to_blk_size(size);
|
| 1073 |
|
| 1074 | begin_lpos = atomic_long_read(&data_ring->head_lpos);
|
| 1075 |
|
| 1076 | do {
|
| 1077 | next_lpos = get_next_lpos(data_ring, begin_lpos, size);
|
| 1078 |
|
| 1079 | |
| 1080 | * data_check_size() prevents data block allocation that could
|
| 1081 | * cause illegal ringbuffer states. But double check that the
|
| 1082 | * used space will not be bigger than the ring buffer. Wrapped
|
| 1083 | * messages need to reserve more space, see get_next_lpos().
|
| 1084 | *
|
| 1085 | * Specify a data-less block when the check or the allocation
|
| 1086 | * fails.
|
| 1087 |
|
| 1088 | if (WARN_ON_ONCE(next_lpos - begin_lpos > DATA_SIZE(data_ring)) ||
|
| 1089 | !data_push_tail(rb, next_lpos - DATA_SIZE(data_ring))) {
|
| 1090 | blk_lpos->begin = FAILED_LPOS;
|
| 1091 | blk_lpos->next = FAILED_LPOS;
|
| 1092 | return NULL;
|
| 1093 | }
|
| 1094 |
|
| 1095 | |
| 1096 | * 1. Guarantee any descriptor states that have transitioned
|
| 1097 | * to reusable are stored before modifying the newly
|
| 1098 | * allocated data area. A full memory barrier is needed
|
| 1099 | * since other CPUs may have made the descriptor states
|
| 1100 | * reusable. See data_push_tail:A about why the reusable
|
| 1101 | * states are visible. This pairs with desc_read:D.
|
| 1102 | *
|
| 1103 | * 2. Guarantee any updated tail lpos is stored before
|
| 1104 | * modifying the newly allocated data area. Another CPU may
|
| 1105 | * be in data_make_reusable() and is reading a block ID
|
| 1106 | * from this area. data_make_reusable() can handle reading
|
| 1107 | * a garbage block ID value, but then it must be able to
|
| 1108 | * load a new tail lpos. A full memory barrier is needed
|
| 1109 | * since other CPUs may have updated the tail lpos. This
|
| 1110 | * pairs with data_push_tail:B.
|
| 1111 |
|
| 1112 | } while (!atomic_long_try_cmpxchg(&data_ring->head_lpos, &begin_lpos,
|
| 1113 | next_lpos));
|
| 1114 |
|
| 1115 | blk = to_block(data_ring, begin_lpos);
|
| 1116 | blk->id = id;
|
| 1117 |
|
| 1118 | if (is_blk_wrapped(data_ring, begin_lpos, next_lpos)) {
|
| 1119 |
|
| 1120 | blk = to_block(data_ring, 0);
|
| 1121 |
|
| 1122 | |
| 1123 | * Store the ID on the wrapped block for consistency.
|
| 1124 | * The printk_ringbuffer does not actually use it.
|
| 1125 |
|
| 1126 | blk->id = id;
|
| 1127 | }
|
| 1128 |
|
| 1129 | blk_lpos->begin = begin_lpos;
|
| 1130 | blk_lpos->next = next_lpos;
|
| 1131 |
|
| 1132 | return &blk->data[0];
|
| 1133 | }
|
| 1134 |
|
| 1135 | |
| 1136 | * Try to resize an existing data block associated with the descriptor
|
| 1137 | * specified by @id. If the resized data block should become wrapped, it
|
| 1138 | * copies the old data to the new data block. If @size yields a data block
|
| 1139 | * with the same or less size, the data block is left as is.
|
| 1140 | *
|
| 1141 | * Fail if this is not the last allocated data block or if there is not
|
| 1142 | * enough space or it is not possible make enough space.
|
| 1143 | *
|
| 1144 | * Return a pointer to the beginning of the entire data buffer or NULL on
|
| 1145 | * failure.
|
| 1146 |
|
| 1147 | static char *data_realloc(struct printk_ringbuffer *rb, unsigned int size,
|
| 1148 | struct prb_data_blk_lpos *blk_lpos, unsigned long id)
|
| 1149 | {
|
| 1150 | struct prb_data_ring *data_ring = &rb->text_data_ring;
|
| 1151 | struct prb_data_block *blk;
|
| 1152 | unsigned long head_lpos;
|
| 1153 | unsigned long next_lpos;
|
| 1154 | bool wrapped;
|
| 1155 |
|
| 1156 |
|
| 1157 | head_lpos = atomic_long_read(&data_ring->head_lpos);
|
| 1158 | if (head_lpos != blk_lpos->next)
|
| 1159 | return NULL;
|
| 1160 |
|
| 1161 |
|
| 1162 | wrapped = is_blk_wrapped(data_ring, blk_lpos->begin, blk_lpos->next);
|
| 1163 |
|
| 1164 | size = to_blk_size(size);
|
| 1165 |
|
| 1166 | next_lpos = get_next_lpos(data_ring, blk_lpos->begin, size);
|
| 1167 |
|
| 1168 | |
| 1169 | * Use the current data block when the size does not increase, i.e.
|
| 1170 | * when @head_lpos is already able to accommodate the new @next_lpos.
|
| 1171 | *
|
| 1172 | * Note that need_more_space() could never return false here because
|
| 1173 | * the difference between the positions was bigger than the data
|
| 1174 | * buffer size. The data block is reopened and can't get reused.
|
| 1175 |
|
| 1176 | if (!need_more_space(data_ring, head_lpos, next_lpos)) {
|
| 1177 | if (wrapped)
|
| 1178 | blk = to_block(data_ring, 0);
|
| 1179 | else
|
| 1180 | blk = to_block(data_ring, blk_lpos->begin);
|
| 1181 | return &blk->data[0];
|
| 1182 | }
|
| 1183 |
|
| 1184 | |
| 1185 | * data_check_size() prevents data block reallocation that could
|
| 1186 | * cause illegal ringbuffer states. But double check that the
|
| 1187 | * new used space will not be bigger than the ring buffer. Wrapped
|
| 1188 | * messages need to reserve more space, see get_next_lpos().
|
| 1189 | *
|
| 1190 | * Specify failure when the check or the allocation fails.
|
| 1191 |
|
| 1192 | if (WARN_ON_ONCE(next_lpos - blk_lpos->begin > DATA_SIZE(data_ring)) ||
|
| 1193 | !data_push_tail(rb, next_lpos - DATA_SIZE(data_ring))) {
|
| 1194 | return NULL;
|
| 1195 | }
|
| 1196 |
|
| 1197 |
|
| 1198 | if (!atomic_long_try_cmpxchg(&data_ring->head_lpos, &head_lpos,
|
| 1199 | next_lpos)) {
|
| 1200 | return NULL;
|
| 1201 | }
|
| 1202 |
|
| 1203 | blk = to_block(data_ring, blk_lpos->begin);
|
| 1204 |
|
| 1205 | if (is_blk_wrapped(data_ring, blk_lpos->begin, next_lpos)) {
|
| 1206 | struct prb_data_block *old_blk = blk;
|
| 1207 |
|
| 1208 |
|
| 1209 | blk = to_block(data_ring, 0);
|
| 1210 |
|
| 1211 | |
| 1212 | * Store the ID on the wrapped block for consistency.
|
| 1213 | * The printk_ringbuffer does not actually use it.
|
| 1214 |
|
| 1215 | blk->id = id;
|
| 1216 |
|
| 1217 | if (!wrapped) {
|
| 1218 | |
| 1219 | * Since the allocated space is now in the newly
|
| 1220 | * created wrapping data block, copy the content
|
| 1221 | * from the old data block.
|
| 1222 |
|
| 1223 | memcpy(&blk->data[0], &old_blk->data[0],
|
| 1224 | (blk_lpos->next - blk_lpos->begin) - sizeof(blk->id));
|
| 1225 | }
|
| 1226 | }
|
| 1227 |
|
| 1228 | blk_lpos->next = next_lpos;
|
| 1229 |
|
| 1230 | return &blk->data[0];
|
| 1231 | }
|
| 1232 |
|
| 1233 |
|
| 1234 | static unsigned int space_used(struct prb_data_ring *data_ring,
|
| 1235 | struct prb_data_blk_lpos *blk_lpos)
|
| 1236 | {
|
| 1237 |
|
| 1238 | if (BLK_DATALESS(blk_lpos))
|
| 1239 | return 0;
|
| 1240 |
|
| 1241 | if (!is_blk_wrapped(data_ring, blk_lpos->begin, blk_lpos->next)) {
|
| 1242 |
|
| 1243 | return (DATA_INDEX(data_ring, blk_lpos->next) -
|
| 1244 | DATA_INDEX(data_ring, blk_lpos->begin));
|
| 1245 | }
|
| 1246 |
|
| 1247 | |
| 1248 | * For wrapping data blocks, the trailing (wasted) space is
|
| 1249 | * also counted.
|
| 1250 |
|
| 1251 | return (DATA_INDEX(data_ring, blk_lpos->next) +
|
| 1252 | DATA_SIZE(data_ring) - DATA_INDEX(data_ring, blk_lpos->begin));
|
| 1253 | }
|
| 1254 |
|
| 1255 | |
| 1256 | * Given @blk_lpos, return a pointer to the writer data from the data block
|
| 1257 | * and calculate the size of the data part. A NULL pointer is returned if
|
| 1258 | * @blk_lpos specifies values that could never be legal.
|
| 1259 | *
|
| 1260 | * This function (used by readers) performs strict validation on the lpos
|
| 1261 | * values to possibly detect bugs in the writer code. A WARN_ON_ONCE() is
|
| 1262 | * triggered if an internal error is detected.
|
| 1263 |
|
| 1264 | static const char *get_data(struct prb_data_ring *data_ring,
|
| 1265 | struct prb_data_blk_lpos *blk_lpos,
|
| 1266 | unsigned int *data_size)
|
| 1267 | {
|
| 1268 | struct prb_data_block *db;
|
| 1269 |
|
| 1270 |
|
| 1271 | if (BLK_DATALESS(blk_lpos)) {
|
| 1272 | |
| 1273 | * Records that are just empty lines are also valid, even
|
| 1274 | * though they do not have a data block. For such records
|
| 1275 | * explicitly return empty string data to signify success.
|
| 1276 |
|
| 1277 | if (blk_lpos->begin == EMPTY_LINE_LPOS &&
|
| 1278 | blk_lpos->next == EMPTY_LINE_LPOS) {
|
| 1279 | *data_size = 0;
|
| 1280 | return "";
|
| 1281 | }
|
| 1282 |
|
| 1283 |
|
| 1284 | return NULL;
|
| 1285 | }
|
| 1286 |
|
| 1287 |
|
| 1288 | if (!is_blk_wrapped(data_ring, blk_lpos->begin, blk_lpos->next)) {
|
| 1289 | db = to_block(data_ring, blk_lpos->begin);
|
| 1290 | *data_size = blk_lpos->next - blk_lpos->begin;
|
| 1291 |
|
| 1292 |
|
| 1293 | } else if (!is_blk_wrapped(data_ring,
|
| 1294 | blk_lpos->begin + DATA_SIZE(data_ring),
|
| 1295 | blk_lpos->next)) {
|
| 1296 | db = to_block(data_ring, 0);
|
| 1297 | *data_size = DATA_INDEX(data_ring, blk_lpos->next);
|
| 1298 |
|
| 1299 |
|
| 1300 | } else {
|
| 1301 | WARN_ON_ONCE(1);
|
| 1302 | return NULL;
|
| 1303 | }
|
| 1304 |
|
| 1305 |
|
| 1306 | if (WARN_ON_ONCE(blk_lpos->begin != ALIGN(blk_lpos->begin, sizeof(db->id))) ||
|
| 1307 | WARN_ON_ONCE(blk_lpos->next != ALIGN(blk_lpos->next, sizeof(db->id)))) {
|
| 1308 | return NULL;
|
| 1309 | }
|
| 1310 |
|
| 1311 | |
| 1312 | * A regular data block will always have an ID and at least
|
| 1313 | * 1 byte of data. Data-less blocks were handled earlier.
|
| 1314 |
|
| 1315 | if (WARN_ON_ONCE(*data_size <= sizeof(db->id)))
|
| 1316 | return NULL;
|
| 1317 |
|
| 1318 |
|
| 1319 | *data_size -= sizeof(db->id);
|
| 1320 |
|
| 1321 |
|
| 1322 | if (WARN_ON_ONCE(!data_check_size(data_ring, *data_size)))
|
| 1323 | return NULL;
|
| 1324 |
|
| 1325 | return &db->data[0];
|
| 1326 | }
|
| 1327 |
|
| 1328 | |
| 1329 | * Attempt to transition the newest descriptor from committed back to reserved
|
| 1330 | * so that the record can be modified by a writer again. This is only possible
|
| 1331 | * if the descriptor is not yet finalized and the provided @caller_id matches.
|
| 1332 |
|
| 1333 | static struct prb_desc *desc_reopen_last(struct prb_desc_ring *desc_ring,
|
| 1334 | u32 caller_id, unsigned long *id_out)
|
| 1335 | {
|
| 1336 | unsigned long prev_state_val;
|
| 1337 | enum desc_state d_state;
|
| 1338 | struct prb_desc desc;
|
| 1339 | struct prb_desc *d;
|
| 1340 | unsigned long id;
|
| 1341 | u32 cid;
|
| 1342 |
|
| 1343 | id = atomic_long_read(&desc_ring->head_id);
|
| 1344 |
|
| 1345 | |
| 1346 | * To reduce unnecessarily reopening, first check if the descriptor
|
| 1347 | * state and caller ID are correct.
|
| 1348 |
|
| 1349 | d_state = desc_read(desc_ring, id, &desc, NULL, &cid);
|
| 1350 | if (d_state != desc_committed || cid != caller_id)
|
| 1351 | return NULL;
|
| 1352 |
|
| 1353 | d = to_desc(desc_ring, id);
|
| 1354 |
|
| 1355 | prev_state_val = DESC_SV(id, desc_committed);
|
| 1356 |
|
| 1357 | |
| 1358 | * Guarantee the reserved state is stored before reading any
|
| 1359 | * record data. A full memory barrier is needed because @state_var
|
| 1360 | * modification is followed by reading. This pairs with _prb_commit:B.
|
| 1361 | *
|
| 1362 | * Memory barrier involvement:
|
| 1363 | *
|
| 1364 | * If desc_reopen_last:A reads from _prb_commit:B, then
|
| 1365 | * prb_reserve_in_last:A reads from _prb_commit:A.
|
| 1366 | *
|
| 1367 | * Relies on:
|
| 1368 | *
|
| 1369 | * WMB from _prb_commit:A to _prb_commit:B
|
| 1370 | * matching
|
| 1371 | * MB from desc_reopen_last:A to prb_reserve_in_last:A
|
| 1372 |
|
| 1373 | if (!atomic_long_try_cmpxchg(&d->state_var, &prev_state_val,
|
| 1374 | DESC_SV(id, desc_reserved))) {
|
| 1375 | return NULL;
|
| 1376 | }
|
| 1377 |
|
| 1378 | *id_out = id;
|
| 1379 | return d;
|
| 1380 | }
|
| 1381 |
|
| 1382 | |
| 1383 | * prb_reserve_in_last() - Re-reserve and extend the space in the ringbuffer
|
| 1384 | * used by the newest record.
|
| 1385 | *
|
| 1386 | * @e: The entry structure to setup.
|
| 1387 | * @rb: The ringbuffer to re-reserve and extend data in.
|
| 1388 | * @r: The record structure to allocate buffers for.
|
| 1389 | * @caller_id: The caller ID of the caller (reserving writer).
|
| 1390 | * @max_size: Fail if the extended size would be greater than this.
|
| 1391 | *
|
| 1392 | * This is the public function available to writers to re-reserve and extend
|
| 1393 | * data.
|
| 1394 | *
|
| 1395 | * The writer specifies the text size to extend (not the new total size) by
|
| 1396 | * setting the @text_buf_size field of @r. To ensure proper initialization
|
| 1397 | * of @r, prb_rec_init_wr() should be used.
|
| 1398 | *
|
| 1399 | * This function will fail if @caller_id does not match the caller ID of the
|
| 1400 | * newest record. In that case the caller must reserve new data using
|
| 1401 | * prb_reserve().
|
| 1402 | *
|
| 1403 | * Context: Any context. Disables local interrupts on success.
|
| 1404 | * Return: true if text data could be extended, otherwise false.
|
| 1405 | *
|
| 1406 | * On success:
|
| 1407 | *
|
| 1408 | * - @r->text_buf points to the beginning of the entire text buffer.
|
| 1409 | *
|
| 1410 | * - @r->text_buf_size is set to the new total size of the buffer.
|
| 1411 | *
|
| 1412 | * - @r->info is not touched so that @r->info->text_len could be used
|
| 1413 | * to append the text.
|
| 1414 | *
|
| 1415 | * - prb_record_text_space() can be used on @e to query the new
|
| 1416 | * actually used space.
|
| 1417 | *
|
| 1418 | * Important: All @r->info fields will already be set with the current values
|
| 1419 | * for the record. I.e. @r->info->text_len will be less than
|
| 1420 | * @text_buf_size. Writers can use @r->info->text_len to know
|
| 1421 | * where concatenation begins and writers should update
|
| 1422 | * @r->info->text_len after concatenating.
|
| 1423 |
|
| 1424 | bool prb_reserve_in_last(struct prb_reserved_entry *e, struct printk_ringbuffer *rb,
|
| 1425 | struct printk_record *r, u32 caller_id, unsigned int max_size)
|
| 1426 | {
|
| 1427 | struct prb_desc_ring *desc_ring = &rb->desc_ring;
|
| 1428 | struct printk_info *info;
|
| 1429 | unsigned int data_size;
|
| 1430 | struct prb_desc *d;
|
| 1431 | unsigned long id;
|
| 1432 |
|
| 1433 | local_irq_save(e->irqflags);
|
| 1434 |
|
| 1435 |
|
| 1436 | d = desc_reopen_last(desc_ring, caller_id, &id);
|
| 1437 | if (!d) {
|
| 1438 | local_irq_restore(e->irqflags);
|
| 1439 | goto fail_reopen;
|
| 1440 | }
|
| 1441 |
|
| 1442 |
|
| 1443 |
|
| 1444 | info = to_info(desc_ring, id);
|
| 1445 |
|
| 1446 | |
| 1447 | * Set the @e fields here so that prb_commit() can be used if
|
| 1448 | * anything fails from now on.
|
| 1449 |
|
| 1450 | e->rb = rb;
|
| 1451 | e->id = id;
|
| 1452 |
|
| 1453 | |
| 1454 | * desc_reopen_last() checked the caller_id, but there was no
|
| 1455 | * exclusive access at that point. The descriptor may have
|
| 1456 | * changed since then.
|
| 1457 |
|
| 1458 | if (caller_id != info->caller_id)
|
| 1459 | goto fail;
|
| 1460 |
|
| 1461 | if (BLK_DATALESS(&d->text_blk_lpos)) {
|
| 1462 | if (WARN_ON_ONCE(info->text_len != 0)) {
|
| 1463 | pr_warn_once("wrong text_len value (%hu, expecting 0)\n",
|
| 1464 | info->text_len);
|
| 1465 | info->text_len = 0;
|
| 1466 | }
|
| 1467 |
|
| 1468 | if (!data_check_size(&rb->text_data_ring, r->text_buf_size))
|
| 1469 | goto fail;
|
| 1470 |
|
| 1471 | if (r->text_buf_size > max_size)
|
| 1472 | goto fail;
|
| 1473 |
|
| 1474 | r->text_buf = data_alloc(rb, r->text_buf_size,
|
| 1475 | &d->text_blk_lpos, id);
|
| 1476 | } else {
|
| 1477 | if (!get_data(&rb->text_data_ring, &d->text_blk_lpos, &data_size))
|
| 1478 | goto fail;
|
| 1479 |
|
| 1480 | |
| 1481 | * Increase the buffer size to include the original size. If
|
| 1482 | * the meta data (@text_len) is not sane, use the full data
|
| 1483 | * block size.
|
| 1484 |
|
| 1485 | if (WARN_ON_ONCE(info->text_len > data_size)) {
|
| 1486 | pr_warn_once("wrong text_len value (%hu, expecting <=%u)\n",
|
| 1487 | info->text_len, data_size);
|
| 1488 | info->text_len = data_size;
|
| 1489 | }
|
| 1490 | r->text_buf_size += info->text_len;
|
| 1491 |
|
| 1492 | if (!data_check_size(&rb->text_data_ring, r->text_buf_size))
|
| 1493 | goto fail;
|
| 1494 |
|
| 1495 | if (r->text_buf_size > max_size)
|
| 1496 | goto fail;
|
| 1497 |
|
| 1498 | r->text_buf = data_realloc(rb, r->text_buf_size,
|
| 1499 | &d->text_blk_lpos, id);
|
| 1500 | }
|
| 1501 | if (r->text_buf_size && !r->text_buf)
|
| 1502 | goto fail;
|
| 1503 |
|
| 1504 | r->info = info;
|
| 1505 |
|
| 1506 | e->text_space = space_used(&rb->text_data_ring, &d->text_blk_lpos);
|
| 1507 |
|
| 1508 | return true;
|
| 1509 | fail:
|
| 1510 | prb_commit(e);
|
| 1511 |
|
| 1512 | fail_reopen:
|
| 1513 |
|
| 1514 | memset(r, 0, sizeof(*r));
|
| 1515 | return false;
|
| 1516 | }
|
| 1517 |
|
| 1518 | |
| 1519 | * @last_finalized_seq value guarantees that all records up to and including
|
| 1520 | * this sequence number are finalized and can be read. The only exception are
|
| 1521 | * too old records which have already been overwritten.
|
| 1522 | *
|
| 1523 | * It is also guaranteed that @last_finalized_seq only increases.
|
| 1524 | *
|
| 1525 | * Be aware that finalized records following non-finalized records are not
|
| 1526 | * reported because they are not yet available to the reader. For example,
|
| 1527 | * a new record stored via printk() will not be available to a printer if
|
| 1528 | * it follows a record that has not been finalized yet. However, once that
|
| 1529 | * non-finalized record becomes finalized, @last_finalized_seq will be
|
| 1530 | * appropriately updated and the full set of finalized records will be
|
| 1531 | * available to the printer. And since each printk() caller will either
|
| 1532 | * directly print or trigger deferred printing of all available unprinted
|
| 1533 | * records, all printk() messages will get printed.
|
| 1534 |
|
| 1535 | static u64 desc_last_finalized_seq(struct printk_ringbuffer *rb)
|
| 1536 | {
|
| 1537 | struct prb_desc_ring *desc_ring = &rb->desc_ring;
|
| 1538 | unsigned long ulseq;
|
| 1539 |
|
| 1540 | |
| 1541 | * Guarantee the sequence number is loaded before loading the
|
| 1542 | * associated record in order to guarantee that the record can be
|
| 1543 | * seen by this CPU. This pairs with desc_update_last_finalized:A.
|
| 1544 |
|
| 1545 | ulseq = atomic_long_read_acquire(&desc_ring->last_finalized_seq
|
| 1546 | );
|
| 1547 |
|
| 1548 | return __ulseq_to_u64seq(rb, ulseq);
|
| 1549 | }
|
| 1550 |
|
| 1551 | static bool _prb_read_valid(struct printk_ringbuffer *rb, u64 *seq,
|
| 1552 | struct printk_record *r, unsigned int *line_count);
|
| 1553 |
|
| 1554 | |
| 1555 | * Check if there are records directly following @last_finalized_seq that are
|
| 1556 | * finalized. If so, update @last_finalized_seq to the latest of these
|
| 1557 | * records. It is not allowed to skip over records that are not yet finalized.
|
| 1558 |
|
| 1559 | static void desc_update_last_finalized(struct printk_ringbuffer *rb)
|
| 1560 | {
|
| 1561 | struct prb_desc_ring *desc_ring = &rb->desc_ring;
|
| 1562 | u64 old_seq = desc_last_finalized_seq(rb);
|
| 1563 | unsigned long oldval;
|
| 1564 | unsigned long newval;
|
| 1565 | u64 finalized_seq;
|
| 1566 | u64 try_seq;
|
| 1567 |
|
| 1568 | try_again:
|
| 1569 | finalized_seq = old_seq;
|
| 1570 | try_seq = finalized_seq + 1;
|
| 1571 |
|
| 1572 |
|
| 1573 | while (_prb_read_valid(rb, &try_seq, NULL, NULL)) {
|
| 1574 | finalized_seq = try_seq;
|
| 1575 | try_seq++;
|
| 1576 | }
|
| 1577 |
|
| 1578 |
|
| 1579 | if (finalized_seq == old_seq)
|
| 1580 | return;
|
| 1581 |
|
| 1582 | oldval = __u64seq_to_ulseq(old_seq);
|
| 1583 | newval = __u64seq_to_ulseq(finalized_seq);
|
| 1584 |
|
| 1585 | |
| 1586 | * Set the sequence number of a later finalized record that has been
|
| 1587 | * seen.
|
| 1588 | *
|
| 1589 | * Guarantee the record data is visible to other CPUs before storing
|
| 1590 | * its sequence number. This pairs with desc_last_finalized_seq:A.
|
| 1591 | *
|
| 1592 | * Memory barrier involvement:
|
| 1593 | *
|
| 1594 | * If desc_last_finalized_seq:A reads from
|
| 1595 | * desc_update_last_finalized:A, then desc_read:A reads from
|
| 1596 | * _prb_commit:B.
|
| 1597 | *
|
| 1598 | * Relies on:
|
| 1599 | *
|
| 1600 | * RELEASE from _prb_commit:B to desc_update_last_finalized:A
|
| 1601 | * matching
|
| 1602 | * ACQUIRE from desc_last_finalized_seq:A to desc_read:A
|
| 1603 | *
|
| 1604 | * Note: _prb_commit:B and desc_update_last_finalized:A can be
|
| 1605 | * different CPUs. However, the desc_update_last_finalized:A
|
| 1606 | * CPU (which performs the release) must have previously seen
|
| 1607 | * _prb_commit:B.
|
| 1608 |
|
| 1609 | if (!atomic_long_try_cmpxchg_release(&desc_ring->last_finalized_seq,
|
| 1610 | &oldval, newval)) {
|
| 1611 | old_seq = __ulseq_to_u64seq(rb, oldval);
|
| 1612 | goto try_again;
|
| 1613 | }
|
| 1614 | }
|
| 1615 |
|
| 1616 | |
| 1617 | * Attempt to finalize a specified descriptor. If this fails, the descriptor
|
| 1618 | * is either already final or it will finalize itself when the writer commits.
|
| 1619 |
|
| 1620 | static void desc_make_final(struct printk_ringbuffer *rb, unsigned long id)
|
| 1621 | {
|
| 1622 | struct prb_desc_ring *desc_ring = &rb->desc_ring;
|
| 1623 | unsigned long prev_state_val = DESC_SV(id, desc_committed);
|
| 1624 | struct prb_desc *d = to_desc(desc_ring, id);
|
| 1625 |
|
| 1626 | if (atomic_long_try_cmpxchg_relaxed(&d->state_var, &prev_state_val,
|
| 1627 | DESC_SV(id, desc_finalized))) {
|
| 1628 | desc_update_last_finalized(rb);
|
| 1629 | }
|
| 1630 | }
|
| 1631 |
|
| 1632 | |
| 1633 | * prb_reserve() - Reserve space in the ringbuffer.
|
| 1634 | *
|
| 1635 | * @e: The entry structure to setup.
|
| 1636 | * @rb: The ringbuffer to reserve data in.
|
| 1637 | * @r: The record structure to allocate buffers for.
|
| 1638 | *
|
| 1639 | * This is the public function available to writers to reserve data.
|
| 1640 | *
|
| 1641 | * The writer specifies the text size to reserve by setting the
|
| 1642 | * @text_buf_size field of @r. To ensure proper initialization of @r,
|
| 1643 | * prb_rec_init_wr() should be used.
|
| 1644 | *
|
| 1645 | * Context: Any context. Disables local interrupts on success.
|
| 1646 | * Return: true if at least text data could be allocated, otherwise false.
|
| 1647 | *
|
| 1648 | * On success, the fields @info and @text_buf of @r will be set by this
|
| 1649 | * function and should be filled in by the writer before committing. Also
|
| 1650 | * on success, prb_record_text_space() can be used on @e to query the actual
|
| 1651 | * space used for the text data block.
|
| 1652 | *
|
| 1653 | * Important: @info->text_len needs to be set correctly by the writer in
|
| 1654 | * order for data to be readable and/or extended. Its value
|
| 1655 | * is initialized to 0.
|
| 1656 |
|
| 1657 | bool prb_reserve(struct prb_reserved_entry *e, struct printk_ringbuffer *rb,
|
| 1658 | struct printk_record *r)
|
| 1659 | {
|
| 1660 | struct prb_desc_ring *desc_ring = &rb->desc_ring;
|
| 1661 | struct printk_info *info;
|
| 1662 | struct prb_desc *d;
|
| 1663 | unsigned long id;
|
| 1664 | u64 seq;
|
| 1665 |
|
| 1666 | if (!data_check_size(&rb->text_data_ring, r->text_buf_size))
|
| 1667 | goto fail;
|
| 1668 |
|
| 1669 | |
| 1670 | * Descriptors in the reserved state act as blockers to all further
|
| 1671 | * reservations once the desc_ring has fully wrapped. Disable
|
| 1672 | * interrupts during the reserve/commit window in order to minimize
|
| 1673 | * the likelihood of this happening.
|
| 1674 |
|
| 1675 | local_irq_save(e->irqflags);
|
| 1676 |
|
| 1677 | if (!desc_reserve(rb, &id)) {
|
| 1678 |
|
| 1679 | atomic_long_inc(&rb->fail);
|
| 1680 | local_irq_restore(e->irqflags);
|
| 1681 | goto fail;
|
| 1682 | }
|
| 1683 |
|
| 1684 | d = to_desc(desc_ring, id);
|
| 1685 | info = to_info(desc_ring, id);
|
| 1686 |
|
| 1687 | |
| 1688 | * All @info fields (except @seq) are cleared and must be filled in
|
| 1689 | * by the writer. Save @seq before clearing because it is used to
|
| 1690 | * determine the new sequence number.
|
| 1691 |
|
| 1692 | seq = info->seq;
|
| 1693 | memset(info, 0, sizeof(*info));
|
| 1694 |
|
| 1695 | |
| 1696 | * Set the @e fields here so that prb_commit() can be used if
|
| 1697 | * text data allocation fails.
|
| 1698 |
|
| 1699 | e->rb = rb;
|
| 1700 | e->id = id;
|
| 1701 |
|
| 1702 | |
| 1703 | * Initialize the sequence number if it has "never been set".
|
| 1704 | * Otherwise just increment it by a full wrap.
|
| 1705 | *
|
| 1706 | * @seq is considered "never been set" if it has a value of 0,
|
| 1707 | * _except_ for @infos[0], which was specially setup by the ringbuffer
|
| 1708 | * initializer and therefore is always considered as set.
|
| 1709 | *
|
| 1710 | * See the "Bootstrap" comment block in printk_ringbuffer.h for
|
| 1711 | * details about how the initializer bootstraps the descriptors.
|
| 1712 |
|
| 1713 | if (seq == 0 && DESC_INDEX(desc_ring, id) != 0)
|
| 1714 | info->seq = DESC_INDEX(desc_ring, id);
|
| 1715 | else
|
| 1716 | info->seq = seq + DESCS_COUNT(desc_ring);
|
| 1717 |
|
| 1718 | |
| 1719 | * New data is about to be reserved. Once that happens, previous
|
| 1720 | * descriptors are no longer able to be extended. Finalize the
|
| 1721 | * previous descriptor now so that it can be made available to
|
| 1722 | * readers. (For seq==0 there is no previous descriptor.)
|
| 1723 |
|
| 1724 | if (info->seq > 0)
|
| 1725 | desc_make_final(rb, DESC_ID(id - 1));
|
| 1726 |
|
| 1727 | r->text_buf = data_alloc(rb, r->text_buf_size, &d->text_blk_lpos, id);
|
| 1728 |
|
| 1729 | if (r->text_buf_size && !r->text_buf) {
|
| 1730 | prb_commit(e);
|
| 1731 |
|
| 1732 | goto fail;
|
| 1733 | }
|
| 1734 |
|
| 1735 | r->info = info;
|
| 1736 |
|
| 1737 |
|
| 1738 | e->text_space = space_used(&rb->text_data_ring, &d->text_blk_lpos);
|
| 1739 |
|
| 1740 | return true;
|
| 1741 | fail:
|
| 1742 |
|
| 1743 | memset(r, 0, sizeof(*r));
|
| 1744 | return false;
|
| 1745 | }
|
| 1746 | EXPORT_SYMBOL_IF_KUNIT(prb_reserve);
|
| 1747 |
|
| 1748 |
|
| 1749 | static void _prb_commit(struct prb_reserved_entry *e, unsigned long state_val)
|
| 1750 | {
|
| 1751 | struct prb_desc_ring *desc_ring = &e->rb->desc_ring;
|
| 1752 | struct prb_desc *d = to_desc(desc_ring, e->id);
|
| 1753 | unsigned long prev_state_val = DESC_SV(e->id, desc_reserved);
|
| 1754 |
|
| 1755 |
|
| 1756 |
|
| 1757 | |
| 1758 | * Set the descriptor as committed. See "ABA Issues" about why
|
| 1759 | * cmpxchg() instead of set() is used.
|
| 1760 | *
|
| 1761 | * 1 Guarantee all record data is stored before the descriptor state
|
| 1762 | * is stored as committed. A write memory barrier is sufficient
|
| 1763 | * for this. This pairs with desc_read:B and desc_reopen_last:A.
|
| 1764 | *
|
| 1765 | * 2. Guarantee the descriptor state is stored as committed before
|
| 1766 | * re-checking the head ID in order to possibly finalize this
|
| 1767 | * descriptor. This pairs with desc_reserve:D.
|
| 1768 | *
|
| 1769 | * Memory barrier involvement:
|
| 1770 | *
|
| 1771 | * If prb_commit:A reads from desc_reserve:D, then
|
| 1772 | * desc_make_final:A reads from _prb_commit:B.
|
| 1773 | *
|
| 1774 | * Relies on:
|
| 1775 | *
|
| 1776 | * MB from _prb_commit:B to prb_commit:A
|
| 1777 | * matching
|
| 1778 | * MB from desc_reserve:D to desc_make_final:A
|
| 1779 |
|
| 1780 | if (!atomic_long_try_cmpxchg(&d->state_var, &prev_state_val,
|
| 1781 | DESC_SV(e->id, state_val))) {
|
| 1782 | WARN_ON_ONCE(1);
|
| 1783 | }
|
| 1784 |
|
| 1785 |
|
| 1786 | local_irq_restore(e->irqflags);
|
| 1787 | }
|
| 1788 |
|
| 1789 | |
| 1790 | * prb_commit() - Commit (previously reserved) data to the ringbuffer.
|
| 1791 | *
|
| 1792 | * @e: The entry containing the reserved data information.
|
| 1793 | *
|
| 1794 | * This is the public function available to writers to commit data.
|
| 1795 | *
|
| 1796 | * Note that the data is not yet available to readers until it is finalized.
|
| 1797 | * Finalizing happens automatically when space for the next record is
|
| 1798 | * reserved.
|
| 1799 | *
|
| 1800 | * See prb_final_commit() for a version of this function that finalizes
|
| 1801 | * immediately.
|
| 1802 | *
|
| 1803 | * Context: Any context. Enables local interrupts.
|
| 1804 |
|
| 1805 | void prb_commit(struct prb_reserved_entry *e)
|
| 1806 | {
|
| 1807 | struct prb_desc_ring *desc_ring = &e->rb->desc_ring;
|
| 1808 | unsigned long head_id;
|
| 1809 |
|
| 1810 | _prb_commit(e, desc_committed);
|
| 1811 |
|
| 1812 | |
| 1813 | * If this descriptor is no longer the head (i.e. a new record has
|
| 1814 | * been allocated), extending the data for this record is no longer
|
| 1815 | * allowed and therefore it must be finalized.
|
| 1816 |
|
| 1817 | head_id = atomic_long_read(&desc_ring->head_id);
|
| 1818 | if (head_id != e->id)
|
| 1819 | desc_make_final(e->rb, e->id);
|
| 1820 | }
|
| 1821 | EXPORT_SYMBOL_IF_KUNIT(prb_commit);
|
| 1822 |
|
| 1823 | |
| 1824 | * prb_final_commit() - Commit and finalize (previously reserved) data to
|
| 1825 | * the ringbuffer.
|
| 1826 | *
|
| 1827 | * @e: The entry containing the reserved data information.
|
| 1828 | *
|
| 1829 | * This is the public function available to writers to commit+finalize data.
|
| 1830 | *
|
| 1831 | * By finalizing, the data is made immediately available to readers.
|
| 1832 | *
|
| 1833 | * This function should only be used if there are no intentions of extending
|
| 1834 | * this data using prb_reserve_in_last().
|
| 1835 | *
|
| 1836 | * Context: Any context. Enables local interrupts.
|
| 1837 |
|
| 1838 | void prb_final_commit(struct prb_reserved_entry *e)
|
| 1839 | {
|
| 1840 | _prb_commit(e, desc_finalized);
|
| 1841 |
|
| 1842 | desc_update_last_finalized(e->rb);
|
| 1843 | }
|
| 1844 |
|
| 1845 | |
| 1846 | * Count the number of lines in provided text. All text has at least 1 line
|
| 1847 | * (even if @text_size is 0). Each '\n' processed is counted as an additional
|
| 1848 | * line.
|
| 1849 |
|
| 1850 | static unsigned int count_lines(const char *text, unsigned int text_size)
|
| 1851 | {
|
| 1852 | unsigned int next_size = text_size;
|
| 1853 | unsigned int line_count = 1;
|
| 1854 | const char *next = text;
|
| 1855 |
|
| 1856 | while (next_size) {
|
| 1857 | next = memchr(next, '\n', next_size);
|
| 1858 | if (!next)
|
| 1859 | break;
|
| 1860 | line_count++;
|
| 1861 | next++;
|
| 1862 | next_size = text_size - (next - text);
|
| 1863 | }
|
| 1864 |
|
| 1865 | return line_count;
|
| 1866 | }
|
| 1867 |
|
| 1868 | |
| 1869 | * Given @blk_lpos, copy an expected @len of data into the provided buffer.
|
| 1870 | * If @line_count is provided, count the number of lines in the data.
|
| 1871 | *
|
| 1872 | * This function (used by readers) performs strict validation on the data
|
| 1873 | * size to possibly detect bugs in the writer code. A WARN_ON_ONCE() is
|
| 1874 | * triggered if an internal error is detected.
|
| 1875 |
|
| 1876 | static bool copy_data(struct prb_data_ring *data_ring,
|
| 1877 | struct prb_data_blk_lpos *blk_lpos, u16 len, char *buf,
|
| 1878 | unsigned int buf_size, unsigned int *line_count)
|
| 1879 | {
|
| 1880 | unsigned int data_size;
|
| 1881 | const char *data;
|
| 1882 |
|
| 1883 |
|
| 1884 | if ((!buf || !buf_size) && !line_count)
|
| 1885 | return true;
|
| 1886 |
|
| 1887 | data = get_data(data_ring, blk_lpos, &data_size);
|
| 1888 | if (!data)
|
| 1889 | return false;
|
| 1890 |
|
| 1891 | |
| 1892 | * Actual cannot be less than expected. It can be more than expected
|
| 1893 | * because of the trailing alignment padding.
|
| 1894 | *
|
| 1895 | * Note that invalid @len values can occur because the caller loads
|
| 1896 | * the value during an allowed data race.
|
| 1897 |
|
| 1898 | if (data_size < (unsigned int)len)
|
| 1899 | return false;
|
| 1900 |
|
| 1901 |
|
| 1902 | if (line_count)
|
| 1903 | *line_count = count_lines(data, len);
|
| 1904 |
|
| 1905 |
|
| 1906 | if (!buf || !buf_size)
|
| 1907 | return true;
|
| 1908 |
|
| 1909 | data_size = min_t(unsigned int, buf_size, len);
|
| 1910 |
|
| 1911 | memcpy(&buf[0], data, data_size);
|
| 1912 | return true;
|
| 1913 | }
|
| 1914 |
|
| 1915 | |
| 1916 | * This is an extended version of desc_read(). It gets a copy of a specified
|
| 1917 | * descriptor. However, it also verifies that the record is finalized and has
|
| 1918 | * the sequence number @seq. On success, 0 is returned.
|
| 1919 | *
|
| 1920 | * Error return values:
|
| 1921 | * -EINVAL: A finalized record with sequence number @seq does not exist.
|
| 1922 | * -ENOENT: A finalized record with sequence number @seq exists, but its data
|
| 1923 | * is not available. This is a valid record, so readers should
|
| 1924 | * continue with the next record.
|
| 1925 |
|
| 1926 | static int desc_read_finalized_seq(struct prb_desc_ring *desc_ring,
|
| 1927 | unsigned long id, u64 seq,
|
| 1928 | struct prb_desc *desc_out)
|
| 1929 | {
|
| 1930 | struct prb_data_blk_lpos *blk_lpos = &desc_out->text_blk_lpos;
|
| 1931 | enum desc_state d_state;
|
| 1932 | u64 s;
|
| 1933 |
|
| 1934 | d_state = desc_read(desc_ring, id, desc_out, &s, NULL);
|
| 1935 |
|
| 1936 | |
| 1937 | * An unexpected @id (desc_miss) or @seq mismatch means the record
|
| 1938 | * does not exist. A descriptor in the reserved or committed state
|
| 1939 | * means the record does not yet exist for the reader.
|
| 1940 |
|
| 1941 | if (d_state == desc_miss ||
|
| 1942 | d_state == desc_reserved ||
|
| 1943 | d_state == desc_committed ||
|
| 1944 | s != seq) {
|
| 1945 | return -EINVAL;
|
| 1946 | }
|
| 1947 |
|
| 1948 | |
| 1949 | * A descriptor in the reusable state may no longer have its data
|
| 1950 | * available; report it as existing but with lost data. Or the record
|
| 1951 | * may actually be a record with lost data.
|
| 1952 |
|
| 1953 | if (d_state == desc_reusable ||
|
| 1954 | (blk_lpos->begin == FAILED_LPOS && blk_lpos->next == FAILED_LPOS)) {
|
| 1955 | return -ENOENT;
|
| 1956 | }
|
| 1957 |
|
| 1958 | return 0;
|
| 1959 | }
|
| 1960 |
|
| 1961 | |
| 1962 | * Copy the ringbuffer data from the record with @seq to the provided
|
| 1963 | * @r buffer. On success, 0 is returned.
|
| 1964 | *
|
| 1965 | * See desc_read_finalized_seq() for error return values.
|
| 1966 |
|
| 1967 | static int prb_read(struct printk_ringbuffer *rb, u64 seq,
|
| 1968 | struct printk_record *r, unsigned int *line_count)
|
| 1969 | {
|
| 1970 | struct prb_desc_ring *desc_ring = &rb->desc_ring;
|
| 1971 | struct printk_info *info = to_info(desc_ring, seq);
|
| 1972 | struct prb_desc *rdesc = to_desc(desc_ring, seq);
|
| 1973 | atomic_long_t *state_var = &rdesc->state_var;
|
| 1974 | struct prb_desc desc;
|
| 1975 | unsigned long id;
|
| 1976 | int err;
|
| 1977 |
|
| 1978 |
|
| 1979 | id = DESC_ID(atomic_long_read(state_var));
|
| 1980 |
|
| 1981 |
|
| 1982 | err = desc_read_finalized_seq(desc_ring, id, seq, &desc);
|
| 1983 |
|
| 1984 | |
| 1985 | * If @r is NULL, the caller is only interested in the availability
|
| 1986 | * of the record.
|
| 1987 |
|
| 1988 | if (err || !r)
|
| 1989 | return err;
|
| 1990 |
|
| 1991 |
|
| 1992 | if (r->info)
|
| 1993 | memcpy(r->info, info, sizeof(*(r->info)));
|
| 1994 |
|
| 1995 |
|
| 1996 | if (!copy_data(&rb->text_data_ring, &desc.text_blk_lpos, info->text_len,
|
| 1997 | r->text_buf, r->text_buf_size, line_count)) {
|
| 1998 | return -ENOENT;
|
| 1999 | }
|
| 2000 |
|
| 2001 |
|
| 2002 | return desc_read_finalized_seq(desc_ring, id, seq, &desc);
|
| 2003 | }
|
| 2004 |
|
| 2005 |
|
| 2006 | u64 prb_first_seq(struct printk_ringbuffer *rb)
|
| 2007 | {
|
| 2008 | struct prb_desc_ring *desc_ring = &rb->desc_ring;
|
| 2009 | enum desc_state d_state;
|
| 2010 | struct prb_desc desc;
|
| 2011 | unsigned long id;
|
| 2012 | u64 seq;
|
| 2013 |
|
| 2014 | for (;;) {
|
| 2015 | id = atomic_long_read(&rb->desc_ring.tail_id);
|
| 2016 |
|
| 2017 | d_state = desc_read(desc_ring, id, &desc, &seq, NULL);
|
| 2018 |
|
| 2019 | |
| 2020 | * This loop will not be infinite because the tail is
|
| 2021 | * _always_ in the finalized or reusable state.
|
| 2022 |
|
| 2023 | if (d_state == desc_finalized || d_state == desc_reusable)
|
| 2024 | break;
|
| 2025 |
|
| 2026 | |
| 2027 | * Guarantee the last state load from desc_read() is before
|
| 2028 | * reloading @tail_id in order to see a new tail in the case
|
| 2029 | * that the descriptor has been recycled. This pairs with
|
| 2030 | * desc_reserve:D.
|
| 2031 | *
|
| 2032 | * Memory barrier involvement:
|
| 2033 | *
|
| 2034 | * If prb_first_seq:B reads from desc_reserve:F, then
|
| 2035 | * prb_first_seq:A reads from desc_push_tail:B.
|
| 2036 | *
|
| 2037 | * Relies on:
|
| 2038 | *
|
| 2039 | * MB from desc_push_tail:B to desc_reserve:F
|
| 2040 | * matching
|
| 2041 | * RMB from prb_first_seq:B to prb_first_seq:A
|
| 2042 |
|
| 2043 | smp_rmb();
|
| 2044 | }
|
| 2045 |
|
| 2046 | return seq;
|
| 2047 | }
|
| 2048 |
|
| 2049 | |
| 2050 | * prb_next_reserve_seq() - Get the sequence number after the most recently
|
| 2051 | * reserved record.
|
| 2052 | *
|
| 2053 | * @rb: The ringbuffer to get the sequence number from.
|
| 2054 | *
|
| 2055 | * This is the public function available to readers to see what sequence
|
| 2056 | * number will be assigned to the next reserved record.
|
| 2057 | *
|
| 2058 | * Note that depending on the situation, this value can be equal to or
|
| 2059 | * higher than the sequence number returned by prb_next_seq().
|
| 2060 | *
|
| 2061 | * Context: Any context.
|
| 2062 | * Return: The sequence number that will be assigned to the next record
|
| 2063 | * reserved.
|
| 2064 |
|
| 2065 | u64 prb_next_reserve_seq(struct printk_ringbuffer *rb)
|
| 2066 | {
|
| 2067 | struct prb_desc_ring *desc_ring = &rb->desc_ring;
|
| 2068 | unsigned long last_finalized_id;
|
| 2069 | atomic_long_t *state_var;
|
| 2070 | u64 last_finalized_seq;
|
| 2071 | unsigned long head_id;
|
| 2072 | struct prb_desc desc;
|
| 2073 | unsigned long diff;
|
| 2074 | struct prb_desc *d;
|
| 2075 | int err;
|
| 2076 |
|
| 2077 | |
| 2078 | * It may not be possible to read a sequence number for @head_id.
|
| 2079 | * So the ID of @last_finailzed_seq is used to calculate what the
|
| 2080 | * sequence number of @head_id will be.
|
| 2081 |
|
| 2082 |
|
| 2083 | try_again:
|
| 2084 | last_finalized_seq = desc_last_finalized_seq(rb);
|
| 2085 |
|
| 2086 | |
| 2087 | * @head_id is loaded after @last_finalized_seq to ensure that
|
| 2088 | * it points to the record with @last_finalized_seq or newer.
|
| 2089 | *
|
| 2090 | * Memory barrier involvement:
|
| 2091 | *
|
| 2092 | * If desc_last_finalized_seq:A reads from
|
| 2093 | * desc_update_last_finalized:A, then
|
| 2094 | * prb_next_reserve_seq:A reads from desc_reserve:D.
|
| 2095 | *
|
| 2096 | * Relies on:
|
| 2097 | *
|
| 2098 | * RELEASE from desc_reserve:D to desc_update_last_finalized:A
|
| 2099 | * matching
|
| 2100 | * ACQUIRE from desc_last_finalized_seq:A to prb_next_reserve_seq:A
|
| 2101 | *
|
| 2102 | * Note: desc_reserve:D and desc_update_last_finalized:A can be
|
| 2103 | * different CPUs. However, the desc_update_last_finalized:A CPU
|
| 2104 | * (which performs the release) must have previously seen
|
| 2105 | * desc_read:C, which implies desc_reserve:D can be seen.
|
| 2106 |
|
| 2107 | head_id = atomic_long_read(&desc_ring->head_id);
|
| 2108 |
|
| 2109 | d = to_desc(desc_ring, last_finalized_seq);
|
| 2110 | state_var = &d->state_var;
|
| 2111 |
|
| 2112 |
|
| 2113 | last_finalized_id = DESC_ID(atomic_long_read(state_var));
|
| 2114 |
|
| 2115 |
|
| 2116 | err = desc_read_finalized_seq(desc_ring, last_finalized_id, last_finalized_seq, &desc);
|
| 2117 |
|
| 2118 | if (err == -EINVAL) {
|
| 2119 | if (last_finalized_seq == 0) {
|
| 2120 | |
| 2121 | * No record has been finalized or even reserved yet.
|
| 2122 | *
|
| 2123 | * The @head_id is initialized such that the first
|
| 2124 | * increment will yield the first record (seq=0).
|
| 2125 | * Handle it separately to avoid a negative @diff
|
| 2126 | * below.
|
| 2127 |
|
| 2128 | if (head_id == DESC0_ID(desc_ring->count_bits))
|
| 2129 | return 0;
|
| 2130 |
|
| 2131 | |
| 2132 | * One or more descriptors are already reserved. Use
|
| 2133 | * the descriptor ID of the first one (@seq=0) for
|
| 2134 | * the @diff below.
|
| 2135 |
|
| 2136 | last_finalized_id = DESC0_ID(desc_ring->count_bits) + 1;
|
| 2137 | } else {
|
| 2138 |
|
| 2139 | goto try_again;
|
| 2140 | }
|
| 2141 | }
|
| 2142 |
|
| 2143 |
|
| 2144 | diff = head_id - last_finalized_id;
|
| 2145 |
|
| 2146 | |
| 2147 | * @head_id points to the most recently reserved record, but this
|
| 2148 | * function returns the sequence number that will be assigned to the
|
| 2149 | * next (not yet reserved) record. Thus +1 is needed.
|
| 2150 |
|
| 2151 | return (last_finalized_seq + diff + 1);
|
| 2152 | }
|
| 2153 |
|
| 2154 | |
| 2155 | * Non-blocking read of a record.
|
| 2156 | *
|
| 2157 | * On success @seq is updated to the record that was read and (if provided)
|
| 2158 | * @r and @line_count will contain the read/calculated data.
|
| 2159 | *
|
| 2160 | * On failure @seq is updated to a record that is not yet available to the
|
| 2161 | * reader, but it will be the next record available to the reader.
|
| 2162 | *
|
| 2163 | * Note: When the current CPU is in panic, this function will skip over any
|
| 2164 | * non-existent/non-finalized records in order to allow the panic CPU
|
| 2165 | * to print any and all records that have been finalized.
|
| 2166 |
|
| 2167 | static bool _prb_read_valid(struct printk_ringbuffer *rb, u64 *seq,
|
| 2168 | struct printk_record *r, unsigned int *line_count)
|
| 2169 | {
|
| 2170 | u64 tail_seq;
|
| 2171 | int err;
|
| 2172 |
|
| 2173 | while ((err = prb_read(rb, *seq, r, line_count))) {
|
| 2174 | tail_seq = prb_first_seq(rb);
|
| 2175 |
|
| 2176 | if (*seq < tail_seq) {
|
| 2177 | |
| 2178 | * Behind the tail. Catch up and try again. This
|
| 2179 | * can happen for -ENOENT and -EINVAL cases.
|
| 2180 |
|
| 2181 | *seq = tail_seq;
|
| 2182 |
|
| 2183 | } else if (err == -ENOENT) {
|
| 2184 |
|
| 2185 | (*seq)++;
|
| 2186 |
|
| 2187 | } else {
|
| 2188 | |
| 2189 | * Non-existent/non-finalized record. Must stop.
|
| 2190 | *
|
| 2191 | * For panic situations it cannot be expected that
|
| 2192 | * non-finalized records will become finalized. But
|
| 2193 | * there may be other finalized records beyond that
|
| 2194 | * need to be printed for a panic situation. If this
|
| 2195 | * is the panic CPU, skip this
|
| 2196 | * non-existent/non-finalized record unless non-panic
|
| 2197 | * CPUs are still running and their debugging is
|
| 2198 | * explicitly enabled.
|
| 2199 | *
|
| 2200 | * Note that new messages printed on panic CPU are
|
| 2201 | * finalized when we are here. The only exception
|
| 2202 | * might be the last message without trailing newline.
|
| 2203 | * But it would have the sequence number returned
|
| 2204 | * by "prb_next_reserve_seq() - 1".
|
| 2205 |
|
| 2206 | if (panic_on_this_cpu() &&
|
| 2207 | (!debug_non_panic_cpus || legacy_allow_panic_sync) &&
|
| 2208 | ((*seq + 1) < prb_next_reserve_seq(rb))) {
|
| 2209 | (*seq)++;
|
| 2210 | } else {
|
| 2211 | return false;
|
| 2212 | }
|
| 2213 | }
|
| 2214 | }
|
| 2215 |
|
| 2216 | return true;
|
| 2217 | }
|
| 2218 |
|
| 2219 | |
| 2220 | * prb_read_valid() - Non-blocking read of a requested record or (if gone)
|
| 2221 | * the next available record.
|
| 2222 | *
|
| 2223 | * @rb: The ringbuffer to read from.
|
| 2224 | * @seq: The sequence number of the record to read.
|
| 2225 | * @r: A record data buffer to store the read record to.
|
| 2226 | *
|
| 2227 | * This is the public function available to readers to read a record.
|
| 2228 | *
|
| 2229 | * The reader provides the @info and @text_buf buffers of @r to be
|
| 2230 | * filled in. Any of the buffer pointers can be set to NULL if the reader
|
| 2231 | * is not interested in that data. To ensure proper initialization of @r,
|
| 2232 | * prb_rec_init_rd() should be used.
|
| 2233 | *
|
| 2234 | * Context: Any context.
|
| 2235 | * Return: true if a record was read, otherwise false.
|
| 2236 | *
|
| 2237 | * On success, the reader must check r->info.seq to see which record was
|
| 2238 | * actually read. This allows the reader to detect dropped records.
|
| 2239 | *
|
| 2240 | * Failure means @seq refers to a record not yet available to the reader.
|
| 2241 |
|
| 2242 | bool prb_read_valid(struct printk_ringbuffer *rb, u64 seq,
|
| 2243 | struct printk_record *r)
|
| 2244 | {
|
| 2245 | return _prb_read_valid(rb, &seq, r, NULL);
|
| 2246 | }
|
| 2247 | EXPORT_SYMBOL_IF_KUNIT(prb_read_valid);
|
| 2248 |
|
| 2249 | |
| 2250 | * prb_read_valid_info() - Non-blocking read of meta data for a requested
|
| 2251 | * record or (if gone) the next available record.
|
| 2252 | *
|
| 2253 | * @rb: The ringbuffer to read from.
|
| 2254 | * @seq: The sequence number of the record to read.
|
| 2255 | * @info: A buffer to store the read record meta data to.
|
| 2256 | * @line_count: A buffer to store the number of lines in the record text.
|
| 2257 | *
|
| 2258 | * This is the public function available to readers to read only the
|
| 2259 | * meta data of a record.
|
| 2260 | *
|
| 2261 | * The reader provides the @info, @line_count buffers to be filled in.
|
| 2262 | * Either of the buffer pointers can be set to NULL if the reader is not
|
| 2263 | * interested in that data.
|
| 2264 | *
|
| 2265 | * Context: Any context.
|
| 2266 | * Return: true if a record's meta data was read, otherwise false.
|
| 2267 | *
|
| 2268 | * On success, the reader must check info->seq to see which record meta data
|
| 2269 | * was actually read. This allows the reader to detect dropped records.
|
| 2270 | *
|
| 2271 | * Failure means @seq refers to a record not yet available to the reader.
|
| 2272 |
|
| 2273 | bool prb_read_valid_info(struct printk_ringbuffer *rb, u64 seq,
|
| 2274 | struct printk_info *info, unsigned int *line_count)
|
| 2275 | {
|
| 2276 | struct printk_record r;
|
| 2277 |
|
| 2278 | prb_rec_init_rd(&r, info, NULL, 0);
|
| 2279 |
|
| 2280 | return _prb_read_valid(rb, &seq, &r, line_count);
|
| 2281 | }
|
| 2282 |
|
| 2283 | |
| 2284 | * prb_first_valid_seq() - Get the sequence number of the oldest available
|
| 2285 | * record.
|
| 2286 | *
|
| 2287 | * @rb: The ringbuffer to get the sequence number from.
|
| 2288 | *
|
| 2289 | * This is the public function available to readers to see what the
|
| 2290 | * first/oldest valid sequence number is.
|
| 2291 | *
|
| 2292 | * This provides readers a starting point to begin iterating the ringbuffer.
|
| 2293 | *
|
| 2294 | * Context: Any context.
|
| 2295 | * Return: The sequence number of the first/oldest record or, if the
|
| 2296 | * ringbuffer is empty, 0 is returned.
|
| 2297 |
|
| 2298 | u64 prb_first_valid_seq(struct printk_ringbuffer *rb)
|
| 2299 | {
|
| 2300 | u64 seq = 0;
|
| 2301 |
|
| 2302 | if (!_prb_read_valid(rb, &seq, NULL, NULL))
|
| 2303 | return 0;
|
| 2304 |
|
| 2305 | return seq;
|
| 2306 | }
|
| 2307 |
|
| 2308 | |
| 2309 | * prb_next_seq() - Get the sequence number after the last available record.
|
| 2310 | *
|
| 2311 | * @rb: The ringbuffer to get the sequence number from.
|
| 2312 | *
|
| 2313 | * This is the public function available to readers to see what the next
|
| 2314 | * newest sequence number available to readers will be.
|
| 2315 | *
|
| 2316 | * This provides readers a sequence number to jump to if all currently
|
| 2317 | * available records should be skipped. It is guaranteed that all records
|
| 2318 | * previous to the returned value have been finalized and are (or were)
|
| 2319 | * available to the reader.
|
| 2320 | *
|
| 2321 | * Context: Any context.
|
| 2322 | * Return: The sequence number of the next newest (not yet available) record
|
| 2323 | * for readers.
|
| 2324 |
|
| 2325 | u64 prb_next_seq(struct printk_ringbuffer *rb)
|
| 2326 | {
|
| 2327 | u64 seq;
|
| 2328 |
|
| 2329 | seq = desc_last_finalized_seq(rb);
|
| 2330 |
|
| 2331 | |
| 2332 | * Begin searching after the last finalized record.
|
| 2333 | *
|
| 2334 | * On 0, the search must begin at 0 because of hack#2
|
| 2335 | * of the bootstrapping phase it is not known if a
|
| 2336 | * record at index 0 exists.
|
| 2337 |
|
| 2338 | if (seq != 0)
|
| 2339 | seq++;
|
| 2340 |
|
| 2341 | |
| 2342 | * The information about the last finalized @seq might be inaccurate.
|
| 2343 | * Search forward to find the current one.
|
| 2344 |
|
| 2345 | while (_prb_read_valid(rb, &seq, NULL, NULL))
|
| 2346 | seq++;
|
| 2347 |
|
| 2348 | return seq;
|
| 2349 | }
|
| 2350 |
|
| 2351 | |
| 2352 | * prb_init() - Initialize a ringbuffer to use provided external buffers.
|
| 2353 | *
|
| 2354 | * @rb: The ringbuffer to initialize.
|
| 2355 | * @text_buf: The data buffer for text data.
|
| 2356 | * @textbits: The size of @text_buf as a power-of-2 value.
|
| 2357 | * @descs: The descriptor buffer for ringbuffer records.
|
| 2358 | * @descbits: The count of @descs items as a power-of-2 value.
|
| 2359 | * @infos: The printk_info buffer for ringbuffer records.
|
| 2360 | *
|
| 2361 | * This is the public function available to writers to setup a ringbuffer
|
| 2362 | * during runtime using provided buffers.
|
| 2363 | *
|
| 2364 | * This must match the initialization of DEFINE_PRINTKRB().
|
| 2365 | *
|
| 2366 | * Context: Any context.
|
| 2367 |
|
| 2368 | void prb_init(struct printk_ringbuffer *rb,
|
| 2369 | char *text_buf, unsigned int textbits,
|
| 2370 | struct prb_desc *descs, unsigned int descbits,
|
| 2371 | struct printk_info *infos)
|
| 2372 | {
|
| 2373 | memset(descs, 0, _DESCS_COUNT(descbits) * sizeof(descs[0]));
|
| 2374 | memset(infos, 0, _DESCS_COUNT(descbits) * sizeof(infos[0]));
|
| 2375 |
|
| 2376 | rb->desc_ring.count_bits = descbits;
|
| 2377 | rb->desc_ring.descs = descs;
|
| 2378 | rb->desc_ring.infos = infos;
|
| 2379 | atomic_long_set(&rb->desc_ring.head_id, DESC0_ID(descbits));
|
| 2380 | atomic_long_set(&rb->desc_ring.tail_id, DESC0_ID(descbits));
|
| 2381 | atomic_long_set(&rb->desc_ring.last_finalized_seq, 0);
|
| 2382 |
|
| 2383 | rb->text_data_ring.size_bits = textbits;
|
| 2384 | rb->text_data_ring.data = text_buf;
|
| 2385 | atomic_long_set(&rb->text_data_ring.head_lpos, BLK0_LPOS(textbits));
|
| 2386 | atomic_long_set(&rb->text_data_ring.tail_lpos, BLK0_LPOS(textbits));
|
| 2387 |
|
| 2388 | atomic_long_set(&rb->fail, 0);
|
| 2389 |
|
| 2390 | atomic_long_set(&(descs[_DESCS_COUNT(descbits) - 1].state_var), DESC0_SV(descbits));
|
| 2391 | descs[_DESCS_COUNT(descbits) - 1].text_blk_lpos.begin = FAILED_LPOS;
|
| 2392 | descs[_DESCS_COUNT(descbits) - 1].text_blk_lpos.next = FAILED_LPOS;
|
| 2393 |
|
| 2394 | infos[0].seq = -(u64)_DESCS_COUNT(descbits);
|
| 2395 | infos[_DESCS_COUNT(descbits) - 1].seq = 0;
|
| 2396 | }
|
| 2397 | EXPORT_SYMBOL_IF_KUNIT(prb_init);
|
| 2398 |
|
| 2399 | |
| 2400 | * prb_record_text_space() - Query the full actual used ringbuffer space for
|
| 2401 | * the text data of a reserved entry.
|
| 2402 | *
|
| 2403 | * @e: The successfully reserved entry to query.
|
| 2404 | *
|
| 2405 | * This is the public function available to writers to see how much actual
|
| 2406 | * space is used in the ringbuffer to store the text data of the specified
|
| 2407 | * entry.
|
| 2408 | *
|
| 2409 | * This function is only valid if @e has been successfully reserved using
|
| 2410 | * prb_reserve().
|
| 2411 | *
|
| 2412 | * Context: Any context.
|
| 2413 | * Return: The size in bytes used by the text data of the associated record.
|
| 2414 |
|
| 2415 | unsigned int prb_record_text_space(struct prb_reserved_entry *e)
|
| 2416 | {
|
| 2417 | return e->text_space;
|
| 2418 | }
|