| 1 | |
| 2 | * linux/fs/hfs/bitmap.c
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| 3 | *
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| 4 | * Copyright (C) 1996-1997 Paul H. Hargrove
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| 5 | * (C) 2003 Ardis Technologies <[email protected]>
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| 6 | * This file may be distributed under the terms of the GNU General Public License.
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| 7 | *
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| 8 | * Based on GPLed code Copyright (C) 1995 Michael Dreher
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| 9 | *
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| 10 | * This file contains the code to modify the volume bitmap:
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| 11 | * search/set/clear bits.
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| 12 |
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| 13 |
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| 14 | #include "hfs_fs.h"
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| 15 |
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| 16 | |
| 17 | * hfs_find_zero_bit()
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| 18 | *
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| 19 | * Description:
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| 20 | * Given a block of memory, its length in bits, and a starting bit number,
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| 21 | * determine the number of the first zero bits (in left-to-right ordering)
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| 22 | * in that range.
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| 23 | *
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| 24 | * Returns >= 'size' if no zero bits are found in the range.
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| 25 | *
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| 26 | * Accesses memory in 32-bit aligned chunks of 32-bits and thus
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| 27 | * may read beyond the 'size'th bit.
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| 28 |
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| 29 | static u32 hfs_find_set_zero_bits(__be32 *bitmap, u32 size, u32 offset, u32 *max)
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| 30 | {
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| 31 | __be32 *curr, *end;
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| 32 | u32 mask, start, len, n;
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| 33 | __be32 val;
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| 34 | int i;
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| 35 |
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| 36 | len = *max;
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| 37 | if (!len)
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| 38 | return size;
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| 39 |
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| 40 | curr = bitmap + (offset / 32);
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| 41 | end = bitmap + ((size + 31) / 32);
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| 42 |
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| 43 |
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| 44 | val = *curr;
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| 45 | if (~val) {
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| 46 | n = be32_to_cpu(val);
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| 47 | i = offset % 32;
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| 48 | mask = (1U << 31) >> i;
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| 49 | for (; i < 32; mask >>= 1, i++) {
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| 50 | if (!(n & mask))
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| 51 | goto found;
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| 52 | }
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| 53 | }
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| 54 |
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| 55 |
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| 56 | while (++curr < end) {
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| 57 | val = *curr;
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| 58 | if (~val) {
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| 59 | n = be32_to_cpu(val);
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| 60 | mask = 1 << 31;
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| 61 | for (i = 0; i < 32; mask >>= 1, i++) {
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| 62 | if (!(n & mask))
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| 63 | goto found;
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| 64 | }
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| 65 | }
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| 66 | }
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| 67 | return size;
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| 68 |
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| 69 | found:
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| 70 | start = (curr - bitmap) * 32 + i;
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| 71 | if (start >= size)
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| 72 | return start;
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| 73 |
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| 74 | len = min(size - start, len);
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| 75 | while (1) {
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| 76 | n |= mask;
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| 77 | if (++i >= 32)
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| 78 | break;
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| 79 | mask >>= 1;
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| 80 | if (!--len || n & mask)
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| 81 | goto done;
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| 82 | }
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| 83 | if (!--len)
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| 84 | goto done;
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| 85 | *curr++ = cpu_to_be32(n);
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| 86 |
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| 87 | while (1) {
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| 88 | n = be32_to_cpu(*curr);
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| 89 | if (len < 32)
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| 90 | break;
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| 91 | if (n) {
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| 92 | len = 32;
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| 93 | break;
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| 94 | }
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| 95 | *curr++ = cpu_to_be32(0xffffffff);
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| 96 | len -= 32;
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| 97 | }
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| 98 |
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| 99 | mask = 1U << 31;
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| 100 | for (i = 0; i < len; i++) {
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| 101 | if (n & mask)
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| 102 | break;
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| 103 | n |= mask;
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| 104 | mask >>= 1;
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| 105 | }
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| 106 | done:
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| 107 | *curr = cpu_to_be32(n);
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| 108 | *max = (curr - bitmap) * 32 + i - start;
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| 109 | return start;
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| 110 | }
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| 111 |
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| 112 | |
| 113 | * hfs_vbm_search_free()
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| 114 | *
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| 115 | * Description:
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| 116 | * Search for 'num_bits' consecutive cleared bits in the bitmap blocks of
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| 117 | * the hfs MDB. 'mdb' had better be locked or the returned range
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| 118 | * may be no longer free, when this functions returns!
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| 119 | * XXX Currently the search starts from bit 0, but it should start with
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| 120 | * the bit number stored in 's_alloc_ptr' of the MDB.
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| 121 | * Input Variable(s):
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| 122 | * struct hfs_mdb *mdb: Pointer to the hfs MDB
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| 123 | * u16 *num_bits: Pointer to the number of cleared bits
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| 124 | * to search for
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| 125 | * Output Variable(s):
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| 126 | * u16 *num_bits: The number of consecutive clear bits of the
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| 127 | * returned range. If the bitmap is fragmented, this will be less than
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| 128 | * requested and it will be zero, when the disk is full.
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| 129 | * Returns:
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| 130 | * The number of the first bit of the range of cleared bits which has been
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| 131 | * found. When 'num_bits' is zero, this is invalid!
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| 132 | * Preconditions:
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| 133 | * 'mdb' points to a "valid" (struct hfs_mdb).
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| 134 | * 'num_bits' points to a variable of type (u16), which contains
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| 135 | * the number of cleared bits to find.
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| 136 | * Postconditions:
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| 137 | * 'num_bits' is set to the length of the found sequence.
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| 138 |
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| 139 | u32 hfs_vbm_search_free(struct super_block *sb, u32 goal, u32 *num_bits)
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| 140 | {
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| 141 | void *bitmap;
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| 142 | u32 pos;
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| 143 |
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| 144 |
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| 145 | if (!*num_bits)
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| 146 | return 0;
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| 147 |
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| 148 | mutex_lock(&HFS_SB(sb)->bitmap_lock);
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| 149 | bitmap = HFS_SB(sb)->bitmap;
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| 150 |
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| 151 | pos = hfs_find_set_zero_bits(bitmap, HFS_SB(sb)->fs_ablocks, goal, num_bits);
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| 152 | if (pos >= HFS_SB(sb)->fs_ablocks) {
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| 153 | if (goal)
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| 154 | pos = hfs_find_set_zero_bits(bitmap, goal, 0, num_bits);
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| 155 | if (pos >= HFS_SB(sb)->fs_ablocks) {
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| 156 | *num_bits = pos = 0;
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| 157 | goto out;
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| 158 | }
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| 159 | }
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| 160 |
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| 161 | hfs_dbg("pos %u, num_bits %u\n", pos, *num_bits);
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| 162 | HFS_SB(sb)->free_ablocks -= *num_bits;
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| 163 | hfs_bitmap_dirty(sb);
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| 164 | out:
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| 165 | mutex_unlock(&HFS_SB(sb)->bitmap_lock);
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| 166 | return pos;
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| 167 | }
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| 168 |
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| 169 |
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| 170 | |
| 171 | * hfs_clear_vbm_bits()
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| 172 | *
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| 173 | * Description:
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| 174 | * Clear the requested bits in the volume bitmap of the hfs filesystem
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| 175 | * Input Variable(s):
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| 176 | * struct hfs_mdb *mdb: Pointer to the hfs MDB
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| 177 | * u16 start: The offset of the first bit
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| 178 | * u16 count: The number of bits
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| 179 | * Output Variable(s):
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| 180 | * None
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| 181 | * Returns:
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| 182 | * 0: no error
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| 183 | * -1: One of the bits was already clear. This is a strange
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| 184 | * error and when it happens, the filesystem must be repaired!
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| 185 | * -2: One or more of the bits are out of range of the bitmap.
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| 186 | * Preconditions:
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| 187 | * 'mdb' points to a "valid" (struct hfs_mdb).
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| 188 | * Postconditions:
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| 189 | * Starting with bit number 'start', 'count' bits in the volume bitmap
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| 190 | * are cleared. The affected bitmap blocks are marked "dirty", the free
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| 191 | * block count of the MDB is updated and the MDB is marked dirty.
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| 192 |
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| 193 | int hfs_clear_vbm_bits(struct super_block *sb, u16 start, u16 count)
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| 194 | {
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| 195 | __be32 *curr;
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| 196 | u32 mask;
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| 197 | int i, len;
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| 198 |
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| 199 |
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| 200 | if (!count)
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| 201 | return 0;
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| 202 |
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| 203 | hfs_dbg("start %u, count %u\n", start, count);
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| 204 |
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| 205 | if ((start + count) > HFS_SB(sb)->fs_ablocks)
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| 206 | return -2;
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| 207 |
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| 208 | mutex_lock(&HFS_SB(sb)->bitmap_lock);
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| 209 |
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| 210 | curr = HFS_SB(sb)->bitmap + (start / 32);
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| 211 | len = count;
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| 212 |
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| 213 |
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| 214 | i = start % 32;
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| 215 | if (i) {
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| 216 | int j = 32 - i;
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| 217 | mask = 0xffffffffU << j;
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| 218 | if (j > count) {
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| 219 | mask |= 0xffffffffU >> (i + count);
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| 220 | *curr &= cpu_to_be32(mask);
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| 221 | goto out;
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| 222 | }
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| 223 | *curr++ &= cpu_to_be32(mask);
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| 224 | count -= j;
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| 225 | }
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| 226 |
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| 227 |
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| 228 | while (count >= 32) {
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| 229 | *curr++ = 0;
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| 230 | count -= 32;
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| 231 | }
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| 232 |
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| 233 | if (count) {
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| 234 | mask = 0xffffffffU >> count;
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| 235 | *curr &= cpu_to_be32(mask);
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| 236 | }
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| 237 | out:
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| 238 | HFS_SB(sb)->free_ablocks += len;
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| 239 | mutex_unlock(&HFS_SB(sb)->bitmap_lock);
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| 240 | hfs_bitmap_dirty(sb);
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| 241 |
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| 242 | return 0;
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| 243 | }
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