| 1 | |
| 2 | |
| 3 | * Copyright (C) 2003 Jana Saout <[email protected]>
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| 4 | *
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| 5 | * This file is released under the GPL.
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| 6 |
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| 7 |
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| 8 | #include <linux/device-mapper.h>
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| 9 |
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| 10 | #include <linux/module.h>
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| 11 | #include <linux/init.h>
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| 12 | #include <linux/bio.h>
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| 13 |
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| 14 | #define DM_MSG_PREFIX "zero"
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| 15 |
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| 16 | |
| 17 | * Construct a dummy mapping that only returns zeros
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| 18 |
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| 19 | static int zero_ctr(struct dm_target *ti, unsigned int argc, char **argv)
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| 20 | {
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| 21 | if (argc != 0) {
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| 22 | ti->error = "No arguments required";
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| 23 | return -EINVAL;
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| 24 | }
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| 25 |
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| 26 | |
| 27 | * Silently drop discards, avoiding -EOPNOTSUPP.
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| 28 |
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| 29 | ti->num_discard_bios = 1;
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| 30 | ti->discards_supported = true;
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| 31 |
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| 32 | return 0;
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| 33 | }
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| 34 |
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| 35 | |
| 36 | * Return zeros only on reads
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| 37 |
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| 38 | static int zero_map(struct dm_target *ti, struct bio *bio)
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| 39 | {
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| 40 | switch (bio_op(bio)) {
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| 41 | case REQ_OP_READ:
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| 42 | if (bio->bi_opf & REQ_RAHEAD) {
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| 43 |
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| 44 | return DM_MAPIO_KILL;
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| 45 | }
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| 46 | zero_fill_bio(bio);
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| 47 | break;
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| 48 | case REQ_OP_WRITE:
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| 49 | case REQ_OP_DISCARD:
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| 50 |
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| 51 | break;
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| 52 | default:
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| 53 | return DM_MAPIO_KILL;
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| 54 | }
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| 55 |
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| 56 | bio_endio(bio);
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| 57 |
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| 58 |
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| 59 | return DM_MAPIO_SUBMITTED;
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| 60 | }
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| 61 |
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| 62 | static void zero_io_hints(struct dm_target *ti, struct queue_limits *limits)
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| 63 | {
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| 64 | limits->max_hw_discard_sectors = UINT_MAX;
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| 65 | limits->discard_granularity = 512;
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| 66 | }
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| 67 |
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| 68 | static struct target_type zero_target = {
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| 69 | .name = "zero",
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| 70 | .version = {1, 2, 0},
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| 71 | .features = DM_TARGET_NOWAIT,
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| 72 | .module = THIS_MODULE,
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| 73 | .ctr = zero_ctr,
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| 74 | .map = zero_map,
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| 75 | .io_hints = zero_io_hints,
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| 76 | };
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| 77 | module_dm(zero);
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| 78 |
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| 79 | MODULE_AUTHOR("Jana Saout <[email protected]>");
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| 80 | MODULE_DESCRIPTION(DM_NAME " dummy target returning zeros");
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| 81 | MODULE_LICENSE("GPL");
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