88 lines
1.5 KiB
C
88 lines
1.5 KiB
C
/*
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* Copyright (C) 2003 Jana Saout <jana@saout.de>
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*
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* This file is released under the GPL.
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*/
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#include <linux/device-mapper.h>
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#include <linux/module.h>
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#include <linux/init.h>
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#include <linux/bio.h>
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#define DM_MSG_PREFIX "zero"
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/*
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* Construct a dummy mapping that only returns zeros
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*/
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static int zero_ctr(struct dm_target *ti, unsigned int argc, char **argv)
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{
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if (argc != 0) {
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ti->error = "No arguments required";
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return -EINVAL;
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}
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/*
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* Silently drop discards, avoiding -EOPNOTSUPP.
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*/
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ti->num_discard_bios = 1;
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return 0;
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}
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/*
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* Return zeros only on reads
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*/
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static int zero_map(struct dm_target *ti, struct bio *bio)
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{
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switch (bio_op(bio)) {
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case REQ_OP_READ:
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if (bio->bi_opf & REQ_RAHEAD) {
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/* readahead of null bytes only wastes buffer cache */
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return -EIO;
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}
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zero_fill_bio(bio);
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break;
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case REQ_OP_WRITE:
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/* writes get silently dropped */
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break;
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default:
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return -EIO;
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}
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bio_endio(bio);
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/* accepted bio, don't make new request */
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return DM_MAPIO_SUBMITTED;
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}
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static struct target_type zero_target = {
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.name = "zero",
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.version = {1, 1, 0},
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.module = THIS_MODULE,
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.ctr = zero_ctr,
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.map = zero_map,
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};
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static int __init dm_zero_init(void)
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{
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int r = dm_register_target(&zero_target);
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if (r < 0)
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DMERR("register failed %d", r);
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return r;
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}
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static void __exit dm_zero_exit(void)
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{
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dm_unregister_target(&zero_target);
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}
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module_init(dm_zero_init)
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module_exit(dm_zero_exit)
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MODULE_AUTHOR("Jana Saout <jana@saout.de>");
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MODULE_DESCRIPTION(DM_NAME " dummy target returning zeros");
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MODULE_LICENSE("GPL");
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