55a62eef8d
Use 'bio' in the name of variables and functions that deal with bios rather than 'request' to avoid confusion with the normal block layer use of 'request'. No functional changes. Signed-off-by: Alasdair G Kergon <agk@redhat.com>
84 lines
1.5 KiB
C
84 lines
1.5 KiB
C
/*
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* Copyright (C) 2003 Christophe Saout <christophe@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_rw(bio)) {
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case READ:
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zero_fill_bio(bio);
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break;
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case READA:
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/* readahead of null bytes only wastes buffer cache */
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return -EIO;
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case WRITE:
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/* writes get silently dropped */
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break;
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}
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bio_endio(bio, 0);
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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("Christophe Saout <christophe@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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