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Add 'discard' request handling

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Some block devices benefit from a hint that they can forget the contents
of certain sectors. Add basic support for this to the block core, along
with a 'blkdev_issue_discard()' helper function which issues such
requests.

The caller doesn't get to provide an end_io functio, since
blkdev_issue_discard() will automatically split the request up into
multiple bios if appropriate. Neither does the function wait for
completion -- it's expected that callers won't care about when, or even
_if_, the request completes. It's only a hint to the device anyway. By
definition, the file system doesn't _care_ about these sectors any more.

[With feedback from OGAWA Hirofumi <hirofumi@mail.parknet.co.jp> and
Jens Axboe <jens.axboe@oracle.com]

Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
This commit is contained in:
David Woodhouse
2008-08-05 18:01:53 +01:00
committed by Jens Axboe
parent d628eaef31
commit fb2dce862d
6 changed files with 130 additions and 11 deletions
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8
include/linux/bio.h
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@@ -149,6 +149,8 @@ struct bio {
* bit 2 -- barrier
* bit 3 -- fail fast, don't want low level driver retries
* bit 4 -- synchronous I/O hint: the block layer will unplug immediately
* bit 5 -- metadata request
* bit 6 -- discard sectors
*/
#define BIO_RW 0 /* Must match RW in req flags (blkdev.h) */
#define BIO_RW_AHEAD 1 /* Must match FAILFAST in req flags */
@@ -156,6 +158,7 @@ struct bio {
#define BIO_RW_FAILFAST 3
#define BIO_RW_SYNC 4
#define BIO_RW_META 5
#define BIO_RW_DISCARD 6
/*
* upper 16 bits of bi_rw define the io priority of this bio
@@ -186,13 +189,14 @@ struct bio {
#define bio_rw_ahead(bio) ((bio)->bi_rw & (1 << BIO_RW_AHEAD))
#define bio_rw_meta(bio) ((bio)->bi_rw & (1 << BIO_RW_META))
#define bio_empty_barrier(bio) (bio_barrier(bio) && !bio_has_data(bio))
#define bio_discard(bio) ((bio)->bi_rw & (1 << BIO_RW_DISCARD))
static inline unsigned int bio_cur_sectors(struct bio *bio)
{
if (bio->bi_vcnt)
return bio_iovec(bio)->bv_len >> 9;
return 0;
else /* dataless requests such as discard */
return bio->bi_size >> 9;
}
static inline void *bio_data(struct bio *bio)