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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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block/blk-settings.c
+17
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@@ -32,6 +32,23 @@ void blk_queue_prep_rq(struct request_queue *q, prep_rq_fn *pfn)
}
EXPORT_SYMBOL(blk_queue_prep_rq);
/**
* blk_queue_set_discard - set a discard_sectors function for queue
* @q: queue
* @dfn: prepare_discard function
*
* It's possible for a queue to register a discard callback which is used
* to transform a discard request into the appropriate type for the
* hardware. If none is registered, then discard requests are failed
* with %EOPNOTSUPP.
*
*/
void blk_queue_set_discard(struct request_queue *q, prepare_discard_fn *dfn)
{
q->prepare_discard_fn = dfn;
}
EXPORT_SYMBOL(blk_queue_set_discard);
/**
* blk_queue_merge_bvec - set a merge_bvec function for queue
* @q: queue