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block: use normal I/O path for discard requests

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prepare_discard_fn() was being called in a place where memory allocation
was effectively impossible.  This makes it inappropriate for all but
the most trivial translations of Linux's DISCARD operation to the block
command set.  Additionally adding a payload there makes the ownership
of the bio backing unclear as it's now allocated by the device driver
and not the submitter as usual.

It is replaced with QUEUE_FLAG_DISCARD which is used to indicate whether
the queue supports discard operations or not.  blkdev_issue_discard now
allocates a one-page, sector-length payload which is the right thing
for the common ATA and SCSI implementations.

The mtd implementation of prepare_discard_fn() is replaced with simply
checking for the request being a discard.

Largely based on a previous patch from Matthew Wilcox <[email protected]>
which did the prepare_discard_fn but not the different payload allocation
yet.

Signed-off-by: Christoph Hellwig <[email protected]>
Signed-off-by: Jens Axboe <[email protected]>
This commit is contained in:
Christoph Hellwig 2009-09-30 13:52:12 +02:00 • committed by Jens Axboe
commit c15227de13
6 changed files with 39 additions and 43 deletions
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17
block/blk-settings.c
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@ -33,23 +33,6 @@ 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