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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 <matthew@wil.cx>
which did the prepare_discard_fn but not the different payload allocation
yet.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
This commit is contained in:
Christoph Hellwig
2009-09-30 13:52:12 +02:00
committed by Jens Axboe
parent 3bd0f0c763
commit c15227de13
6 changed files with 39 additions and 43 deletions
Download Patch File Download Diff File Expand all files Collapse all files

35
block/blk-barrier.c
View File

@@ -350,6 +350,7 @@ static void blkdev_discard_end_io(struct bio *bio, int err)
if (bio->bi_private)
complete(bio->bi_private);
__free_page(bio_page(bio));
bio_put(bio);
}
@@ -372,26 +373,44 @@ int blkdev_issue_discard(struct block_device *bdev, sector_t sector,
struct request_queue *q = bdev_get_queue(bdev);
int type = flags & DISCARD_FL_BARRIER ?
DISCARD_BARRIER : DISCARD_NOBARRIER;
struct bio *bio;
struct page *page;
int ret = 0;
if (!q)
return -ENXIO;
if (!q->prepare_discard_fn)
if (!blk_queue_discard(q))
return -EOPNOTSUPP;
while (nr_sects && !ret) {
struct bio *bio = bio_alloc(gfp_mask, 0);
if (!bio)
return -ENOMEM;
unsigned int sector_size = q->limits.logical_block_size;
bio = bio_alloc(gfp_mask, 1);
if (!bio)
goto out;
bio->bi_sector = sector;
bio->bi_end_io = blkdev_discard_end_io;
bio->bi_bdev = bdev;
if (flags & DISCARD_FL_WAIT)
bio->bi_private = &wait;
bio->bi_sector = sector;
/*
* Add a zeroed one-sector payload as that's what
* our current implementations need. If we'll ever need
* more the interface will need revisiting.
*/
page = alloc_page(GFP_KERNEL | __GFP_ZERO);
if (!page)
goto out_free_bio;
if (bio_add_pc_page(q, bio, page, sector_size, 0) < sector_size)
goto out_free_page;
/*
* And override the bio size - the way discard works we
* touch many more blocks on disk than the actual payload
* length.
*/
if (nr_sects > queue_max_hw_sectors(q)) {
bio->bi_size = queue_max_hw_sectors(q) << 9;
nr_sects -= queue_max_hw_sectors(q);
@@ -414,5 +433,11 @@ int blkdev_issue_discard(struct block_device *bdev, sector_t sector,
bio_put(bio);
}
return ret;
out_free_page:
__free_page(page);
out_free_bio:
bio_put(bio);
out:
return -ENOMEM;
}
EXPORT_SYMBOL(blkdev_issue_discard);

3
block/blk-core.c
View File

@@ -1124,7 +1124,6 @@ void init_request_from_bio(struct request *req, struct bio *bio)
req->cmd_flags |= REQ_DISCARD;
if (bio_rw_flagged(bio, BIO_RW_BARRIER))
req->cmd_flags |= REQ_SOFTBARRIER;
req->q->prepare_discard_fn(req->q, req);
} else if (unlikely(bio_rw_flagged(bio, BIO_RW_BARRIER)))
req->cmd_flags |= REQ_HARDBARRIER;
@@ -1470,7 +1469,7 @@ static inline void __generic_make_request(struct bio *bio)
goto end_io;
if (bio_rw_flagged(bio, BIO_RW_DISCARD) &&
!q->prepare_discard_fn) {
!blk_queue_discard(q)) {
err = -EOPNOTSUPP;
goto end_io;
}

17
block/blk-settings.c
View File

@@ -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