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block: simplify bio_add_page()
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Since generic_make_request() can now handle arbitrary size bios, all we
have to do is make sure the bvec array doesn't overflow.
__bio_add_page() doesn't need to call ->merge_bvec_fn(), where
we can get rid of unnecessary code paths.

Removing the call to ->merge_bvec_fn() is also fine, as no driver that
implements support for BLOCK_PC commands even has a ->merge_bvec_fn()
method.

Cc: Christoph Hellwig <hch@infradead.org>
Cc: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>
[dpark: rebase and resolve merge conflicts, change a couple of comments,
 make bio_add_page() warn once upon a cloned bio.]
Signed-off-by: Dongsu Park <dpark@posteo.net>
Signed-off-by: Ming Lin <ming.l@ssi.samsung.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
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Kent Overstreet authored and Jens Axboe committed Aug 13, 2015
1 parent 54efd50 commit c66a14d
Showing 1 changed file with 55 additions and 80 deletions.
135 changes: 55 additions & 80 deletions block/bio.c
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Original file line number Diff line number Diff line change
Expand Up @@ -716,9 +716,23 @@ int bio_get_nr_vecs(struct block_device *bdev)
}
EXPORT_SYMBOL(bio_get_nr_vecs);

static int __bio_add_page(struct request_queue *q, struct bio *bio, struct page
*page, unsigned int len, unsigned int offset,
unsigned int max_sectors)
/**
* bio_add_pc_page - attempt to add page to bio
* @q: the target queue
* @bio: destination bio
* @page: page to add
* @len: vec entry length
* @offset: vec entry offset
*
* Attempt to add a page to the bio_vec maplist. This can fail for a
* number of reasons, such as the bio being full or target block device
* limitations. The target block device must allow bio's up to PAGE_SIZE,
* so it is always possible to add a single page to an empty bio.
*
* This should only be used by REQ_PC bios.
*/
int bio_add_pc_page(struct request_queue *q, struct bio *bio, struct page
*page, unsigned int len, unsigned int offset)
{
int retried_segments = 0;
struct bio_vec *bvec;
Expand All @@ -729,7 +743,7 @@ static int __bio_add_page(struct request_queue *q, struct bio *bio, struct page
if (unlikely(bio_flagged(bio, BIO_CLONED)))
return 0;

if (((bio->bi_iter.bi_size + len) >> 9) > max_sectors)
if (((bio->bi_iter.bi_size + len) >> 9) > queue_max_hw_sectors(q))
return 0;

/*
Expand All @@ -742,28 +756,7 @@ static int __bio_add_page(struct request_queue *q, struct bio *bio, struct page

if (page == prev->bv_page &&
offset == prev->bv_offset + prev->bv_len) {
unsigned int prev_bv_len = prev->bv_len;
prev->bv_len += len;

if (q->merge_bvec_fn) {
struct bvec_merge_data bvm = {
/* prev_bvec is already charged in
bi_size, discharge it in order to
simulate merging updated prev_bvec
as new bvec. */
.bi_bdev = bio->bi_bdev,
.bi_sector = bio->bi_iter.bi_sector,
.bi_size = bio->bi_iter.bi_size -
prev_bv_len,
.bi_rw = bio->bi_rw,
};

if (q->merge_bvec_fn(q, &bvm, prev) < prev->bv_len) {
prev->bv_len -= len;
return 0;
}
}

bio->bi_iter.bi_size += len;
goto done;
}
Expand Down Expand Up @@ -806,27 +799,6 @@ static int __bio_add_page(struct request_queue *q, struct bio *bio, struct page
blk_recount_segments(q, bio);
}

/*
* if queue has other restrictions (eg varying max sector size
* depending on offset), it can specify a merge_bvec_fn in the
* queue to get further control
*/
if (q->merge_bvec_fn) {
struct bvec_merge_data bvm = {
.bi_bdev = bio->bi_bdev,
.bi_sector = bio->bi_iter.bi_sector,
.bi_size = bio->bi_iter.bi_size - len,
.bi_rw = bio->bi_rw,
};

/*
* merge_bvec_fn() returns number of bytes it can accept
* at this offset
*/
if (q->merge_bvec_fn(q, &bvm, bvec) < bvec->bv_len)
goto failed;
}

/* If we may be able to merge these biovecs, force a recount */
if (bio->bi_vcnt > 1 && (BIOVEC_PHYS_MERGEABLE(bvec-1, bvec)))
bio_clear_flag(bio, BIO_SEG_VALID);
Expand All @@ -843,28 +815,6 @@ static int __bio_add_page(struct request_queue *q, struct bio *bio, struct page
blk_recount_segments(q, bio);
return 0;
}

/**
* bio_add_pc_page - attempt to add page to bio
* @q: the target queue
* @bio: destination bio
* @page: page to add
* @len: vec entry length
* @offset: vec entry offset
*
* Attempt to add a page to the bio_vec maplist. This can fail for a
* number of reasons, such as the bio being full or target block device
* limitations. The target block device must allow bio's up to PAGE_SIZE,
* so it is always possible to add a single page to an empty bio.
*
* This should only be used by REQ_PC bios.
*/
int bio_add_pc_page(struct request_queue *q, struct bio *bio, struct page *page,
unsigned int len, unsigned int offset)
{
return __bio_add_page(q, bio, page, len, offset,
queue_max_hw_sectors(q));
}
EXPORT_SYMBOL(bio_add_pc_page);

/**
Expand All @@ -874,22 +824,47 @@ EXPORT_SYMBOL(bio_add_pc_page);
* @len: vec entry length
* @offset: vec entry offset
*
* Attempt to add a page to the bio_vec maplist. This can fail for a
* number of reasons, such as the bio being full or target block device
* limitations. The target block device must allow bio's up to PAGE_SIZE,
* so it is always possible to add a single page to an empty bio.
* Attempt to add a page to the bio_vec maplist. This will only fail
* if either bio->bi_vcnt == bio->bi_max_vecs or it's a cloned bio.
*/
int bio_add_page(struct bio *bio, struct page *page, unsigned int len,
unsigned int offset)
int bio_add_page(struct bio *bio, struct page *page,
unsigned int len, unsigned int offset)
{
struct request_queue *q = bdev_get_queue(bio->bi_bdev);
unsigned int max_sectors;
struct bio_vec *bv;

max_sectors = blk_max_size_offset(q, bio->bi_iter.bi_sector);
if ((max_sectors < (len >> 9)) && !bio->bi_iter.bi_size)
max_sectors = len >> 9;
/*
* cloned bio must not modify vec list
*/
if (WARN_ON_ONCE(bio_flagged(bio, BIO_CLONED)))
return 0;

return __bio_add_page(q, bio, page, len, offset, max_sectors);
/*
* For filesystems with a blocksize smaller than the pagesize
* we will often be called with the same page as last time and
* a consecutive offset. Optimize this special case.
*/
if (bio->bi_vcnt > 0) {
bv = &bio->bi_io_vec[bio->bi_vcnt - 1];

if (page == bv->bv_page &&
offset == bv->bv_offset + bv->bv_len) {
bv->bv_len += len;
goto done;
}
}

if (bio->bi_vcnt >= bio->bi_max_vecs)
return 0;

bv = &bio->bi_io_vec[bio->bi_vcnt];
bv->bv_page = page;
bv->bv_len = len;
bv->bv_offset = offset;

bio->bi_vcnt++;
done:
bio->bi_iter.bi_size += len;
return len;
}
EXPORT_SYMBOL(bio_add_page);

Expand Down

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