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block: support adding less than len in bio_add_hw_page 

bio_add_hw_page currently always fails or succeeds.  This is fine for
the existing callers that always add PAGE_SIZE worth given that the
max_segment_size and max_sectors must always allow at least a page
worth of data.  But when we want to add it for bigger amounts of data
this means it can also fail when adding the data to a bio, and creating
a fallback for that becomes really annoying in the callers.

Make use of the existing API design that allows to return a smaller
length than the one passed in and add up to max_segment_size worth
of data from a larger input.  All the existing callers are fine with
this - not because they handle this return correctly, but because they
never pass more than a page in.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Link: https://lore.kernel.org/r/20231204173419.782378-3-hch@lst.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Christoph Hellwig 2023-12-04 18:34:19 +01:00 committed by Jens Axboe
parent 3f034c374a
commit 6ef02df154
1 changed files with 4 additions and 1 deletions
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5
block/bio.c
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@ -966,10 +966,13 @@ int bio_add_hw_page(struct request_queue *q, struct bio *bio,
struct page *page, unsigned int len, unsigned int offset,
unsigned int max_sectors, bool *same_page)
{
unsigned int max_size = max_sectors << SECTOR_SHIFT;
if (WARN_ON_ONCE(bio_flagged(bio, BIO_CLONED)))
return 0;
if (((bio->bi_iter.bi_size + len) >> SECTOR_SHIFT) > max_sectors)
len = min3(len, max_size, queue_max_segment_size(q));
if (len > max_size - bio->bi_iter.bi_size)
return 0;
if (bio->bi_vcnt > 0) {