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block: bio_iov_iter_get_pages: fix size of last iovec 

If the last page of the bio is not "full", the length of the last
vector slot needs to be corrected. This slot has the index
(bio->bi_vcnt - 1), but only in bio->bi_io_vec. In the "bv" helper
array, which is shifted by the value of bio->bi_vcnt at function
invocation, the correct index is (nr_pages - 1).

v2: improved readability following suggestions from Ming Lei.
v3: followed a formatting suggestion from Christoph Hellwig.

Fixes: 2cefe4dbaa ("block: add bio_iov_iter_get_pages()")
Reviewed-by: Hannes Reinecke <hare@suse.com>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Martin Wilck <mwilck@suse.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Martin Wilck 2018-07-25 23:15:07 +02:00 committed by Jens Axboe
parent 78e18063a9
commit b403ea2404
1 changed files with 8 additions and 10 deletions
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18
block/bio.c
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@ -912,16 +912,16 @@ EXPORT_SYMBOL(bio_add_page);
*/
int bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)
{
unsigned short nr_pages = bio->bi_max_vecs - bio->bi_vcnt;
unsigned short nr_pages = bio->bi_max_vecs - bio->bi_vcnt, idx;
struct bio_vec *bv = bio->bi_io_vec + bio->bi_vcnt;
struct page **pages = (struct page **)bv;
size_t offset, diff;
size_t offset;
ssize_t size;
size = iov_iter_get_pages(iter, pages, LONG_MAX, nr_pages, &offset);
if (unlikely(size <= 0))
return size ? size : -EFAULT;
nr_pages = (size + offset + PAGE_SIZE - 1) / PAGE_SIZE;
idx = nr_pages = (size + offset + PAGE_SIZE - 1) / PAGE_SIZE;
/*
* Deep magic below: We need to walk the pinned pages backwards
@ -934,17 +934,15 @@ int bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)
bio->bi_iter.bi_size += size;
bio->bi_vcnt += nr_pages;
diff = (nr_pages * PAGE_SIZE - offset) - size;
while (nr_pages--) {
bv[nr_pages].bv_page = pages[nr_pages];
bv[nr_pages].bv_len = PAGE_SIZE;
bv[nr_pages].bv_offset = 0;
while (idx--) {
bv[idx].bv_page = pages[idx];
bv[idx].bv_len = PAGE_SIZE;
bv[idx].bv_offset = 0;
}
bv[0].bv_offset += offset;
bv[0].bv_len -= offset;
if (diff)
bv[bio->bi_vcnt - 1].bv_len -= diff;
bv[nr_pages - 1].bv_len -= nr_pages * PAGE_SIZE - offset - size;
iov_iter_advance(iter, size);
return 0;