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block: bio_iov_iter_get_pages: fix size of last iovec

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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;