[PATCH 1/2] block: bio_iov_iter_get_pages: fix size of last iovec
From: Martin Wilck <hidden>
Date: 2018-07-19 09:39:17
Subsystem:
block layer, the rest · Maintainers:
Jens Axboe, Linus Torvalds
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.
Fixes: 2cefe4dbaadf ("block: add bio_iov_iter_get_pages()")
Signed-off-by: Martin Wilck <redacted>
---
block/bio.c | 18 ++++++++----------
1 file changed, 8 insertions(+), 10 deletions(-)
diff --git a/block/bio.c b/block/bio.c
index 67eff5e..0964328 100644
--- a/block/bio.c
+++ b/block/bio.c@@ -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 idx, nr_pages = bio->bi_max_vecs - bio->bi_vcnt; 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;
--
2.17.1