Re: [PATCH 11/19] block: implement bio helper to add iter bvec pages to bio
From: Ming Lei <hidden>
Date: 2019-02-20 22:59:11
Also in:
linux-block
Subsystem:
block layer, the rest · Maintainers:
Jens Axboe, Linus Torvalds
On Mon, Feb 11, 2019 at 12:00:41PM -0700, Jens Axboe wrote:
quoted hunk ↗ jump to hunk
For an ITER_BVEC, we can just iterate the iov and add the pages to the bio directly. This requires that the caller doesn't releases the pages on IO completion, we add a BIO_NO_PAGE_REF flag for that. The current two callers of bio_iov_iter_get_pages() are updated to check if they need to release pages on completion. This makes them work with bvecs that contain kernel mapped pages already. Reviewed-by: Hannes Reinecke <hare@suse.com> Reviewed-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Jens Axboe <axboe@kernel.dk> --- block/bio.c | 59 ++++++++++++++++++++++++++++++++------- fs/block_dev.c | 5 ++-- fs/iomap.c | 5 ++-- include/linux/blk_types.h | 1 + 4 files changed, 56 insertions(+), 14 deletions(-)diff --git a/block/bio.c b/block/bio.c index 4db1008309ed..330df572cfb8 100644 --- a/block/bio.c +++ b/block/bio.c@@ -828,6 +828,23 @@ int bio_add_page(struct bio *bio, struct page *page, } EXPORT_SYMBOL(bio_add_page); +static int __bio_iov_bvec_add_pages(struct bio *bio, struct iov_iter *iter) +{ + const struct bio_vec *bv = iter->bvec; + unsigned int len; + size_t size; + + len = min_t(size_t, bv->bv_len, iter->count); + size = bio_add_page(bio, bv->bv_page, len, + bv->bv_offset + iter->iov_offset);
iter->iov_offset needs to be subtracted from 'len', looks the following delta change[1] is required, otherwise memory corruption can be observed when running xfstests over loop/dio. Another interesting thing is that bio_add_page() is capable of adding multi contiguous pages actually, especially loop uses ITER_BVEC to pass multi-page bvecs. Even though pages in loop's ITER_BVEC may belong to user-space, looks it is still safe to not grab the page ref given it has been done by fs. [1]
diff --git a/block/bio.c b/block/bio.c
index 3b49963676fc..df99bb3816a1 100644
--- a/block/bio.c
+++ b/block/bio.c@@ -842,7 +842,10 @@ static int __bio_iov_bvec_add_pages(struct bio *bio, struct iov_iter *iter) unsigned int len; size_t size; - len = min_t(size_t, bv->bv_len, iter->count); + if (WARN_ON_ONCE(iter->iov_offset > bv->bv_len)) + return -EINVAL; + + len = min_t(size_t, bv->bv_len - iter->iov_offset, iter->count); size = bio_add_page(bio, bv->bv_page, len, bv->bv_offset + iter->iov_offset); if (size == len) {
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