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From: Pavel Begunkov <asml.silence@gmail.com>
To: linux-block@vger.kernel.org
Cc: Jens Axboe <axboe@kernel.dk>,
	Christoph Hellwig <hch@infradead.org>,
	Matthew Wilcox <willy@infradead.org>,
	Ming Lei <ming.lei@redhat.com>,
	Johannes Weiner <hannes@cmpxchg.org>,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	"Darrick J . Wong" <darrick.wong@oracle.com>,
	"Martin K . Petersen" <martin.petersen@oracle.com>,
	Jonathan Corbet <corbet@lwn.net>,
	linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org,
	io-uring@vger.kernel.org, linux-kernel@vger.kernel.org,
	target-devel@vger.kernel.org, linux-scsi@vger.kernel.org,
	linux-doc@vger.kernel.org
Subject: [PATCH v2 2/7] bvec/iter: disallow zero-length segment bvecs
Date: Sat,  2 Jan 2021 15:17:34 +0000	[thread overview]
Message-ID: <b46b8c1943bbefcb90ea5c4dd9beaad8bbc15448.1609461359.git.asml.silence@gmail.com> (raw)
In-Reply-To: <cover.1609461359.git.asml.silence@gmail.com>

zero-length bvec segments are allowed in general, but not handled by bio
and down the block layer so filtered out. This inconsistency may be
confusing and prevent from optimisations. As zero-length segments are
useless and places that were generating them are patched, declare them
not allowed.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
---
 Documentation/filesystems/porting.rst | 7 +++++++
 lib/iov_iter.c                        | 2 --
 2 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/Documentation/filesystems/porting.rst b/Documentation/filesystems/porting.rst
index 867036aa90b8..c722d94f29ea 100644
--- a/Documentation/filesystems/porting.rst
+++ b/Documentation/filesystems/porting.rst
@@ -865,3 +865,10 @@ no matter what.  Everything is handled by the caller.
 
 clone_private_mount() returns a longterm mount now, so the proper destructor of
 its result is kern_unmount() or kern_unmount_array().
+
+---
+
+**mandatory**
+
+zero-length bvec segments are disallowed, they must be filtered out before
+passed on to an iterator.
diff --git a/lib/iov_iter.c b/lib/iov_iter.c
index 1635111c5bd2..7de304269641 100644
--- a/lib/iov_iter.c
+++ b/lib/iov_iter.c
@@ -72,8 +72,6 @@
 	__start.bi_bvec_done = skip;			\
 	__start.bi_idx = 0;				\
 	for_each_bvec(__v, i->bvec, __bi, __start) {	\
-		if (!__v.bv_len)			\
-			continue;			\
 		(void)(STEP);				\
 	}						\
 }
-- 
2.24.0


  parent reply	other threads:[~2021-01-02 15:22 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-01-02 15:17 [PATCH v2 0/7] no-copy bvec Pavel Begunkov
2021-01-02 15:17 ` [PATCH v2 1/7] splice: don't generate zero-len segement bvecs Pavel Begunkov
2021-01-04 16:17   ` Christoph Hellwig
2021-01-04 16:54     ` Pavel Begunkov
2021-01-02 15:17 ` Pavel Begunkov [this message]
2021-01-04 16:18   ` [PATCH v2 2/7] bvec/iter: disallow zero-length segment bvecs Christoph Hellwig
2021-01-04 16:37   ` Matthew Wilcox
2021-01-04 17:23     ` Pavel Begunkov
2021-01-02 15:17 ` [PATCH v2 3/7] block/psi: remove PSI annotations from direct IO Pavel Begunkov
2021-01-04 16:45   ` Christoph Hellwig
2021-01-02 15:17 ` [PATCH v2 4/7] target/file: allocate the bvec array as part of struct target_core_file_cmd Pavel Begunkov
2021-01-02 15:17 ` [PATCH v2 5/7] iov_iter: optimise bvec iov_iter_advance() Pavel Begunkov
2021-01-02 15:17 ` [PATCH v2 6/7] bio: add a helper calculating nr segments to alloc Pavel Begunkov
2021-01-02 15:17 ` [PATCH v2 7/7] bio: don't copy bvec for direct IO Pavel Begunkov
2021-01-04 16:20   ` Christoph Hellwig

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