From: Ming Lei <[email protected]>
To: Pavel Begunkov <[email protected]>
Cc: [email protected], Jens Axboe <[email protected]>,
Christoph Hellwig <[email protected]>,
Matthew Wilcox <[email protected]>,
Johannes Weiner <[email protected]>,
Alexander Viro <[email protected]>,
"Darrick J . Wong" <[email protected]>,
"Martin K . Petersen" <[email protected]>,
Jonathan Corbet <[email protected]>,
[email protected], [email protected],
[email protected], [email protected],
[email protected], [email protected],
[email protected], Christoph Hellwig <[email protected]>
Subject: Re: [PATCH v3 2/7] bvec/iter: disallow zero-length segment bvecs
Date: Mon, 11 Jan 2021 10:49:20 +0800 [thread overview]
Message-ID: <20210111024920.GC4147870@T590> (raw)
In-Reply-To: <4570836cc62137a9ee788d9c820f58ed8efe9b37.1610170479.git.asml.silence@gmail.com>
On Sat, Jan 09, 2021 at 04:02:58PM +0000, Pavel Begunkov wrote:
> 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.
>
> Reviewed-by: Christoph Hellwig <[email protected]>
> Signed-off-by: Pavel Begunkov <[email protected]>
> ---
> Documentation/block/biovecs.rst | 2 ++
> Documentation/filesystems/porting.rst | 7 +++++++
> lib/iov_iter.c | 2 --
> 3 files changed, 9 insertions(+), 2 deletions(-)
>
> diff --git a/Documentation/block/biovecs.rst b/Documentation/block/biovecs.rst
> index 36771a131b56..ddb867e0185b 100644
> --- a/Documentation/block/biovecs.rst
> +++ b/Documentation/block/biovecs.rst
> @@ -40,6 +40,8 @@ normal code doesn't have to deal with bi_bvec_done.
> There is a lower level advance function - bvec_iter_advance() - which takes
> a pointer to a biovec, not a bio; this is used by the bio integrity code.
>
> +As of 5.12 bvec segments with zero bv_len are not supported.
> +
> What's all this get us?
> =======================
>
> 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
>
Reviewed-by: Ming Lei <[email protected]>
--
Ming
next prev parent reply other threads:[~2021-01-11 2:51 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-09 16:02 [PATCH v3 0/7] no-copy bvec Pavel Begunkov
2021-01-09 16:02 ` [PATCH v3 1/7] splice: don't generate zero-len segement bvecs Pavel Begunkov
2021-01-11 2:48 ` Ming Lei
2021-01-09 16:02 ` [PATCH v3 2/7] bvec/iter: disallow zero-length segment bvecs Pavel Begunkov
2021-01-11 2:49 ` Ming Lei [this message]
2021-01-09 16:02 ` [PATCH v3 3/7] block/psi: remove PSI annotations from direct IO Pavel Begunkov
2021-01-11 2:52 ` Ming Lei
2021-01-09 16:03 ` [PATCH v3 4/7] target/file: allocate the bvec array as part of struct target_core_file_cmd Pavel Begunkov
2021-01-11 2:53 ` Ming Lei
2021-01-09 16:03 ` [PATCH v3 5/7] iov_iter: optimise bvec iov_iter_advance() Pavel Begunkov
2021-01-11 2:55 ` Ming Lei
2021-01-09 16:03 ` [PATCH v3 6/7] bio: add a helper calculating nr segments to alloc Pavel Begunkov
2021-01-11 2:57 ` Ming Lei
2021-01-09 16:03 ` [PATCH v3 7/7] bio: don't copy bvec for direct IO Pavel Begunkov
2021-01-11 3:00 ` Ming Lei
2021-01-25 15:58 ` [PATCH v3 0/7] no-copy bvec Jens Axboe
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