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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


  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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