From: James Bottomley <James.Bottomley@HansenPartnership.com>
To: Christoph Hellwig <hch@infradead.org>,
Pavel Begunkov <asml.silence@gmail.com>
Cc: Ming Lei <ming.lei@redhat.com>,
linux-block@vger.kernel.org, Jens Axboe <axboe@kernel.dk>,
Matthew Wilcox <willy@infradead.org>,
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: Re: [PATCH v1 0/6] no-copy bvec
Date: Wed, 23 Dec 2020 08:04:22 -0800 [thread overview]
Message-ID: <f06ece44a86eb9c8ef07bbd9f6f53342366b7751.camel@HansenPartnership.com> (raw)
In-Reply-To: <20201223155145.GA5902@infradead.org>
On Wed, 2020-12-23 at 15:51 +0000, Christoph Hellwig wrote:
> On Wed, Dec 23, 2020 at 12:52:59PM +0000, Pavel Begunkov wrote:
> > Can scatterlist have 0-len entries? Those are directly translated
> > into bvecs, e.g. in nvme/target/io-cmd-file.c and
> > target/target_core_file.c. I've audited most of others by this
> > moment, they're fine.
>
> For block layer SGLs we should never see them, and for nvme neither.
> I think the same is true for the SCSI target code, but please double
> check.
Right, no-one ever wants to see a 0-len scatter list entry. The reason
is that every driver uses the sgl to program the device DMA engine in
the way NVME does. a 0 length sgl would be a dangerous corner case:
some DMA engines would ignore it and others would go haywire, so if we
ever let a 0 length list down into the driver, they'd have to
understand the corner case behaviour of their DMA engine and filter it
accordingly, which is why we disallow them in the upper levels, since
they're effective nops anyway.
James
next prev parent reply other threads:[~2020-12-23 16:05 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-12-15 0:20 [PATCH v1 0/6] no-copy bvec Pavel Begunkov
2020-12-15 0:20 ` [PATCH v1 1/6] target/file: allocate the bvec array as part of struct target_core_file_cmd Pavel Begunkov
2020-12-15 0:20 ` [PATCH v1 2/6] iov_iter: optimise bvec iov_iter_advance() Pavel Begunkov
2020-12-15 9:37 ` David Laight
2020-12-15 11:23 ` Pavel Begunkov
2020-12-15 13:54 ` David Laight
2020-12-15 13:56 ` Pavel Begunkov
2020-12-22 14:03 ` Christoph Hellwig
2020-12-15 0:20 ` [PATCH v1 3/6] bio: deduplicate adding a page into bio Pavel Begunkov
2020-12-22 14:04 ` Christoph Hellwig
2020-12-15 0:20 ` [PATCH v1 4/6] block/psi: remove PSI annotations from direct IO Pavel Begunkov
2020-12-15 0:56 ` Dave Chinner
2020-12-15 1:03 ` Pavel Begunkov
2020-12-15 1:33 ` Dave Chinner
2020-12-15 11:41 ` Pavel Begunkov
2020-12-22 14:07 ` Christoph Hellwig
2020-12-15 0:20 ` [PATCH v1 5/6] bio: add a helper calculating nr segments to alloc Pavel Begunkov
2020-12-15 1:00 ` Dave Chinner
2020-12-15 1:07 ` Pavel Begunkov
2020-12-15 1:09 ` Dave Chinner
2020-12-22 14:07 ` Christoph Hellwig
2020-12-15 0:20 ` [PATCH v1 6/6] block/iomap: don't copy bvec for direct IO Pavel Begunkov
2020-12-15 1:09 ` Dave Chinner
2020-12-15 1:15 ` Pavel Begunkov
2020-12-22 14:15 ` Christoph Hellwig
2020-12-15 1:41 ` [PATCH v1 0/6] no-copy bvec Ming Lei
2020-12-15 11:14 ` Pavel Begunkov
2020-12-15 12:03 ` Ming Lei
2020-12-15 14:05 ` Pavel Begunkov
2020-12-22 14:11 ` Christoph Hellwig
2020-12-23 12:52 ` Pavel Begunkov
2020-12-23 15:51 ` Christoph Hellwig
2020-12-23 16:04 ` James Bottomley [this message]
2020-12-23 20:23 ` Douglas Gilbert
2020-12-23 20:32 ` Pavel Begunkov
2020-12-24 6:41 ` Christoph Hellwig
2020-12-24 16:45 ` Douglas Gilbert
2020-12-24 17:30 ` James Bottomley
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