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Message-ID: <20201215120357.GA1798021@T590>
Date: Tue, 15 Dec 2020 20:03:57 +0800
From: Ming Lei <ming.lei@...hat.com>
To: Pavel Begunkov <asml.silence@...il.com>
Cc: linux-block@...r.kernel.org, Jens Axboe <axboe@...nel.dk>,
Christoph Hellwig <hch@...radead.org>,
Matthew Wilcox <willy@...radead.org>,
Johannes Weiner <hannes@...xchg.org>,
Alexander Viro <viro@...iv.linux.org.uk>,
"Darrick J . Wong" <darrick.wong@...cle.com>,
"Martin K . Petersen" <martin.petersen@...cle.com>,
Jonathan Corbet <corbet@....net>, linux-xfs@...r.kernel.org,
linux-fsdevel@...r.kernel.org, io-uring@...r.kernel.org,
linux-kernel@...r.kernel.org, target-devel@...r.kernel.org,
linux-scsi@...r.kernel.org, linux-doc@...r.kernel.org
Subject: Re: [PATCH v1 0/6] no-copy bvec
On Tue, Dec 15, 2020 at 11:14:20AM +0000, Pavel Begunkov wrote:
> On 15/12/2020 01:41, Ming Lei wrote:
> > On Tue, Dec 15, 2020 at 12:20:19AM +0000, Pavel Begunkov wrote:
> >> Instead of creating a full copy of iter->bvec into bio in direct I/O,
> >> the patchset makes use of the one provided. It changes semantics and
> >> obliges users of asynchronous kiocb to track bvec lifetime, and [1/6]
> >> converts the only place that doesn't.
> >
> > Just think of one corner case: iov_iter(BVEC) may pass bvec table with zero
> > length bvec, which may not be supported by block layer or driver, so
> > this patchset has to address this case first.
>
> The easiest for me would be to fallback to copy if there are zero bvecs,
> e.g. finding such during iov_iter_alignment(), but do we know from where
> zero bvecs can came? As it's internals we may want to forbid them if
> there is not too much hassle.
You may find clue from the following link:
https://www.mail-archive.com/linux-kernel@vger.kernel.org/msg2262077.html
Thanks,
Ming
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