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Date:   Tue, 15 Dec 2020 20:03:57 +0800
From:   Ming Lei <ming.lei@redhat.com>
To:     Pavel Begunkov <asml.silence@gmail.com>
Cc:     linux-block@vger.kernel.org, Jens Axboe <axboe@kernel.dk>,
        Christoph Hellwig <hch@infradead.org>,
        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
Message-ID: <20201215120357.GA1798021@T590>
References: <cover.1607976425.git.asml.silence@gmail.com>
 <20201215014114.GA1777020@T590>
 <103235c1-e7d0-0b55-65d0-013d1a09304e@gmail.com>
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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