linux-kernel - Re: [PATCH v1 0/6] no-copy bvec

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Message-ID: <20201222141112.GE13079@infradead.org>
Date:   Tue, 22 Dec 2020 14:11:12 +0000
From:   Christoph Hellwig <hch@...radead.org>
To:     Pavel Begunkov <asml.silence@...il.com>
Cc:     Ming Lei <ming.lei@...hat.com>, 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 02:05:35PM +0000, Pavel Begunkov wrote:
> > You may find clue from the following link:
> > 
> > https://www.mail-archive.com/linux-kernel@vger.kernel.org/msg2262077.html
> 
> Thanks for the link!
> 
> Al, you mentioned "Zero-length segments are not disallowed", do you have
> a strong opinion on that? Apart from already diverged behaviour from the
> block layer and getting in the way of this series, without it we'd also be
> able to remove some extra ifs, e.g. in iterate_bvec()

I'd prefer not to support zero-length ITER_BVEC and catching them
early, as the block layer can't deal with them either.  From a quick
look at iter_file_splice_write it should be pretty trivial to fix there,
although we'll need to audit other callers as well (even if I don't
expect them to submit this degenerate case).