linux-kernel - Re: [PATCH 1/2] iov: introduce ITER_BVEC_FLAG

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Message-ID: <20201209182456.GR7338@casper.infradead.org>
Date:   Wed, 9 Dec 2020 18:24:56 +0000
From:   Matthew Wilcox <willy@...radead.org>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     Pavel Begunkov <asml.silence@...il.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        Jens Axboe <axboe@...nel.dk>, linux-fsdevel@...r.kernel.org,
        io-uring@...r.kernel.org, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] iov: introduce ITER_BVEC_FLAG_FIXED

On Wed, Dec 09, 2020 at 05:55:53PM +0000, Christoph Hellwig wrote:
> On Wed, Dec 09, 2020 at 01:37:05PM +0000, Pavel Begunkov wrote:
> > Yeah, I had troubles to put comments around, and it's still open.
> > 
> > For current cases it can be bound to kiocb, e.g. "if an bvec iter passed
> > "together" with kiocb then the vector should stay intact up to 
> > ->ki_complete()". But that "together" is rather full of holes.
> 
> What about: "For bvec based iters the bvec must not be freed until the
> I/O has completed.  For asynchronous I/O that means it must be freed
> no earlier than from ->ki_complete."

Perhaps for the second sentence "If the I/O is completed asynchronously,
the bvec must not be freed before ->ki_complete() has been called"?