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Date:   Wed, 18 Nov 2020 15:18:06 +0000
From:   Christoph Hellwig <hch@infradead.org>
To:     Michal Kubecek <mkubecek@suse.cz>
Cc:     Alexander Viro <viro@zeniv.linux.org.uk>,
        linux-fsdevel@vger.kernel.org, Jens Axboe <axboe@kernel.dk>,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH] eventfd: convert to ->write_iter()
Message-ID: <20201118151806.GA25804@infradead.org>
References: <8a4f07e6ec47b681a32c6df5d463857e67bfc965.1605690824.git.mkubecek@suse.cz>
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On Wed, Nov 18, 2020 at 10:19:17AM +0100, Michal Kubecek wrote:
> While eventfd ->read() callback was replaced by ->read_iter() recently,
> it still provides ->write() for writes. Since commit 4d03e3cc5982 ("fs:
> don't allow kernel reads and writes without iter ops"), this prevents
> kernel_write() to be used for eventfd and with set_fs() removal,
> ->write() cannot be easily called directly with a kernel buffer.
> 
> According to eventfd(2), eventfd descriptors are supposed to be (also)
> used by kernel to notify userspace applications of events which now
> requires ->write_iter() op to be available (and ->write() not to be).
> Therefore convert eventfd_write() to ->write_iter() semantics. This
> patch also cleans up the code in a similar way as commit 12aceb89b0bc
> ("eventfd: convert to f_op->read_iter()") did in read_iter().

A far as I can tell we don't have an in-tree user that writes to an
eventfd.  We can merge something like this once there is a user.