From: Jens Axboe <axboe@kernel.dk>
To: Michal Kubecek <mkubecek@suse.cz>, Christoph Hellwig <hch@infradead.org>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>,
linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] eventfd: convert to ->write_iter()
Date: Wed, 18 Nov 2020 14:27:08 -0700 [thread overview]
Message-ID: <4e4d222c-ed8b-a40d-0cdc-cf152573645c@kernel.dk> (raw)
In-Reply-To: <20201118195936.p33qlcjc7gp2zezz@lion.mk-sys.cz>
On 11/18/20 12:59 PM, Michal Kubecek wrote:
> On Wed, Nov 18, 2020 at 03:18:06PM +0000, Christoph Hellwig wrote:
>> 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.
>
> As far as I can say, we don't have an in-tree user that reads from
> sysctl. But you not only did not object to commit 4bd6a7353ee1 ("sysctl:
> Convert to iter interfaces") which adds ->read_iter() for sysctl, that
> commit even bears your Signed-off-by. There may be other examples like
> that.
A better justification for this patch is that users like io_uring can
potentially write non-blocking to the file if ->write_iter() is
supported.
--
Jens Axboe
next prev parent reply other threads:[~2020-11-18 21:27 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-18 9:19 [PATCH] eventfd: convert to ->write_iter() Michal Kubecek
2020-11-18 15:18 ` Christoph Hellwig
2020-11-18 19:59 ` Michal Kubecek
2020-11-18 21:27 ` Jens Axboe [this message]
2020-11-18 23:18 ` Michal Kubecek
2020-11-18 23:25 ` Jens Axboe
2020-11-18 23:34 ` Michal Kubecek
2020-11-22 14:42 ` [eventfd] 5cb13cb023: will-it-scale.per_thread_ops -6.3% regression kernel test robot
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