linux-kernel - Re: [PATCH v2] vfs: add RWF

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Date: Thu, 18 Jan 2024 09:02:11 -0700
From: Jens Axboe <axboe@...nel.dk>
To: Rich Felker <dalias@...c.org>
Cc: Jann Horn <jannh@...gle.com>, Alexander Viro <viro@...iv.linux.org.uk>,
 linux-fsdevel <linux-fsdevel@...r.kernel.org>,
 kernel list <linux-kernel@...r.kernel.org>,
 Linux API <linux-api@...r.kernel.org>,
 Pavel Begunkov <asml.silence@...il.com>,
 Christian Brauner <brauner@...nel.org>
Subject: Re: [PATCH v2] vfs: add RWF_NOAPPEND flag for pwritev2

On 1/18/24 8:57 AM, Rich Felker wrote:
> On Mon, Aug 31, 2020 at 11:05:34AM -0600, Jens Axboe wrote:
>> On 8/31/20 9:46 AM, Jann Horn wrote:
>>> On Mon, Aug 31, 2020 at 5:32 PM Rich Felker <dalias@...c.org> wrote:
>>>> The pwrite function, originally defined by POSIX (thus the "p"), is
>>>> defined to ignore O_APPEND and write at the offset passed as its
>>>> argument. However, historically Linux honored O_APPEND if set and
>>>> ignored the offset. This cannot be changed due to stability policy,
>>>> but is documented in the man page as a bug.
>>>>
>>>> Now that there's a pwritev2 syscall providing a superset of the pwrite
>>>> functionality that has a flags argument, the conforming behavior can
>>>> be offered to userspace via a new flag. Since pwritev2 checks flag
>>>> validity (in kiocb_set_rw_flags) and reports unknown ones with
>>>> EOPNOTSUPP, callers will not get wrong behavior on old kernels that
>>>> don't support the new flag; the error is reported and the caller can
>>>> decide how to handle it.
>>>>
>>>> Signed-off-by: Rich Felker <dalias@...c.org>
>>>
>>> Reviewed-by: Jann Horn <jannh@...gle.com>
>>>
>>> Note that if this lands, Michael Kerrisk will probably be happy if you
>>> send a corresponding patch for the manpage man2/readv.2.
>>>
>>> Btw, I'm not really sure whose tree this should go through - VFS is
>>> normally Al Viro's turf, but it looks like the most recent
>>> modifications to this function have gone through Jens Axboe's tree?
>>
>> Should probably go through Al's tree, I've only carried them when
>> they've been associated with io_uring in some shape or form.
> 
> This appears to have slipped through the cracks. Do I need to send an
> updated rebase of it? Were there any objections to it I missed?

Let's add Christian.

-- 
Jens Axboe