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

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Date: Thu, 18 Jan 2024 10:57:37 -0500
From: Rich Felker <dalias@...c.org>
To: Jens Axboe <axboe@...nel.dk>
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>
Subject: Re: [PATCH v2] vfs: add RWF_NOAPPEND flag for pwritev2

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?

Rich