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From: Omar Sandoval <>
To: Christoph Hellwig <>
Cc: Al Viro <>,,
	Linus Torvalds <>,,,
	Xi Wang <>
Subject: Re: [RFC PATCH v3 0/2] fs: add AT_REPLACE flag for linkat()
Date: Thu, 26 Apr 2018 00:49:33 -0700	[thread overview]
Message-ID: <20180426074933.GA16273@vader> (raw)
In-Reply-To: <20180424152610.GA6989@vader>

On Tue, Apr 24, 2018 at 08:26:10AM -0700, Omar Sandoval wrote:
> On Tue, Apr 24, 2018 at 06:21:07AM -0700, Christoph Hellwig wrote:
> > > Patch 1 implements the VFS support for this flag. The implementation
> > > resembles sys_renameat2(), and I took care to preserve all of the
> > > original error cases and make the new error cases consistent with
> > > rename.
> > 
> > Shouldn't we try to reuse the rename code and the ->rename method
> > instead of largely duplicating it?
> As I mentioned in my cover letter, I did try, and it was uglier to reuse
> rename. 
> For O_TMPFILE, we can't pass a meaningful old_dir to ->rename(), so now
> every ->rename() supporting AT_EMPTY_PATH has to grow a bunch of special
> cases for ignoring old_dir (I looked at Btrfs, ext4, and XFS, and it'd
> be messy for all three). Conversely, ->link() just needs the extra
> unlink before link logic (I added ->link2() for this RFC, but for the
> actual patch I'll just add the flag to ->link()).
> On the VFS side, in my opinion, there isn't that much duplication -- we
> have the may_delete()/is_local_mountpoint() a la unlink, delegation
> handling, and some specific error cases we need to handle similarly to
> rename, but that's not too suprising for a new primitive.
> > In fact I wonder if a better interface would just use renameat(2)
> > and accept the AT_EMPTY_PATH (for the source name only).
> renameat() makes sense for the O_TMPFILE case, but linkat() + AT_REPLACE
> also supports a normal, named source file, and renameat() +
> AT_EMPTY_PATH for that doesn't make sense at all (rename this file by
> file descriptor, but don't really rename it?).

Oh, another argument in favor of linkat() is that existing programs
which are naming an O_TMPFILE will already be using linkat(), and it's
just a matter of adding the AT_REPLACE flag and skipping the temporary
name/rename dance.

  reply	other threads:[~2018-04-26  7:49 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-04-24  6:19 [RFC PATCH v3 0/2] fs: add AT_REPLACE flag for linkat() Omar Sandoval
2018-04-24  6:19 ` [RFC PATCH v3 1/2] fs: add AT_REPLACE flag for linkat() which replaces the target Omar Sandoval
2018-04-24 22:14   ` Omar Sandoval
2018-04-24  6:19 ` [RFC PATCH v3 2/2] Btrfs: add support for linkat() AT_REPLACE Omar Sandoval
2018-04-24 13:21 ` [RFC PATCH v3 0/2] fs: add AT_REPLACE flag for linkat() Christoph Hellwig
2018-04-24 15:26   ` Omar Sandoval
2018-04-26  7:49     ` Omar Sandoval [this message]
2018-04-27 12:00 ` Michael Kerrisk (man-pages)
2018-05-04 18:29   ` Omar Sandoval
2018-05-04 18:30 ` Omar Sandoval

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