archive mirror
 help / color / mirror / Atom feed
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: Tue, 24 Apr 2018 08:26:10 -0700	[thread overview]
Message-ID: <20180424152610.GA6989@vader> (raw)
In-Reply-To: <>

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

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?).

  reply	other threads:[~2018-04-24 15:26 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 [this message]
2018-04-26  7:49     ` Omar Sandoval
2018-04-27 12:00 ` Michael Kerrisk (man-pages)
2018-05-04 18:29   ` Omar Sandoval
2018-05-04 18:30 ` Omar Sandoval

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20180424152610.GA6989@vader \ \ \ \ \ \ \ \ \

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).