From: "Pali Rohár" <pali.rohar@gmail.com>
To: Christoph Hellwig <hch@infradead.org>
Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
Alexander Viro <viro@zeniv.linux.org.uk>, Jan Kara <jack@suse.cz>
Subject: Re: Race-free unlinking of directory entries
Date: Mon, 9 Apr 2018 12:10:09 +0200 [thread overview]
Message-ID: <20180409101009.6kxd47jeowef7wt2@pali> (raw)
In-Reply-To: <20180409095919.GA9621@infradead.org>
On Monday 09 April 2018 02:59:19 Christoph Hellwig wrote:
> On Mon, Apr 09, 2018 at 09:42:41AM +0200, Pali Rohár wrote:
> > Hi! I would like to remind this my older email about race free
> > unlinking. Is there any plan to provide such support?
>
> Given that in Linux we know which directory entry a given fd refers to,
> we shouldn't even need a new syscall, but simply support the
> AT_EMPTY_PATH flag for funlinkat.
I do not think it is enough, specially in cases when hard links are in
use. Example:
fd = open("/a")
link("/a", "/b")
link("/a", "/c")
unlink("/a")
And now I want to call funlink for "fd". Which file should be unlinked?
"/b" or "/c" or none or both?
Another example:
fd = open("/a")
link("/a", "/b")
unlink("/a")
Calling funlink for fd should unlink "/b" or it should fail?
And another example:
fd = open("/a")
rename("/a", "/b")
What should funlink do for fd now?
Note that there is difference which symlink is shown in /proc/<pid>/fd
between last two examples -- even those two examples results in the same
state (if there is no race). For last example <fd> points to "/b", for
previous <fd> points to "/a (deleted)".
--
Pali Rohár
pali.rohar@gmail.com
next prev parent reply other threads:[~2018-04-09 10:10 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-12-20 19:18 Race-free unlinking of directory entries Pali Rohár
2018-04-09 7:42 ` Pali Rohár
2018-04-09 9:59 ` Christoph Hellwig
2018-04-09 10:10 ` Pali Rohár [this message]
2018-04-09 10:24 ` Christoph Hellwig
2018-04-09 10:35 ` Pali Rohár
2018-10-01 20:26 ` Pali Rohár
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:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20180409101009.6kxd47jeowef7wt2@pali \
--to=pali.rohar@gmail.com \
--cc=hch@infradead.org \
--cc=jack@suse.cz \
--cc=linux-fsdevel@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=viro@zeniv.linux.org.uk \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* 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).