From: Al Viro <viro@zeniv.linux.org.uk>
To: Omar Sandoval <osandov@osandov.com>
Cc: Trond Myklebust <trondmy@hammerspace.com>,
"amir73il@gmail.com" <amir73il@gmail.com>,
"dhowells@redhat.com" <dhowells@redhat.com>,
"lsf-pc@lists.linux-foundation.org"
<lsf-pc@lists.linux-foundation.org>, "hch@lst.de" <hch@lst.de>,
"miklos@szeredi.hu" <miklos@szeredi.hu>,
"linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>
Subject: Re: [LSF/MM/BPF TOPIC] Allowing linkat() to replace the destination
Date: Sat, 18 Jan 2020 00:47:38 +0000 [thread overview]
Message-ID: <20200118004738.GQ8904@ZenIV.linux.org.uk> (raw)
In-Reply-To: <20200117235444.GC295250@vader>
On Fri, Jan 17, 2020 at 03:54:44PM -0800, Omar Sandoval wrote:
> > 3) permission checks need to be specified
>
> I believe the only difference here vs standard linkat is that newpath
> must not be immutable or append-only?
I would bloody hope not - at the very least you want sticky bit on parent
to have effect, same as with rename()/rmdir()/unlink()...
> > references to pathconf, Cthulhu and other equally delightful entities
> > are not really welcome.
>
> EOPNOTSUPP is probably the most helpful.
Umm... What would you feed it, though? You need to get past your
"links to the same file, do nothing" escape...
> Based on my previous attempt at it [1], it's not too bad.
+ error = may_delete(dir, new_dentry, d_is_dir(old_dentry));
Why bother with d_is_dir(), when you are going to reject directories
anyway?
+ if (dir->i_op->link)
+ error = dir->i_op->link(old_dentry, dir, new_dentry);
+ else
+ error = dir->i_op->link2(old_dentry, dir, new_dentry, flags);
+ if (error)
+ goto out;
+
No. This is completely wrong; just make it ->link_replace() and be done
with that; no extra arguments and *always* the same conditions wrt
positive/negative. One of the reasons why ->rename() tends to be
ugly (and a source of quite a few bugs over years) are those "if
target is positive/if target is negative" scattered over the instances.
Make the choice conditional upon the positivity of target.
And you don't need to reproduce every quirk of rename() error values.
Really. Unless you really intend to have userland do a loop of
linkat(2) attempts (a-la mkstemp(3)), followed by rename(2) for
fallback...
next prev parent reply other threads:[~2020-01-18 0:47 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-17 12:49 [LSF/MM/BPF TOPIC] Allowing linkat() to replace the destination David Howells
2020-01-17 14:33 ` Trond Myklebust
2020-01-17 15:46 ` Al Viro
2020-01-17 16:12 ` Trond Myklebust
2020-01-17 16:48 ` Al Viro
2020-01-17 16:36 ` Omar Sandoval
2020-01-17 16:59 ` Al Viro
2020-01-17 17:28 ` Omar Sandoval
2020-01-17 18:17 ` Al Viro
2020-01-17 20:22 ` Omar Sandoval
2020-01-17 22:22 ` Al Viro
2020-01-17 23:54 ` Omar Sandoval
2020-01-18 0:47 ` Al Viro [this message]
2020-01-18 1:17 ` Omar Sandoval
2020-01-18 2:20 ` Al Viro
2020-01-21 23:05 ` Omar Sandoval
2020-01-22 6:57 ` Amir Goldstein
2020-01-22 22:10 ` Omar Sandoval
2020-01-23 3:47 ` Al Viro
2020-01-23 7:16 ` Dave Chinner
2020-01-23 7:47 ` Amir Goldstein
2020-01-24 21:25 ` Dave Chinner
2020-01-31 5:24 ` Darrick J. Wong
2020-01-31 5:29 ` hch
2020-01-31 7:00 ` Amir Goldstein
2020-01-31 20:33 ` Omar Sandoval
2020-01-31 21:55 ` Amir Goldstein
2020-01-28 1:27 ` Omar Sandoval
2020-01-28 14:35 ` David Howells
2020-01-31 5:31 ` hch
2020-01-31 8:04 ` David Howells
2020-01-31 8:56 ` Amir Goldstein
2020-01-22 9:53 ` David Howells
2020-01-17 14:47 ` David Howells
2020-01-17 14:56 ` Trond Myklebust
2020-01-17 16:01 ` Al Viro
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