From: Omar Sandoval <osandov@osandov.com>
To: Al Viro <viro@zeniv.linux.org.uk>
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: Fri, 17 Jan 2020 09:28:55 -0800 [thread overview]
Message-ID: <20200117172855.GA295250@vader> (raw)
In-Reply-To: <20200117165904.GN8904@ZenIV.linux.org.uk>
On Fri, Jan 17, 2020 at 04:59:04PM +0000, Al Viro wrote:
> On Fri, Jan 17, 2020 at 08:36:16AM -0800, Omar Sandoval wrote:
>
> > The semantics I implemented in my series were basically "linkat with
> > AT_REPLACE replaces the target iff rename would replace the target".
> > Therefore, symlinks are replaced, not followed, and mountpoints get
> > EXDEV. In my opinion that's both sane and unsurprising.
>
> Umm... EXDEV in rename() comes when _parents_ are on different mounts.
> rename() over a mountpoint is EBUSY if it has mounts in caller's
> namespace, but it succeeds (and detaches all mounts on the victim
> in any namespaces) otherwise.
>
> When are you returning EXDEV?
EXDEV was a thinko, the patch does what rename does:
+ if (is_local_mountpoint(new_dentry)) {
+ error = -EBUSY;
+ goto out;
+ }
...
+ if (target) {
+ dont_mount(new_dentry);
+ detach_mounts(new_dentry);
+ }
Anyways, my point is that the rename semantics cover 90% of AT_REPLACE.
Before I resend the patches, I'll write up the documentation and we can
see what other corner cases I missed.
> Incidentally, mounts _are_ traversed on
> the link source, so what should that variant do when /tmp/foo is
> a mountpoint and you feed it "/tmp/foo" both for source and target?
EBUSY and noop both seem reasonable in this case, so we pick one and
document it.
next prev parent reply other threads:[~2020-01-17 17:28 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 [this message]
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
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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