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.
