Subject: Re: bug#6960: mv refuses to move a symlink over a hard link to the same file

From: Eric Blake <[email-masked]>
Date: Wed, 04 Jan 2012 13:46:27 -0700

On 01/04/2012 01:32 PM, Anders Kaseorg wrote:
> This refusal makes it impossible to overwrite a hard link with a symlink 
> _atomically_.

It is already impossible to overwrite a directory with a symlink
atomically; then again, the only time rename() allows overwriting a
directory is if it is empty, and removing an empty directory before
putting a symlink in its place is not a form of data loss.  But whether
the inability to atomically overwrite a directory with a symlink should
carry over to a refusal to atomically overwrite a regular file with a
symlink is a different matter.

>> Personally, I prefer the semantics of 'mv -f --backup=numbered' so use a 
>> shell alias.
> 
> mv --backup=numbered is not atomic; it expands to two rename() syscalls, 
> between which the target doesn’t exist at all.

Maybe we should fix that, to make mv --backup use link()/rename() rather
than rename()/rename(), so that there is no window where the target
doesn't exist.

-- 
Eric Blake   [email-masked]    +1-919-301-3266
Libvirt virtualization library http://libvirt.org