[lxc-devel] [RFC] rootfs pinning

[Rob Landley]

On 09/12/2013 01:27:07 PM, Christian Seiler wrote:
> Hi there,
> 
> just a quick question: currently, rootfs is pinned with a .hold file  
> in
> the parent directory (which btw. does not help against file systems  
> that
> are already mounted on the host but directly in the rootfs directory).
> The problem with the .hold file is that it doesn't make the directory
> necessarily pretty; I tend to mount all rootfs to /srv/lxc/$container
> (config remaining in /var/lib/lxc), and then when doing a ls  
> /srv/lxc, I
> see tons of .hold files. (I'm not even sure that they are removed  
> after
> container termination - but even if they are, the default state of a
> typical system tends to be that at least some containers are  
> running...)
> 
> Couldn't we just open $rootfs/lxc.hold for writing, keep the fd (as
> current pinfd) and then unlink (!) the file directly? According to  
> POSIX
> semantics, the file is then still open and the pinning should work  
> (now
> also for the above case), but there are no files lying around anymore.
> (Note: I didn't test that, it could well be that that doesn't work.)
> 
> Thoughts?

Why doesn't keeping a file open to the directory itself work? (I'm  
assuming it doesn't, I'm wondering why.)

Rob