Re: [Patch] Support overriding uid/gid in overlayfs

[Miklos Szeredi <miklos@szeredi.hu>]

On Mon, Jan 28, 2013 at 4:58 PM, Alessandro Pignotti
<alexpigna.dev@gmail.com> wrote:
> Hi everyone,
>
> the proposed patch would be useful in the following scenario
>
> 1) There is a large directory tree which needs to be fully read/write
> accessible from many different users, although in an isolated way (i.d.
> the changes made by Alice should not be visible to Bob)
> 2) All users expect to be owning the files. (i.d. that everything is
> private)
>
> With the proposed patch it is possible to store a single copy of the
> base directory tree and use it as the lowerdir. The upperdir is then set
> to a private user-writable directory. Each user as the illusion of a
> private fully-writable installation as required. Moreover, since all the
> changed files ends up in the upperdir it's easy to pack them for backup
> purposes.

Okay, makes sense.

One issue, though, is that stat("x") and fd=open("x"); fstat(fd) will
return different file stats (the fstat one will return the stats for
the original file).   This may confuse some apps.

This is a something a "true" union filesystem can do better that
union-mounts or overlayfs.

Thanks,
Miklos