On Tue, Jul 21, 2009 at 5:02 AM, Priyanka
Sharma<[email protected]> wrote:
>
> Now,
> I read about union mount(for MBEFORE and MAFTER), this is the most dificult
> part to implement in my project.
> I am looking at aufs filesystem service for linux. I haven't got proper idea
> yet but I am looking on this.
>
> It will be very helpful, If anyone can give me some advise regarding union
> mount implementation and aufs.
>
Its not an easy solution, but there have been several attempts in the
Linux community with resulting advantages and problems. Make sure you
read all the unionfs papers as they suggest several approaches (and
pitfalls). Plan 9 unions are a bit easier because its single
directory and we don't do whiteouts. Last time I looked at it, I was
thinking of adding a union flag to the vfsmount structure which the
user can apply as an open to the bind mount and then writing some
meta-operations to union component binds within the namespace for
certain ops (readdir, lookup, etc.) The big downside with that
approach is you'll get the duplicates in the readdir and Linux won't
know how to deal with them. You could filter on them within the
meta-ops, but that isn't really what Plan 9 does.
I haven't looked at that portion of the Linux kernel code for some
time, but when you come up with a plan I'd be happy to review it.
-eric
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