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Re: [RFC PATCH 1/2] Union Mount: glibc readdir support
- From: Erez Zadok <ezk at cs dot sunysb dot edu>
- To: bharata at linux dot vnet dot ibm dot com
- Cc: Ulrich Drepper <drepper at redhat dot com>, bsn dot 0007 at gmail dot com, libc-alpha at sourceware dot org, Jan Blunck <jblunck at suse dot de>, Erez Zadok <ezk at cs dot sunysb dot edu>, linux-kernel at vger dot kernel dot org, linux-fsdevel at vger dot kernel dot org, viro at zeniv dot linux dot org dot uk, Christoph Hellwig <hch at lst dot de>, Mingming Cao <cmm at us dot ibm dot com>, Dave Hansen <haveblue at us dot ibm dot com>, Trond Myklebust <trond dot myklebust at fys dot uio dot no>, David Woodhouse <dwmw2 at infradead dot org>
- Date: Fri, 9 May 2008 16:05:54 -0400
- Subject: Re: [RFC PATCH 1/2] Union Mount: glibc readdir support
In message <20080506042117.GA29298@in.ibm.com>, Bharata B Rao writes:
> On Wed, Apr 30, 2008 at 11:08:41PM -0700, Ulrich Drepper wrote:
> >
> > Before anything further is discussed I need to know how you expect to
> > handle NFS? I don't see how, with a userlevel readdir implementation,
> > you can support NFS.
>
> At the client side, I don't see a problem with unioning NFS with other
> FS. Kernel would still return all dirents of the union including those
> from NFS and glibc readdir would be able to handle them appropriately.
> Or am I missing something ?
>
> At the server side, I can't see how NFS server could export a union.
> I don't see how this could be sanely done with Union Mount. Erez, how
> does Unionfs handle this ?
[...]
The ODF version of unionfs stores, among other things, persistent inode
numbers in a small/special /odf partition. If the inums aren't persistent,
they could get flushed out of memory, making it very difficult to
reconstruct the inode w/ the same inum later on.
Erez.