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Re: [RFC] Union mount readdir support in glibc
- From: Al Viro <viro at ZenIV dot linux dot org dot uk>
- To: Ulrich Drepper <drepper at redhat dot com>
- Cc: bharata at linux dot vnet dot ibm 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, 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>
- Date: Fri, 14 Mar 2008 05:39:25 +0000
- Subject: Re: [RFC] Union mount readdir support in glibc
- References: <20080311055527.GA7256@in.ibm.com> <47D9F6CC.6010009@redhat.com>
On Thu, Mar 13, 2008 at 08:53:48PM -0700, Ulrich Drepper wrote:
> To handle union FS at userlevel somewhere in that code sequence (perhaps
> in the fstat call) we'd have to recognize such mounts.
*Snort*
How about "the first entry returned by getdents(3) after open() is a whiteout
for e.g. '.'"? No fstat needed, zero impact for normal directories,
zero impact for any binaries on old kernels (where you wouldn't have
unions) and zero impact for old binaries on new kernels unless they
do getdents() on directory that happens to be a union.
And no lockstep...
> Before any
> agreement on userlevel sorting can be made you'll have to answer a
> question Roland already asked:
>
> - - How does this work with NFS?
It won't, kernel-side or done in userland.
> re seeking: you have to support seeking. There is no way around it.
Actually, do we really need it other than to 0 and to current position
(i.e. full rewind and a no-op)?