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Re: [Qemu-devel] [PATCH] Disk image shared and exclusive locks.


From: Anthony Liguori
Subject: Re: [Qemu-devel] [PATCH] Disk image shared and exclusive locks.
Date: Mon, 07 Dec 2009 07:47:39 -0600
User-agent: Thunderbird 2.0.0.23 (X11/20090825)

Chris Webb wrote:
Anthony Liguori <address@hidden> writes:

I've resisted this because I'm concerned that if we delay the
opening of the file on the destination, it could fail.  That's a
very late failure and that makes me uncomfortable as just a work
around for NFS.

I don't know much about NFS's semantics with cache-coherency, but I take it
there isn't some sort of synchronisation operation that works on a file
descriptor and could be done instead as the vm starts and stops to avoid
having to delay the open itself? I agree with you that failing this late
could make for some rather nasty behaviour compared to the current version.

I think this is a case of spec vs. in practice. By the NFS spec, coherence is only guaranteed as close-after-open. Let me poke around and see if I can find anyone with better info.

Regards,

Anthony Liguori
Cheers,

Chris.





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