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

[Anthony Liguori <anthony@codemonkey.ws>]

Chris Webb wrote:
> Anthony Liguori <anthony@codemonkey.ws> 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.
>