[sheepdog] [PATCH 2/2] farm: drop fcntl lock

[Liu Yuan]

On 06/05/2012 09:23 PM, Christoph Hellwig wrote:

> On Tue, Jun 05, 2012 at 09:20:30PM +0800, Liu Yuan wrote:
>> You meant the requests from Guest could be overlapped? Disk is seen by
>> guest OS as an array of blocks, I can't imagine any sane driver issue
>> overlapped requests to disk drive controller.
> 
> Yes, we've seen overlapping or duplicate requests from the OS.
> 
> Assuming any sort of sanity from the OS is unfortunately not an option
> in virtualized environments.


This would be something odd, but we have to face up with. Well, then
there might be problems with overlapped requests:

Ordering:
1 over network, the requests seen by Sheepdog might not be the same as
is from Guest.
2 how do we deal with overlapped read/write, write/write pair?

Looks to me, even with locks, we can't cope with it.

Thanks,
Yuan