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

[Liu Yuan]

On 06/05/2012 07:55 PM, Christoph Hellwig wrote:

> On Mon, Jun 04, 2012 at 10:42:00AM +0800, Liu Yuan wrote:
>> From: Liu Yuan <tailai.ly at taobao.com>
>>
>> For a second thought, even QEMU can issue multiple requests to the same object
>> we are guaranteed that those requests don't overlap on each other. Recovery
>> code and IO code might access the same object, but the race is excluded by epoch
>> so we don't need per-object lock at all for now.
> 
> How are we guaranteed that?  I'm pretty sure I debugged a problem with
> the kernel AIO code a while ago where that was not the case when using
> windows guests. (Using the qemu raw-posix backend, not sheepdog)
> 


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.

Thanks,
Yuan