[sheepdog] [PATCH 2/4] farm: add basic concurrent support

[Liu Yuan]

On 05/18/2012 07:34 PM, Christoph Hellwig wrote:

>> From: Liu Yuan <tailai.ly at taobao.com>
>> > 
>> > refactor strcut siocb, this makes the code more clean, also we can call xlockf()
>> > inside sd_store->read/write to support concurrent access.
>> > 
>> > - let sd_store->read/write() use open() internally.
>> > - remove sd_store->open()/close()
>> > - add sd_store->exist()
>> > 
>> > But now we don't actually have concurrent requests to the same object, because
>> > upper layer have exclude concurrent access by check_request().
>> > 
>> > We'll remove this constaint by later patch set.
> Can you split the refactoring from the actual concurrency changes?
> 
> Also I'd really prefer not having to call lockf twice for every single
> I/O, the kernel file locking code isn't exacly scalable.  Any pure
> userland locking will scale a lot better.
> 


Okay, I'll drop lockf and only do the refactoring and leave the locking
mechanism to be implemented later, for now I can't come up with a simple
userland lock mechanism.

Thanks,
Yuan