[Qemu-devel] Re: [PATCH][RFC] Refactor AIO to allow multiple AIO implementations

[Anthony Liguori <aliguori@us.ibm.com>]

Gerd Hoffmann wrote:
> Anthony Liguori wrote:
>   
>> This patch refactors the AIO layer to allow multiple AIO implementations.  It's
>> only possible because of the recent signalfd() patch.  
>>
>> Right now, the AIO infrastructure is pretty specific to the block raw backend.
>> For other block devices to implement AIO, the qemu_aio_wait function must support
>> registration.  This patch introduces a new function, qmeu_aio_set_fd_handler, which
>> can be used to register a file descriptor to be called back.  qemu_aio_wait() now
>> polls a set of file descriptors registered with this function until one becomes
>> readable or writable.
>>     
>
> Hmm, what is the long-term plan for this?

Step one is to move the generic aio bits out of block-raw-posix (which 
this patch does).

Step two is to move the posix-aio routines out of block-raw-posix.

Step three would be to add a generic interface to allow block-raw-posix 
to use multiple aio implementations

Step four would be to add a new aio implementation (I think the best 
route is a thread-pool based implementation).

Regards,

Anthony Liguori

>   Separating out the completion
> notification is a nice first step.  Most of the aio infrastructure is
> still in the block raw backend though.  IMHO it doesn't belong there.
>
> The aio implementation(s) should be a separate entity usable by all
> block backends to invoke aio requests, without having to care about how
> this is actually implemented (threads, linux aio, posix aio, whatever).
>
> cheers,
>   Gerd
>
>