Re: [Qemu-devel] coroutine bug?, was Re: [PATCH] sheepdog: use coroutines

[Paolo Bonzini]

On 01/04/2012 04:58 PM, Christoph Hellwig wrote:
> Btw, what is the plan forward for the block I/O interface?  Only
> qcow2, sheepdog and nbd implement the coroutine interfaces

Actually all formats implement a coroutine interface except raw, qed and 
vdi (IIRC).  But the "minor" formats do not implement scatter/gather 
I/O, and use a bounce buffer instead.

Among the protocols, only nbd implements coroutines, the others use AIO.

> , and none of the
> hardware emulations calls them directly.

Yes, AIO is often simpler to use for hardware emulation (or anyway it 
has smaller advantages).  But I do expect that SD could easily switch 
from synchronous to coroutines, for example.  Floppy is a mess.

IMO both coroutines and AIO have their uses.  Converting qed to 
coroutines would make sense, but this is much less true for converting 
raw and even less for rbd or iscsi (the external libraries are 
callback-based).

On the other hand, changing all formats to support scatter/gather I/O 
should not be hard, and would enable some nice simplifications in the 
code.  I have enough other cleanups on my plate, though. :/

Paolo