Re: [Qemu-devel] [RFC PATCH 00/11] aio: Introduce handler type to fix nested aio_poll for dataplane

[Paolo Bonzini <pbonzini@redhat.com>]

On 23/07/2015 08:32, Fam Zheng wrote:
> 
> What is realized in this series is similar except the "disable, poll, enable"
> method, instead the bit mask of interesting client types is passed to
> aio_poll() (to be exact, passed to aio_poll_clients()). That is because,
> aio_poll may release the AioContext lock around ppoll, avoiding state will make
> the interface clearer.

However, this means that you must keep the AioContext lock during all
the long-running operations.  Is this actually necessary?  The original
purpose of keeping the lock (which didn't quite work) was to block out
dataplane operations.

Also, this requirements means you really need the AioContext lock to be
recursive.  This is not a huge deal, but I'd prefer that requirement not
to be too ingrained.

Paolo

> After this series, block layer aio_poll() will only process those "protocol"
> fds that are used in block I/O, plus the ctx->notifier for aio_notify();  other
> aio_poll()'s keep unchanged.
> 
> The biggest advantage over approaches [1] and [2] is, no change is needed in
> virtio-{blk,scsi}-dataplane code, also this doesn't depend on converting QMP to
> coroutines.