Re: [Qemu-devel] [PATCH v3 2/5] block: extract AIO_WAIT_WHILE() from BlockDriverState

[Eric Blake <eblake@redhat.com>]

On 02/16/2018 10:50 AM, Stefan Hajnoczi wrote:
> BlockDriverState has the BDRV_POLL_WHILE() macro to wait on event loop
> activity while a condition evaluates to true.  This is used to implement
> synchronous operations where it acts as a condvar between the IOThread
> running the operation and the main loop waiting for the operation.  It
> can also be called from the thread that owns the AioContext and in that
> case it's just a nested event loop.
> 
> BlockBackend needs this behavior but doesn't always have a
> BlockDriverState it can use.  This patch extracts BDRV_POLL_WHILE() into
> the AioWait abstraction, which can be used with AioContext and isn't
> tied to BlockDriverState anymore.
> 
> This feature could be built directly into AioContext but then all users
> would kick the event loop even if they signal different conditions.
> Imagine an AioContext with many BlockDriverStates, each time a request
> completes any waiter would wake up and re-check their condition.  It's
> nicer to keep a separate AioWait object for each condition instead.
> 
> Please see "block/aio-wait.h" for details on the API.
> 
> The name AIO_WAIT_WHILE() avoids the confusion between AIO_POLL_WHILE()
> and AioContext polling.
> 
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> ---

Reviewed-by: Eric Blake <eblake@redhat.com>

-- 
Eric Blake, Principal Software Engineer
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