[Qemu-devel] Re: [PATCH] fix qemu_aio_flush

[Kevin Wolf <kwolf@redhat.com>]

Andrea Arcangeli schrieb:
> From: Andrea Arcangeli <aarcange@redhat.com>
> 
> qemu_aio_wait by invoking the bh or one of the aio completion
> callbacks, could end up submitting new pending aio, breaking the
> invariant that qemu_aio_poll returns only when no pending aio is
> outstanding (possibly a problem for migration as such).
> 
> Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>

You mean qemu_aio_flush, not poll. Anyway, the code looks fine.

Acked-by: Kevin Wolf <kwolf@redhat.com>

> ---
> 
> diff --git a/aio.c b/aio.c
> index 11fbb6c..dc9b85d 100644
> --- a/aio.c
> +++ b/aio.c
> @@ -103,11 +103,15 @@ void qemu_aio_flush(void)
>      do {
>          ret = 0;
>  
> +	/*
> +	 * If there are pending emulated aio start them now so flush
> +	 * will be able to return 1.
> +	 */
> +        qemu_aio_wait();
> +
>          LIST_FOREACH(node, &aio_handlers, node) {
>              ret |= node->io_flush(node->opaque);
>          }
> -
> -        qemu_aio_wait();
>      } while (ret > 0);
>  }
>  
> diff --git a/qemu-aio.h b/qemu-aio.h
> index 7967829..f262344 100644
> --- a/qemu-aio.h
> +++ b/qemu-aio.h
> @@ -24,9 +24,10 @@ typedef int (AioFlushHandler)(void *opaque);
>   * outstanding AIO operations have been completed or cancelled. */
>  void qemu_aio_flush(void);
>  
> -/* Wait for a single AIO completion to occur.  This function will until a
> - * single AIO opeartion has completed.  It is intended to be used as a looping
> - * primative when simulating synchronous IO based on asynchronous IO. */
> +/* Wait for a single AIO completion to occur.  This function will wait
> + * until a single AIO event has completed and it will ensure something
> + * has moved before returning. This can issue new pending aio as
> + * result of executing I/O completion or bh callbacks. */
>  void qemu_aio_wait(void);
>  
>  /* Register a file descriptor and associated callbacks.  Behaves very similarly
>