Re: [Qemu-devel] [PATCH v6 06/18] aio: stop using .io_flush()

[Jeff Cody <jcody@redhat.com>]

On Thu, Jul 25, 2013 at 05:18:13PM +0200, Stefan Hajnoczi wrote:
> Now that aio_poll() users check their termination condition themselves,
> it is no longer necessary to call .io_flush() handlers.
> 
> The behavior of aio_poll() changes as follows:
> 
> 1. .io_flush() is no longer invoked and file descriptors are *always*
> monitored.  Previously returning 0 from .io_flush() would skip this file
> descriptor.
> 
> Due to this change it is essential to check that requests are pending
> before calling qemu_aio_wait().  Failure to do so means we block, for
> example, waiting for an idle iSCSI socket to become readable when there
> are no requests.  Currently all qemu_aio_wait()/aio_poll() callers check
> before calling.
> 
> 2. aio_poll() now returns true if progress was made (BH or fd handlers
> executed) and false otherwise.  Previously it would return true whenever
> 'busy', which means that .io_flush() returned true.  The 'busy' concept
> no longer exists so just progress is returned.
> 
> Due to this change we need to update tests/test-aio.c which asserts
> aio_poll() return values.  Note that QEMU doesn't actually rely on these
> return values so only tests/test-aio.c cares.
> 
> Note that ctx->notifier, the EventNotifier fd used for aio_notify(), is
> now handled as a special case.  This is a little ugly but maintains
> aio_poll() semantics, i.e. aio_notify() does not count as 'progress' and
> aio_poll() avoids blocking when the user has not set any fd handlers yet.
> 
> Patches after this remove .io_flush() handler code until we can finally
> drop the io_flush arguments to aio_set_fd_handler() and friends.
> 
> Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> ---
>  aio-posix.c      | 29 +++++++++--------------------
>  aio-win32.c      | 34 ++++++++++++++--------------------
>  tests/test-aio.c | 10 +++++-----
>  3 files changed, 28 insertions(+), 45 deletions(-)
> 

Reviewed-by: Jeff Cody <jcody@redhat.com>