Re: [PATCH 6/8] virtio-blk: mark IO_CODE functions

[Stefan Hajnoczi]

On Thu, Jun 09, 2022 at 10:37:25AM -0400, Emanuele Giuseppe Esposito wrote:
> Just as done in the block API, mark functions in virtio-blk
> that are called also from iothread(s).
> 
> We know such functions are IO because many are blk_* callbacks,
> running always in the device iothread, and remaining are propagated
> from the leaf IO functions (if a function calls a IO_CODE function,
> itself is categorized as IO_CODE too).
> 
> Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
> ---
>  hw/block/dataplane/virtio-blk.c |  4 ++++
>  hw/block/virtio-blk.c           | 35 +++++++++++++++++++++++++++++++++
>  2 files changed, 39 insertions(+)

The definition of IO_CODE() is:

  I/O API functions. These functions are thread-safe, and therefore
  can run in any thread as long as the thread has called
  aio_context_acquire/release().

I'm not sure it matches with the exact semantics you have in mind. Are
they really allowed to be called from any thread and even from multiple
threads? Or maybe just from the BlockBackend's AioContext thread?

We need to be very careful to define these terms precisely and avoid
applying them in cases that are similar but different as that will cause
problems in the future.

Otherwise:
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>

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