Re: [Qemu-devel] [PATCH 2/5] qemu_coroutine_self should not be marked coroutine_fn as it cannot yield

[Stefan Hajnoczi <stefanha@gmail.com>]

On Mon, Aug 05, 2013 at 08:44:04PM +0200, Charlie Shepherd wrote:
> From: Charlie Shepherd <cs648@cam.ac.uk>
> 
> While it only really makes sense to call qemu_coroutine_self() in a coroutine
> context, it cannot actually yield execution itself, so remove the coroutine_fn
> annotation.
> ---
>  include/block/coroutine.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)

By removing coroutine_fn the rules have changed:

It's now legal to call qemu_coroutine_self() outside a coroutine.
Previously only callers that knew the internals of the coroutine
implementation did that.

coroutine_fn gives coroutine backend implementors more flexibility in
how they choose to implement qemu_coroutine_self().  From an API
perspective I prefer to keep qemu_coroutine_self() marked as a
coroutine_fn.

I guess the practical problem is that CPC will get
upset that it's being called by the coroutine implementation from
non-coroutine contexts.  This can be solved:

1. Keep the public qemu_coroutine_self() marked coroutine_fn.

2. Have it call an internal coroutine_self() function that is not
   coroutine_fn.

This way the API stays strict and the internal implementation doesn't
violate the coroutine_fn calling rule.

Stefan