Re: [PATCH v7 11/13] util/async: Add aio_co_reschedule_self()

[Markus Armbruster <armbru@redhat.com>]

Additional nitpick detail on Kevin's request.

Kevin Wolf <kwolf@redhat.com> writes:

> Add a function that can be used to move the currently running coroutine
> to a different AioContext (and therefore potentially a different
> thread).
>
> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
> ---
>  include/block/aio.h | 10 ++++++++++
>  util/async.c        | 30 ++++++++++++++++++++++++++++++
>  2 files changed, 40 insertions(+)
>
> diff --git a/include/block/aio.h b/include/block/aio.h
> index b2f703fa3f..c37617b404 100644
> --- a/include/block/aio.h
> +++ b/include/block/aio.h
> @@ -17,6 +17,7 @@
>  #ifdef CONFIG_LINUX_IO_URING
>  #include <liburing.h>
>  #endif
> +#include "qemu/coroutine.h"
>  #include "qemu/queue.h"
>  #include "qemu/event_notifier.h"
>  #include "qemu/thread.h"
> @@ -654,6 +655,15 @@ static inline bool aio_node_check(AioContext *ctx, bool is_external)
>   */
>  void aio_co_schedule(AioContext *ctx, struct Coroutine *co);
>  
> +/**
> + * aio_co_reschedule_self:
> + * @new_ctx: the new context
> + *
> + * Move the currently running coroutine to new_ctx. If the coroutine is already
> + * running in new_ctx, do nothing.

Wrapping the comment around column 70 or so would make it easier to
read.  Up to you.

> + */
> +void coroutine_fn aio_co_reschedule_self(AioContext *new_ctx);
> +
>  /**
>   * aio_co_wake:
>   * @co: the coroutine
> diff --git a/util/async.c b/util/async.c
> index 4266745dee..a609e18693 100644
> --- a/util/async.c
> +++ b/util/async.c
> @@ -569,6 +569,36 @@ void aio_co_schedule(AioContext *ctx, Coroutine *co)
>      aio_context_unref(ctx);
>  }
>  
> +typedef struct AioCoRescheduleSelf {
> +    Coroutine *co;
> +    AioContext *new_ctx;
> +} AioCoRescheduleSelf;
> +
> +static void aio_co_reschedule_self_bh(void *opaque)
> +{
> +    AioCoRescheduleSelf *data = opaque;
> +    aio_co_schedule(data->new_ctx, data->co);
> +}
> +
> +void coroutine_fn aio_co_reschedule_self(AioContext *new_ctx)
> +{
> +    AioContext *old_ctx = qemu_get_current_aio_context();
> +
> +    if (old_ctx != new_ctx) {
> +        AioCoRescheduleSelf data = {
> +            .co = qemu_coroutine_self(),
> +            .new_ctx = new_ctx,
> +        };
> +        /*
> +         * We can't directly schedule the coroutine in the target context
> +         * because this would be racy: The other thread could try to enter the
> +         * coroutine before it has yielded in this one.
> +         */

Likewise.

> +        aio_bh_schedule_oneshot(old_ctx, aio_co_reschedule_self_bh, &data);
> +        qemu_coroutine_yield();
> +    }
> +}
> +
>  void aio_co_wake(struct Coroutine *co)
>  {
>      AioContext *ctx;