[Qemu-devel] Re: [patch 04/11] qemu: introduce main_loop_break

[Anthony Liguori]

address@hidden wrote:
> Use a pipe to signal pending work for the iothread.
>
> Signed-off-by: Marcelo Tosatti <address@hidden>
>
> Index: trunk/qemu-common.h
> ===================================================================
> --- trunk.orig/qemu-common.h
> +++ trunk/qemu-common.h
> @@ -186,6 +186,8 @@ int cpu_load(QEMUFile *f, void *opaque, 
>  /* Force QEMU to stop what it's doing and service IO */
>  void qemu_service_io(void);
>
> +void main_loop_break(void);
> +
>  /* Force QEMU to process pending events */
>  void qemu_notify_event(void);
>
> Index: trunk/vl.c
> ===================================================================
> --- trunk.orig/vl.c
> +++ trunk/vl.c
> @@ -276,6 +276,8 @@ static QEMUTimer *nographic_timer;
>
>  uint8_t qemu_uuid[16];
>
> +static int io_thread_fd = -1;
> +
>  /***********************************************************/
>  /* x86 ISA bus support */
>
> @@ -3632,6 +3634,55 @@ void qemu_notify_event(void)
>       }
>  }
>
> +void main_loop_break(void)
> +{
> +    uint64_t value = 1;
> +    char buffer[8];
> +    size_t offset = 0;
> +
> +    if (io_thread_fd == -1)
> +        return;
> +
> +    memcpy(buffer, &value, sizeof(value));
> +
> +    while (offset < 8) {
> +        ssize_t len;
> +
> +        len = write(io_thread_fd, buffer + offset, 8 - offset);
> +        if (len == -1 && errno == EINTR)
> +            continue;
> +
> +        if (len <= 0)
> +            break;
> +
> +        offset += len;
> +    }
> +
> +    if (offset != 8)
> +        fprintf(stderr, "failed to notify io thread\n");
> +}
>   

I'd like to see a higher level abstraction here.  This is trying to be 
eventfd compatible which is great, but we should have something like:

qemu_event_increment();
qemu_event_read();

It'll simplify this code a lot.  We can also switch some of the other 
existing code to use this too later.

Regards,

Anthony Liguori