Re: [Qemu-devel] [PATCH] qxl: replace pipe signaling with bottom half

[Alon Levy]

On 10/30/2013 10:17 AM, Gerd Hoffmann wrote:
> qxl creates a pipe, then writes something to it to wake up the iothread
> from the spice server thread to raise an irq.  These days qemu bottom
> halves can be scheduled from threads and signals, so there is no reason
> to do this any more.  Time to clean it up.
> 
> Signed-off-by: Gerd Hoffmann <address@hidden>

Reviewed-by: Alon Levy <address@hidden>

> ---
>  hw/display/qxl.c | 33 +++------------------------------
>  hw/display/qxl.h |  3 +--
>  2 files changed, 4 insertions(+), 32 deletions(-)
> 
> diff --git a/hw/display/qxl.c b/hw/display/qxl.c
> index de835d6..41c34b1 100644
> --- a/hw/display/qxl.c
> +++ b/hw/display/qxl.c
> @@ -1701,15 +1701,9 @@ static const MemoryRegionOps qxl_io_ops = {
>      },
>  };
>  
> -static void pipe_read(void *opaque)
> +static void qxl_update_irq_bh(void *opaque)
>  {
>      PCIQXLDevice *d = opaque;
> -    char dummy;
> -    int len;
> -
> -    do {
> -        len = read(d->pipe[0], &dummy, sizeof(dummy));
> -    } while (len == sizeof(dummy));
>      qxl_update_irq(d);
>  }
>  
> @@ -1730,28 +1724,7 @@ static void qxl_send_events(PCIQXLDevice *d, uint32_t 
> events)
>      if ((old_pending & le_events) == le_events) {
>          return;
>      }
> -    if (qemu_thread_is_self(&d->main)) {
> -        qxl_update_irq(d);
> -    } else {
> -        if (write(d->pipe[1], d, 1) != 1) {
> -            dprint(d, 1, "%s: write to pipe failed\n", __func__);
> -        }
> -    }
> -}
> -
> -static void init_pipe_signaling(PCIQXLDevice *d)
> -{
> -    if (pipe(d->pipe) < 0) {
> -        fprintf(stderr, "%s:%s: qxl pipe creation failed\n",
> -                __FILE__, __func__);
> -        exit(1);
> -    }
> -    fcntl(d->pipe[0], F_SETFL, O_NONBLOCK);
> -    fcntl(d->pipe[1], F_SETFL, O_NONBLOCK);
> -    fcntl(d->pipe[0], F_SETOWN, getpid());
> -
> -    qemu_thread_get_self(&d->main);
> -    qemu_set_fd_handler(d->pipe[0], pipe_read, NULL, d);
> +    qemu_bh_schedule(d->update_irq);
>  }
>  
>  /* graphics console */
> @@ -2044,7 +2017,7 @@ static int qxl_init_common(PCIQXLDevice *qxl)
>      }
>      qemu_add_vm_change_state_handler(qxl_vm_change_state_handler, qxl);
>  
> -    init_pipe_signaling(qxl);
> +    qxl->update_irq = qemu_bh_new(qxl_update_irq_bh, qxl);
>      qxl_reset_state(qxl);
>  
>      qxl->update_area_bh = qemu_bh_new(qxl_render_update_area_bh, qxl);
> diff --git a/hw/display/qxl.h b/hw/display/qxl.h
> index 84f0182..c5de3d7 100644
> --- a/hw/display/qxl.h
> +++ b/hw/display/qxl.h
> @@ -81,8 +81,7 @@ typedef struct PCIQXLDevice {
>      QemuMutex          track_lock;
>  
>      /* thread signaling */
> -    QemuThread         main;
> -    int                pipe[2];
> +    QEMUBH             *update_irq;
>  
>      /* ram pci bar */
>      QXLRam             *ram;
>