Re: [Xen-devel] [PATCH] serial: poll the serial console with G_IO_HUP

[Paolo Bonzini <pbonzini@xxxxxxxxxx>]

Il 22/04/2014 19:08, Roger Pau Monne ha scritto:
> On FreeBSD polling a master pty while the other end is not connected
> with G_IO_OUT only results in an endless wait. This is different from
> the Linux behaviour, that returns immediately. In order to demonstrate
> this, I have the following example code:
> 
> http://xenbits.xen.org/people/royger/test_poll.c
> 
> When executed on Linux:
> 
> $ ./test_poll
> In callback
> 
> On FreeBSD instead, the callback never gets called:
> 
> $ ./test_poll
> 
> So, in order to workaround this, poll the source with G_IO_HUP (which
> makes the code behave the same way on both Linux and FreeBSD).
> 
> Signed-off-by: Roger Pau Monnà <roger.pau@xxxxxxxxxx>
> Cc: Peter Crosthwaite <peter.crosthwaite@xxxxxxxxxx>
> Cc: Michael Tokarev <mjt@xxxxxxxxxx>
> Cc: "Andreas FÃrber" <afaerber@xxxxxxx>
> Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx
> ---
>  hw/char/serial.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/hw/char/serial.c b/hw/char/serial.c
> index 6025592..ab9c40f 100644
> --- a/hw/char/serial.c
> +++ b/hw/char/serial.c
> @@ -243,7 +243,7 @@ static gboolean serial_xmit(GIOChannel *chan, 
> GIOCondition cond, void *opaque)
>          serial_receive1(s, &s->tsr, 1);
>      } else if (qemu_chr_fe_write(s->chr, &s->tsr, 1) != 1) {
>          if (s->tsr_retry >= 0 && s->tsr_retry < MAX_XMIT_RETRY &&
> -            qemu_chr_fe_add_watch(s->chr, G_IO_OUT, serial_xmit, s) > 0) {
> +            qemu_chr_fe_add_watch(s->chr, G_IO_OUT|G_IO_HUP, serial_xmit, s) 
> > 0) {
>              s->tsr_retry++;
>              return FALSE;
>          }
> 

The patch looks good.  However, the same problem is most likely there
in other places:

hw/char/cadence_uart.c:        int r = qemu_chr_fe_add_watch(s->chr, G_IO_OUT, 
cadence_uart_xmit, s);
hw/char/serial.c:            qemu_chr_fe_add_watch(s->chr, G_IO_OUT, 
serial_xmit, s) > 0) {
hw/char/virtio-console.c:                vcon->watch = 
qemu_chr_fe_add_watch(vcon->chr, G_IO_OUT,
hw/usb/redirect.c:            dev->watch = qemu_chr_fe_add_watch(dev->cs, 
G_IO_OUT,
monitor.c:            mon->watch = qemu_chr_fe_add_watch(mon->chr, G_IO_OUT,

Should we add G_IO_HUP everywhere we have G_IO_OUT?

Or perhaps even in qemu_chr_fe_add_watch (I don't really like this,
but I will shoot it out...)?

Paolo

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