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

[Roger Pau Monnà <roger.pau@xxxxxxxxxx>]

On 28/04/14 11:19, Paolo Bonzini wrote:
> 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) {

This is the one I've fixed.

> 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?

IMOH it seems better to add G_IO_HUP to those other callers rather than
appending it in qemu_chr_fe_add_watch unconditionally, but I don't have
a strong opinion. If no one else expresses an interest into having it
added to qemu_chr_fe_add_watch I will send a new version that also fixes
the other callers listed above.

Roger.


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