Re: [Qemu-devel] [PATCH 2/6] serial: reinstate watch after migration

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Paolo Bonzini (pbonzini@redhat.com) wrote:
> 
> 
> On 22/06/2016 17:05, Dr. David Alan Gilbert wrote:
> > * Paolo Bonzini (pbonzini@redhat.com) wrote:
> >> Otherwise, a serial port can get stuck if it is migrated while flow control
> >> is in effect.
> >>
> >> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> >> ---
> >>  hw/char/serial.c         | 16 ++++++++++++++--
> >>  include/hw/char/serial.h |  1 +
> >>  2 files changed, 15 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/hw/char/serial.c b/hw/char/serial.c
> >> index e65e9e0..6f0a49e 100644
> >> --- a/hw/char/serial.c
> >> +++ b/hw/char/serial.c
> >> @@ -639,8 +639,20 @@ static int serial_post_load(void *opaque, int version_id)
> >>      if (s->thr_ipending == -1) {
> >>          s->thr_ipending = ((s->iir & UART_IIR_ID) == UART_IIR_THRI);
> >>      }
> >> -    if (s->tsr_retry > MAX_XMIT_RETRY) {
> >> -        s->tsr_retry = MAX_XMIT_RETRY;
> > 
> > Why remove the check you just added?
> 
> Because I'm dumb. :)
> 
> >> +
> >> +    if (s->tsr_retry > 0) {
> >> +        /* tsr_retry > 0 implies LSR.TEMT = 0 (transmitter not empty).  */
> >> +        if (s->lsr & UART_LSR_TEMT) {
> >> +            return -1;
> >> +        }
> >> +
> >> +        assert(s->watch_tag == 0);
> >> +        s->watch_tag = qemu_chr_fe_add_watch(s->chr, G_IO_OUT|G_IO_HUP, serial_xmit, s);
> >> +    } else {
> >> +        /* tsr_retry == 0 implies LSR.TEMT = 1 (transmitter empty).  */
> >> +        if (!(s->lsr & UART_LSR_TEMT)) {
> >> +            return -1;
> > 
> > If you're failing migration (-1) then please error_report to say why
> > so when someone hits it I can immediately see why.
> 
> Ok, something like
> 
>     error_report("inconsistent state in serial device");
> 
> ?

Yeh, feel free to add tsr_retry and lsr to the message as well so that if you're
looking at it you can figure out what happened.

Dave

> 
> Paolo
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK