[Qemu-devel] Re: more about serial ports: do they even work?

[Michael Tokarev <mjt@tls.msk.ru>]

David S. Ahern wrote:
> Michael Tokarev wrote:
>> David S. Ahern wrote:
>>> I don't recall seeing a followup to this post.
>>>
>>> To put Michael's second suggestion into patch form, the following fixes
>>> the problem for me:
>>>
>>> --- kvm-81.orig/qemu/qemu-char.c        2008-12-14 06:16:27.000000000 -0700
>>> +++ kvm-81/qemu/qemu-char.c     2009-02-02 14:12:20.000000000 -0700
>>> @@ -1078,20 +1078,21 @@
>>>              if (sarg | TIOCM_DTR)
>>>                  *targ |= CHR_TIOCM_DTR;
>>>              if (sarg | TIOCM_RTS)
>>>                  *targ |= CHR_TIOCM_RTS;
>>>          }
>>>          break;
>>>      case CHR_IOCTL_SERIAL_SET_TIOCM:
>>>          {
>>>              int sarg = *(int *)arg;
>>>              int targ = 0;
>>> +            ioctl(s->fd_in, TIOCMGET, &targ);
>> here, one more operation is necessary:
>>                targ &= ~(TIOCM_DTR|TIOCM_RTS);
> 
> Interesting. that change was not needed to fix my problem.

It just means you (or, rather, your guests) never really needed to
DROP those signal lines, only to raise them.

>>>              if (sarg | CHR_TIOCM_DTR)
>>>                  targ |= TIOCM_DTR;
>>>              if (sarg | CHR_TIOCM_RTS)
>>>                  targ |= TIOCM_RTS;

Without that line above, the code never drops the two bits, once
set they can't be "removed" anymore.

By the way, this is upstream qemu issue, not kvm one, and has to be
pushed as such.  Good you CC'd qemu list.

/mjt