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

[Stefano Stabellini]

Michael Tokarev wrote:

> David S. Ahern wrote:
>> Michael Tokarev wrote:
>>> David S. Ahern wrote:
>>>>      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.
> 


Either the two lines above or we could parse the whole set of possible
flags, like we do in the CHR_IOCTL_SERIAL_GET_TIOCM case.