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[Libvir] Re: [PATCH 2/7] Fix issues with QEMU monitor interface.



On Mon, Aug 13, 2007 at 12:54:05PM +0100, Daniel P. Berrange wrote:
> On Mon, Aug 13, 2007 at 05:59:15AM -0400, Daniel Veillard wrote:
> > On Sun, Aug 12, 2007 at 07:11:34PM -0400, Jim Paris wrote:
> > > Due to the TTY layer, sending "\n" to the qemu monitor translates
> > > into "\r\n" when received.  This triggers a bug in older versions of
> > > QEMU (KVM <= 33) because the same command is executed twice, and
> > > still has problems with fixed QEMU because the "(qemu)" prompt is
> > > printed twice.  Switch all monitor commands to end with "\r" which
> > > avoids both issues.
> > > 
> > > The QEMU monitor sends frequent terminal escape sequences, typically
> > > \033[D and \033[K.  At times, these interfere with the prompt
> > > detection when they get sent between "\n" and "(qemu) ".  Fix the
> > > issue by filtering out these sequences when they are received.
> > 
> >   I think DanP can better comment on the QEmu interaction than me,
> > but the patch looks simple and clean except:
> 
> It looks sane to me - I had no idea QEMU was sending this escape sequences.
> 
> > 
> > > @@ -1333,14 +1335,23 @@ static int qemudMonitorCommand(struct qemud_driver *driver ATTRIBUTE_UNUSED,
> > >                  return -1;
> > >              }
> > >              buf = b;
> > > -            memmove(buf+size, data, got);
> > > -            buf[size+got] = '\0';
> > > -            size += got;
> > > +
> > > +            /* Copy data, skipping 3-byte escape sequences */
> > > +            for (i = 0; i < got; i++) {
> > > +                if (data[i] == '\033')
> > > +                    skip = 3;
> > > +                if (skip)
> > > +                    skip--;
> > > +                else
> > > +                    buf[size++] = data[i];
> > > +            }
> > > +            buf[size] = '\0';
> > >          }
> > 
> >   It seems that if for some reason you do a partial read on the QEmu
> > console descriptor ending in the middle of the escape command you may
> > have a problem. But it's possible that the way reads are done, and input
> > is chunked garantees that this won't happen, DanP can probably confirm 
> > it's just fine :-)
> 
> We're reading from a Psuedo-TTY which is line buffered, so I think the OS 
> should guarentee that we can read a whole lines worth of data without 
> getting EAGAIN.

  +1 then

Daniel

-- 
Red Hat Virtualization group http://redhat.com/virtualization/
Daniel Veillard      | virtualization library  http://libvirt.org/
veillard redhat com  | libxml GNOME XML XSLT toolkit  http://xmlsoft.org/
http://veillard.com/ | Rpmfind RPM search engine  http://rpmfind.net/


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