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

[Daniel Veillard]

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:

> @@ -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 :-)

Daniel

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