Re: [Qemu-devel] [PATCH] pty: Fix byte loss bug when connecting to pty

[Michael Roth]

Quoting Paolo Bonzini (2014-07-28 07:59:19)
> Il 28/07/2014 13:39, Sebastian Tanase ha scritto:
> > When trying to print data to the pty, we first check if it is connected.
> > If not, we try to reconnect, but we drop the pending data even if we
> > have successfully reconnected; this makes us lose the first byte of the very
> > first transmission.
> > This small fix addresses the issue by checking once more if the pty is 
> > connected
> > after having tried to reconnect.
> > 
> > Signed-off-by: Sebastian Tanase <address@hidden>
> > ---
> > 
> > To reproduce the bug, launch a qemu image that has a parallel port (say lp0)
> > and redirect it to a pty (-parallel pty). After the VM is launched,
> > open the corresponding pty on your host (cat /dev/pts/X) and send some
> > data from the VM to the host: echo "abcd" > /dev/lp0
> > The first time, the received string will be "bcd" instead of "abcd".
> > This bug can have important consequences if you try, for example,
> > to send a postscript file from a printer within the VM. Losing the
> > first character will render the .ps file unusable.
> > ---
> >  qemu-char.c | 4 +++-
> >  1 file changed, 3 insertions(+), 1 deletion(-)
> > 
> > diff --git a/qemu-char.c b/qemu-char.c
> > index 7acc03f..ce52d0f 100644
> > --- a/qemu-char.c
> > +++ b/qemu-char.c
> > @@ -1160,7 +1160,9 @@ static int pty_chr_write(CharDriverState *chr, const 
> > uint8_t *buf, int len)
> >      if (!s->connected) {
> >          /* guest sends data, check for (re-)connect */
> >          pty_chr_update_read_handler_locked(chr);
> > -        return 0;
> > +        if (!s->connected) {
> > +            return 0;
> > +        }
> >      }
> >      return io_channel_send(s->fd, buf, len);
> >  }
> > 
> 
> Looks ok, though only for 2.2 and 2.1.1.  Gerd, can you take care of
> this patch?

Ping for qemu-stable 2.1.1, freeze is tomorrow.

> 
> Paolo