Re: [Qemu-devel] [PATCH 1/2] char: add qemu_chr_be_is_fe_connected

[Alon Levy <alevy@redhat.com>]

> Alon Levy <alevy@redhat.com> writes:
> 
> > Note that the handler is called chr_is_guest_connected and not
> > chr_is_fe_connected, consistent with other members of
> > CharDriverState.
> 
> Sorry, I don't get it.
> 
> There isn't a notion of "connected" for the front-ends in the char
> layer.  The closest thing is whether add_handlers() have been called
> or
> not.

It makes sense for virtio-console - it matches exactly the internal guest_connected port state.

> 
> I really dislike the idea of introduction a new concept to the char
> layer in a half baked way.

Is the fact there is only one user, virtio-console, the reason you call this half baked?

> 
> Why can't migration notifiers be used for this?  I think Gerd
> objected
> to using a migration *handler* but not necessarily a state notifier.

Because if you have two chardevices, i.e.
 -chardev spicevmc,name=vdagent,id=spice1 -chardev spicevmc,name=vdagent,id=spice2

Then the two on-the-wire vmstates will be identical.

> 
> Regards,
> 
> Anthony Liguori
> 
> >
> > Signed-off-by: Alon Levy <alevy@redhat.com>
> > ---
> >  hw/virtio-console.c |  9 +++++++++
> >  include/char/char.h | 11 +++++++++++
> >  qemu-char.c         |  9 +++++++++
> >  3 files changed, 29 insertions(+)
> >
> > diff --git a/hw/virtio-console.c b/hw/virtio-console.c
> > index e2d1c58..643e24e 100644
> > --- a/hw/virtio-console.c
> > +++ b/hw/virtio-console.c
> > @@ -120,6 +120,13 @@ static void chr_event(void *opaque, int event)
> >      }
> >  }
> >  
> > +static bool chr_is_guest_connected(void *opaque)
> > +{
> > +    VirtConsole *vcon = opaque;
> > +
> > +    return vcon->port.guest_connected;
> > +}
> > +
> >  static int virtconsole_initfn(VirtIOSerialPort *port)
> >  {
> >      VirtConsole *vcon = DO_UPCAST(VirtConsole, port, port);
> > @@ -133,6 +140,8 @@ static int virtconsole_initfn(VirtIOSerialPort
> > *port)
> >      if (vcon->chr) {
> >          qemu_chr_add_handlers(vcon->chr, chr_can_read, chr_read,
> >          chr_event,
> >                                vcon);
> > +        /* only user of chr_is_guest_connected so leave it as
> > special cased*/
> > +        vcon->chr->chr_is_guest_connected =
> > chr_is_guest_connected;
> >      }
> >  
> >      return 0;
> > diff --git a/include/char/char.h b/include/char/char.h
> > index 0326b2a..b41ddc0 100644
> > --- a/include/char/char.h
> > +++ b/include/char/char.h
> > @@ -52,6 +52,7 @@ typedef struct {
> >  #define CHR_TIOCM_RTS	0x004
> >  
> >  typedef void IOEventHandler(void *opaque, int event);
> > +typedef bool IOIsGuestConnectedHandler(void *opaque);
> >  
> >  struct CharDriverState {
> >      void (*init)(struct CharDriverState *s);
> > @@ -64,6 +65,7 @@ struct CharDriverState {
> >      IOEventHandler *chr_event;
> >      IOCanReadHandler *chr_can_read;
> >      IOReadHandler *chr_read;
> > +    IOIsGuestConnectedHandler *chr_is_guest_connected;
> >      void *handler_opaque;
> >      void (*chr_close)(struct CharDriverState *chr);
> >      void (*chr_accept_input)(struct CharDriverState *chr);
> > @@ -229,6 +231,15 @@ void qemu_chr_be_write(CharDriverState *s,
> > uint8_t *buf, int len);
> >   */
> >  void qemu_chr_be_event(CharDriverState *s, int event);
> >  
> > +/**
> > + * @qemu_chr_be_is_fe_connected:
> > + *
> > + * Back end calls this to check if the front end is connected.
> > + *
> > + * Returns: true if the guest (front end) is connected, false
> > otherwise.
> > + */
> > +bool qemu_chr_be_is_fe_connected(CharDriverState *s);
> > +
> >  void qemu_chr_add_handlers(CharDriverState *s,
> >                             IOCanReadHandler *fd_can_read,
> >                             IOReadHandler *fd_read,
> > diff --git a/qemu-char.c b/qemu-char.c
> > index 4e011df..77a501a 100644
> > --- a/qemu-char.c
> > +++ b/qemu-char.c
> > @@ -120,6 +120,15 @@ void qemu_chr_be_event(CharDriverState *s, int
> > event)
> >      s->chr_event(s->handler_opaque, event);
> >  }
> >  
> > +bool qemu_chr_be_is_fe_connected(CharDriverState *s)
> > +{
> > +    if (s->chr_is_guest_connected) {
> > +        return s->chr_is_guest_connected(s->handler_opaque);
> > +    }
> > +    /* default to always connected */
> > +    return true;
> > +}
> > +
> >  static gboolean qemu_chr_generic_open_bh(gpointer opaque)
> >  {
> >      CharDriverState *s = opaque;
> > --
> > 1.8.1.4
> 
> 
>