Re: [Xen-devel] [PATCH v2] xenfb: remove xen_init_display "temporary" hack

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Thu, 29 Jun 2017, Paul Durrant wrote:
> > -----Original Message-----
> > From: Stefano Stabellini [mailto:sstabellini@xxxxxxxxxx]
> > Sent: 28 June 2017 19:37
> > To: xen-devel@xxxxxxxxxxxxxxxxxxxx; qemu-devel@xxxxxxxxxx
> > Cc: sstabellini@xxxxxxxxxx; peter.maydell@xxxxxxxxxx; Anthony Perard
> > <anthony.perard@xxxxxxxxxx>; kraxel@xxxxxxxxxx; Paul Durrant
> > <Paul.Durrant@xxxxxxxxxx>
> > Subject: [PATCH v2] xenfb: remove xen_init_display "temporary" hack
> > 
> > Initialize xenfb properly, as all other backends, from its own
> > "initialise" function.
> > 
> > Signed-off-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>
> > 
> > ---
> > Changes in v2:
> > - remove xen_init_display from xen_backend.h
> > - handle cases where vkbd is missing
> > 
> > diff --git a/hw/display/xenfb.c b/hw/display/xenfb.c
> > index e76c0d8..3b0168b 100644
> > --- a/hw/display/xenfb.c
> > +++ b/hw/display/xenfb.c
> > @@ -71,7 +71,6 @@ struct XenFB {
> >      int               fbpages;
> >      int               feature_update;
> >      int               bug_trigger;
> > -    int               have_console;
> >      int               do_resize;
> > 
> >      struct {
> > @@ -80,6 +79,7 @@ struct XenFB {
> >      int               up_count;
> >      int               up_fullscreen;
> >  };
> > +static const GraphicHwOps xenfb_ops;
> > 
> >  /* -------------------------------------------------------------------- */
> > 
> > @@ -855,6 +855,8 @@ static int fb_init(struct XenDevice *xendev)
> >  static int fb_initialise(struct XenDevice *xendev)
> >  {
> >      struct XenFB *fb = container_of(xendev, struct XenFB, c.xendev);
> > +    struct XenDevice *xin;
> > +    struct XenInput *in;
> 
> I think the scope of 'in' can be limited to the 'else' clause where it is 
> used below.
> 
> >      struct xenfb_page *fb_page;
> >      int videoram;
> >      int rc;
> > @@ -877,16 +879,16 @@ static int fb_initialise(struct XenDevice *xendev)
> >      if (rc != 0)
> >     return rc;
> > 
> > -#if 0  /* handled in xen_init_display() for now */
> > -    if (!fb->have_console) {
> > -        fb->c.ds = graphic_console_init(xenfb_update,
> > -                                        xenfb_invalidate,
> > -                                        NULL,
> > -                                        NULL,
> > -                                        fb);
> > -        fb->have_console = 1;
> > +    fb->c.con = graphic_console_init(NULL, 0, &xenfb_ops, fb);
> > +
> > +    xin = xen_pv_find_xendev("vkbd", xen_domid, 0);
> > +    if (xin == NULL) {
> > +        xen_pv_printf(xendev, 1, "xenfb is up, but vkbd is not present\n");
> > +    } else {
> > +        in = container_of(xin, struct XenInput, c.xendev);
> > +        in->c.con = fb->c.con;
> 
> I notice that in->c.con is tested in input_initialise() and it will fail if 
> NULL, so there is an inherent race between the frontends and also processing 
> of xenstore watches. That seems a little fragile at best, but the dependency 
> of input_initialise() on in->c.con is also somewhat bogus as the vkbd backend 
> is created for xenfv machine types whereas xenfb is only there for xenpv 
> machine types. I think this needs to be fixed before xenfb can be relied on 
> to initialize correctly in all circumstances.

Yes, you are right that it is fragile. Also, there is no need for this
dependency: I'll remove it, and use qemu_console_lookup_by_index
instead.

Owen's patch will take care of making the qemu_console_lookup_by_index
call conditional on xenfb->raw_pointer_wanted != 1. 


> > +        xen_be_check_state(xin);
> >      }
> > -#endif
> > 
> >      if (xenstore_read_fe_int(xendev, "feature-update", &fb-
> > >feature_update) == -1)
> >     fb->feature_update = 0;
> > @@ -972,42 +974,3 @@ static const GraphicHwOps xenfb_ops = {
> >      .gfx_update  = xenfb_update,
> >      .update_interval = xenfb_update_interval,
> >  };
> > -
> > -/*
> > - * FIXME/TODO: Kill this.
> > - * Temporary needed while DisplayState reorganization is in flight.
> > - */
> > -void xen_init_display(int domid)
> > -{
> > -    struct XenDevice *xfb, *xin;
> > -    struct XenFB *fb;
> > -    struct XenInput *in;
> > -    int i = 0;
> > -
> > -wait_more:
> > -    i++;
> > -    main_loop_wait(true);
> > -    xfb = xen_pv_find_xendev("vfb", domid, 0);
> > -    xin = xen_pv_find_xendev("vkbd", domid, 0);
> > -    if (!xfb || !xin) {
> > -        if (i < 256) {
> > -            usleep(10000);
> > -            goto wait_more;
> > -        }
> > -        xen_pv_printf(NULL, 1, "displaystate setup failed\n");
> > -        return;
> > -    }
> > -
> > -    /* vfb */
> > -    fb = container_of(xfb, struct XenFB, c.xendev);
> > -    fb->c.con = graphic_console_init(NULL, 0, &xenfb_ops, fb);
> > -    fb->have_console = 1;
> > -
> > -    /* vkbd */
> > -    in = container_of(xin, struct XenInput, c.xendev);
> > -    in->c.con = fb->c.con;
> > -
> > -    /* retry ->init() */
> > -    xen_be_check_state(xin);
> > -    xen_be_check_state(xfb);
> > -}
> > diff --git a/hw/xenpv/xen_machine_pv.c b/hw/xenpv/xen_machine_pv.c
> > index 79aef4e..31d2f25 100644
> > --- a/hw/xenpv/xen_machine_pv.c
> > +++ b/hw/xenpv/xen_machine_pv.c
> > @@ -94,9 +94,6 @@ static void xen_init_pv(MachineState *machine)
> > 
> >      /* config cleanup hook */
> >      atexit(xen_config_cleanup);
> > -
> > -    /* setup framebuffer */
> > -    xen_init_display(xen_domid);
> >  }
> > 
> >  static void xenpv_machine_init(MachineClass *mc)
> > diff --git a/include/hw/xen/xen_backend.h
> > b/include/hw/xen/xen_backend.h
> > index 852c2ea..8a6fbcb 100644
> > --- a/include/hw/xen/xen_backend.h
> > +++ b/include/hw/xen/xen_backend.h
> > @@ -55,8 +55,6 @@ extern struct XenDevOps xen_netdev_ops;       /*
> > xen_nic.c         */
> >  extern struct XenDevOps xen_usb_ops;          /* xen-usb.c         */
> >  #endif
> > 
> > -void xen_init_display(int domid);
> > -
> >  /* configuration (aka xenbus setup) */
> >  void xen_config_cleanup(void);
> >  int xen_config_dev_blk(DriveInfo *disk);
> 

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