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

[Paul Durrant <Paul.Durrant@citrix.com>]

> -----Original Message-----
> From: Stefano Stabellini [mailto:sstabellini@kernel.org]
> Sent: 28 June 2017 19:37
> To: xen-devel@lists.xenproject.org; qemu-devel@nongnu.org
> Cc: sstabellini@kernel.org; peter.maydell@linaro.org; Anthony Perard
> <anthony.perard@citrix.com>; kraxel@redhat.com; Paul Durrant
> <Paul.Durrant@citrix.com>
> 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@kernel.org>
> 
> ---
> 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.

  Paul

> +        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);