Re: [Qemu-devel] [PATCH 2/3] xenfb: Add option to use grant ref for shared page.

[Stefano Stabellini <stefano.stabellini@eu.citrix.com>]

On Wed, 10 Sep 2014, Owen smith wrote:
> The vkbd device should be able to use a grant reference to map the
> shared page.
> 
> Signed-off-by: Owen smith <owen.smith@citrix.com>
> ---
>  hw/display/xenfb.c | 39 +++++++++++++++++++++++++++++----------
>  1 file changed, 29 insertions(+), 10 deletions(-)
> 
> diff --git a/hw/display/xenfb.c b/hw/display/xenfb.c
> index 2c39753..c4375c8 100644
> --- a/hw/display/xenfb.c
> +++ b/hw/display/xenfb.c
> @@ -54,6 +54,7 @@
>  struct common {
>      struct XenDevice  xendev;  /* must be first */
>      void              *page;
> +    int               page_gref;
>      QemuConsole       *con;
>  };
>  
> @@ -96,22 +97,36 @@ static int common_bind(struct common *c)
>  {
>      uint64_t mfn;
>  
> -    if (xenstore_read_fe_uint64(&c->xendev, "page-ref", &mfn) == -1)
> -	return -1;
> -    assert(mfn == (xen_pfn_t)mfn);
> -
>      if (xenstore_read_fe_int(&c->xendev, "event-channel", &c->xendev.remote_port) == -1)
>  	return -1;
>  
> -    c->page = xc_map_foreign_range(xen_xc, c->xendev.dom,
> -				   XC_PAGE_SIZE,
> -				   PROT_READ | PROT_WRITE, mfn);
> +    if (xenstore_read_fe_uint64(&c->xendev, "page-ref", &mfn) == -1) {
> +        if (xenstore_read_fe_int(&c->xendev, "page-gref", &c->page_gref) == -1) {
> +            return -1;
> +        }
> +        c->page = xc_gnttab_map_grant_ref(c->xendev.gnttabdev,
> +                                          c->xendev.dom,
> +                                          c->page_gref,
> +                                          PROT_READ | PROT_WRITE);
> +    } else {
> +        assert(mfn == (xen_pfn_t)mfn);
> +
> +        c->page = xc_map_foreign_range(xen_xc, c->xendev.dom,
> +                                       XC_PAGE_SIZE,
> +                                       PROT_READ | PROT_WRITE, mfn);
> +    }

This is an extension of the protocol. It should be documented somewhere.
At least in the commit message and somewhere under docs/misc or
xen/include/public/io/fbif.h.


>      if (c->page == NULL)
>  	return -1;
>  
>      xen_be_bind_evtchn(&c->xendev);
> -    xen_be_printf(&c->xendev, 1, "ring mfn %"PRIx64", remote-port %d, local-port %d\n",
> -		  mfn, c->xendev.remote_port, c->xendev.local_port);
> +
> +    if (c->page_gref) {
> +        xen_be_printf(&c->xendev, 1, "ring gref %d, remote-port %d, local-port %d\n",
> +                      c->page_gref, c->xendev.remote_port, c->xendev.local_port);
> +    } else {
> +        xen_be_printf(&c->xendev, 1, "ring mfn %"PRIx64", remote-port %d, local-port %d\n",
> +                      mfn, c->xendev.remote_port, c->xendev.local_port);
> +    }
>  
>      return 0;
>  }
> @@ -120,8 +135,13 @@ static void common_unbind(struct common *c)
>  {
>      xen_be_unbind_evtchn(&c->xendev);
>      if (c->page) {
> -	munmap(c->page, XC_PAGE_SIZE);
> +        if (c->page_gref) {
> +            xc_gnttab_munmap(c->xendev.gnttabdev, c->page, 1);
> +        } else {
> +            munmap(c->page, XC_PAGE_SIZE);
> +        }
>  	c->page = NULL;
> +        c->page_gref = 0;
>      }
>  }
>  
> @@ -954,6 +974,7 @@ static void fb_event(struct XenDevice *xendev)
>  
>  struct XenDevOps xen_kbdmouse_ops = {
>      .size       = sizeof(struct XenInput),
> +    .flags      = DEVOPS_FLAG_NEED_GNTDEV,
>      .init       = input_init,
>      .initialise = input_initialise,
>      .connected  = input_connected,
> -- 
> 2.1.0
>