Re: [Xen-devel] [PATCH] [qemu] xen_be_init under stubdom

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Wed, 19 Jan 2011, Kamala Narasimhan wrote:
> Do nothing in xen_be_init under stubdom plus a minor inconsequential cleanup.
> 
> Signed-off-by: Kamala Narasimhan <kamala.narasimhan@xxxxxxxxxx>
> 
> Kamala
> 
> diff --git a/hw/xen_backend.c b/hw/xen_backend.c
> index d9be513..61e1210 100644
> --- a/hw/xen_backend.c
> +++ b/hw/xen_backend.c
> @@ -613,7 +613,7 @@ static void xenstore_update(void *unused)
> 
>      vec = xs_read_watch(xenstore, &count);
>      if (vec == NULL)
> -       goto cleanup;
> +        return;
> 
>      if (sscanf(vec[XS_WATCH_TOKEN], "be:%" PRIxPTR ":%d:%" PRIxPTR,
>                 &type, &dom, &ops) == 3)
> @@ -621,7 +621,6 @@ static void xenstore_update(void *unused)
>      if (sscanf(vec[XS_WATCH_TOKEN], "fe:%" PRIxPTR, &ptr) == 1)
>         xenstore_update_fe(vec[XS_WATCH_PATH], (void*)ptr);
> 
> -cleanup:
>      qemu_free(vec);
>  }
> 
> @@ -646,6 +645,10 @@ static void xen_be_evtchn_event(void *opaque)
> 
>  int xen_be_init(void)
>  {
> +#ifdef CONFIG_STUBDOM
> +    return 0;
> +#endif
> +
>      xenstore = xs_daemon_open();
>      if (!xenstore) {
>         xen_be_printf(NULL, 0, "can't connect to xenstored\n");
 
I think it would be better if we actually return an error from
xen_be_init and we just print a warning in hw/xen_machine_fv.c if the
backends fail to initialize instead of exit.
It is OK to just call exit in hw/xen_machine_pv.c, because nothing is
running in qemu apart from backends in that case.

Also having another #ifdef CONFIG_STUBDOM might be OK in qemu-xen, but
in qemu upstream we can get away without it implementing a function
like:

int xen_qemu_is_a_stubdom();

that returns 1 in case qemu is running in a stubdom and 0 otherwise.
I would make domid_s a global int variable (see vl.c:5827) so that
xen_qemu_is_a_stubdom can be implemented like this:

return domid_s;

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