Re: [Xen-devel] [PATCH 1/3] xenstore: setup xenstore stubdom console interface properly

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 28/01/2020 14:28, Juergen Gross wrote:
> In order to be able to get access to the console of Xenstore stubdom
> we need an appropriate granttab entry. So call xc_dom_gnttab_init()
> when constructing the domain and preset some information needed
> for that function in the dom structure.
>
> We need to create the event channel for the console, too. Do that and
> store all necessary data locally.
>
> Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
> ---
>  tools/helpers/init-xenstore-domain.c | 13 +++++++++++++
>  1 file changed, 13 insertions(+)
>
> diff --git a/tools/helpers/init-xenstore-domain.c 
> b/tools/helpers/init-xenstore-domain.c
> index adb8408b63..a312bc38b8 100644
> --- a/tools/helpers/init-xenstore-domain.c
> +++ b/tools/helpers/init-xenstore-domain.c
> @@ -24,6 +24,8 @@ static char *param;
>  static char *name = "Xenstore";
>  static int memory;
>  static int maxmem;
> +static xen_pfn_t console_mfn;
> +static unsigned int console_evtchn;
>  
>  static struct option options[] = {
>      { "kernel", 1, NULL, 'k' },
> @@ -113,6 +115,7 @@ static int build(xc_interface *xch)
>          fprintf(stderr, "xc_domain_setmaxmem failed\n");
>          goto err;
>      }
> +    console_evtchn = xc_evtchn_alloc_unbound(xch, domid, 0);

Presumably some form of error checking?

Also, while it is probably fine for now, I think this does highlight a
future issue.  What happens when xenconsoled is also a stubdomain?

I suspect we have a looming chicken&egg problem, where the toolstack is
going to have to do some careful domid and plumbing to set up build both
stubdoms in tandem.

>      rv = xc_domain_set_memmap_limit(xch, domid, limit_kb);
>      if ( rv )
>      {
> @@ -133,6 +136,9 @@ static int build(xc_interface *xch)
>          snprintf(cmdline, 512, "--event %d --internal-db", rv);
>  
>      dom = xc_dom_allocate(xch, cmdline, NULL);

Any chance of some error handling, unlikely as it is to go wrong?

> +    dom->container_type = XC_DOM_PV_CONTAINER;
> +    dom->xenstore_domid = domid;
> +    dom->console_evtchn = console_evtchn;

and a newline here?

>      rv = xc_dom_kernel_file(dom, kernel);
>      if ( rv )
>      {
> @@ -186,6 +192,12 @@ static int build(xc_interface *xch)
>          fprintf(stderr, "xc_dom_boot_image failed\n");
>          goto err;
>      }
> +    rv = xc_dom_gnttab_init(dom);
> +    if ( rv )
> +    {
> +        fprintf(stderr, "xc_dom_gnttab_init failed\n");
> +        goto err;
> +    }
>  
>      rv = xc_domain_set_virq_handler(xch, domid, VIRQ_DOM_EXC);
>      if ( rv )
> @@ -201,6 +213,7 @@ static int build(xc_interface *xch)
>      }
>  
>      rv = 0;
> +    console_mfn = xc_dom_p2m(dom, dom->console_pfn);

This doesn't appear to be used.

~Andrew

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