Re: [Xen-devel] xenbus and the message of doom

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Wed, 2012-01-04 at 15:57 +0000, Olaf Hering wrote:
> On Tue, Jan 03, Ian Campbell wrote:
> 
> > As I said in the bit you trimmed the precedent seems to be to
> > write /local/domain/<N>/control/platform-feature-<X> for each guest that
> > you want to expose the feature to. I think a per-guest key makes sense
> > since even if something seems obviously global you never know when you
> > might need to hide it from a guest (e.g. to workaround an in-guest bug).
> > 
> > I'm afraid I don't have time to work on this myself but it seems pretty
> > simple?
> 
> After looking at this, the (compile tested) patch below should be enough:
> 
> 
> diff -r 3a22ed3ec534 tools/xenstore/xs.c
> --- a/tools/xenstore/xs.c
> +++ b/tools/xenstore/xs.c

I think the toolstack needs to be involved with this. IOW this should be
done in libxl__domain_make() around the same place as
control/platform-feature-multiprocessor-suspend is written.

Ian.

> @@ -884,6 +884,10 @@ bool xs_introduce_domain(struct xs_handl
>       char mfn_str[MAX_STRLEN(mfn)];
>       char eventchn_str[MAX_STRLEN(eventchn)];
>       struct iovec iov[3];
> +     static const char feat[] = "control/platform-feature-xs_reset_watches";
> +     int len;
> +     char *dom_path, *feat_path;
> +     bool ret;
>  
>       snprintf(domid_str, sizeof(domid_str), "%u", domid);
>       snprintf(mfn_str, sizeof(mfn_str), "%lu", mfn);
> @@ -896,8 +900,21 @@ bool xs_introduce_domain(struct xs_handl
>       iov[2].iov_base = eventchn_str;
>       iov[2].iov_len = strlen(eventchn_str) + 1;
>  
> -     return xs_bool(xs_talkv(h, XBT_NULL, XS_INTRODUCE, iov,
> +     ret = xs_bool(xs_talkv(h, XBT_NULL, XS_INTRODUCE, iov,
>                               ARRAY_SIZE(iov), NULL));
> +
> +     dom_path = xs_get_domain_path(h, domid);
> +     if (dom_path) {
> +             len = strlen(dom_path) + 1 + strlen(feat);
> +             feat_path = malloc(len + 1);
> +             if (feat_path) {
> +                     snprintf(feat_path, len + 1, "%s/%s", dom_path, feat);
> +                     xs_write(h, XBT_NULL, feat_path, "1", 1);
> +                     free(feat_path);
> +             }
> +             free(dom_path);
> +     }
> +     return ret;
>  }
>  
>  bool xs_set_target(struct xs_handle *h,



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