Re: [Qemu-devel] [RfC / Patch] xenner: event channel implementation.

[Avi Kivity <avi@redhat.com>]

Gerd Hoffmann wrote:
>   Hi,
>
> Merging the xen bits seems to be on a good way.  Time to look at 
> un-bitrotting the xenner bits ...
>
> Here is a first patch for comments.  Not useful on its own.  Right now 
> I'm looking more for comments on the way the integration is done.
>
> Event channels on Xen are managed by calling the xc_evtchn_* functions 
> provided by libxenctrl.  The library in turn does does hypercalls into 
> the xen kernel.  xenner obviously has to provide an alternative 
> implementation for these functions.  Also for others.  This patch 
> starts with just the event channels though.
>
> It works this way:  There is a struct with function pointers to the 
> event channel functions.  The struct can be switched at runtime to the 
> xen or xenner version of the functions depending on the qemu operation 
> mode.
>
> The struct is named "xc_evtchn", the function pointer are named like 
> the xc_evtchn_* functions, but without the xc_evtchn_ prefix, i.e. 
> "xc_evtchn_open(...)" becomes xc_evtchn.open(...).
>
> The function calls in the source code (xen backend drivers) are not 
> changed directly, but using a include file with a bunch of #defines. 
> That way I don't have to change s/xc_evtchn_/xc_evtchn./ all over the 
> place.  Also xenner can easily be disabled at compile time and the 
> indirect function pointer calls simply go away then.
>

I don't think the last bit is worthwhile.  Function pointers these days 
are pretty fast, their cost will be dwarfed by the syscall and hypercall 
overhead.

> pecific
> @@ -422,7 +423,9 @@ for opt do
>    ;;
>    --disable-kqemu) kqemu="no"
>    ;;
> -  --disable-xen) xen="no"
> +  --disable-xen) xen="no"; xenner="no"
> +  ;;
> +  --disable-xenner) xenner="no"

It would be nice to be able to build without the original Xen libraries.

>
> +
> +static struct domain *get_domain(int domid)
> +{
> +    struct domain *domain;
> +
> +    TAILQ_FOREACH(domain, &domains, list) {
> +    if (domain->domid == domid)
> +        goto done;
> +    }
> +
> +    domain = qemu_mallocz(sizeof(*domain));
> +    if (domid)
> +    domain->domid = domid;
> +    TAILQ_INSERT_TAIL(&domains, domain, list);
> +    if (debug)
> +    qemu_log("xen ev:  ?: new domain id %d\n", domain->domid);
> +
> +done:
> +    domain->refcount++;
> +    return domain;
> +}

Curious, can there be any domain other than the guest and the fake dom0 
you're emulating?



-- 
error compiling committee.c: too many arguments to function