Re: [PATCH v4 06/12] tools/xenstored: Add get_domain_evtchn() to find evtchn

[Jason Andryuk <jason.andryuk@xxxxxxx>]

On 2025-07-25 02:41, Jürgen Groß wrote:
> On 25.07.25 04:28, Jason Andryuk wrote:
> > Add a helper to lookup the event channel for a domid.  This hides some
> > of the differences between dom0 and stubdom xenstored.
> >
> > It highlights the different meanings between get_xenbus_evtchn() in a
> > stubdom, where it looks up dom0's event channel, and dom0, where it
> > looks up the local event channel.
> >
> > The default return 0 will be fine as any other auto-introduced domain
> > will needs the event channel populated in the grant.
> >
> > Signed-off-by: Jason Andryuk <jason.andryuk@xxxxxxx>
> > ---
> >   tools/xenstored/domain.c | 38 ++++++++++++++++++++++++++++++++++++--
> >   1 file changed, 36 insertions(+), 2 deletions(-)
> >
> > diff --git a/tools/xenstored/domain.c b/tools/xenstored/domain.c
> > index 1241f8c73e..1c52254ba8 100644
> > --- a/tools/xenstored/domain.c
> > +++ b/tools/xenstored/domain.c
> > @@ -1251,12 +1251,41 @@ const char *get_implicit_path(const struct 
> > connection *conn)
> >       return conn->domain->path;
> >   }
> > +/*
> > + * dom0 xenstored (posix.c) uses get_xenbus_evtchn() to lookup with
> > + * XENSTORED_PORT_DEV.
> > + *
> > + * minios stubdom uses get_xenbus_evtchn() to look up dom0's event 
> > channel
> > + * from the command line (--event).  The stubdom's own event channel is
> > + * returned directly.
> > + *
> > + * Any other existing domains from dom0less/Hyperlaunch will have
> > + * the event channel in the xenstore page, so lookup here isn't 
> > necessary.
> > + * --event would not be set, so it would default to 0.
> > + */
> > +evtchn_port_t get_domain_evtchn(domid_t domid)
> > +{
> > +#ifdef __MINIOS__
> > +    if (domid == stub_domid) {
> > +        return xenbus_evtchn;
> > +    } else if (domid == priv_domid) {
> > +        return get_xenbus_evtchn();
> > +    }
> > +#else
> > +    if (domid == xenbus_master_domid()) {
> > +        return get_xenbus_evtchn();
> > +    }
> > +#endif
> > +
> > +    return 0;
> > +}
> > +
> I'd prefer to have 2 get_domain_evtchn() variants, one in posix.c and
> one in minios.c. This way you can avoid the #ifdef.
Sounds good.

> >   void dom0_init(void)
> >   {
> >       evtchn_port_t port;
> >       struct domain *dom0;
> > -    port = get_xenbus_evtchn();
> > +    port = get_domain_evtchn(xenbus_master_domid());
> >       if (port == -1)
> >           barf_perror("Failed to initialize dom0 port");
> > @@ -1271,11 +1300,16 @@ void stubdom_init(void)
> >   {
> >   #ifdef __MINIOS__
> >       struct domain *stubdom;
> > +    evtchn_port_t port;
> >       if (stub_domid < 0)
> >           return;
> > -    stubdom = introduce_domain(NULL, stub_domid, xenbus_evtchn, false);
> > +    port = get_domain_evtchn(stub_domid);
> > +    if (port == -1)
> > +        barf_perror("Failed to initialize dom0 port");
> s/dom0/stubdom/
Thanks,
Jason