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

[Jürgen Groß <jgross@xxxxxxxx>]

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.

>   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/

> +
> +       stubdom = introduce_domain(NULL, stub_domid, port, false);
>         if (!stubdom)
>                 barf_perror("Failed to initialize stubdom");
>   
Juergen

Attachment: OpenPGP_0xB0DE9DD628BF132F.asc
Description: OpenPGP public key

Attachment: OpenPGP_signature.asc
Description: OpenPGP digital signature