[PATCH v3 2/5] Mini-OS: get own domid

[Juergen Gross <jgross@xxxxxxxx>]

Get the own domid via creation of a temporary event channel. There is
no "official" way to read the own domid in PV guests, so use the event
channel interface to get it:

- allocate an unbound event channel specifying DOMID_SELF for the
  other end

- read the event channel status which will contain the own domid in
  unbound.dom

- close the event channel

Signed-off-by: Juergen Gross <jgross@xxxxxxxx
---
V2:
- new patch
V3:
- rename function to get_domid() (Julien Grall)
Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
---
 events.c      | 33 +++++++++++++++++++++++++++++++++
 include/lib.h |  3 +++
 2 files changed, 36 insertions(+)

diff --git a/events.c b/events.c
index cdae90f4..4683e8e1 100644
--- a/events.c
+++ b/events.c
@@ -261,6 +261,39 @@ int evtchn_get_peercontext(evtchn_port_t local_port, char 
*ctx, int size)
     return rc;
 }
 
+/* Replace below when a hypercall is available to get the domid. */
+domid_t get_domid(void)
+{
+    int rc;
+    domid_t domid = DOMID_INVALID;
+    evtchn_alloc_unbound_t op;
+    struct evtchn_status status;
+    struct evtchn_close close;
+
+    op.dom = DOMID_SELF;
+    op.remote_dom = DOMID_SELF;
+    rc = HYPERVISOR_event_channel_op(EVTCHNOP_alloc_unbound, &op);
+    if ( rc )
+    {
+        printk("ERROR: alloc_unbound failed with rc=%d", rc);
+        return domid;
+    }
+
+    status.dom = DOMID_SELF;
+    status.port = op.port;
+    rc = HYPERVISOR_event_channel_op(EVTCHNOP_status, &status);
+    if ( rc )
+        printk("ERROR: EVTCHNOP_status failed with rc=%d", rc);
+    else
+        domid = status.u.unbound.dom;
+
+    close.port = op.port;
+    rc = HYPERVISOR_event_channel_op(EVTCHNOP_close, &close);
+    if ( rc )
+        printk("WARN: close_port %d failed rc=%d. ignored\n", close.port, rc);
+
+    return domid;
+}
 
 /*
  * Local variables:
diff --git a/include/lib.h b/include/lib.h
index fd8c36de..dd68985a 100644
--- a/include/lib.h
+++ b/include/lib.h
@@ -154,6 +154,9 @@ do {                                                        
   \
 /* Consistency check as much as possible. */
 void sanity_check(void);
 
+/* Get own domid. */
+domid_t get_domid(void);
+
 #ifdef HAVE_LIBC
 extern struct wait_queue_head event_queue;
 
-- 
2.35.3