[PATCH 2/8] xen/evtchn: modify evtchn_alloc_unbound to allocate specified port

[Rahul Singh <rahul.singh@xxxxxxx>]

evtchn_alloc_unbound() always allocates the next available port. Static
event channel support for dom0less domains requires allocating a
specified port.

Modify the evtchn_alloc_unbound() to accept the port number as an
argument and allocate the specified port if available. If the port
number argument is zero, the next available port will be allocated.

Signed-off-by: Rahul Singh <rahul.singh@xxxxxxx>
---
 xen/arch/arm/domain_build.c |  2 +-
 xen/common/event_channel.c  | 26 +++++++++++++++++++++-----
 xen/include/xen/event.h     |  3 ++-
 3 files changed, 24 insertions(+), 7 deletions(-)

diff --git a/xen/arch/arm/domain_build.c b/xen/arch/arm/domain_build.c
index 7ddd16c26d..5f97d9d181 100644
--- a/xen/arch/arm/domain_build.c
+++ b/xen/arch/arm/domain_build.c
@@ -3171,7 +3171,7 @@ static int __init alloc_xenstore_evtchn(struct domain *d)
 
     alloc.dom = d->domain_id;
     alloc.remote_dom = hardware_domain->domain_id;
-    rc = evtchn_alloc_unbound(&alloc);
+    rc = evtchn_alloc_unbound(&alloc, 0);
     if ( rc )
     {
         printk("Failed allocating event channel for domain\n");
diff --git a/xen/common/event_channel.c b/xen/common/event_channel.c
index 8cbe9681da..80a88c1544 100644
--- a/xen/common/event_channel.c
+++ b/xen/common/event_channel.c
@@ -290,11 +290,15 @@ void evtchn_free(struct domain *d, struct evtchn *chn)
     xsm_evtchn_close_post(chn);
 }
 
-int evtchn_alloc_unbound(evtchn_alloc_unbound_t *alloc)
+/*
+ * If port is zero get the next free port and allocate. If port is non-zero
+ * allocate the specified port.
+ */
+int evtchn_alloc_unbound(evtchn_alloc_unbound_t *alloc, evtchn_port_t port)
 {
     struct evtchn *chn;
     struct domain *d;
-    int            port, rc;
+    int            rc;
     domid_t        dom = alloc->dom;
 
     d = rcu_lock_domain_by_any_id(dom);
@@ -303,8 +307,20 @@ int evtchn_alloc_unbound(evtchn_alloc_unbound_t *alloc)
 
     spin_lock(&d->event_lock);
 
-    if ( (port = get_free_port(d)) < 0 )
-        ERROR_EXIT_DOM(port, d);
+    if ( port != 0 )
+    {
+        if ( (rc = evtchn_allocate_port(d, port)) != 0 )
+            ERROR_EXIT_DOM(rc, d);
+    }
+    else
+    {
+        int alloc_port = get_free_port(d);
+
+        if ( alloc_port < 0 )
+            ERROR_EXIT_DOM(alloc_port, d);
+        port = alloc_port;
+    }
+
     chn = evtchn_from_port(d, port);
 
     rc = xsm_evtchn_unbound(XSM_TARGET, d, chn, alloc->remote_dom);
@@ -1206,7 +1222,7 @@ long cf_check do_event_channel_op(int cmd, 
XEN_GUEST_HANDLE_PARAM(void) arg)
         struct evtchn_alloc_unbound alloc_unbound;
         if ( copy_from_guest(&alloc_unbound, arg, 1) != 0 )
             return -EFAULT;
-        rc = evtchn_alloc_unbound(&alloc_unbound);
+        rc = evtchn_alloc_unbound(&alloc_unbound, 0);
         if ( !rc && __copy_to_guest(arg, &alloc_unbound, 1) )
             rc = -EFAULT; /* Cleaning up here would be a mess! */
         break;
diff --git a/xen/include/xen/event.h b/xen/include/xen/event.h
index 61615ebbe3..48820e393e 100644
--- a/xen/include/xen/event.h
+++ b/xen/include/xen/event.h
@@ -72,7 +72,8 @@ void evtchn_free(struct domain *d, struct evtchn *chn);
 int evtchn_allocate_port(struct domain *d, unsigned int port);
 
 /* Allocate a new event channel */
-int __must_check evtchn_alloc_unbound(evtchn_alloc_unbound_t *alloc);
+int __must_check evtchn_alloc_unbound(evtchn_alloc_unbound_t *alloc,
+                                      evtchn_port_t port);
 
 /* Bind an event channel port to interdomain */
 int __must_check evtchn_bind_interdomain(evtchn_bind_interdomain_t *bind);
-- 
2.25.1