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@arm.com>
---
Changes in v2:
 - fix minor comments
---
---
 xen/arch/arm/domain_build.c |  2 +-
 xen/common/event_channel.c  | 17 ++++++++++++-----
 xen/include/xen/event.h     |  3 ++-
 3 files changed, 15 insertions(+), 7 deletions(-)

diff --git a/xen/arch/arm/domain_build.c b/xen/arch/arm/domain_build.c
index 6d447367be..11a8c6b8b5 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 eed0e94d07..f2d8c2d61a 100644
--- a/xen/common/event_channel.c
+++ b/xen/common/event_channel.c
@@ -316,11 +316,15 @@ static int evtchn_get_port(struct domain *d, evtchn_port_t port)
     return rc ?: port;
 }
 
-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);
@@ -329,8 +333,11 @@ int evtchn_alloc_unbound(evtchn_alloc_unbound_t *alloc)
 
     write_lock(&d->event_lock);
 
-    if ( (port = get_free_port(d)) < 0 )
-        ERROR_EXIT_DOM(port, d);
+    port = rc = evtchn_get_port(d, port);
+    if ( rc < 0 )
+        ERROR_EXIT(rc);
+    rc = 0;
+
     chn = evtchn_from_port(d, port);
 
     rc = xsm_evtchn_unbound(XSM_TARGET, d, chn, alloc->remote_dom);
@@ -1229,7 +1236,7 @@ long 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 f29b1123d9..8eae9984a9 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

Hi Rahul,

On 19/08/2022 11:02, Rahul Singh wrote:
> evtchn_alloc_unbound() always allocates the next available port. Static
> event channel support for dom0less domains requires allocating a
> specified port.

NIT: Same as patch #4, it is not clear you are talking about the current 
behavior.

> 
> 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@arm.com>

Reviewed-by: Julien Grall <jgrall@amazon.com>

Cheers,

-- 
Julien Grall

Hi Julien,

> On 23 Aug 2022, at 9:31 am, Julien Grall <julien@xen.org> wrote:
> 
> Hi Rahul,
> 
> On 19/08/2022 11:02, Rahul Singh wrote:
>> evtchn_alloc_unbound() always allocates the next available port. Static
>> event channel support for dom0less domains requires allocating a
>> specified port.
> 
> NIT: Same as patch #4, it is not clear you are talking about the current behavior.
> 

Ack. I will add “currently” in next version.
 
Regards,
Rahul

On 19.08.2022 12:02, Rahul Singh wrote:
> 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@arm.com>

Acked-by: Jan Beulich <jbeulich@suse.com>

As a minor remark: Personally I'd find it more logical if the alloc-unbound
adjustments came ahead of the bind-interdomain ones.

Jan

Hi Jan,

> On 22 Aug 2022, at 2:57 pm, Jan Beulich <jbeulich@suse.com> wrote:
> 
> On 19.08.2022 12:02, Rahul Singh wrote:
>> 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@arm.com>
> 
> Acked-by: Jan Beulich <jbeulich@suse.com>
> 
> As a minor remark: Personally I'd find it more logical if the alloc-unbound
> adjustments came ahead of the bind-interdomain ones.
>  

I will move this patch before evtchn_bind_interdomain() patch.

Regard,
Rahul