[XEN PATCH v11 4/8] x86/physdev: Return pirq that irq was already mapped to

[Jiqian Chen <Jiqian.Chen@xxxxxxx>]

allocate_pirq is to allocate a pirq for a irq, and it supports to
allocate a free pirq(pirq parameter is <0) or a specific pirq (pirq
parameter is > 0).

For current code, it has four usecases.

First, pirq>0 and current_pirq>0, (current_pirq means if irq already
has a mapped pirq), if pirq==current_pirq means the irq already has
mapped to the pirq expected by the caller, it successes, if
pirq!=current_pirq means the pirq expected by the caller has been
mapped into other irq, it fails.

Second, pirq>0 and current_pirq<0, it means pirq expected by the
caller has not been allocated to any irqs, so it can be allocated to
caller, it successes.

Third, pirq<0 and current_pirq<0, it means caller want to allocate a
free pirq for irq and irq has no mapped pirq, it successes.

Fourth, pirq<0 and current_pirq>0, it means caller want to allocate
a free pirq for irq but irq has a mapped pirq, then it returns the
negative pirq, so it fails.

The problem is in Fourth, since the irq has a mapped pirq(current_pirq),
and the caller doesn't want to allocate a specified pirq to the irq, so
the current_pirq should be returned directly in this case, indicating
that the allocation is successful. That can help caller to success when
caller just want to allocate a free pirq but doesn't know if the irq
already has a mapped pirq or not.

Signed-off-by: Jiqian Chen <Jiqian.Chen@xxxxxxx>
Signed-off-by: Huang Rui <ray.huang@xxxxxxx>
Signed-off-by: Jiqian Chen <Jiqian.Chen@xxxxxxx>
---
 xen/arch/x86/irq.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/xen/arch/x86/irq.c b/xen/arch/x86/irq.c
index 9a611c79e024..5ccca1646eb1 100644
--- a/xen/arch/x86/irq.c
+++ b/xen/arch/x86/irq.c
@@ -2897,6 +2897,8 @@ static int allocate_pirq(struct domain *d, int index, int 
pirq, int irq,
                     d->domain_id, index, pirq, current_pirq);
             if ( current_pirq < 0 )
                 return -EBUSY;
+            else
+                return current_pirq;
         }
         else if ( type == MAP_PIRQ_TYPE_MULTI_MSI )
         {
-- 
2.34.1