tools/lsevtchn: Use errno macro to handle hypercall error cases

Currently, lsevtchn aborts its event channel enumeration when it hits
an event channel that is owned by Xen.

lsevtchn does not distinguish between different hypercall errors, which
results in lsevtchn missing potential relevant event channels with
higher port numbers.

Use the errno macro to distinguish between hypercall errors, and
continue event channel enumeration if the hypercall error is not
critical to enumeration.

Signed-off-by: Matthew Barnes <matthew.barnes@cloud.com>
Reviewed-by: Anthony PERARD <anthony.perard@vates.tech>

tools/xcutils/lsevtchn.c

@@ -3,6 +3,7 @@
 #include <stdint.h>
 #include <string.h>
 #include <stdio.h>
+#include <errno.h>
 
 #include <xenctrl.h>
 
@@ -24,8 +25,24 @@ int main(int argc, char **argv)
         status.port = port;
         rc = xc_evtchn_status(xch, &status);
         if ( rc < 0 )
+        {
+            switch ( errno )
+            {
+            case EACCES: /* Xen-owned evtchn */
+                continue;
+
+            case EINVAL: /* Port enumeration has ended */
+                rc = 0;
                 break;
 
+            default:
+                perror("xc_evtchn_status");
+                rc = 1;
+                break;
+            }
+            goto out;
+        }
+
         if ( status.status == EVTCHNSTAT_closed )
             continue;
 
@@ -58,7 +75,8 @@ int main(int argc, char **argv)
         printf("\n");
     }
 
+ out:
     xc_interface_close(xch);
 
-    return 0;
+    return rc;
 }