[XEN PATCH v6] tools/lsevtchn: Use errno macro to handle hypercall error cases

[Matthew Barnes <matthew.barnes@cloud.com>]

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>
---
Changes in v6:
- Add blank space before label

Changes in v5:
- Code style changes to switch statement

Changes in v4:
- Catch non-critical errors and fail on everything else, instead of
  catching few known critical errors and ignoring everything else
- Use 'perror' to describe miscellaneous critical errors
- Return appropriate error code from lsevtchn tool
- Tweak commit description
---
 tools/xcutils/lsevtchn.c | 27 +++++++++++++++++++++++++--
 1 file changed, 25 insertions(+), 2 deletions(-)

diff --git a/tools/xcutils/lsevtchn.c b/tools/xcutils/lsevtchn.c
index d1710613ddc5..29504c9d2077 100644
--- a/tools/xcutils/lsevtchn.c
+++ b/tools/xcutils/lsevtchn.c
@@ -3,6 +3,7 @@
 #include <stdint.h>
 #include <string.h>
 #include <stdio.h>
+#include <errno.h>
 
 #include <xenctrl.h>
 
@@ -24,7 +25,28 @@ int main(int argc, char **argv)
         status.port = port;
         rc = xc_evtchn_status(xch, &status);
         if ( rc < 0 )
-            break;
+        {
+            switch ( errno )
+            {
+            case EACCES: /* Xen-owned evtchn */
+                continue;
+
+            case EINVAL: /* Port enumeration has ended */
+                rc = 0;
+                break;
+
+            case ESRCH:
+                perror("Domain ID does not correspond to valid domain");
+                rc = ESRCH;
+                break;
+
+            default:
+                perror(NULL);
+                rc = errno;
+                break;
+            }
+            goto out;
+        }
 
         if ( status.status == EVTCHNSTAT_closed )
             continue;
@@ -58,7 +80,8 @@ int main(int argc, char **argv)
         printf("\n");
     }
 
+ out:
     xc_interface_close(xch);
 
-    return 0;
+    return rc;
 }
-- 
2.34.1