api: fix vac_read return codes

- vac_read was returning the same code for multiple errors.
- Refactor VppTransportShmemIOError to capture rv and description.

Type: refactor

Change-Id: Ifb8ca5ff679f658bcd92a43ecddaffd2fc18dbd5
Signed-off-by: Paul Vinciguerra <pvinci@vinciconsulting.com>

2 files changed, 13 insertions, 4 deletions

diff --git a/src/vpp-api/client/client.c b/src/vpp-api/client/client.c
index 5b47fd4dd7d..50d088c1bfb 100644
--- a/src/vpp-api/client/client.c
+++ b/src/vpp-api/client/client.c
@@ -450,11 +450,13 @@ vac_read (char **p, int *l, u16 timeout)
   int rv;
   vl_shmem_hdr_t *shmem_hdr;
 
-  if (!pm->connected_to_vlib) return -1;
+  /* svm_queue_sub(below) returns {-1, -2} */
+  if (!pm->connected_to_vlib) return -3;
 
   *l = 0;
 
-  if (am->our_pid == 0) return (-1);
+  /* svm_queue_sub(below) returns {-1, -2} */
+  if (am->our_pid == 0) return (-4);
 
   /* Poke timeout thread */
   if (timeout)
diff --git a/src/vpp-api/python/vpp_papi/vpp_transport_shmem.py b/src/vpp-api/python/vpp_papi/vpp_transport_shmem.py
index 53ae775069f..64c1a59ba74 100644
--- a/src/vpp-api/python/vpp_papi/vpp_transport_shmem.py
+++ b/src/vpp-api/python/vpp_papi/vpp_transport_shmem.py
@@ -48,7 +48,13 @@ def vac_error_handler(arg, msg, msg_len):
 
 
 class VppTransportShmemIOError(IOError):
-    pass
+    """ exception communicating with vpp over shared memory """
+
+    def __init__(self, rv, descr):
+        self.rv = rv
+        self.desc = descr
+
+        super(VppTransportShmemIOError, self).__init__(rv, descr)
 
 
 class VppTransport(object):
@@ -117,7 +123,8 @@ class VppTransport(object):
         size = ffi.new("int *")
         rv = vpp_api.vac_read(mem, size, self.read_timeout)
         if rv:
-            raise VppTransportShmemIOError(rv, 'vac_read failed')
+            strerror = 'vac_read failed.  It is likely that VPP died.'
+            raise VppTransportShmemIOError(rv, strerror)
         msg = bytes(ffi.buffer(mem[0], size[0]))
         vpp_api.vac_free(mem[0])
         return msg