[PATCH] virNetDevOpenvswitchInterfaceStats: Be more forgiving when fetching stats

[Michal Privoznik <mprivozn@xxxxxxxxxx>]

https://bugzilla.redhat.com/show_bug.cgi?id=1461270

When fetching stats for a vhost-user type of interface, we run
couple of ovs-vsctl commands and parse their output. However, not
all stats exist at all times, for instance "rx_dropped" or
"tx_errors" can be missing. Thing is, we ask for a bulk of
statistics and if one of them is missing an error is reported
instead of returning the rest. Since we ignore errors, we fail to
set statistics. Fix this by asking for each piece alone.

Signed-off-by: Michal Privoznik <mprivozn@xxxxxxxxxx>
---
 src/util/virnetdevopenvswitch.c | 96 +++++++++++++++--------------------------
 1 file changed, 34 insertions(+), 62 deletions(-)

diff --git a/src/util/virnetdevopenvswitch.c b/src/util/virnetdevopenvswitch.c
index 8f7215e06..6848f65b7 100644
--- a/src/util/virnetdevopenvswitch.c
+++ b/src/util/virnetdevopenvswitch.c
@@ -317,14 +317,8 @@ virNetDevOpenvswitchInterfaceStats(const char *ifname,
 {
     virCommandPtr cmd = NULL;
     char *output;
-    long long rx_bytes;
-    long long rx_packets;
-    long long tx_bytes;
-    long long tx_packets;
-    long long rx_errs;
-    long long rx_drop;
-    long long tx_errs;
-    long long tx_drop;
+    char *tmp;
+    bool gotStats = false;
     int ret = -1;
 
     /* Just ensure the interface exists in ovs */
@@ -340,67 +334,45 @@ virNetDevOpenvswitchInterfaceStats(const char *ifname,
         goto cleanup;
     }
 
-    VIR_FREE(output);
-    virCommandFree(cmd);
-
-    cmd = virCommandNew(OVSVSCTL);
-    virNetDevOpenvswitchAddTimeout(cmd);
-    virCommandAddArgList(cmd, "get", "Interface", ifname,
-                         "statistics:rx_bytes",
-                         "statistics:rx_packets",
-                         "statistics:tx_bytes",
-                         "statistics:tx_packets", NULL);
-    virCommandSetOutputBuffer(cmd, &output);
-
-    if (virCommandRun(cmd, NULL) < 0) {
-        virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
-                       _("Interface doesn't have statistics"));
-        goto cleanup;
-    }
+#define GET_STAT(name, member)                                              \
+    do {                                                                    \
+        VIR_FREE(output);                                                   \
+        virCommandFree(cmd);                                                \
+        cmd = virCommandNew(OVSVSCTL);                                      \
+        virNetDevOpenvswitchAddTimeout(cmd);                                \
+        virCommandAddArgList(cmd, "get", "Interface", ifname,               \
+                             "statistics:" name, NULL);                     \
+        virCommandSetOutputBuffer(cmd, &output);                            \
+        if (virCommandRun(cmd, NULL) < 0) {                                 \
+            stats->member = -1;                                             \
+        } else {                                                            \
+            if (virStrToLong_ll(output, &tmp, 10, &stats->member) < 0 ||    \
+                *tmp != '\n') {                                             \
+                virReportError(VIR_ERR_INTERNAL_ERROR, "%s",                \
+                               _("Fail to parse ovs-vsctl output"));        \
+                goto cleanup;                                               \
+            }                                                               \
+            gotStats = true;                                                \
+        }                                                                   \
+    } while (0)
 
     /* The TX/RX fields appear to be swapped here
      * because this is the host view. */
-    if (sscanf(output, "%lld\n%lld\n%lld\n%lld\n",
-               &tx_bytes, &tx_packets, &rx_bytes, &rx_packets) != 4) {
-        virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
-                       _("Fail to parse ovs-vsctl output"));
-        goto cleanup;
-    }
+    GET_STAT("rx_bytes", tx_bytes);
+    GET_STAT("rx_packets", tx_packets);
+    GET_STAT("rx_errors", tx_errs);
+    GET_STAT("rx_dropped", tx_drop);
+    GET_STAT("tx_bytes", rx_bytes);
+    GET_STAT("tx_packets", rx_packets);
+    GET_STAT("tx_errors", rx_errs);
+    GET_STAT("tx_dropped", rx_drop);
 
-    stats->rx_bytes = rx_bytes;
-    stats->rx_packets = rx_packets;
-    stats->tx_bytes = tx_bytes;
-    stats->tx_packets = tx_packets;
-
-    VIR_FREE(output);
-    virCommandFree(cmd);
-
-    cmd = virCommandNew(OVSVSCTL);
-    virNetDevOpenvswitchAddTimeout(cmd);
-    virCommandAddArgList(cmd, "get", "Interface", ifname,
-                         "statistics:rx_errors",
-                         "statistics:rx_dropped",
-                         "statistics:tx_errors",
-                         "statistics:tx_dropped", NULL);
-    virCommandSetOutputBuffer(cmd, &output);
-    if (virCommandRun(cmd, NULL) < 0) {
-        /* This interface don't have errors or dropped, so set them to 0 */
-        stats->rx_errs = 0;
-        stats->rx_drop = 0;
-        stats->tx_errs = 0;
-        stats->tx_drop = 0;
-    } else if (sscanf(output, "%lld\n%lld\n%lld\n%lld\n",
-                      &tx_errs, &tx_drop, &rx_errs, &rx_drop) == 4) {
-        stats->rx_errs = rx_errs;
-        stats->rx_drop = rx_drop;
-        stats->tx_errs = tx_errs;
-        stats->tx_drop = tx_drop;
-        ret = 0;
-    } else {
+    if (!gotStats) {
         virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
-                       _("Fail to parse ovs-vsctl output"));
+                       _("Interface doesn't have statistics"));
         goto cleanup;
     }
+
     ret = 0;
 
  cleanup:
-- 
2.13.0

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