[PATCH v2 3/5] qemu_passt: Make passt report errors to stderr whenever possible

[Michal Privoznik]

Passt has '--stderr' argument which makes it report error onto
stderr rather to system log. Unfortunately, it's currently
impossible to use both '--log-file' and '--stderr', so pass the
latter only if the former isn't passed. Then, use the stderr to
produce more user friendly error message on failed start.

Signed-off-by: Michal Privoznik <mprivozn at redhat.com>
---
 src/qemu/qemu_passt.c | 22 +++++++++++++++++++---
 1 file changed, 19 insertions(+), 3 deletions(-)

diff --git a/src/qemu/qemu_passt.c b/src/qemu/qemu_passt.c
index c082c149cd..881205449b 100644
--- a/src/qemu/qemu_passt.c
+++ b/src/qemu/qemu_passt.c
@@ -171,8 +171,13 @@ qemuPasstStart(virDomainObj *vm,
     if (net->sourceDev)
         virCommandAddArgList(cmd, "--interface", net->sourceDev, NULL);
 
-    if (net->backend.logFile)
+    if (net->backend.logFile) {
         virCommandAddArgList(cmd, "--log-file", net->backend.logFile, NULL);
+    } else {
+        /* By default, passt logs into system logger. But we are interested
+         * into errors too. Make it print errors onto stderr. */
+        virCommandAddArg(cmd, "--stderr");
+    }
 
     /* Add IP address info */
     for (i = 0; i < net->guestIP.nips; i++) {
@@ -265,8 +270,19 @@ qemuPasstStart(virDomainObj *vm,
         goto error;
 
     if (cmdret < 0 || exitstatus != 0) {
-        virReportError(VIR_ERR_INTERNAL_ERROR,
-                       _("Could not start 'passt': %s"), NULLSTR(errbuf));
+        if (STRNEQ_NULLABLE(errbuf, "")) {
+            virReportError(VIR_ERR_INTERNAL_ERROR,
+                           _("Could not start 'passt': %s"), errbuf);
+        } else if (net->backend.logFile) {
+            virReportError(VIR_ERR_INTERNAL_ERROR,
+                           _("Could not start 'passt': look into %s for error"),
+                           net->backend.logFile);
+        } else {
+            virReportError(VIR_ERR_INTERNAL_ERROR,
+                           _("Could not start 'passt': exit status = '%d'"),
+                           exitstatus);
+        }
+
         goto error;
     }
 
-- 
2.39.1