tests: commandtest: Make 'test4' checking daemonization more reliable

The 'commandhelper' checks effectively whether the parent process is
still around to report whether it was daemonized or not.

This creates a unlikely race condition in cases when we do actually
daemonize the process as the intermediate process used for the
daemonization might not have terminated yet which would report wrong
result leading to test failure.

For now there's just 'test4' which actually daemonizes the process.

Add an argument '--check-daemonize' which asks for retries of the
daemonization check in cases where we expect that the commandhelper is
going to be daemonized and use it in 'test4' to make the test more
reliable.

I've observed the test failure sporadically when my box is under load
e.g. while building two trees at once.

Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>

tests/commanddata/test4.log

@@ -1,3 +1,4 @@
+ARG:--check-daemonize
 ENV:DISPLAY=:0.0
 ENV:HOME=/home/test
 ENV:HOSTNAME=test

tests/commandhelper.c

@@ -72,6 +72,8 @@ int main(int argc, char **argv) {
     char *buffers[3] = {NULL, NULL, NULL};
     size_t buflen[3] = {0, 0, 0};
     char c;
+    bool daemonize_check = false;
+    size_t daemonize_retries = 3;
 
     if (!log)
         return ret;
@@ -83,6 +85,8 @@ int main(int argc, char **argv) {
             sscanf(argv[i], "%u%c", &readfds[numreadfds++], &c) != 1) {
             printf("Could not parse fd %s\n", argv[i]);
             goto cleanup;
+        } else if (STREQ(argv[i], "--check-daemonize")) {
+            daemonize_check = true;
         }
     }
 
@@ -126,7 +130,18 @@ int main(int argc, char **argv) {
             fprintf(log, "FD:%zu\n", i);
     }
 
-    fprintf(log, "DAEMON:%s\n", getpgrp() != getppid() ? "yes" : "no");
+    while (true) {
+        bool daemonized = getpgrp() != getppid();
+
+        if (daemonize_check && !daemonized && daemonize_retries-- > 0) {
+            usleep(100*1000);
+            continue;
+        }
+
+        fprintf(log, "DAEMON:%s\n", daemonized ? "yes" : "no");
+        break;
+    }
+
     if (!(cwd = getcwd(NULL, 0)))
         goto cleanup;
     if (strlen(cwd) > strlen(".../commanddata") &&

tests/commandtest.c

@@ -255,7 +255,8 @@ static int test3(const void *unused G_GNUC_UNUSED)
  */
 static int test4(const void *unused G_GNUC_UNUSED)
 {
-    virCommandPtr cmd = virCommandNew(abs_builddir "/commandhelper");
+    virCommandPtr cmd = virCommandNewArgList(abs_builddir "/commandhelper",
+                                             "--check-daemonize", NULL);
     char *pidfile = virPidFileBuildPath(abs_builddir, "commandhelper");
     pid_t pid;
     int ret = -1;