libqtest: Wait for the right child PID after killing QEMU

When running "make check" with gcov enabled, we get the following
message:

   hw/tmp105.gcda:cannot open data file, assuming not executed

The problem happens because:

 * tmp105-test exits before QEMU exits, because waitpid() at
   qtest_quit() fails;
 * waitpid() fails because there's another process already
   waiting for the QEMU process;
 * The process that is already waiting for QEMU is the child created by
   qtest_init() to run system();
 * qtest_quit() is incorrectly waiting for the QEMU PID directly instead
   of the child created by qtest_init().

This fixes the problem by sending SIGTERM to QEMU, but waiting for the
child process created by qtest_init() (that exits immediately after QEMU
exits).

Reported-by: Andreas Färber <afaerber@suse.de>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

1 files changed, 5 insertions, 2 deletions

diff --git a/tests/libqtest.c b/tests/libqtest.c
index 913fa0535c..762dec4ac0 100644
--- a/tests/libqtest.c
+++ b/tests/libqtest.c
@@ -39,7 +39,8 @@ struct QTestState
     int qmp_fd;
     bool irq_level[MAX_IRQ];
     GString *rx;
-    gchar *pid_file;
+    gchar *pid_file; /* QEMU PID file */
+    int child_pid;   /* Child process created to execute QEMU */
     char *socket_path, *qmp_socket_path;
 };
 
@@ -144,6 +145,7 @@ QTestState *qtest_init(const char *extra_args)
 
     s->rx = g_string_new("");
     s->pid_file = pid_file;
+    s->child_pid = pid;
     for (i = 0; i < MAX_IRQ; i++) {
         s->irq_level[i] = false;
     }
@@ -165,8 +167,9 @@ void qtest_quit(QTestState *s)
 
     pid_t pid = qtest_qemu_pid(s);
     if (pid != -1) {
+        /* kill QEMU, but wait for the child created by us to run system() */
         kill(pid, SIGTERM);
-        waitpid(pid, &status, 0);
+        waitpid(s->child_pid, &status, 0);
     }
 
     unlink(s->pid_file);