qtest: implement QTEST_STOP

It is quite difficult to debug qtest test cases without extra wrapper
scripts for QEMU or similar.  This patch adds a simple environment
variable-based trigger that sends a STOP signal to the QEMU instance
under test, before attempting to connect to its QMP session.

This will block execution of the testcase and give time to attach a
debugger to the stopped QEMU process.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

1 files changed, 25 insertions, 13 deletions

diff --git a/tests/libqtest.c b/tests/libqtest.c
index 02d039218d..71b84c12dd 100644
--- a/tests/libqtest.c
+++ b/tests/libqtest.c
@@ -85,6 +85,22 @@ static int socket_accept(int sock)
     return ret;
 }
 
+static pid_t qtest_qemu_pid(QTestState *s)
+{
+    FILE *f;
+    char buffer[1024];
+    pid_t pid = -1;
+
+    f = fopen(s->pid_file, "r");
+    if (f) {
+        if (fgets(buffer, sizeof(buffer), f)) {
+            pid = atoi(buffer);
+        }
+    }
+    fclose(f);
+    return pid;
+}
+
 QTestState *qtest_init(const char *extra_args)
 {
     QTestState *s;
@@ -136,25 +152,21 @@ QTestState *qtest_init(const char *extra_args)
     qtest_qmp(s, "");
     qtest_qmp(s, "{ 'execute': 'qmp_capabilities' }");
 
+    if (getenv("QTEST_STOP")) {
+        kill(qtest_qemu_pid(s), SIGSTOP);
+    }
+
     return s;
 }
 
 void qtest_quit(QTestState *s)
 {
-    FILE *f;
-    char buffer[1024];
-
-    f = fopen(s->pid_file, "r");
-    if (f) {
-        if (fgets(buffer, sizeof(buffer), f)) {
-            pid_t pid = atoi(buffer);
-            int status = 0;
-
-            kill(pid, SIGTERM);
-            waitpid(pid, &status, 0);
-        }
+    int status;
 
-        fclose(f);
+    pid_t pid = qtest_qemu_pid(s);
+    if (pid != -1) {
+        kill(pid, SIGTERM);
+        waitpid(pid, &status, 0);
     }
 
     unlink(s->pid_file);