[PATCH v2 04/12] libqtest: add qtest_remove_abrt_handler()

[Stefan Hajnoczi <stefanha@redhat.com>]

Add a function to remove previously-added abrt handler functions.

Now that a symmetric pair of add/remove functions exists we can also
balance the SIGABRT handler installation. The signal handler was
installed each time qtest_add_abrt_handler() was called. Now it is
installed when the abrt handler list becomes non-empty and removed again
when the list becomes empty.

The qtest_remove_abrt_handler() function will be used by
vhost-user-blk-test.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
 tests/qtest/libqos/libqtest.h | 18 ++++++++++++++++++
 tests/qtest/libqtest.c        | 35 +++++++++++++++++++++++++++++------
 2 files changed, 47 insertions(+), 6 deletions(-)

diff --git a/tests/qtest/libqos/libqtest.h b/tests/qtest/libqos/libqtest.h
index 51287b9276..a68dcd79d4 100644
--- a/tests/qtest/libqos/libqtest.h
+++ b/tests/qtest/libqos/libqtest.h
@@ -649,8 +649,26 @@ void qtest_add_data_func_full(const char *str, void *data,
         g_free(path); \
     } while (0)
 
+/**
+ * qtest_add_abrt_handler:
+ * @fn: Handler function
+ * @data: Argument that is passed to the handler
+ *
+ * Add a handler function that is invoked on SIGABRT. This can be used to
+ * terminate processes and perform other cleanup. The handler can be removed
+ * with qtest_remove_abrt_handler().
+ */
 void qtest_add_abrt_handler(GHookFunc fn, const void *data);
 
+/**
+ * qtest_remove_abrt_handler:
+ * @data: Argument previously passed to qtest_add_abrt_handler()
+ *
+ * Remove an abrt handler that was previously added with
+ * qtest_add_abrt_handler().
+ */
+void qtest_remove_abrt_handler(void *data);
+
 /**
  * qtest_qmp_assert_success:
  * @qts: QTestState instance to operate on
diff --git a/tests/qtest/libqtest.c b/tests/qtest/libqtest.c
index cc2cec4a35..7cf247baf0 100644
--- a/tests/qtest/libqtest.c
+++ b/tests/qtest/libqtest.c
@@ -196,15 +196,30 @@ static void cleanup_sigabrt_handler(void)
     sigaction(SIGABRT, &sigact_old, NULL);
 }
 
+static bool hook_list_is_empty(GHookList *hook_list)
+{
+    GHook *hook = g_hook_first_valid(hook_list, TRUE);
+
+    if (!hook) {
+        return false;
+    }
+
+    g_hook_unref(hook_list, hook);
+    return true;
+}
+
 void qtest_add_abrt_handler(GHookFunc fn, const void *data)
 {
     GHook *hook;
 
-    /* Only install SIGABRT handler once */
     if (!abrt_hooks.is_setup) {
         g_hook_list_init(&abrt_hooks, sizeof(GHook));
     }
-    setup_sigabrt_handler();
+
+    /* Only install SIGABRT handler once */
+    if (hook_list_is_empty(&abrt_hooks)) {
+        setup_sigabrt_handler();
+    }
 
     hook = g_hook_alloc(&abrt_hooks);
     hook->func = fn;
@@ -213,6 +228,17 @@ void qtest_add_abrt_handler(GHookFunc fn, const void *data)
     g_hook_prepend(&abrt_hooks, hook);
 }
 
+void qtest_remove_abrt_handler(void *data)
+{
+    GHook *hook = g_hook_find_data(&abrt_hooks, TRUE, data);
+    g_hook_destroy_link(&abrt_hooks, hook);
+
+    /* Uninstall SIGABRT handler on last instance */
+    if (hook_list_is_empty(&abrt_hooks)) {
+        cleanup_sigabrt_handler();
+    }
+}
+
 static const char *qtest_qemu_binary(void)
 {
     const char *qemu_bin;
@@ -369,10 +395,7 @@ QTestState *qtest_init_with_serial(const char *extra_args, int *sock_fd)
 
 void qtest_quit(QTestState *s)
 {
-    g_hook_destroy_link(&abrt_hooks, g_hook_find_data(&abrt_hooks, TRUE, s));
-
-    /* Uninstall SIGABRT handler on last instance */
-    cleanup_sigabrt_handler();
+    qtest_remove_abrt_handler(s);
 
     qtest_kill_qemu(s);
     close(s->fd);
-- 
2.28.0