[v2,3/4] qga: Don't daemonize before channel is initialized

Commit Message

Michal Privoznik Dec. 5, 2024, 4:18 p.m. UTC

If the agent is set to daemonize but for whatever reason fails to
init the channel, the error message is lost. Worse, the agent
daemonizes needlessly and returns success. For instance:

  # qemu-ga -m virtio-serial \
            -p /dev/nonexistent_device \
            -f /run/qemu-ga.pid \
            -t /run \
            -d
  # echo $?
  0

This makes it needlessly hard for init scripts to detect a
failure in qemu-ga startup. Though, they shouldn't pass '-d' in
the first place.

Let's open the channel first and only after that become a daemon.

Related bug: https://bugs.gentoo.org/810628

Signed-off-by: Michal Privoznik <[e-mail]>
Reviewed-by: Ján Tomko <[e-mail]>
---
 qga/main.c | 24 ++++++++++++++++++------
 1 file changed, 18 insertions(+), 6 deletions(-)

Patch

diff --git a/qga/main.c b/qga/main.c
index 68ea7f275a..35f061b5ea 100644
--- a/qga/main.c
+++ b/qga/main.c
@@ -1430,7 +1430,6 @@  static GAState *initialize_agent(GAConfig *config, int socket_activation)
         if (config->daemonize) {
             /* delay opening/locking of pidfile till filesystems are unfrozen */
             s->deferred_options.pid_filepath = config->pid_filepath;
-            become_daemon(NULL);
         }
         if (config->log_filepath) {
             /* delay opening the log file till filesystems are unfrozen */
@@ -1438,9 +1437,6 @@  static GAState *initialize_agent(GAConfig *config, int socket_activation)
         }
         ga_disable_logging(s);
     } else {
-        if (config->daemonize) {
-            become_daemon(config->pid_filepath);
-        }
         if (config->log_filepath) {
             FILE *log_file = ga_open_logfile(config->log_filepath);
             if (!log_file) {
@@ -1487,6 +1483,20 @@  static GAState *initialize_agent(GAConfig *config, int socket_activation)
 
     ga_apply_command_filters(s);
 
+    if (!channel_init(s, s->config->method, s->config->channel_path,
+                      s->socket_activation ? FIRST_SOCKET_ACTIVATION_FD : -1)) {
+        g_critical("failed to initialize guest agent channel");
+        return NULL;
+    }
+
+    if (config->daemonize) {
+        if (ga_is_frozen(s)) {
+            become_daemon(NULL);
+        } else {
+            become_daemon(config->pid_filepath);
+        }
+    }
+
     ga_state = s;
     return s;
 }
@@ -1513,8 +1523,9 @@  static void cleanup_agent(GAState *s)
 
 static int run_agent_once(GAState *s)
 {
-    if (!channel_init(s, s->config->method, s->config->channel_path,
-                      s->socket_activation ? FIRST_SOCKET_ACTIVATION_FD : -1)) {
+    if (!s->channel &&
+        channel_init(s, s->config->method, s->config->channel_path,
+                     s->socket_activation ? FIRST_SOCKET_ACTIVATION_FD : -1)) {
         g_critical("failed to initialize guest agent channel");
         return EXIT_FAILURE;
     }
@@ -1523,6 +1534,7 @@  static int run_agent_once(GAState *s)
 
     if (s->channel) {
         ga_channel_free(s->channel);
+        s->channel = NULL;
     }
 
     return EXIT_SUCCESS;