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 <mprivozn@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>
---
 qga/main.c | 24 ++++++++++++++++++------
 1 file changed, 18 insertions(+), 6 deletions(-)

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;
-- 
2.45.2

Reviewed-by: Konstantin Kostiuk <kkostiuk@redhat.com>

On Tue, Jan 7, 2025 at 4:52 PM Michal Privoznik <mprivozn@redhat.com> wrote:

> 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 <mprivozn@redhat.com>
> Reviewed-by: Ján Tomko <jtomko@redhat.com>
> ---
>  qga/main.c | 24 ++++++++++++++++++------
>  1 file changed, 18 insertions(+), 6 deletions(-)
>
> 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;
> --
> 2.45.2
>
>