shared: log error when execve fail

If there is an error with the execv call in fork_agent the
program exits without any meaningful log message. Log the
command and errno so the user gets more information about
the failure.

Fixes: #33418

Signed-off-by: Mauri de Souza Meneguzzo <mauri870@gmail.com>
(cherry picked from commit a408d4453145621902b9a3ef78a552f83b09bd8d)
(cherry picked from commit 7fcfb73d71ed1d4230f58de1a94790e0c28719ea)
(cherry picked from commit 76fe6eb)

src/shared/exec-util.c

@@ -601,5 +601,6 @@ int fork_agent(const char *name, const int except[], size_t n_except, pid_t *ret
         va_end(ap);
 
         execv(path, l);
+        log_error_errno(errno, "Failed to execute %s: %m", path);
         _exit(EXIT_FAILURE);
 }

src/shared/spawn-polkit-agent.c

@@ -43,16 +43,21 @@ int polkit_agent_open(void) {
         xsprintf(notify_fd, "%i", pipe_fd[1]);
 
         r = fork_agent("(polkit-agent)",
-                       &pipe_fd[1], 1,
+                       &pipe_fd[1],
+                       1,
                        &agent_pid,
                        POLKIT_AGENT_BINARY_PATH,
-                       POLKIT_AGENT_BINARY_PATH, "--notify-fd", notify_fd, "--fallback", NULL);
+                       POLKIT_AGENT_BINARY_PATH,
+                       "--notify-fd",
+                       notify_fd,
+                       "--fallback",
+                       NULL);
 
         /* Close the writing side, because that's the one for the agent */
         safe_close(pipe_fd[1]);
 
         if (r < 0)
-                log_error_errno(r, "Failed to fork TTY ask password agent: %m");
+                log_error_errno(r, "Failed to fork polkit agent: %m");
         else
                 /* Wait until the agent closes the fd */
                 (void) fd_wait_for_event(pipe_fd[0], POLLHUP, USEC_INFINITY);