cli: Add sd-notify integration

Let's make sysprof-cli send a READY=1 sd-notify message when it's
finished its setup logic. This allows starting sysprof as a systemd
service and delaying startup of other services until sysprof has
finished its setup logic. This ensures we don't miss any profiling
data when running sysprof-cli in a systemd service as part of the
bootup process.

We skip this step for now when we're running a child process so that
we don't accidentally interfere with a child process that receives
an sd-notify socket and is supposed to send notifications on it instead
of sysprof-cli.

src/sysprof-cli/meson.build

@@ -13,6 +13,10 @@ if polkit_agent_dep.found()
   sysprof_cli_deps += polkit_agent_dep
 endif
 
+if libsystemd_dep.found()
+  sysprof_cli_deps += libsystemd_dep
+endif
+
 sysprof_cli = executable('sysprof-cli', sysprof_cli_sources,
   dependencies: sysprof_cli_deps,
         c_args: release_flags + sysprof_cli_c_args,

src/sysprof-cli/sysprof-cli.c

@@ -38,6 +38,10 @@
 # include <polkitagent/polkitagent.h>
 #endif
 
+#if HAVE_LIBSYSTEMD
+# include <systemd/sd-daemon.h>
+#endif
+
 #include "sysprof-capture-util-private.h"
 
 #define DEFAULT_BUFFER_SIZE (1024L * 1024L * 8L /* 8mb */)
@@ -625,6 +629,11 @@ Examples:\n\
 
   g_printerr ("Recording, press ^C to exit\n");
 
+#if HAVE_LIBSYSTEMD
+  if (command == NULL && child_argv == NULL)
+    sd_notify (TRUE, "READY=1");
+#endif
+
   g_main_loop_run (main_loop);
 
   sysprof_capture_writer_flush (writer);