global: reexpand the conf meta in all the child processes

Especially for the tools or the daemons whose config options need
to expand the '$pid', they will be always expanded with the parent
processes. We need to reexpand them in child processes just after
the fork is done.

Fixes: https://tracker.ceph.com/issues/48240
Signed-off-by: Xiubo Li <xiubli@redhat.com>

PendingReleaseNotes

@@ -1,5 +1,9 @@
 >=16.0.0
 --------
+* $pid expansion in config paths like `admin_socket` will now properly expand
+  to the daemon pid for commands like `ceph-mds` or `ceph-osd`. Previously only
+  `ceph-fuse`/`rbd-nbd` expanded `$pid` with the actual daemon pid.
+
 * The allowable options for some "radosgw-admin" commands have been changed.
 
   * "mdlog-list", "datalog-list", "sync-error-list" no longer accepts

src/ceph_fuse.cc

@@ -179,9 +179,8 @@ int main(int argc, const char **argv, const char *envp[]) {
   }
 
   {
-    g_ceph_context->_conf.finalize_reexpand_meta();
     common_init_finish(g_ceph_context);
-   
+
     init_async_signal_handler();
     register_async_signal_handler(SIGHUP, sighup_handler);
 

src/global/global_init.cc

@@ -515,6 +515,9 @@ int reopen_as_null(CephContext *cct, int fd)
 
 void global_init_postfork_start(CephContext *cct)
 {
+  // reexpand the meta in child process
+  cct->_conf.finalize_reexpand_meta();
+
   // restart log thread
   cct->_log->start();
   cct->notify_post_fork();

src/tools/rbd_nbd/rbd-nbd.cc

@@ -1594,7 +1594,6 @@ static int do_map(int argc, const char *argv[], Config *cfg, bool reconnect)
     global_init_postfork_start(g_ceph_context);
   }
 
-  g_ceph_context->_conf.finalize_reexpand_meta();
   common_init_finish(g_ceph_context);
   global_init_chdir(g_ceph_context);