fix(node_info): reap zombie pve_mod_worker and orphaned collector processes (#307)

* fix(node_info): reap zombie pve_mod_worker and orphaned collector processes

Double-forks pve_mod_worker so it is reparented to init instead of the calling process, which reaps it immediately on exit and prevents it lingering as a <defunct> zombie. Also adds startup-time reaping of orphaned collector-* processes (ppid==1) left behind if a worker was previously killed with SIGKILL, and an opportunistic waitpid(WNOHANG) in _worker_lock_file_exists as a cheap supplemental reap.

* fix compile error and reap orphans

---------

Co-authored-by: Meliox <na>

src/modules/node_info/files/Utils.pm

@@ -15,6 +15,7 @@ our @EXPORT_OK = qw(
     debug
     read_sysfs
     is_process_alive
+    get_process_ppid
     read_lock_pid
     acquire_exclusive_lock
     ensure_pve_mod_directory_exists
@@ -102,6 +103,24 @@ sub is_process_alive {
     return 1;
 }
 
+# Returns the parent PID of $pid, or undef if it can't be determined.
+sub get_process_ppid {
+    my ($pid) = @_;
+    return undef unless open my $fh, '<', "/proc/$pid/stat";
+    my $line = <$fh>;
+    close $fh;
+    return undef unless defined $line;
+
+    # comm field (2nd, in parens) can itself contain ')', so split on the
+    # last one before parsing the remaining space-separated fields.
+    my $last_paren = rindex($line, ')');
+    return undef if $last_paren < 0;
+
+    my @fields = split ' ', substr($line, $last_paren + 1);
+    return undef unless defined $fields[1] && $fields[1] =~ /^(\d+)$/;
+    return $1;
+}
+
 sub read_lock_pid {
     my ($lock_path) = @_;