[RFC v2] lei: close inotify FD in forked child

[Eric Wong <e@80x24.org>]

It looks like Linux::Inotify2 2.3+ will include an ->fh method
to give us the ability to safely close an FD without hitting
EBADF (and automatically use FD_CLOEXEC).

We'll still need a new wrapper class (LI2Wrap) to handle it for
users of old versions, though.

http://lists.schmorp.de/pipermail/perl/2021q3/thread.html
---
 MANIFEST                   |  1 +
 lib/PublicInbox/DirIdle.pm | 11 +++++++++++
 lib/PublicInbox/LEI.pm     |  2 +-
 lib/PublicInbox/LI2Wrap.pm | 20 ++++++++++++++++++++
 4 files changed, 33 insertions(+), 1 deletion(-)
 create mode 100644 lib/PublicInbox/LI2Wrap.pm

diff --git a/MANIFEST b/MANIFEST
index a3913501..fb9f16bf 100644
--- a/MANIFEST
+++ b/MANIFEST
@@ -197,6 +197,7 @@ lib/PublicInbox/InputPipe.pm
 lib/PublicInbox/Isearch.pm
 lib/PublicInbox/KQNotify.pm
 lib/PublicInbox/LEI.pm
+lib/PublicInbox/LI2Wrap.pm
 lib/PublicInbox/LeiALE.pm
 lib/PublicInbox/LeiAddWatch.pm
 lib/PublicInbox/LeiAuth.pm
diff --git a/lib/PublicInbox/DirIdle.pm b/lib/PublicInbox/DirIdle.pm
index 65896f95..d572c274 100644
--- a/lib/PublicInbox/DirIdle.pm
+++ b/lib/PublicInbox/DirIdle.pm
@@ -84,4 +84,15 @@ sub event_step {
 	warn "$self->{inot}->read err: $@\n" if $@;
 }
 
+sub force_close {
+	my ($self) = @_;
+	my $inot = delete $self->{inot} // return;
+	if ($inot->can('fh')) { # Linux::Inotify2 2.3+
+		close($inot->fh) or warn "CLOSE ERROR: $!";
+	} elsif ($inot->isa('Linux::Inotify2')) {
+		require PublicInbox::LI2Wrap;
+		PublicInbox::LI2Wrap::wrapclose($inot);
+	}
+}
+
 1;
diff --git a/lib/PublicInbox/LEI.pm b/lib/PublicInbox/LEI.pm
index d9fd40fd..e6f763e1 100644
--- a/lib/PublicInbox/LEI.pm
+++ b/lib/PublicInbox/LEI.pm
@@ -556,7 +556,7 @@ sub _lei_atfork_child {
 	}
 	close $listener if $listener;
 	undef $listener;
-	undef $dir_idle;
+	$dir_idle->force_close if $dir_idle;
 	%PATH2CFG = ();
 	$MDIR2CFGPATH = {};
 	eval 'no warnings; undef $PublicInbox::LeiNoteEvent::to_flush';
diff --git a/lib/PublicInbox/LI2Wrap.pm b/lib/PublicInbox/LI2Wrap.pm
new file mode 100644
index 00000000..b0f4f8b8
--- /dev/null
+++ b/lib/PublicInbox/LI2Wrap.pm
@@ -0,0 +1,20 @@
+# Copyright (C) all contributors <meta@public-inbox.org>
+# License: AGPL-3.0+ <https://www.gnu.org/licenses/agpl-3.0.txt>
+
+# Wrapper for Linux::Inotify2 < 2.3 which lacked ->fh and auto-close
+# Remove this when supported LTS/enterprise distros are all
+# Linux::Inotify2 >= 2.3
+package PublicInbox::LI2Wrap;
+use v5.10.1;
+our @ISA = qw(Linux::Inotify2);
+
+sub wrapclose {
+	my ($inot) = @_;
+	my $fd = $inot->fileno;
+	open my $fh, '<&=', $fd or die "open <&= $fd $!";
+
+}
+
+sub DESTROY {} # no-op
+
+1