listener: warn on some accept()/accept4() errors

We need to warn when hitting file or socket memory limits
or misconfigurations which clear O_NONBLOCK to make it easier
to diagnose configuration problems.  We'll also warn on
some other errors in case bugs creep in...

diff --git a/lib/PublicInbox/Listener.pm b/lib/PublicInbox/Listener.pm
index f6a5da694041bfb89656eb43b3ecafc468c234ec..821c34583e24a75c386bc6f650a3fd1186479f12 100644 (file)
--- a/lib/PublicInbox/Listener.pm
+++ b/lib/PublicInbox/Listener.pm
@@ -10,6 +10,13 @@ use Socket qw(SOL_SOCKET SO_KEEPALIVE IPPROTO_TCP TCP_NODELAY);
 use fields qw(post_accept);
 require IO::Handle;
 use PublicInbox::Syscall qw(EPOLLIN EPOLLEXCLUSIVE EPOLLET);
+use Errno qw(EAGAIN ECONNABORTED EPERM);
+
+# Warn on transient errors, mostly resource limitations.
+# EINTR would indicate the failure to set NonBlocking in systemd or similar
+my %ERR_WARN = map {;
+       eval("Errno::$_()") => $_
+} qw(EMFILE ENFILE ENOBUFS ENOMEM EINTR);
 
 sub new ($$$) {
        my ($class, $s, $cb) = @_;
@@ -35,6 +42,18 @@ sub event_step {
                IO::Handle::blocking($c, 0); # no accept4 :<
                $self->{post_accept}->($c, $addr, $sock);
                $self->requeue;
+       } elsif ($! == EAGAIN || $! == ECONNABORTED || $! == EPERM) {
+               # EAGAIN is common and likely
+               # ECONNABORTED is common with bad connections
+               # EPERM happens if firewall rules prevent a connection
+               # on Linux (and everything that emulates Linux).
+               # Firewall rules are sometimes intentional, so we don't
+               # warn on EPERM to avoid being too noisy...
+               return;
+       } elsif (my $sym = $ERR_WARN{int($!)}) {
+               warn "W: accept(): $! ($sym)\n";
+       } else {
+               warn "BUG?: accept(): $!\n";
        }
 }