[PATCH v2 2/2] test_common: avoid needless fcntl in start_script

[Eric Wong]

POSIX::dup2 does not do anything in addition to dup2(2) and is
thus immune to Perl automatically setting FD_CLOEXEC on FDs it
makes into IO objects/globs.  We only need to account for the
case when both args for dup2 are identical, in which case the
kernel treats it as a no-op and then thus we need to clear
FD_CLOEXEC ourselves.
---
  v2 now accounts for oldfd == newfd for dup2(2).

Interdiff:
  diff --git a/lib/PublicInbox/TestCommon.pm b/lib/PublicInbox/TestCommon.pm
  index 179f8bae..b36c71a6 100644
  --- a/lib/PublicInbox/TestCommon.pm
  +++ b/lib/PublicInbox/TestCommon.pm
  @@ -6,7 +6,7 @@ package PublicInbox::TestCommon;
   use strict;
   use parent qw(Exporter);
   use v5.10.1;
  -use Fcntl qw(FD_CLOEXEC F_SETFD F_GETFD :seek);
  +use Fcntl qw(F_SETFD :seek);
   use POSIX qw(dup2);
   use IO::Socket::INET;
   use File::Spec;
  @@ -481,7 +481,12 @@ sub start_script {
                my $fd;
                for ($fd = 0; $fd < 3 || defined($opt->{$fd}); $fd++) {
                        my $io = $opt->{$fd} // next;
  -                     dup2(fileno($io), $fd) or die "dup2($io, $fd): $!";
  +                     my $old = fileno($io);
  +                     if ($old == $fd) {
  +                             fcntl($io, F_SETFD, 0) // die "F_SETFD: $!";
  +                     } else {
  +                             dup2($old, $fd) // die "dup2($old, $fd): $!";
  +                     }
                }
                %ENV = (%ENV, %$env) if $env;
                my $fds = $fd - 3;

 lib/PublicInbox/TestCommon.pm | 18 ++++++++----------
 1 file changed, 8 insertions(+), 10 deletions(-)

diff --git a/lib/PublicInbox/TestCommon.pm b/lib/PublicInbox/TestCommon.pm
index 888c1f1e..b36c71a6 100644
--- a/lib/PublicInbox/TestCommon.pm
+++ b/lib/PublicInbox/TestCommon.pm
@@ -6,7 +6,7 @@ package PublicInbox::TestCommon;
 use strict;
 use parent qw(Exporter);
 use v5.10.1;
-use Fcntl qw(FD_CLOEXEC F_SETFD F_GETFD :seek);
+use Fcntl qw(F_SETFD :seek);
 use POSIX qw(dup2);
 use IO::Socket::INET;
 use File::Spec;
@@ -479,16 +479,14 @@ sub start_script {
                # pretend to be systemd (cf. sd_listen_fds(3))
                # 3 == SD_LISTEN_FDS_START
                my $fd;
-               for ($fd = 0; 1; $fd++) {
-                       my $s = $opt->{$fd};
-                       last if $fd >= 3 && !defined($s);
-                       next unless $s;
-                       my $fl = fcntl($s, F_GETFD, 0);
-                       if (($fl & FD_CLOEXEC) != FD_CLOEXEC) {
-                               warn "got FD:".fileno($s)." w/o CLOEXEC\n";
+               for ($fd = 0; $fd < 3 || defined($opt->{$fd}); $fd++) {
+                       my $io = $opt->{$fd} // next;
+                       my $old = fileno($io);
+                       if ($old == $fd) {
+                               fcntl($io, F_SETFD, 0) // die "F_SETFD: $!";
+                       } else {
+                               dup2($old, $fd) // die "dup2($old, $fd): $!";
                        }
-                       fcntl($s, F_SETFD, $fl &= ~FD_CLOEXEC);
-                       dup2(fileno($s), $fd) or die "dup2 failed: $!\n";
                }
                %ENV = (%ENV, %$env) if $env;
                my $fds = $fd - 3;