[PATCH 2/2] treewide: lose F_SETPIPE_SZ page size assumptions

[Alyssa Ross <hi@alyssa.is>]

fcntl(2) is documented as rounding up sizes to an integer multiple of
the page size.  When a pipe buffer as small as possible is desired,
it's cleaner to pass 0 and let the kernel set the pipe buffer to
exactly one page than it is to assume that pages are 4096 bytes.

Currently, Linux doesn't support pages smaller than 4096 bytes, so this 
is a purely stylistic change, but I think it will help avoid future 
bugs caused by assuming page sizes are 4096 bytes.

 lib/PublicInbox/EOFpipe.pm        | 4 ++--
 lib/PublicInbox/LeiXSearch.pm     | 6 +++---
 lib/PublicInbox/SearchIdxShard.pm | 2 +-
 t/gcf2.t                          | 4 ++--
 t/lei-sigpipe.t                   | 2 +-
 5 files changed, 9 insertions(+), 9 deletions(-)

diff --git a/lib/PublicInbox/EOFpipe.pm b/lib/PublicInbox/EOFpipe.pm
index 3eaa0e4e..9fe9f67d 100644
--- a/lib/PublicInbox/EOFpipe.pm
+++ b/lib/PublicInbox/EOFpipe.pm
@@ -10,8 +10,8 @@ use Errno qw(EAGAIN);
 sub new {
 	my (undef, $rd, @cb_args) = @_;
 	my $self = bless { cb_args => \@cb_args }, __PACKAGE__;
-	# 4096: page size
-	fcntl($rd, $F_SETPIPE_SZ, 4096) if $F_SETPIPE_SZ;
+	# 0: one page
+	fcntl($rd, $F_SETPIPE_SZ, 0) if $F_SETPIPE_SZ;
 	$rd->blocking(0); # avoid EINTR
 	$self->SUPER::new($rd, EPOLLIN); # level trigger for spurious wakeup
 }
diff --git a/lib/PublicInbox/LeiXSearch.pm b/lib/PublicInbox/LeiXSearch.pm
index e20b13c6..909e16ed 100644
--- a/lib/PublicInbox/LeiXSearch.pm
+++ b/lib/PublicInbox/LeiXSearch.pm
@@ -545,16 +545,16 @@ sub do_query {
 			# setup two barriers to coordinate ->has_entries
 			# between l2m workers
 			pipe(my ($a_r, $a_w)) or die "pipe: $!";
-			fcntl($a_r, $F_SETPIPE_SZ, 4096) if $F_SETPIPE_SZ;
+			fcntl($a_r, $F_SETPIPE_SZ, 0) if $F_SETPIPE_SZ;
 			pipe(my ($b_r, $b_w)) or die "pipe: $!";
-			fcntl($b_r, $F_SETPIPE_SZ, 4096) if $F_SETPIPE_SZ;
+			fcntl($b_r, $F_SETPIPE_SZ, 0) if $F_SETPIPE_SZ;
 			$l2m->{au_peers} = [ $a_r, $a_w, $b_r, $b_w ];
 		}
 		$l2m->wq_workers_start('lei2mail', undef,
 					$lei->oldset, { lei => $lei },
 					\&xsearch_done_wait, $lei);
 		pipe($lei->{startq}, $lei->{au_done}) or die "pipe: $!";
-		fcntl($lei->{startq}, $F_SETPIPE_SZ, 4096) if $F_SETPIPE_SZ;
+		fcntl($lei->{startq}, $F_SETPIPE_SZ, 0) if $F_SETPIPE_SZ;
 		delete $l2m->{au_peers};
 		close(delete $l2m->{-wq_s2}); # share wq_s1 with lei_xsearch
 	}
diff --git a/lib/PublicInbox/SearchIdxShard.pm b/lib/PublicInbox/SearchIdxShard.pm
index 7ee8a121..c12aef9e 100644
--- a/lib/PublicInbox/SearchIdxShard.pm
+++ b/lib/PublicInbox/SearchIdxShard.pm
@@ -26,7 +26,7 @@ sub new {
 		# are small, make the response pipe as small as possible
 		if ($F_SETPIPE_SZ) {
 			fcntl($self->{-ipc_req}, $F_SETPIPE_SZ, 1048576);
-			fcntl($self->{-ipc_res}, $F_SETPIPE_SZ, 4096);
+			fcntl($self->{-ipc_res}, $F_SETPIPE_SZ, 0);
 		}
 	}
 	$self;
diff --git a/t/gcf2.t b/t/gcf2.t
index 33f3bbca..28c69a01 100644
--- a/t/gcf2.t
+++ b/t/gcf2.t
@@ -110,7 +110,7 @@ SKIP: {
 	for my $blk (1, 0) {
 		my ($r, $w);
 		pipe($r, $w) or BAIL_OUT $!;
-		fcntl($w, $F_SETPIPE_SZ, 4096) or
+		fcntl($w, $F_SETPIPE_SZ, 0) or
 			skip('Linux too old for F_SETPIPE_SZ', 14);
 		$w->blocking($blk);
 		seek($fh, 0, SEEK_SET) or BAIL_OUT "seek: $!";
@@ -130,7 +130,7 @@ SKIP: {
 		$ck_copying->("pipe blocking($blk)");
 
 		pipe($r, $w) or BAIL_OUT $!;
-		fcntl($w, $F_SETPIPE_SZ, 4096) or BAIL_OUT $!;
+		fcntl($w, $F_SETPIPE_SZ, 0) or BAIL_OUT $!;
 		$w->blocking($blk);
 		close $r;
 		local $SIG{PIPE} = 'IGNORE';
diff --git a/t/lei-sigpipe.t b/t/lei-sigpipe.t
index c01d9f83..f093dc5c 100644
--- a/t/lei-sigpipe.t
+++ b/t/lei-sigpipe.t
@@ -33,7 +33,7 @@ test_lei(sub {
 	my $imported;
 	for my $out ([], [qw(-f mboxcl2)], [qw(-f text)]) {
 		pipe(my $r, my $w);
-		my $size = ($F_SETPIPE_SZ && fcntl($w, $F_SETPIPE_SZ, 4096)) ||
+		my $size = ($F_SETPIPE_SZ && fcntl($w, $F_SETPIPE_SZ, 0)) ||
 		    65536;
 		unless (-f $f) {
 			my $fh = write_file '>', $f, <<'EOM';
-- 
2.47.0