treewide: reduce $PATH checks for `git' executable

Repeatedly checking $PATH for `git' when we need to call it
multiple times in quick succession doesn't seem useful.  So
avoid some expensive stat(2) syscalls to make things less bad
for systems which require expensive CPU vulnerability
mitigations.

This also saves a bunch of memory allocations since we do the
$PATH lookup in pure Perl to avoid doing the uncacheable lookup
in a vfork-ed child.

1 files changed, 16 insertions, 13 deletions

diff --git a/lib/PublicInbox/LeiMirror.pm b/lib/PublicInbox/LeiMirror.pm
index 08e61e4b..e7c265bd 100644
--- a/lib/PublicInbox/LeiMirror.pm
+++ b/lib/PublicInbox/LeiMirror.pm
@@ -24,6 +24,7 @@ use POSIX qw(strftime);
 use PublicInbox::Admin qw(fmt_localtime);
 use autodie qw(chdir chmod close open pipe readlink
                 seek symlink sysopen sysseek truncate unlink);
+use PublicInbox::Git qw(git_exe);
 
 our $LIVE; # pid => callback
 our $FGRP_TODO; # objstore -> [[ to resume ], [ to clone ]]
@@ -105,7 +106,7 @@ E: confused by scraping <$uri>, got ambiguous results:
 
 sub clone_cmd {
         my ($lei, $opt) = @_;
-        my @cmd = qw(git);
+        my @cmd = (git_exe);
         $opt->{$_} = $lei->{$_} for (0..2);
         # we support "-c $key=$val" for arbitrary git config options
         # e.g.: git -c http.proxy=socks5h://127.0.0.1:9050
@@ -291,7 +292,7 @@ sub upr { # feed `git update-ref --stdin -z' verbosely
 sub start_update_ref {
         my ($fgrp) = @_;
         pipe(my $r, my $w);
-        my $cmd = [ 'git', "--git-dir=$fgrp->{cur_dst}",
+        my $cmd = [ git_exe, "--git-dir=$fgrp->{cur_dst}",
                 qw(update-ref --stdin -z) ];
         my $pack = on_destroy \&satellite_done, $fgrp;
         start_cmd($fgrp, $cmd, { 0 => $r, 2 => $fgrp->{lei}->{2} }, $pack);
@@ -353,7 +354,7 @@ sub satellite_done {
 
 sub pack_refs {
         my ($self, $git_dir) = @_;
-        my $cmd = [ 'git', "--git-dir=$git_dir", qw(pack-refs --all --prune) ];
+        my $cmd = [git_exe, "--git-dir=$git_dir", qw(pack-refs --all --prune)];
         start_cmd($self, $cmd, { 2 => $self->{lei}->{2} });
 }
 
@@ -374,14 +375,15 @@ sub fgrpv_done {
                 my $rn = $fgrp->{-remote};
                 my %opt = ( 2 => $fgrp->{lei}->{2} );
                 my $update_ref = on_destroy \&fgrp_update, $fgrp;
-                my $src = [ 'git', "--git-dir=$fgrp->{-osdir}", 'for-each-ref',
+                my $src = [ git_exe, "--git-dir=$fgrp->{-osdir}",
+                        'for-each-ref',
                         "--format=refs/%(refname:lstrip=3)%00%(objectname)",
                         "refs/remotes/$rn/" ];
                 open(my $sfh, '+>', undef);
                 $fgrp->{srcfh} = $sfh;
                 start_cmd($fgrp, $src, { %opt, 1 => $sfh }, $update_ref);
-                my $dst = [ 'git', "--git-dir=$fgrp->{cur_dst}", 'for-each-ref',
-                        '--format=%(refname)%00%(objectname)' ];
+                my $dst = [ git_exe, "--git-dir=$fgrp->{cur_dst}",
+                        'for-each-ref', '--format=%(refname)%00%(objectname)' ];
                 open(my $dfh, '+>', undef);
                 $fgrp->{dstfh} = $dfh;
                 start_cmd($fgrp, $dst, { %opt, 1 => $dfh }, $update_ref);
@@ -399,7 +401,7 @@ sub fgrp_fetch_all {
         # system argv limits:
         my $grp = 'fgrptmp';
 
-        my @git = (@{$self->{-torsocks}}, 'git');
+        my @git = (@{$self->{-torsocks}}, git_exe);
         my $j = $self->{lei}->{opt}->{jobs};
         my $opt = {};
         my @fetch = do {
@@ -413,7 +415,7 @@ sub fgrp_fetch_all {
                 my ($old, $new) = @$fgrp_old_new;
                 @$old = sort { $b->{-sort} <=> $a->{-sort} } @$old;
                 # $new is ordered by {references}
-                my $cmd = ['git', "--git-dir=$osdir", qw(config -f), $f ];
+                my $cmd = [ git_exe, "--git-dir=$osdir", qw(config -f), $f ];
 
                 # clobber settings from previous run atomically
                 for ("remotes.$grp", 'fetch.hideRefs') {
@@ -541,7 +543,7 @@ sub cmp_fp_do {
                 return if $cur_ent->{fingerprint} eq $new;
         }
         my $dst = $self->{cur_dst} // $self->{dst};
-        my $cmd = ['git', "--git-dir=$dst", 'show-ref'];
+        my $cmd = [git_exe, "--git-dir=$dst", 'show-ref'];
         my $opt = { 2 => $self->{lei}->{2} };
         open($opt->{1}, '+>', undef);
         $self->{-show_ref} = $opt->{1};
@@ -555,7 +557,7 @@ sub resume_fetch {
         my ($self, $uri, $fini) = @_;
         return if !keep_going($self);
         my $dst = $self->{cur_dst} // $self->{dst};
-        my @git = ('git', "--git-dir=$dst");
+        my @git = (git_exe, "--git-dir=$dst");
         my $opt = { 2 => $self->{lei}->{2} };
         my $rn = 'random'.int(rand(1 << 30));
         for ("url=$uri", "fetch=+refs/*:refs/*", 'mirror=true') {
@@ -755,7 +757,7 @@ sub update_ent {
         my $cur = $self->{-local_manifest}->{$key}->{fingerprint} // "\0";
         my $dst = $self->{cur_dst} // $self->{dst};
         if (defined($new) && $new ne $cur) {
-                my $cmd = ['git', "--git-dir=$dst", 'show-ref'];
+                my $cmd = [git_exe, "--git-dir=$dst", 'show-ref'];
                 my $opt = { 2 => $self->{lei}->{2} };
                 open($opt->{1}, '+>', undef);
                 $self->{-show_ref_up} = $opt->{1};
@@ -766,7 +768,7 @@ sub update_ent {
         $cur = $self->{-local_manifest}->{$key}->{head} // "\0";
         if (defined($new) && $new ne $cur) {
                 # n.b. grokmirror writes raw contents to $dst/HEAD w/o locking
-                my $cmd = [ 'git', "--git-dir=$dst" ];
+                my $cmd = [ git_exe, "--git-dir=$dst" ];
                 if ($new =~ s/\Aref: //) {
                         push @$cmd, qw(symbolic-ref HEAD), $new;
                 } elsif ($new =~ /\A[a-f0-9]{40,}\z/) {
@@ -811,7 +813,8 @@ sub update_ent {
         $cur = $self->{-local_manifest}->{$key}->{owner} // "\0";
         return if $cur eq $new;
         utf8::encode($new); # to octets
-        my $cmd = [ qw(git config -f), "$dst/config", 'gitweb.owner', $new ];
+        my $cmd = [ git_exe, qw(config -f), "$dst/config",
+                        'gitweb.owner', $new ];
         start_cmd($self, $cmd, { 2 => $self->{lei}->{2} });
 }