checkpatch: enable GIT_DIR environment use to set git repository location

If set, use the environment variable GIT_DIR to change the default .git
location of the kernel git tree.

If GIT_DIR is unset, keep using the current ".git" default.

Link: https://lkml.kernel.org/r/c5e23b45562373d632fccb8bc04e563abba4dd1d.camel@perches.comSigned-off-by: Joe Perches <joe@perches.com>
Tested-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

scripts/checkpatch.pl

@@ -43,6 +43,8 @@ my $list_types = 0;
 my $fix = 0;
 my $fix_inplace = 0;
 my $root;
+my $gitroot = $ENV{'GIT_DIR'};
+$gitroot = ".git" if !defined($gitroot);
 my %debug;
 my %camelcase = ();
 my %use_type = ();
@@ -908,7 +910,7 @@ sub is_maintained_obsolete {
 sub is_SPDX_License_valid {
 	my ($license) = @_;
 
-	return 1 if (!$tree || which("python") eq "" || !(-e "$root/scripts/spdxcheck.py") || !(-e "$root/.git"));
+	return 1 if (!$tree || which("python") eq "" || !(-e "$root/scripts/spdxcheck.py") || !(-e "$gitroot"));
 
 	my $root_path = abs_path($root);
 	my $status = `cd "$root_path"; echo "$license" | python scripts/spdxcheck.py -`;
@@ -926,7 +928,7 @@ sub seed_camelcase_includes {
 
 	$camelcase_seeded = 1;
 
-	if (-e ".git") {
+	if (-e "$gitroot") {
 		my $git_last_include_commit = `${git_command} log --no-merges --pretty=format:"%h%n" -1 -- include`;
 		chomp $git_last_include_commit;
 		$camelcase_cache = ".checkpatch-camelcase.git.$git_last_include_commit";
@@ -954,7 +956,7 @@ sub seed_camelcase_includes {
 		return;
 	}
 
-	if (-e ".git") {
+	if (-e "$gitroot") {
 		$files = `${git_command} ls-files "include/*.h"`;
 		@include_files = split('\n', $files);
 	}
@@ -987,7 +989,7 @@ sub git_is_single_file {
 sub git_commit_info {
 	my ($commit, $id, $desc) = @_;
 
-	return ($id, $desc) if ((which("git") eq "") || !(-e ".git"));
+	return ($id, $desc) if ((which("git") eq "") || !(-e "$gitroot"));
 
 	my $output = `${git_command} log --no-color --format='%H %s' -1 $commit 2>&1`;
 	$output =~ s/^\s*//gm;
@@ -1026,7 +1028,7 @@ my $fixlinenr = -1;
 
 # If input is git commits, extract all commits from the commit expressions.
 # For example, HEAD-3 means we need check 'HEAD, HEAD~1, HEAD~2'.
-die "$P: No git repository found\n" if ($git && !-e ".git");
+die "$P: No git repository found\n" if ($git && !-e "$gitroot");
 
 if ($git) {
 	my @commits = ();