Dgit.pm: rename_link_xf: Avoid copying if src is a link to dst

Signed-off-by: Ian Jackson <ijackson@chiark.greenend.org.uk>

1 files changed, 32 insertions, 9 deletions

diff --git a/Debian/Dgit.pm b/Debian/Dgit.pm
index 19ea85b..5b1feff 100644
--- a/Debian/Dgit.pm
+++ b/Debian/Dgit.pm
@@ -434,6 +434,8 @@ sub rename_link_xf ($$$) {
     #    $@ to a reason message
     #    $! to an errno value, or -1 if not known
     # having possibly printed something about mv to stderr.
+    # Not safe to use without $keeporig if $dst might be a symlink
+    # to $src, as it might delete $src leaving $dst invalid.
     my ($keeporig,$src,$dst) = @_;
     if ($keeporig
 	? link   $src, $dst
@@ -444,19 +446,40 @@ sub rename_link_xf ($$$) {
 	$@ = "$!";
 	return 0;
     }
-    $!=0; $?=0;
-    my @cmd = (qw(cp --), $src, "$dst.tmp");
-    debugcmd '+',@cmd;
-    if (system @cmd) {
-	failedcmd_report_cmd undef, @cmd;
-	$@ = failedcmd_waitstatus();
-	$! = -1;
+    if (!stat $src) {
+	$@ = f_ "stat source file: %S", $!;
 	return 0;
     }
-    if (!rename "$dst.tmp", $dst) {
-	$@ = f_ "finally install file after cp: %S", $!;
+    my @src_stat = (stat _)[0..1];
+
+    my @dst_stat;
+    if (stat $dst) {
+	@dst_stat = (stat _)[0..1];
+    } elsif ($! == ENOENT) {
+    } else {
+	$@ = f_ "stat destination file: %S", $!;
 	return 0;
     }
+
+    if ("@src_stat" eq "@dst_stat") {
+	# (Symlinks to) the same file.  No need for a copy but
+	# we may need to delete the original.
+	printdebug "rename_link_xf $keeporig $src $dst EXDEV but same\n";
+    } else {
+	$!=0; $?=0;
+	my @cmd = (qw(cp --), $src, "$dst.tmp");
+	debugcmd '+',@cmd;
+	if (system @cmd) {
+	    failedcmd_report_cmd undef, @cmd;
+	    $@ = failedcmd_waitstatus();
+	    $! = -1;
+	    return 0;
+	}
+	if (!rename "$dst.tmp", $dst) {
+	    $@ = f_ "finally install file after cp: %S", $!;
+	    return 0;
+	}
+    }
     if (!$keeporig) {
 	if (!unlink $src) {
 	    $@ = f_ "delete old file after cp: %S", $!;