From fd37519dbb05cea1e1f8d20fbc944f9380f71f70 Mon Sep 17 00:00:00 2001
From: Zygo Blaxell <zblaxell@esightcorp.com>
Date: Thu, 13 May 2010 16:07:52 -0400
Subject: [PATCH] dm6: finish WIP

---
 dm6 | 104 +++++++++++++++++++++++++++++++++++++++++++++++++++++-------
 1 file changed, 93 insertions(+), 11 deletions(-)

diff --git a/dm6 b/dm6
index c5ce5d4..b7a9cdf 100755
--- a/dm6
+++ b/dm6
@@ -6,6 +6,7 @@ use Fcntl qw(:DEFAULT :flock);
 use File::Compare;
 use File::Path;
 use File::Temp;
+use File::stat;
 
 # Copyright (C) 2010 Zygo Blaxell <dm5@mailtoo.hungrycats.org>
 
@@ -45,6 +46,7 @@ USAGE
 sub link_files {
 	my ($from, $to) = (@_);
 
+	print STDERR "link '$from' '$to' ...";
 	my $inode_dir = $to;
 	my $inode_base = $to;
 	$inode_dir =~ s:[^/]*$::o;
@@ -56,26 +58,106 @@ sub link_files {
 		unlink($tmp_to) or warn "unlink: $tmp_to: $!";	# Try, possibly in vain, to clean up
 		die "rename: $tmp_to -> $from: $saved_bang";
 	}
+	print STDERR "\n";
 }
 
 my $link_dir = shift @ARGV;
 (-d $link_dir) or usage;
 
+sub slash_prefix {
+	my ($file) = @_;
+	my $prefix = substr($file, 0, 3);
+	my $suffix = substr($file, 3);
+	$prefix =~ s:(.):$1/:osg;
+	chop($prefix);
+	return ($prefix, $suffix);
+}
+
+sub prepare_parents {
+	my ($link_dir, $file) = @_;
+	my ($prefix, $suffix) = slash_prefix($file);
+	my $parent = "$link_dir/$prefix";
+	mkpath($parent, { verbose => 1 });
+	die "mkpath: $parent: $!" unless -d $parent;
+	return "$parent/$prefix/$suffix";
+}
+
+# ext3 cannot handle more than 32000 links to a file.  Leave some headroom.
+my $link_count_max = 31990;
+
 $/ = "\0";
 while (<STDIN>) {
 	my $file = $_;
 	eval {
-		chomp $file;
-		print STDERR "digest($file) = ";
-		my $digest = digest($file);
-		$digest =~ y:/:_:;
-		print STDERR "$digest\n";
-		$digest =~ s:^(.)(.)(.):$1/$2/$3:osg;
-		my ($parent) = ($digest =~ m:^(.*/):osg);
-		$parent = "$link_dir/$parent";
-		mkpath($parent, { verbose => 1 });
-		die "mkpath: $parent: $!" unless -d $parent;
-		link_files($file, "$link_dir/$digest");
+		for (1) {
+			chomp $file;
+
+			# Get file stat data
+			my $st = lstat($file);
+			die "lstat: $file: $!" unless $st;
+
+			# Oops?
+			next unless -f _;
+
+			# Skip the file if it has far too many links already
+			next if ($st->nlink > $link_count_max);
+
+			# Check link to inode
+			my $inode_link = prepare_parents("$link_dir/inode", $st->ino);
+			my $inode_st = lstat($inode_link);
+			my $update_links;
+			if ($inode_st) {
+				my $inode_dev = $inode_st->dev;
+				my $inode_ino = $inode_st->ino;
+				my $file_dev = $st->dev;
+				my $file_ino = $st->ino;
+				if ($inode_ino != $file_ino || $inode_dev != $file_dev) {
+					warn "inode link '$inode_link' is wrong (inode $inode_ino should be $file_ino)" if $inode_ino != $file_ino;
+					warn "inode link '$inode_link' is wrong (dev $inode_dev should be $file_dev)" if $inode_dev != $file_dev;
+					$update_links = 1;
+				}
+			} else {
+				$update_links = 1;
+			}
+
+			# If neither criteria for updating link is met, leave it as-is
+			next unless $update_links;
+
+			# Compute digest
+			print STDERR "digest($file) = ";
+			my $digest = digest($file);
+
+			# Base64 uses /, we prefer _
+			$digest =~ y:/:_:;
+
+			print STDERR "$digest\n";
+
+			# Check link to digest
+			my $digest_link = prepare_parents("$link_dir/digest", $digest);
+			my $digest_st = lstat($digest_link);
+			if ($digest_st) {
+				my $digest_nlink = $digest_st->nlink;
+				if ($digest_nlink > 31990) {
+					print STDERR "Removing '$digest_link' with $digest_nlink links\n";
+					unlink($digest_link) or die "unlink: $digest_link: $!";
+					undef $digest_st;
+				}
+			}
+
+			# If digest link exists, link it to file
+			if ($digest_st) {
+				print STDERR "cmp '$digest_link' '$file' ...";
+				die "NOT identical!" if compare($digest_link, $file);
+				print STDERR "\n";
+				link_files($digest_link, $file);
+			} else {
+				link_files($file, $digest_link);
+			}
+
+			# A link to the inode indicates we are done, so do it last
+			link_files($file, $inode_link);
+
+		}
 	};
 	warn "$file: $@" if $@;
 }
-- 
2.30.2