1 files changed, 68 insertions, 0 deletions
diff --git a/nixos/modules/system/etc/setup-etc.pl b/nixos/modules/system/etc/setup-etc.pl
new file mode 100644
index 00000000000..7cb6d2a6a45
--- /dev/null
+++ b/nixos/modules/system/etc/setup-etc.pl
@@ -0,0 +1,68 @@
+use strict;
+use File::Find;
+use File::Copy;
+use File::Path;
+use File::Basename;
+
+my $etc = $ARGV[0] or die;
+my $static = "/etc/static";
+
+sub atomicSymlink {
+    my ($source, $target) = @_;
+    my $tmp = "$target.tmp";
+    unlink $tmp;
+    symlink $source, $tmp or return 1;
+    rename $tmp, $target or return 1;
+    return 1;
+}
+
+
+# Atomically update /etc/static to point at the etc files of the
+# current configuration.
+atomicSymlink $etc, $static or die;
+
+
+# Remove dangling symlinks that point to /etc/static.  These are
+# configuration files that existed in a previous configuration but not
+# in the current one.  For efficiency, don't look under /etc/nixos
+# (where all the NixOS sources live).
+sub cleanup {
+    if ($File::Find::name eq "/etc/nixos") {
+        $File::Find::prune = 1;
+        return;
+    }
+    if (-l $_) {
+        my $target = readlink $_;
+        if (substr($target, 0, length $static) eq $static) {
+            my $x = "/etc/static/" . substr($File::Find::name, length "/etc/");
+            unless (-l $x) {
+                print STDERR "removing obsolete symlink ‘$File::Find::name’...\n";
+                unlink "$_";
+            }
+        }
+    }
+}
+
+find(\&cleanup, "/etc");
+
+
+# For every file in the etc tree, create a corresponding symlink in
+# /etc to /etc/static.  The indirection through /etc/static is to make
+# switching to a new configuration somewhat more atomic.
+sub link {
+    my $fn = substr $File::Find::name, length($etc) + 1 or next;
+    my $target = "/etc/$fn";
+    File::Path::make_path(dirname $target);
+    if (-e "$_.mode") {
+        open MODE, "<$_.mode";
+        my $mode = <MODE>; chomp $mode;
+        close MODE;
+        copy "$static/$fn", "$target.tmp" or warn;
+        chmod oct($mode), "$target.tmp" or warn;
+        rename "$target.tmp", $target or warn;
+    } elsif (-l "$_") {
+        atomicSymlink "$static/$fn", $target or warn;
+    }
+}
+
+find(\&link, $etc);