make back /etc/static absolute symlink

2 files changed, 27 insertions, 14 deletions

diff --git a/nixos/doc/manual/release-notes/rl-1903.xml b/nixos/doc/manual/release-notes/rl-1903.xml
index 3e42294a5f8..0a51e5b1a93 100644
--- a/nixos/doc/manual/release-notes/rl-1903.xml
+++ b/nixos/doc/manual/release-notes/rl-1903.xml
@@ -459,10 +459,16 @@
    </listitem>
    <listitem>
     <para>
-     Symlinks in <filename>/etc</filename> are now relative instead of absolute,
-     so that the links can be followed if the NixOS installation is not mounted as filesystem root.
-     In particular, this makes <filename>/etc/os-release</filename> adhere to
-     <link xlink:href="https://www.freedesktop.org/software/systemd/man/os-release.html">the standard</link>.
+     Symlinks in <filename>/etc</filename> (except <filename>/etc/static</filename>)
+     are now relative instead of absolute. This makes possible to examine
+     NixOS container's <filename>/etc</filename> directory from host system
+     (previously it pointed to host <filename>/etc</filename> when viewed from host,
+     and to container <filename>/etc</filename> when viewed from container chroot).
+    </para>
+    <para>
+     This also makes <filename>/etc/os-release</filename> adhere to
+     <link xlink:href="https://www.freedesktop.org/software/systemd/man/os-release.html">the standard</link>
+     for NixOS containers.
     </para>
    </listitem>
    <listitem>
diff --git a/nixos/modules/system/etc/setup-etc.pl b/nixos/modules/system/etc/setup-etc.pl
index 6cbf0e17793..82ef49a2a27 100644
--- a/nixos/modules/system/etc/setup-etc.pl
+++ b/nixos/modules/system/etc/setup-etc.pl
@@ -13,18 +13,26 @@ sub atomicSymlink {
     my ($source, $target) = @_;
     my $tmp = "$target.tmp";
     unlink $tmp;
-    # Create relative symlinks, so that the links can be followed if
-    # the NixOS installation is not mounted as filesystem root.
-    # Absolute symlinks violate the os-release format
-    # at https://www.freedesktop.org/software/systemd/man/os-release.html
-    # and break e.g. systemd-nspawn and os-prober.
+    symlink $source, $tmp or return 0;
+    rename $tmp, $target or return 0;
+    return 1;
+}
+
+# Create relative symlinks, so that the links can be followed if
+# the NixOS installation is not mounted as filesystem root.
+# Absolute symlinks violate the os-release format
+# at https://www.freedesktop.org/software/systemd/man/os-release.html
+# and break e.g. systemd-nspawn and os-prober.
+sub atomicRelativeSymlink {
+    my ($source, $target) = @_;
+    my $tmp = "$target.tmp";
+    unlink $tmp;
     my $rel = File::Spec->abs2rel($source, dirname $target);
     symlink $rel, $tmp or return 0;
     rename $tmp, $target or return 0;
     return 1;
 }
 
-
 # Atomically update /etc/static to point at the etc files of the
 # current configuration.
 atomicSymlink $etc, $static or die;
@@ -37,8 +45,7 @@ sub isStatic {
 
     if (-l $path) {
         my $target = readlink $path;
-        my $rel = File::Spec->abs2rel("/etc/static", dirname $path);
-        return substr($target, 0, length $rel) eq $rel;
+        return substr($target, 0, length "/etc/static/") eq "/etc/static/";
     }
 
     if (-d $path) {
@@ -111,7 +118,7 @@ sub link {
     if (-e "$_.mode") {
         my $mode = read_file("$_.mode"); chomp $mode;
         if ($mode eq "direct-symlink") {
-            atomicSymlink readlink("$static/$fn"), $target or warn;
+            atomicRelativeSymlink readlink("$static/$fn"), $target or warn;
         } else {
             my $uid = read_file("$_.uid"); chomp $uid;
             my $gid = read_file("$_.gid"); chomp $gid;
@@ -125,7 +132,7 @@ sub link {
         push @copied, $fn;
         print CLEAN "$fn\n";
     } elsif (-l "$_") {
-        atomicSymlink "$static/$fn", $target or warn;
+        atomicRelativeSymlink "$static/$fn", $target or warn;
     }
 }