bcachefs-unlock: respect x-systemd mount options

This will allow unlocking to take place *after* all of the devices have
been probed, as indicated by the x-systemd.wants and x-systemd.requires
options. This allows for multi-device bcachefs volumes to be reliably
unlocked.

doc/release-notes/rl-2511.section.md

@@ -37,6 +37,8 @@
 
 - Added `rewriteURL` attribute to the nixpkgs `config`, to allow for rewriting the URLs downloaded by `fetchurl`.
 
+- The systemd initrd will now respect `x-systemd.wants` and `x-systemd.requires` for reliably unlocking multi-disk bcachefs volumes.
+
 - New hardening flags, `strictflexarrays1` and `strictflexarrays3` were made available, corresponding to the gcc/clang options `-fstrict-flex-arrays=1` and `-fstrict-flex-arrays=3` respectively.
 
 - `gramps` has been updated to 6.0.0

nixos/modules/tasks/filesystems/bcachefs.nix

@@ -93,19 +93,27 @@ let
     let
       mountUnit = "${utils.escapeSystemdPath (prefix + (lib.removeSuffix "/" fs.mountPoint))}.mount";
       device = firstDevice fs;
-      deviceUnit = "${utils.escapeSystemdPath device}.device";
+      mkDeviceUnit = device: "${utils.escapeSystemdPath device}.device";
+      deviceUnit = mkDeviceUnit device;
+      extractProperty =
+        prop: options: (map (lib.removePrefix "${prop}=") (builtins.filter (lib.hasPrefix prop) options));
+      normalizeUnits = unit: if lib.hasPrefix "/" unit then mkDeviceUnit unit else unit;
+      requiredUnits = map normalizeUnits (extractProperty "x-systemd.requires" fs.options);
+      wantedUnits = map normalizeUnits (extractProperty "x-systemd.wants" fs.options);
     in
     {
       name = "unlock-bcachefs-${utils.escapeSystemdPath fs.mountPoint}";
       value = {
         description = "Unlock bcachefs for ${fs.mountPoint}";
         requiredBy = [ mountUnit ];
-        after = [ deviceUnit ];
+        after = [ deviceUnit ] ++ requiredUnits ++ wantedUnits;
         before = [
           mountUnit
           "shutdown.target"
         ];
         bindsTo = [ deviceUnit ];
+        requires = requiredUnits;
+        wants = wantedUnits;
         conflicts = [ "shutdown.target" ];
         unitConfig.DefaultDependencies = false;
         serviceConfig = {