From 590de6c248a61dbbb317ea42dd1e7e418a3f3430 Mon Sep 17 00:00:00 2001
From: Francesco Zanini <francesco@zanini.me>
Date: Fri, 6 Jun 2025 15:22:13 +0200
Subject: [PATCH] Better handling of bind mounts in make-disk-image

The device of the bind mounts is incorrectly taken verbatim while making the image.
The root hierarchy is mounted at `config.rootMountDir` (`/mnt` by default) during the process,
and this commit prepends that path to the `device` in these cases.
---
 lib/types/nodev.nix | 23 ++++++++++++++---------
 1 file changed, 14 insertions(+), 9 deletions(-)

diff --git a/lib/types/nodev.nix b/lib/types/nodev.nix
index f0d3c503..55845c84 100644
--- a/lib/types/nodev.nix
+++ b/lib/types/nodev.nix
@@ -46,15 +46,20 @@
     };
     _mount = diskoLib.mkMountOption {
       inherit config options;
-      default = lib.optionalAttrs (config.mountpoint != null) {
-        fs.${config.mountpoint} = ''
-          if ! findmnt ${config.fsType} "${rootMountPoint}${config.mountpoint}" > /dev/null 2>&1; then
-            mount -t ${config.fsType} "${config.device}" "${rootMountPoint}${config.mountpoint}" \
-            ${lib.concatMapStringsSep " " (opt: "-o ${opt}") config.mountOptions} \
-            -o X-mount.mkdir
-          fi
-        '';
-      };
+      default =
+        let
+          isBindMount = builtins.elem "bind" config.mountOptions;
+          device = if isBindMount then "${rootMountPoint}${config.device}" else config.device;
+        in
+        lib.optionalAttrs (config.mountpoint != null) {
+          fs.${config.mountpoint} = ''
+            if ! findmnt ${config.fsType} "${rootMountPoint}${config.mountpoint}" > /dev/null 2>&1; then
+              mount -t ${config.fsType} "${device}" "${rootMountPoint}${config.mountpoint}" \
+              ${lib.concatMapStringsSep " " (opt: "-o ${opt}") config.mountOptions} \
+              -o X-mount.mkdir
+            fi
+          '';
+        };
     };
     _unmount = diskoLib.mkUnmountOption {
       inherit config options;