From 986445f05604def9f0483622e0f5772c508c23d1 Mon Sep 17 00:00:00 2001
From: Kira Bruneau <kira.bruneau@pm.me>
Date: Fri, 17 Jan 2025 14:18:51 -0500
Subject: [PATCH] install-grub.pl: support bindmounts

Specifically this allows bind-mounting your `/boot` directory with
NixOS impermanence.
---
 .../modules/system/boot/loader/grub/grub.nix  |  3 +-
 .../system/boot/loader/grub/install-grub.pl   | 34 +++----------------
 2 files changed, 5 insertions(+), 32 deletions(-)

diff --git a/nixos/modules/system/boot/loader/grub/grub.nix b/nixos/modules/system/boot/loader/grub/grub.nix
index 81f94e8639d9d..f1a352867016b 100644
--- a/nixos/modules/system/boot/loader/grub/grub.nix
+++ b/nixos/modules/system/boot/loader/grub/grub.nix
@@ -90,7 +90,7 @@ let
         timeoutStyle
       ;
       path = with pkgs; makeBinPath (
-        [ coreutils gnused gnugrep findutils diffutils btrfs-progs util-linux mdadm ]
+        [ coreutils gnused gnugrep findutils diffutils util-linux mdadm ]
         ++ optional cfg.efiSupport efibootmgr
         ++ optionals cfg.useOSProber [ busybox os-prober ]);
       font = lib.optionalString (cfg.font != null) (
@@ -730,7 +730,6 @@ in
           install-grub-pl = pkgs.substituteAll {
             src = ./install-grub.pl;
             utillinux = pkgs.util-linux;
-            btrfsprogs = pkgs.btrfs-progs;
             inherit (config.system.nixos) distroName;
           };
           perl = pkgs.perl.withPackages (p: with p; [
diff --git a/nixos/modules/system/boot/loader/grub/install-grub.pl b/nixos/modules/system/boot/loader/grub/install-grub.pl
index c3652e8835117..71a9c5e1cff02 100644
--- a/nixos/modules/system/boot/loader/grub/install-grub.pl
+++ b/nixos/modules/system/boot/loader/grub/install-grub.pl
@@ -110,6 +110,7 @@ sub runCommand {
 # Discover information about the location of the bootPath
 struct(Fs => {
     device => '$',
+    root => '$',
     type => '$',
     mount => '$',
 });
@@ -117,12 +118,12 @@ sub runCommand {
 # Figure out what filesystem is used for the directory with init/initrd/kernel files
 sub GetFs {
     my ($dir) = @_;
-    my ($status, @pathInfo) = runCommand("@utillinux@/bin/findmnt", "-n", "-v", "-o", "SOURCE,FSTYPE,TARGET", "-T", @{[$dir]});
+    my ($status, @pathInfo) = runCommand("@utillinux@/bin/findmnt", "-n", "-u", "-v", "-o", "SOURCE,FSROOT,FSTYPE,TARGET", "-T", @{[$dir]});
     if ($status != 0 || @pathInfo != 1) {
         die "Failed to get file system (returned $status) for @{[$dir]}";
     }
     my @fields = split /\s+/, $pathInfo[0];
-    return Fs->new(device => $fields[0], type => $fields[1], mount => $fields[2]);
+    return Fs->new(device => $fields[0], root => $fields[1], type => $fields[2], mount => $fields[3]);
 }
 struct (Grub => {
     path => '$',
@@ -132,10 +133,7 @@ sub GetFs {
 sub GrubFs {
     my ($dir) = @_;
     my $fs = GetFs($dir);
-    my $path = substr($dir, length($fs->mount));
-    if (substr($path, 0, 1) ne "/") {
-        $path = "/$path";
-    }
+    my $path = File::Spec->catdir($fs->root, substr($dir, length($fs->mount)));
     my $search = "";
 
     # ZFS is completely separate logic as zpools are always identified by a label
@@ -177,30 +175,6 @@ sub GrubFs {
             }
             $search .= $matches[0];
         }
-
-        # BTRFS is a special case in that we need to fix the referenced path based on subvolumes
-        if ($fs->type eq 'btrfs') {
-            my ($status, @id_info) = runCommand("@btrfsprogs@/bin/btrfs", "subvol", "show", @{[$fs->mount]});
-            if ($status != 0) {
-                die "Failed to retrieve subvolume info for @{[$fs->mount]}\n";
-            }
-            my @ids = join("\n", @id_info) =~ m/^(?!\/\n).*Subvolume ID:[ \t\n]*([0-9]+)/s;
-            if ($#ids > 0) {
-                die "Btrfs subvol name for @{[$fs->device]} listed multiple times in mount\n"
-            } elsif ($#ids == 0) {
-                my ($status, @path_info) = runCommand("@btrfsprogs@/bin/btrfs", "subvol", "list", @{[$fs->mount]});
-                if ($status != 0) {
-                    die "Failed to find @{[$fs->mount]} subvolume id from btrfs\n";
-                }
-                my @paths = join("", @path_info) =~ m/ID $ids[0] [^\n]* path ([^\n]*)/;
-                if ($#paths > 0) {
-                    die "Btrfs returned multiple paths for a single subvolume id, mountpoint @{[$fs->mount]}\n";
-                } elsif ($#paths != 0) {
-                    die "Btrfs did not return a path for the subvolume at @{[$fs->mount]}\n";
-                }
-                $path = "/$paths[0]$path";
-            }
-        }
     }
     if (not $search eq "") {
         $search = "search --set=drive$driveid " . $search;