[PATCH v2 3/3] host/rootfs: add run-flatpak script

[Alyssa Ross <hi@alyssa.is>]

This is the entrypoint for running Flatpak applications.

It would be good to only add mounts for the VM in virtiofsd's mount
namespace, so we don't need to do lots of manual unmounts, but that's
a wider change affecting more than just Flatpak.

I've tested this by copying my host's Flatpak repository into a disk
image, and attaching that as a drive to the VM.

Signed-off-by: Alyssa Ross <hi@alyssa.is>
---
v2: • Avoid dangerous serial substitution with arguments
    • Add missing --
v1: https://spectrum-os.org/lists/archives/spectrum-devel/20251113120452.65711-3-hi@alyssa.is/

 host/rootfs/default.nix               |  9 ++---
 host/rootfs/file-list.mk              |  1 +
 host/rootfs/image/usr/bin/run-flatpak | 51 +++++++++++++++++++++++++++
 3 files changed, 57 insertions(+), 4 deletions(-)
 create mode 100755 host/rootfs/image/usr/bin/run-flatpak

diff --git a/host/rootfs/default.nix b/host/rootfs/default.nix
index 0ac70c7..6fe2f5f 100644
--- a/host/rootfs/default.nix
+++ b/host/rootfs/default.nix
@@ -11,8 +11,9 @@ pkgsStatic.callPackage (
 { spectrum-host-tools
 , lib, stdenvNoCC, nixos, runCommand, writeClosure, erofs-utils, s6-rc
 , busybox, cloud-hypervisor, cryptsetup, dbus, execline, inkscape
-, iproute2, inotify-tools, jq, mdevd, s6, s6-linux-init, socat
-, util-linuxMinimal, virtiofsd, xorg, xdg-desktop-portal-spectrum-host
+, iproute2, inotify-tools, jq, mdevd, mount-flatpak, s6, s6-linux-init
+, socat, util-linuxMinimal, virtiofsd, xorg
+, xdg-desktop-portal-spectrum-host
 }:
 
 let
@@ -34,8 +35,8 @@ let
 
   packages = [
     cloud-hypervisor cryptsetup dbus execline inotify-tools iproute2
-    jq mdevd s6 s6-linux-init s6-rc socat spectrum-host-tools
-    virtiofsd xdg-desktop-portal-spectrum-host
+    jq mdevd mount-flatpak s6 s6-linux-init s6-rc socat
+    spectrum-host-tools virtiofsd xdg-desktop-portal-spectrum-host
 
     (busybox.override {
       extraConfig = ''
diff --git a/host/rootfs/file-list.mk b/host/rootfs/file-list.mk
index ff6fd1b..ad2b408 100644
--- a/host/rootfs/file-list.mk
+++ b/host/rootfs/file-list.mk
@@ -44,6 +44,7 @@ FILES = \
 	image/usr/bin/assign-devices \
 	image/usr/bin/create-vm-dependencies \
 	image/usr/bin/run-appimage \
+	image/usr/bin/run-flatpak \
 	image/usr/bin/run-vmm \
 	image/usr/bin/vm-console \
 	image/usr/bin/vm-import \
diff --git a/host/rootfs/image/usr/bin/run-flatpak b/host/rootfs/image/usr/bin/run-flatpak
new file mode 100755
index 0000000..f0a7ad0
--- /dev/null
+++ b/host/rootfs/image/usr/bin/run-flatpak
@@ -0,0 +1,51 @@
+#!/bin/execlineb -W
+# SPDX-License-Identifier: EUPL-1.2+
+# SPDX-FileCopyrightText: 2024-2025 Alyssa Ross <hi@alyssa.is>
+
+backtick -E dir { mktemp -d /run/vm/by-id/XXXXXX }
+backtick -E id { basename -- $dir }
+
+if {
+  elgetpositionals -P 2
+
+  if { mkdir -p /run/configs/${id}/fs }
+  if { redirfd -w 1 /run/configs/${id}/fs/type echo flatpak }
+  if { cd /run/configs/${id}/fs mount-flatpak $1 $2 }
+  if {
+    ln -s /usr/lib/spectrum/img/appvm/blk /usr/lib/spectrum/img/appvm/vmlinux
+      /run/configs/${id}
+  }
+
+  if { ln -s /run/configs/${id} ${dir}/config }
+
+  if { create-vm-dependencies $id }
+
+  piperw 4 3
+  background {
+    fdclose 3
+    fdmove 0 4
+
+    # Wait for the VMM to be up, then start the VM.
+    if { redirfd -w 1 /dev/null head -1 }
+    vm-start $id
+  }
+  fdclose 4
+
+  foreground { run-vmm $id }
+}
+
+if { s6-instance-delete -- /run/service/vm-services $id }
+
+if {
+  elglob -0 flatpak_dir_mounts /run/configs/${id}/fs/flatpak/*/*/*/*/*
+  forx -E mount {
+    ${dir}/fs/doc
+    /run/configs/${id}/fs/flatpak/repo/config
+    $flatpak_dir_mounts
+    /run/configs/${id}/fs/flatpak
+    ${dir}/fs/config
+  }
+  umount $mount
+}
+
+rm -r $dir /run/configs/${id}

-- 
2.51.0