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

[Demi Marie Obenour <demiobenour@gmail.com>]

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On 11/13/25 07:04, Alyssa Ross wrote:
> 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.
> 
> Signed-off-by: Alyssa Ross <hi@alyssa.is>
> ---
>  host/rootfs/file-list.mk              |  1 +
>  host/rootfs/image/usr/bin/run-flatpak | 56 +++++++++++++++++++++++++++
>  2 files changed, 57 insertions(+)
>  create mode 100755 host/rootfs/image/usr/bin/run-flatpak
> 
> diff --git a/host/rootfs/file-list.mk b/host/rootfs/file-list.mk
> index 9acaa1d..a796b90 100644
> --- a/host/rootfs/file-list.mk
> +++ b/host/rootfs/file-list.mk
> @@ -48,6 +48,7 @@ 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..39ee17b
> --- /dev/null
> +++ b/host/rootfs/image/usr/bin/run-flatpak
> @@ -0,0 +1,56 @@
> +#!/bin/execlineb -S2

Missing -W?

> +# SPDX-License-Identifier: EUPL-1.2+
> +# SPDX-FileCopyrightText: 2024 Alyssa Ross <hi@alyssa.is>
> +
> +backtick -E dir { mktemp -d /run/vm/by-id/XXXXXX }
> +backtick -E id { basename -- $dir }

Serial substitution: if $1 or $2 contains something like ${dir} or ${id}
they will be expanded again.  Can be avoided with multisubstitute:

backtick dir { mktemp -d /run/vm/by-id/XXXXXX }
backtick id { importas -iS dir basename -- $dir }
multisubstitute {
   import -iS dir
   import -iS id
   define install_dir $1
   define app_id $2
}

The general rule I follow is to never substitute a parameter into
an argv that has already been substituted into.  This can be done
by renaming all "variables" whenever one does a substitution.

> +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 $id }
> +fdclose 3
> +
> +if {
> +  forx -pE service {
> +    dbus
> +    vhost-user-fs
> +    vhost-user-gpu
> +    xdg-desktop-portal-spectrum-host
> +  }
> +  s6-instance-delete /run/service/${service} $id
> +}

Serial substitution again.  This should not be an issue: POSIX requires
mktemp to use only characters in the portable filename character set,
and $ is not in that set.  An execline static analyzer would flag
this, though.

If you want to avoid serial substitution, the usual workaround of
multisubstitute should do the job.

In the future, it would be best to run all of these services in their
own PID namespace, so after exit() they get destroyed by the kernel.
Essentially, every VM should be run inside a container.

This might also be one of the reasons that s6 isn't an ideal fit for
some of the future improvements I'd like to make.  Those require a
super-simple container manager, and s6 definitely isn't one.

> +if {
> +  elglob -0 flatpak_dir_mounts /run/configs/${id}/fs/flatpak/*/*/*/*/*

That's a lot of subdirectories!

> +  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}
-- 
Sincerely,
Demi Marie Obenour (she/her/hers)

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