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

[Alyssa Ross <hi@alyssa.is>]

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Demi Marie Obenour <demiobenour@gmail.com> writes:

> On 11/13/25 07:04, Alyssa Ross wrote:
>> +# 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.
>

Minor correction: POSIX doesn't specify mktemp(1), only the library
functions, but Busybox mktemp uses mkdtemp(3), which is also specified
to use the portable character set.

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