Re: [PATCH 1/1] wic: disable generation of python bytecode cache

["'Heinisch, Alexander' via isar-users" <isar-users@googlegroups.com>]

On Thu, 2025-06-05 at 16:58 +0200, 'Felix Moessbauer' via isar-users
wrote:
> Wic is executed as root, so the python bytecode cache is also
> created as root. This is problematic as the cache is created inside
> the
> source tree in a folder__pycache__ next to the python script itself.
> By
> that, we end up with files belonging to root inside the repo source
> tree, which makes it impossible to delete the source tree as a
> regular
> user.
> 
> This problem became visible with the kas purge plugin that removes
> the
> fetched layers as a regular user (these layers are fetched and
> managed
> by kas). Also the read-only mounting of repos in kas does not help
> here,
> as the fetched repos are not mounted ro for obvious reasons.
> 
> Anyways, we should not create files inside the source tree that do
> not
> belong to the calling user. To fix this, we just disable the python
> cache for the wic task. This is the only task that executes a python
> script from the source tree as root.

Hi Felix,

What about moving the cache to the build dir?

I just did a quick test using `PYTHONPYCACHEPREFIX` (see [1]) which was
added in Python 3.8 (so works for hosts >= bullseye)

```
diff --git a/meta/classes/imagetypes_wic.bbclass
b/meta/classes/imagetypes_wic.bbclass
index 38b5f0e1..7b8dc38c 100644
--- a/meta/classes/imagetypes_wic.bbclass
+++ b/meta/classes/imagetypes_wic.bbclass
@@ -157,6 +157,7 @@ generate_wic_image() {
     export FAKEROOTCMD=${FAKEROOTCMD}
     export BUILDDIR=${TOPDIR}
     export MTOOLS_SKIP_CHECK=1
+    export PYTHONPYCACHEPREFIX="${TOPDIR}/__pycache__"
     mkdir -p ${IMAGE_ROOTFS}/../pseudo
     touch ${IMAGE_ROOTFS}/../pseudo/files.db```

and it seems to do the job. In depth testing still required!

[1]:
https://docs.python.org/3/using/cmdline.html#envvar-PYTHONPYCACHEPREFIX

BR Alexander

> 
> Signed-off-by: Felix Moessbauer <felix.moessbauer@siemens.com>
> ---
>  meta/classes/imagetypes_wic.bbclass | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/meta/classes/imagetypes_wic.bbclass
> b/meta/classes/imagetypes_wic.bbclass
> index 7a050e73..fb0b81a9 100644
> --- a/meta/classes/imagetypes_wic.bbclass
> +++ b/meta/classes/imagetypes_wic.bbclass
> @@ -157,6 +157,7 @@ generate_wic_image() {
>      export FAKEROOTCMD=${FAKEROOTCMD}
>      export BUILDDIR=${TOPDIR}
>      export MTOOLS_SKIP_CHECK=1
> +    export PYTHONDONTWRITEBYTECODE=1
>      mkdir -p ${IMAGE_ROOTFS}/../pseudo
>      touch ${IMAGE_ROOTFS}/../pseudo/files.db
>  
> -- 
> 2.49.0
> 

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