Re: [PATCH 0/4] fontcache: make the caches built into an image valid

["Paul Barker" <paul@pbarker.dev>]

On Tue Oct 13, 2026 at 11:49 AM BST, Alex Kiernan wrote:
> The fontconfig caches update_font_cache builds into an image are never
> used on the target. fontconfig accepts a cache only while the directory
> mtime it recorded matches the directory, and three things disagree about
> that mtime:
>
> - fc-cache records min(directory mtime, SOURCE_DATE_EPOCH). When the
>   intercept runs, the font directories still carry their packages'
>   mtimes and SOURCE_DATE_EPOCH is the image's fallback value.
> - reproducible_final_image_task then sets every mtime in the rootfs to
>   REPRODUCIBLE_TIMESTAMP_ROOTFS.
> - mke2fs clamps every inode time to the SOURCE_DATE_EPOCH in its
>   environment, so an ext image ends up with a different time again from
>   a tar or squashfs image of the same rootfs.
>
> So every process using fonts rescans and writes a cache of its own, or
> fails to on a read-only rootfs. fc-cache also deletes a cache it has
> just written for a directory newer than SOURCE_DATE_EPOCH, so with the
> default values some caches are missing from the image entirely.
>
> Patches 1-2 run fc-cache under REPRODUCIBLE_TIMESTAMP_ROOTFS, with the
> font directories' mtimes already set to it. Patch 3 keeps that time in ext
> images, as oe_mksquashfs already does for squashfs. That moves every
> inode and superblock time in an ext image from
> SOURCE_DATE_EPOCH_FALLBACK to REPRODUCIBLE_TIMESTAMP_ROOTFS, which with
> the bitbake.conf defaults is from 2011-04-05 to 2018-03-09. Patch 4
> adds a selftest that boots an image carrying a font and checks that
> fontconfig accepts every cache and writes none. On qemuarm64 it fails
> without patches 1-3 and passes with them.

Hi Alex,

If the selftest case in patch 4 is ran without the other changes in this
series, does it fail? I'd like to confirm that this test case would
catch the failure case.

Thanks,

-- 
Paul Barker