[Fontconfig] [PATCH] Please make the output of cache files reproducible

[Akira TAGOH]

Thanks. fixing a typo and then merged.

On Wed, May 16, 2018 at 5:13 AM, Chris Lamb <lamby at debian.org> wrote:
> Hi Akira,
>
>> Please mention about SOURCE_DATE_EPOCH at the section of the
>> Environment variables in doc/fontconfig-user.sgml
>
> Whoops, I somehow forgot this bit. Updated patch attached:
>
>   commit 9213848ca27ccc3587a1a60539ec7c02fb02016f
>   Author: Chris Lamb <chris at chris-lamb.co.uk>
>   Date:   Tue May 15 22:11:24 2018 +0200
>
>       Ensure cache checksums are deterministic
>
>       Whilst working on the Reproducible Builds[0] effort, we noticed that
>       fontconfig generates unreproducible cache files.
>
>       This is due to fc-cache uses the modification timestamps of each
>       directory in the "checksum" and "checksum_nano" members of the _FcCache
>       struct. This is so that it can identify which cache files are valid
>       and/or require regeneration.
>
>       This patch changes the behaviour of the checksum calculations to prefer
>       the value of the SOURCE_DATE_EPOCH[1] environment variable over the
>       directory's own mtime. This variable can then be exported by build
>       systems to ensure reproducible output.
>
>       If SOURCE_DATE_EPOCH is not set or is newer than the mtime of the
>       directory, the existing behaviour is unchanged.
>
>       This work was sponsored by Tails[2].
>
>        [0] https://reproducible-builds.org/
>        [1] https://reproducible-builds.org/specs/source-date-epoch/
>        [2] https://tails.boum.org/
>
>    doc/fontconfig-user.sgml |  6 ++++-
>    src/fccache.c            | 58 +++++++++++++++++++++++++++++++++++++++++++-----
>    2 files changed, 57 insertions(+), 7 deletions(-)
>
>
> You can also merge from the "864082-FcConfigGetFontDirs" branch of
> https://github.com/lamby/fontconfig if that is more convenient.
>
>
> Best wishes,
>
> --
>       ,''`.
>      : :'  :     Chris Lamb
>      `. `'`      lamby at debian.org / chris-lamb.co.uk
>        `-



-- 
Akira TAGOH