[Fontconfig] Re: incompatible changes in cache format

[Patrick Lam]

Mike FABIAN wrote:
> run as root doesn't generate new caches in /var/cache/fontconfig,
> it just skips:
> 
>     mfabian at magellan:~$ sudo fc-cache -v
>     fc-cache: "/usr/share/fonts": skipping, 0 fonts, 3 dirs
>     [...]
> 
> It skips very slowly though, it takes as much time for skipping as for
> generating new cache files, i.e. fontconfig seems to notice that there
> is something wrong with these caches. Nevertheless fc-cache doesn't
> write new files unless called with "-f". After that, "fc-cache -v"
> skips fast again.

It currently isn't part of FcDirCacheValid or FcDirCacheCurrentArch's
contract to read in the cache file and determine if the cache has the
correct MAGIC.  However, it would seem to be trivial to add it to
FcDirCacheCurrentArch, which should fix this problem.  I'll do that in a
few minutes.

Also, fc-cache has a sleep for 2 seconds, so that might be why it seems
to be skipping slowly.  fc-cache runs pretty quickly for me, except for
the pause at the end.

pat