[Fontconfig] mmap-ed caches + patch

[Patrick Lam]

Lubos Lunak wrote:
>  However, when I tested the 2.3.90 release yesterday, I was originally 
> disappointed to see it performed noticeably worse than the last stable 
> version. Short version: Please apply the attached patch. Longer version: The 
> problem turned out to be directories that contain files that fontconfig 
> doesn't seem to use yet it analyses them (.pcf.gz files). If a directory 
> contains only .pcf.gz files and has no subdirectories, then the code that the 
> patch removes will not write a cache file, yet the return FcTrue means the 
> directory has been successfully cached. However if you look in 
> FcCacheReadDirs() you can see that if it can't use the cache file it will 
> call FcDirScanConfig(). So I suggest the attached patch which will write a 
> more or less empty cache file even in such directories.

I'm not sure that this patch will not cause problems.  I think that I
want to generate a zero-length file in such a case, without a header at
all.  But I'm a bit confused: when I run fc-cache in a directory with
only pcf.gz files, fc-cache *does* generate a fonts.cache-2 file for me.
 Why is this different for you?

>  And, actually, it seems I've just found another problem :(. If I run 
> Konqueror, run 'fc-cache -f' and go back to Konqueror, it crashes quite soon. 
> Guessing from strace of fc-cache, where I cannot see any call to unlink(), 
> and from the calls to ftruncate() I assume that the new cache file contents 
> are written directly in the same file instead of unlinking the old file 
> first, and fontconfig doesn't survive that. As I don't understand the code 
> that much I cannot confirm this theory for sure, which also means no patch 
> for this, sorry :).

Which cache file are you talking about?  $HOME/.fonts.cache-2, or a
directory cache?  (Are you running fc-cache as root?)

pat