Re: RFC: writable private scratch XDG_CACHE_HOME in build enviroment?

[Mathieu Lirzin]

Andy Wingo <address@hidden> writes:

> On Tue 21 Feb 2017 13:13, Mathieu Lirzin <address@hidden> writes:
>
>> IIUC the problem you have is that in a Guix build environmnent, Guile
>> tries but *fails* to autocompile ".scm" files because it doesn't find
>> any directory that it can write on?
>
> Correct.
>
>> Since /tmp is writeable in a Guix build environment and in most POSIX
>> systems (I guess), Would it make sense for Guile itself to fallback to
>> /tmp for its compilation cache?
>
> It's possible.  It's a bit gnarly though:
>
>   * you get the usual race conditions between users and /tmp that you
>     have to mitigate

Nothing different from the race conditions for a single user using
XDG_CACHE_HOME when compilation is done by multiple threads?

>   * you have to be more careful about permissions (it could be that the
>     .go embeds something secret)
>     - each user would have to have their own path here

Indeed.

>   * guile would have to look in /tmp in addition to XDG_CACHE_HOME when
>     looking for autocompiled files
>
>   * what if the one in /tmp is fresh but the one in XDG_CACHE_HOME is
>     not, or vice versa?

This two last points makes me think of a the general issue with caching.
Maybe we could apply the the sane principles of memoization by computing
the "value" of a file (by hashing it?) and search it in the different
".go" stores (GUILE_LOAD_COMPILED_PATH, XDG_CACHE_HOME, site-ccache,
...)?

I don't know if the idea is stupid or not, maybe I miss an obvious
point.  Anyway this doesn't fit the purpose of fixing your issue in the
short term.

> I'd rather use XDG_CACHE_HOME for this as it's already well specified
> and actually not Guile-specific
> (https://specifications.freedesktop.org/basedir-spec/basedir-spec-latest.html).

Setting XDG_CACHE_HOME to the build directory or /tmp in the Guix build
environnement seems fine to me.

Thanks.

-- 
Mathieu Lirzin
GPG: F2A3 8D7E EB2B 6640 5761  070D 0ADE E100 9460 4D37