Daemon update

[Ludovic Courtès]

Hello!

I have pushed a big update of the daemon code.  We were using a copy of
the Nix code from May 2014, and there have been worthwhile changes in
the meantime (thanks for the Nix folks!).

There have also been undesirable changes, such as the gratuitous switch
to multithreading, which entails various issues (see
<http://lists.gnu.org/archive/html/guix-devel/2014-12/msg00363.html>.)

Thus, in our ‘nix’ branch, I have selected a the best of those changes
;-).  The main difference is that I didn’t take said
multithreading-related commits, as well as a couple of less significant,
Nix-specific changes.

The new changes include some refactorization and cosmetic changes (a
bunch of C++11 lambdas here, a bit of ‘auto’ there.)  Interesting
changes include:

  • The possibility to use regular files as GC roots, where the file
    name denotes a store item; this reduces I/O compared to using
    symlinks.

  • Slightly reduced I/O for GC.

  • New ‘disallowedReferences’ and ‘disallowedRequisites’ attributes for
    derivations (akin to our #:allowed-references.)

  • New ‘optimiseStore’ RPC.

  • ASLR disabled in the build environment.

Please report any issues with the daemon!

Thanks,
Ludo’.