From mboxrd@z Thu Jan  1 00:00:00 1970
From: ludo@gnu.org (Ludovic =?utf-8?Q?Court=C3=A8s?=)
Subject: Re: 'guix build' and garbage collection
Date: Mon, 03 Apr 2017 10:53:08 +0200
Message-ID: <87shlprhxn.fsf@gnu.org>
References: <878tnjk489.fsf@gmail.com> <87inmnb1ha.fsf@gnu.org>
	<871stakn8v.fsf@gmail.com>
Mime-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: quoted-printable
Return-path: <guix-devel-bounces+gcggd-guix-devel=m.gmane.org@gnu.org>
Received: from eggs.gnu.org ([2001:4830:134:3::10]:54393)
	by lists.gnu.org with esmtp (Exim 4.71)
	(envelope-from <ludo@gnu.org>) id 1cuxjf-00029l-JB
	for guix-devel@gnu.org; Mon, 03 Apr 2017 04:53:16 -0400
Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71)
	(envelope-from <ludo@gnu.org>) id 1cuxja-0001kn-P0
	for guix-devel@gnu.org; Mon, 03 Apr 2017 04:53:15 -0400
In-Reply-To: <871stakn8v.fsf@gmail.com> (Chris Marusich's message of "Sun, 02
	Apr 2017 23:40:16 -0700")
List-Id: "Development of GNU Guix and the GNU System distribution."
	<guix-devel.gnu.org>
List-Unsubscribe: <https://lists.gnu.org/mailman/options/guix-devel>,
	<mailto:guix-devel-request@gnu.org?subject=unsubscribe>
List-Archive: <http://lists.gnu.org/archive/html/guix-devel/>
List-Post: <mailto:guix-devel@gnu.org>
List-Help: <mailto:guix-devel-request@gnu.org?subject=help>
List-Subscribe: <https://lists.gnu.org/mailman/listinfo/guix-devel>,
	<mailto:guix-devel-request@gnu.org?subject=subscribe>
Errors-To: guix-devel-bounces+gcggd-guix-devel=m.gmane.org@gnu.org
Sender: "Guix-devel" <guix-devel-bounces+gcggd-guix-devel=m.gmane.org@gnu.org>
To: Chris Marusich <cmmarusich@gmail.com>
Cc: guix-devel@gnu.org

Hi Chris,

Chris Marusich <cmmarusich@gmail.com> skribis:

> My understanding is that Nix builds derivations in a temporary
> directory.  My understanding is that eventually, we copy the results of
> the build into the final, content-addressed store path.  Since we don't
> know the final, content-addressed store path until after we calculate
> the hash of the output, how do we prevent that final store path from
> being garbage collected while the build process is running?  Do we use
> addTempRoot to add the final, content-addressed store path as a
> temporary root, too?  I looked in the code but couldn't figure this out.

Store items are not content-addressed, except for fixed-output
derivations and things added with =E2=80=98add-to-store=E2=80=99 and
=E2=80=98add-text-to-store=E2=80=99.

Leaving these two special cases aside, store file names are computed as
a function of the build inputs of a derivation.  In Eelco Dolstra=E2=80=99s
thesis, both models are described: the =E2=80=9Cextensional model=E2=80=9D =
(the one Nix
and Guix use) and the =E2=80=9Cintensional model=E2=80=9D (content-addressa=
bility, which
has never been deployed, and which is challenging in many ways.)

HTH!

Ludo=E2=80=99.