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gconf-defaults-hack
===================
This is a small LD_PRELOAD library designed to fix problems with GConf
defaults when running with a partial install of some GNOME components
into a non-system directory.
Namely:
- At make install time, schemas are installed in $sysconfdir/gconf/schemas
- Schema installation into the system defaults database in /etc fails
- When we run apps, they talk to the system copy of gconfd which is looking
in /etc/ for defaults.
What the LD_PRELOAD library does is override libgconf functions so that
if a lookup from gconfd totally fails - no entry for the user, no entry
from the installed schemas - then it looks in $sysconfdir/gconf/schemas
(or the directory given by GCONF_DEFAULTS_SCHEMAS_DIR) and sees if it
can extract a default from there.
To avoid parsing a lot of XML files every time the application is executed,
the extracted values are cached in a SQLite database. If the schemas
dir is writable by the user, the database is stored in
$schemadir/.gconfdefaults.sqlite
Otherwise the database is stored in:
$home/.gconfdefaults.<mangled version $schemadir>.sqlite
Notes:
* Performance was not the primary consideration here; for each
application, the first time a default lookup is triggered, it needs to look
at the modification times for all schema files in $schemadir to see
if the database needs to be rebuilt. If the set of locally built modules
is large, this could take a measurable amount of time.
* One issue of setting a LD_PRELOAD in a .jhbuildrc is that the library
and dependencies will get loaded into *every* process, including /bin/sh,
gcc, etc, slowing down the build.
* Because the defaults lookup is last-resort measure, if the same schemas
are installed on the system with *different* default values, the system
default values will be preferred. In general, default values shouldn't change
very often.
* This doesn't help for cases where schemas are actually needed; in particular,
gconf-editor won't have any access to the documentation for the schemas.
You could imagine a more sophisticated version of this library that provided
the schemas as well, but that's would be considerably more code.
Usage
=====
Using gconf-defaults-hack with JHBuild:
A) Add gconf-defaults-hack to your moduleset
B) Add to your ~/.jhbuildrc
os.environ['GCONF_DISABLE_MAKEFILE_SCHEMA_INSTALL'] = '1'
addpath('LD_PRELOAD', os.path.join(prefix, "lib", "libgconf-defaults-hack.so"))
Legal
=====
gconf-defaults-hack is Copyright 1999-2009 Red Hat, Inc, and licensed
under the terms of the GNU Library General License, version 2 or
later. See the file COPYING for details.
Owen Taylor
7 June 2009
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