Elixir is a source code cross-referencer inspired by LXR. It's written in Python and its main purpose is to index every release of the Linux kernel while keeping a minimal footprint.

It uses Git as a source-code file store and Berkeley DB for cross-reference data. Internally, it indexes Git blobs rather than trees of files to avoid duplicating work and data. It has a straightforward data structure (reminiscent of older LXR releases) to keep queries simple and fast.

• = Python 3.5

• The Jinja2 and Pygments Python libraries
• Berkeley DB (and its Python binding)
• Exuberant Ctags
• Perl (for non-greedy regexes)

Elixir has the following architecture:

.---------------.
| CGI interface |
|---------------|----------------.
| Query command | Update command |
|---------------|----------------|
|          Shell script          |
'--------------------------------'

The shell script ("script.sh") is the lower layer and provides commands to interact with Git and other Unix utilities. The Python commands use the shell script's services to provide access to the annotated source code and identifier lists ("query.py") or to create and update the databases ("update.py"). Finally, the CGI interface ("web.py") uses the query interface to generate HTML pages.

When installing the system, you should test each layer manually and make sure it works correctly before moving on to the next one.

Two environment variables are used to tell Elixir where to find its local Git repository and its database directory:

• LXR_REPO_DIR (the directory that contains your Git project)
• LXR_DATA_DIR (the directory that will contain your databases)

When both are set up, you should be able to test that the script works:

$ ./script.sh list-tags

then generate the databases:

$ ./update.py

and verify that the queries work:

$ ./query.py file v4.10 /kernel/sched/clock.c
$ ./query.py ident v4.10 raw_spin_unlock_irq

Generating the full database can take a long time: it takes about 15 hours on a Xeon E3-1245 v5 to index 1800 tags in the Linux kernel. For that reason, you may want to tweak the script (for example, by limiting the number of tags with a "head") in order to test the update and query commands.

The CGI interface ("web.py") is meant to be called from your web server. Since it includes support for indexing multiple projects, it expects a different variable ("LXR_PROJ_DIR") which points to a directory with a specific structure:

• <LXR_PROJ_DIR>
  • <project 1>
    • data
    • repo
  • <project 2>
    • data
    • repo
  • <project 3>
    • data
    • repo

It will then generate the other two variables upon calling the query command. For now, three projects are hard-coded into the shell script (to handle version grouping and display): Linux, U-Boot and Busybox.

Here is an example configuration for Apache:

<Directory /usr/local/elixir/http/>
    Options +ExecCGI
    AllowOverride None
    Require all granted
    SetEnv PYTHONIOENCODING utf-8
    SetEnv LXR_PROJ_DIR /srv/elixir-data
</Directory>

AddHandler cgi-script .py

<VirtualHost *:80>
    ServerName elixir.example.com
    DocumentRoot /usr/local/elixir/http

    RewriteEngine on
    RewriteRule "^/$" "/linux/latest/source" [R]
    RewriteRule "^/.*/(source|ident|search)" "/web.py" [PT]
</VirtualHost>

Don't forget to enable cgi and rewrite support with a2enmod cgi rewrite.

Note: this documentation applies to version 0.2 of Elixir.