Taste the Rainbow:0.7.8

This page is a guided tour of the source code of the rainbow-0.7.8 release.

Source Code Overview

Please start in my rainbow-0.7.8 tree.

 ./
  |--- README : Standard boilerplate about where work gets done; somewhat dated in this release.
  |--- rainbow.spec.in : spec-file template for building RPMS
  |--- Makefile.package : package-specific variables for use in ../Makefile.fedora
  |--- conf : installation-time configuration files
  |     \--- session-olpc.conf : applies some unusual dbus rules to allow many uids
  |                              to use the same session bus and enables OLPC-specific 
  |                              dbus access checks. When /etc/olpc-security exists, 
  |                              session-olpc.conf is loaded by /usr/bin/sugar 
  | 
  |--- docs : explanations & notes
  |     |--- NOTES : various problems I have encountered and thoughts on how to solve them.
  |     *--- rainbow.txt : a sketch & justification of the current design
  |
  \--- rainbow : source code
        |--- util : functions wrapping frequently used idioms or useful syscalls
        |--- inject.py : logic implementing activity launching
        \--- service.py : dbus service entry-point

Activity Launching

Activity launching begins when the rainbow D-Bus service receives a CreateActivity message:

• service.py:Rainbow.CreateActivity()

The CreateActivity handler first attempts to reap zombie children, then it clones() the current process and delegates control to

• inject.py:run()

which interleaves calls to the activity-launching primitives:

• inject.py:strace(),
• inject.py:reserve_elt(),
• inject.py:reserve_credentials(),
• inject.py:grab_home(),
• inject.py:configure_home(), and
• inject.py:launch().

and the assumption-checking procedures:

• inject.py:check_bundle_id(),
• inject.py:check_bundle_path(),
• inject.py:check_argv(),
• inject.py:check_cwd(),
• inject.py:check_spool(),
• inject.py:check_owner(),
• inject.py:check_home_dirs(),
• inject.py:check_home(),

Resource Collection

When the rainbow-daemon D-Bus service starts, it performs a garbage collection pass to reclaim resources allocated in its spool. At present, this garbage collection pass simply deallocates any allocated uids and unlinks their instance and home directories.

• gc.py:active_uid(), test for active uids
• gc.py:gc_uid(), unlink the home dirs and instance dirs of uids which are inactive
• gc.py:gc_spool(), iterate over all available uids

This design is consistent with rainbow-0.7.8's simplifying decision to never reuse uids but is inconsistent with the architectural goal of supporting persistent activity instances. This design may be revisited in future releases.

Developing Rainbow

I develop Rainbow in two basic modes, which I call 'snapshot', 'candidate', and 'release' modes:

• By packaging snapshots of a git clone to try out packaging changes.

 make snapshot

• With locally-built or scratch-built packages, when I'm getting ready to tag a release.

 make release

• With an official release, built with Fedora's Koji build system from sources archived in Fedora CVS.
  • Fedora Package Update HOWTO