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Update generation

One of the key features of Firefox is the update system that allows Mozilla to push out bug fixes and new features to users automatically.

Current processes

Currently we use two different sets of processes and tools to generate updates for nightly updates and releases.

Nightly updates during code development

We make updates available for official nightly builds for all current code branches. This helps ensure that our nightly testers are always running the most recent code with the least possible effort. These updates are offered on the 'nightly' update channels, or derivates like 'nightly-ux', and for 'aurora'.

Both complete and partial updates are offered. If the user is running the most recent previous nightly build, the partial update is served. Otherwise, the complete update is always served. This greatly simplifies/expedites the update generation matrix.

Steps for nightly update generation:

  • nightly builder generate complete MAR using Makefile
  • nightly builder downloads the previous complete MAR from the latest dir on the staging server (eg)
  • nightly builder generates partial MAR containing the differences between the two complete MARS using Makefile
  • nightly builder generates snippets for both the complete and partial updates
  • nightly builder uploads snippets directly to the AUS2 server

For more information about how the update MAR files are actually created, please see the section below entitled How to make your own updates.

Updates for end users

We create both partial and complete updates for the 'release' and 'beta' channel too.

Legitimate partial updates, i.e. binary diffs, are generated for migrating users from the previous security release to the new security release, e.g. 13.0->13.0.1. Complete mars are served to those users on older security releases, e.g. 12.0.

Steps for end-user update generation:

  • similar to the nightly case, the build slave generates both a complete and a partial update
  • snippets are generated using the patcher2 tool: http://mxr.mozilla.org/mozilla/source/tools/patcher/
  • patcher generates both production ('release'/'beta') and testing ('releasetest'/'betatest') snippets, for QA to verify

Updates between major branches (aka major update)

Prior to Firefox 4.0, there were long lived branches that produced 3.5.x and 3.6.x releases. An update that converted users from 3.5.x to 3.6.x, or from 3.6.x to the latest release was known as a major update. They were characterised by displaying a dialog offering the user the new branch (ie new features) and asking them to accept the update. In the post-4.0 world these are not used as everyone gets a background update to the latest release, modulo OS compatibility. The only exceptions have been attempts to get people on older releases to update (eg Fx10 is current, offer to 6.0 and older).

What the Makefiles do, or How to make your own updates

The build system generates update MAR files using the Makefile and associated scripts in the tools/update-packaging source directory. The Makefile isn't strictly necessary though. It simply formats the calls to the other scripts based on values stored in environment variables, making it easier to automate update generation.

The scripts rely on some tools that normally get built as part of a nightly Firefox build, namely mar and mbsdiff. You can either builds your own set of tools from the mozilla source, or use a pre-packaged version of the tools for your platform.

These pre-packaged tools were taken from mozilla-central nightly builds on May 17, 2010:

XXX: These need updating for the maintenance service changes

Creating a complete MAR

This script used to generate a complete MAR file is make_full_update.sh.

Here's a example of how you might use the complete update script:

BZIP2=/usr/bin/bzip2 \
MAR=~/bin/mar \
/tools/update-packaging/make_full_update.sh \
dist/update/firefox-3.7a5pre.en-US.linux-i686.complete.mar \
  • You need to provide the path to your MAR and BZIP2 executables as environment variables.
  • The make_full_update.sh will then look in dist/firefox and generate a manifest of the files in that directory.
  • That manifest will then be added to the output file specified, in this case dist/update/firefox-3.7a5pre.en-US.linux-i686.complete.mar, along with all the files themselves.

Creating a partial MAR

This script used to generate a partial MAR file is make_incremental_update.sh.

You'll need two complete MAR files in order to generate a partial MAR file that contains the delta between the two. The delta is computed using the binary patch generator, mbsdiff.

Once you have your two complete MAR files, you can unpack them each into their own directory by using the unwrap_full_update.sh script as follows:

# Given two MAR files, current.complete.mar and previous.complete.mar
export BZIP2=/usr/bin/bzip2
export MAR=~/bin/mar
mkdir current
pushd current
../tools/update-packaging/unwrap_full_update.sh /path/to/current.complete.mar
mkdir previous
pushd previous
../tools/update-packaging/unwrap_full_update.sh /path/to/previous.complete.mar

NOTE: you *MAY* need to modify the source of the make_incremental_update.sh script before you attempt to generate a the partial MAR. Specifically, the script contains a variable, requested_forced_updates. Mozilla uses this variable to which control files that we want to *always* update.

If you have files in your MARs that should always be updated via a partial update (due to checksum changes, timestamps, whatever), you can either change the value of the variable in the script or simply pass the filenames via the -f flag to the make_incremental_update.sh script.

Here's a example of how you might use the partial update script:

BZIP2=/usr/bin/bzip2 \
MAR=~/bin/mar \
MBSDIFF=~/bin/mbsdiff \
tools/update-packaging/make_incremental_update.sh \
firefox-3.7a5pre.en-US.linux-i686.partial.previous-current.mar \
./previous \
  • As for the complete MAR file, you need to provide the path to your MAR and BZIP2 executables as environment variables, but also must provide the path to MBSDIFF.
  • The make_incremental_update.sh will then compare the contents of the previous/ and current/ directories and generate a manifest and a binary diff of the files in those directory.
  • That manifest will then be added to the output file specified, in this case firefox-3.7a5pre.en-US.linux-i686.partial.previous-current.mar, along with the binary diff of the changed files.

Delivering updates via snippets

The actual delivery of updates is beyond the scope of this page on update generation, but I'd feel remiss if I didn't at least mention in passing how it's done.

After the complete and partial MAR files are generated and uploaded to the ftp server every night, we create a simple text file containing information about those MAR files. We call these files "snippets" and they have the following format:

  • Complete:
  • Partial:

We then upload these snippets to the Mozilla AUS2 server. The AUS2 server has internal logic to determine the most recent complete and partial updates available for a given product/branch/version, so that when the client updater requests an update from the server, it's able to redirect to the correct MAR file.