README.android - platform/system/timezone - Gitiles

 This directory contains code, tools and data related to time zone rules data
 and updates.

 Directory structure
 ===================

 apex
   - Code related to the Android time zone update APEX file that can be used
     to update time zone rules on Android devices.

 debug_tools
   - Contains tools useful for debugging time zone issues on Android devices.

 distro
   - Code related to "distros", the collection of files that can be used to
     update time zone rules on Android devices. See distro/README for details.

 input_data
   - Contains files that provide inputs to the time zone rules update process.
     Some files come from external sources and some are mastered in Android.
     See also download-iana-data.py.

 input_tools
   - Contains tools that generate Android time zone files.

 output_data
   - Contains some derived files from the time zone rules update process and
     used in the Android system image, distros and APEX files. Some files are
     also held by ICU - see also update-tzdata.py

 testing
   - Contains tools and scripts related to testing time zone update code. See
     testing/data/README for details.

 tzdatacheck
   - This is for the "time zone updates via APK" feature.
     Source code for a binary executed during boot and used to ensure that a
     device doesn't boot with incompatible/outdated time zone data installed
     in /data (as could happen if the device has just received an OTA upgrade).
     It is also responsible for committing staged install/uninstalls.


 Data file update tools
 ======================

 download-iana-files.py
   - A helper script run before update-tzdata.py.
     It downloads the latest tzdata and/or tzcode files from IANA and puts them
     in the input_data/iana and input_tools/iana directories for use by the
     update-tzdata.py script. See download-iana-files.py --help for more.

 update-tzdata.py
   - Regenerates the external/icu and system/timezone/output_data timezone
     data files.

 See update instructions below for how these tools are used.

 IANA rules data changes
 =======================

 When IANA release new time zone rules, the update process is:

 1) Run "download-iana-files.py --data" to update the input_data/iana file.
 2) Make manual modifications to input_data/android files as needed.
 3) There are sometimes code and metadata changes associated with tzdata updates
   that should be applied to Android's copy of ICU.
   e.g. see http://bugs.icu-project.org/trac/search?q=2015d
 4) Run update-tzdata.py to regenerate the system/timezone/output_data,
   system/timezone/testing/data, external/icu runtime files and testing equivalents.
 5) Build/flash a device image with the changes and run CTS:
     cts-tradefed
     run cts -m CtsLibcoreTestCases
     run cts -m CtsIcuTestCases
    (And any others that you think may have been affected)
 6) Upload, review, submit the changes from external/icu and system/timezone.

 REMINDER: Any prebuilt apks of OEM-specific time zone data apps .apk files
 (i.e. ones that that contain distro files) will also need to be regenerated
 with a new version code / string and any OEM-specific tests should be run.
 APEX files containing time zone data files will also need to be regenerated.

 IANA tools changes
 ==================

 Occasionally it might be necessary / desirable to update the version of zic
 used to generate Android's tzdata file. For example, if IANA introduce new
 syntax to the text rules files (e.g. asia, north_america, etc.) or adds useful
 command-line arguments to zic. This should be needed very rarely.

 It is recommended that this is done independently of a data update to help
 isolate unexpected changes to behavior.

 Note that updating the version of zic used to create the tzdata file is
 independent of the copy of zic used by ICU. Also, bionic contains
 a copy of tzcode (e.g. localtime.c) which is based on yet another IANA
 release so compatibility and consistency is a consideration.

 The steps for updating IANA tools are similar to updating IANA data except
 you can use "download-iana-files.py --tools" instead of "--data" and testing
 should be more rigorous.

 REMINDER: As above, having updated the tooling then all binaries that contain
 tzdata should also be regenerated. e.g. APK and APEX files.


 Time Zone Data Set Versioning
 =============================

 Android needs various files to be updated to take a time zone data update.
 These files come from various sources and we needed a concise shorthand
 to indicate compatibility between a set of files and an Android release. This is
 known as the "Time Zone Data Set Version". Currently we expect to increment this
 version with every dessert release, though this may change in future.

 The idea of a single version to describe time zone data updates was first
 introduced in O-MR1 with the concept of a "distro" which could be delivered by
 an APK. The Android time zone "distro" is a zip archive containing the files
 needed to update a device's time zone rules by overlaying files into locations
 in /data. See distro/ for details.

 The "distro" concept will be removed in a future release of Android as it is
 being replaced by an APEX file containing the same data. As the APEX contains
 the same files we continue to use a shorthand version code. See apex/ for
 details.

 Time Zone Data Set Versions have a major and minor version number:

 - Major version numbers are mutually incompatible. e.g. v2 is not compatible
   with a v1 or a v3 device.
 - Minor version numbers are backwards compatible. e.g. a v2.2 distro will work
   on a v2.1 device but not a v2.3 device.
 - The minor version is reset to 1 when the major version is incremented.

 The most obvious/common change that can occur between Android releases is an
 ICU upgrade, which currently requires a major version increment: Android uses
 the ICU4C's native file format for both ICU4C and ICU4J time zone code which is
 tied to the ICU major version. The main .dat file used by ICU is held in
 external/icu and will naturally be updated when ICU is updated. Less obviously,
 the time zone data set version code and files must be updated as well.

 Other examples of changes that affect format versioning:

 Major version increment:
 - A non-backwards compatible change to the tzdata or tzlookup.xml files used
   by bionic / com/android/i18n/timezone code.
 - Removal of an existing file from the distro.

 Minor version increment:
 - Backwards compatible changes:
   - A new file in the distro.
   - Additional required data in an existing file (e.g. a backwards compatible
     change to tzdata / tzlookup.xml).


 Changing the Time Zone Data Set Version
 ---------------------------------------

 1) Modify android_icu4j/libcore_bridge/src/java/com/android/i18n/timezone/TzDataSetVersion.java
   - CURRENT_FORMAT_MAJOR_VERSION, CURRENT_FORMAT_MINOR_VERSION
 2) Run update-tzdata.py to regenerate the system/timezone/output_data,
    system/timezone/testing/data, external/icu runtime files and testing equivalents.
 3) Build/flash a device image with the changes and run CTS tests:
     atest CtsHostTzDataTests
     atest CtsIcuTestCases
 4) Run non-CTS test cases:
     atest FrameworksServicesTests:com.android.server.timezone
 5) Upload, review, submit the changes from system/timezone and external/icu/.

 REMINDER: Any prebuilt apks / apex files (i.e. ones that that contain time zone files)
 will also need to be regenerated after this change.
	This directory contains code, tools and data related to time zone rules data
	and updates.

	Directory structure
	===================

	apex
	- Code related to the Android time zone update APEX file that can be used
	to update time zone rules on Android devices.

	debug_tools
	- Contains tools useful for debugging time zone issues on Android devices.

	distro
	- Code related to "distros", the collection of files that can be used to
	update time zone rules on Android devices. See distro/README for details.

	input_data
	- Contains files that provide inputs to the time zone rules update process.
	Some files come from external sources and some are mastered in Android.
	See also download-iana-data.py.

	input_tools
	- Contains tools that generate Android time zone files.

	output_data
	- Contains some derived files from the time zone rules update process and
	used in the Android system image, distros and APEX files. Some files are
	also held by ICU - see also update-tzdata.py

	testing
	- Contains tools and scripts related to testing time zone update code. See
	testing/data/README for details.

	tzdatacheck
	- This is for the "time zone updates via APK" feature.
	Source code for a binary executed during boot and used to ensure that a
	device doesn't boot with incompatible/outdated time zone data installed
	in /data (as could happen if the device has just received an OTA upgrade).
	It is also responsible for committing staged install/uninstalls.



	Data file update tools
	======================

	download-iana-files.py
	- A helper script run before update-tzdata.py.
	It downloads the latest tzdata and/or tzcode files from IANA and puts them
	in the input_data/iana and input_tools/iana directories for use by the
	update-tzdata.py script. See download-iana-files.py --help for more.

	update-tzdata.py
	- Regenerates the external/icu and system/timezone/output_data timezone
	data files.

	See update instructions below for how these tools are used.

	IANA rules data changes
	=======================

	When IANA release new time zone rules, the update process is:

	1) Run "download-iana-files.py --data" to update the input_data/iana file.
	2) Make manual modifications to input_data/android files as needed.
	3) There are sometimes code and metadata changes associated with tzdata updates
	that should be applied to Android's copy of ICU.
	e.g. see http://bugs.icu-project.org/trac/search?q=2015d
	4) Run update-tzdata.py to regenerate the system/timezone/output_data,
	system/timezone/testing/data, external/icu runtime files and testing equivalents.
	5) Build/flash a device image with the changes and run CTS:
	cts-tradefed
	run cts -m CtsLibcoreTestCases
	run cts -m CtsIcuTestCases
	(And any others that you think may have been affected)
	6) Upload, review, submit the changes from external/icu and system/timezone.

	REMINDER: Any prebuilt apks of OEM-specific time zone data apps .apk files
	(i.e. ones that that contain distro files) will also need to be regenerated
	with a new version code / string and any OEM-specific tests should be run.
	APEX files containing time zone data files will also need to be regenerated.

	IANA tools changes
	==================

	Occasionally it might be necessary / desirable to update the version of zic
	used to generate Android's tzdata file. For example, if IANA introduce new
	syntax to the text rules files (e.g. asia, north_america, etc.) or adds useful
	command-line arguments to zic. This should be needed very rarely.

	It is recommended that this is done independently of a data update to help
	isolate unexpected changes to behavior.

	Note that updating the version of zic used to create the tzdata file is
	independent of the copy of zic used by ICU. Also, bionic contains
	a copy of tzcode (e.g. localtime.c) which is based on yet another IANA
	release so compatibility and consistency is a consideration.

	The steps for updating IANA tools are similar to updating IANA data except
	you can use "download-iana-files.py --tools" instead of "--data" and testing
	should be more rigorous.

	REMINDER: As above, having updated the tooling then all binaries that contain
	tzdata should also be regenerated. e.g. APK and APEX files.


	Time Zone Data Set Versioning
	=============================

	Android needs various files to be updated to take a time zone data update.
	These files come from various sources and we needed a concise shorthand
	to indicate compatibility between a set of files and an Android release. This is
	known as the "Time Zone Data Set Version". Currently we expect to increment this
	version with every dessert release, though this may change in future.

	The idea of a single version to describe time zone data updates was first
	introduced in O-MR1 with the concept of a "distro" which could be delivered by
	an APK. The Android time zone "distro" is a zip archive containing the files
	needed to update a device's time zone rules by overlaying files into locations
	in /data. See distro/ for details.

	The "distro" concept will be removed in a future release of Android as it is
	being replaced by an APEX file containing the same data. As the APEX contains
	the same files we continue to use a shorthand version code. See apex/ for
	details.

	Time Zone Data Set Versions have a major and minor version number:

	- Major version numbers are mutually incompatible. e.g. v2 is not compatible
	with a v1 or a v3 device.
	- Minor version numbers are backwards compatible. e.g. a v2.2 distro will work
	on a v2.1 device but not a v2.3 device.
	- The minor version is reset to 1 when the major version is incremented.

	The most obvious/common change that can occur between Android releases is an
	ICU upgrade, which currently requires a major version increment: Android uses
	the ICU4C's native file format for both ICU4C and ICU4J time zone code which is
	tied to the ICU major version. The main .dat file used by ICU is held in
	external/icu and will naturally be updated when ICU is updated. Less obviously,
	the time zone data set version code and files must be updated as well.

	Other examples of changes that affect format versioning:

	Major version increment:
	- A non-backwards compatible change to the tzdata or tzlookup.xml files used
	by bionic / com/android/i18n/timezone code.
	- Removal of an existing file from the distro.

	Minor version increment:
	- Backwards compatible changes:
	- A new file in the distro.
	- Additional required data in an existing file (e.g. a backwards compatible
	change to tzdata / tzlookup.xml).


	Changing the Time Zone Data Set Version
	---------------------------------------

	1) Modify android_icu4j/libcore_bridge/src/java/com/android/i18n/timezone/TzDataSetVersion.java
	- CURRENT_FORMAT_MAJOR_VERSION, CURRENT_FORMAT_MINOR_VERSION
	2) Run update-tzdata.py to regenerate the system/timezone/output_data,
	system/timezone/testing/data, external/icu runtime files and testing equivalents.
	3) Build/flash a device image with the changes and run CTS tests:
	atest CtsHostTzDataTests
	atest CtsIcuTestCases
	4) Run non-CTS test cases:
	atest FrameworksServicesTests:com.android.server.timezone
	5) Upload, review, submit the changes from system/timezone and external/icu/.

	REMINDER: Any prebuilt apks / apex files (i.e. ones that that contain time zone files)
	will also need to be regenerated after this change.