Hi,
On Tue, 27 Nov 2018 at 12:57, Ruslan Trofymenko ruslan.trofymenko@linaro.org wrote:
Add a short documentation for A/B enablement and 'android_ab_select' command usage.
Signed-off-by: Ruslan Trofymenko ruslan.trofymenko@linaro.org
doc/README.android-ab | 67 +++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 67 insertions(+) create mode 100644 doc/README.android-ab
diff --git a/doc/README.android-ab b/doc/README.android-ab new file mode 100644 index 0000000..230088c --- /dev/null +++ b/doc/README.android-ab @@ -0,0 +1,67 @@ +Android A/B updates +===================
+Overview +--------
+A/B system updates ensures modern approach for system update. This feature +allows one to use two sets (or more) of partitions referred to as slots +(normally slot A and slot B). The system runs from the current slot while the +partitions in the unused slot can be updated [1].
+A/B enablement +--------------
+The A/B updates support can be activated by specifying next options in +your board configuration file:
- CONFIG_ANDROID_AB=y
- CONFIG_CMD_ANDROID_AB_SELECT=y
+The disk space on target device must be partitioned in a way so that each +partition which needs to be updated has two or more instances. The name of +each instance must be formed by adding suffixes: _a, _b, _c, etc. +For example: boot_a, boot_b, system_a, system_b, vendor_a, vendor_b.
+As a result you can use 'android_ab_select' command to ensure A/B boot process +in your boot script. This command analyzes and processes A/B metadata stored +on a special partition (e.g. "misc") and determines which slot should be used +for booting up.
+Command usage +-------------
- android_ab_select <slot_var_name> <interface> <dev[:part_number|#part_name]>
Can we have a shorter command?
Perhaps we need a new 'android' command with an 'ab_select' subcommand? Then the automatica abbreviation will work.
+for example:
- => android_ab_select slot_name mmc 1:4
+or
- => android_ab_select slot_name mmc 1#misc
+Result:
- => printenv slot_name
- slot_name=a
+Based on this slot information, the current boot partition should be defined, +and next kernel command line parameters should be generated:
- androidboot.slot_suffix=
- root=
+For example:
- androidboot.slot_suffix=_a root=/dev/mmcblk1p12
+A/B metadata is organized according to AOSP reference [2]. On the first system +start with A/B enabled, when 'misc' partition doesn't contain required data, +the default A/B metadata will be created and written to 'misc' partition.
+References +----------
+[1] https://source.android.com/devices/tech/ota/ab
+[2] bootable/recovery/bootloader_message/include/bootloader_message/bootloader_message.h
2.7.4
Regards, Simon