[U-Boot] [PATCH 6/7] doc: android: Add simple guide for A/B updates

[Simon Glass]

Hi,

On Mon, 10 Dec 2018 at 12:11, Ruslan Trofymenko
<ruslan.trofymenko at linaro.org> wrote:
>
> Hi Simon,
>
> On Thu, 6 Dec 2018 at 03:31, Simon Glass <sjg at chromium.org> wrote:
> >
> > Hi,
> >
> > On Tue, 27 Nov 2018 at 12:57, Ruslan Trofymenko
> > <ruslan.trofymenko at linaro.org> wrote:
> > >
> > > Add a short documentation for A/B enablement and 'android_ab_select'
> > > command usage.
> > >
> > > Signed-off-by: Ruslan Trofymenko <ruslan.trofymenko at 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.
> >
>
> Agree with all your previous comments, will send v2 shortly. But this
> one I'd like to leave as is (I will drop android_ prefix though). I
> think adding "android" command may lead to unneeded architecture
> complexity in future, e.g.:
>   - we will need to re-work next commands as sub-commands of "android"
> command: fastboot, dtimg, mmc_swrite (which can be hard as ab_select
> command file has BSD license and other commands have GPL license)
>  - we will need to implement sub-sub-commands (e.g. for "android dtimg
> dump ..." etc.)
>  - having "android" command can be inconvenient for users and may
> break existing API (e.g. it will force users to use "android fastboot"
> instead of just "fastboot" command)
>  - actually I don't see any namespace issues that can be solved by
> adding "android" command
>
> Also, in subsequent patch, I will add the dedicated menu option for
> Android-related commands and will pull all existing Android commands
> (along with ab_select) to that menu entry.
>
> So I hope it's fine with you if I leave this command as "ab_select"?

Yes I think that is OK.

Regards,
Simon