Re: [PATCH 0/5] dm: Initial work on a device mapper

[Tobias Waldekranz <tobias@waldekranz.com>]

On tis, sep 02, 2025 at 16:46, Jan Lübbe <jlu@pengutronix.de> wrote:
> On Tue, 2025-09-02 at 11:03 +0200, Ahmad Fatoum wrote:
>> > Yeah I noticed that, _very_ useful. For Infix, if we end up going with
>> > LVM, I suspect we won't be able to send all of that info along with the
>> > commandline, and will end up needing to figure that out (again) in an
>> > initramfs - but for most cases I think it would work really well!
>> 
>> Ah, didn't think of LVM. If mix-and-match is no problem for you, then
>> doing it in the initramfs is a workable solution of course.
>
> If you are thinking about LVM, you may want to take a look at how Android is
> using dm-linear for "dynamic partitions":
> https://source.android.com/docs/core/ota/dynamic_partitions/ab_launch
> https://source.android.com/docs/core/ota/dynamic_partitions/implement
>
> This is also related to virtual A/B:
> https://source.android.com/docs/core/ota/virtual_ab
>
> The components are "snapuserd" and "dm-user" (which was not merged):
> https://lpc.events/event/11/contributions/1049/attachments/826/1562/2021%20LPC_%20dm-snapshot%20in%20user%20space.pdf
> https://lwn.net/Articles/838986/
>
> I'm not sure what they use at the moment...

Very interesting, thank you!

I get why they want something like that for Android, but it does feel
quite daunting to deploy for the systems I typically work on.

If one was to ignore the business of background-merging of COW data
etc. and was just looking to have a way of allocating volumes from
persistent storage, do you see any advantages with Android's metadata
format and/or tooling over that provided by the LVM2 project?

> Regards,
> Jan
>
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