On ons, sep 03, 2025 at 08:50, Jan Lübbe <j...@pengutronix.de> wrote: > On Tue, 2025-09-02 at 23:34 +0200, Tobias Waldekranz wrote: >> On tis, sep 02, 2025 at 16:46, Jan Lübbe <j...@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? > > LVM2 in general is quite complex.
Oh yes, full LVM support would be mind-bendingly complicated in a bootloader. I am aiming for an extremely small subset: Being able to parse a VG made up of a single PV, containing LV's made up of only linear segments. > Some people don't like that it's not easily > possible to know (in udev/systemd) when all volumes are found and set-up, > making > boot time dependencies difficult. I see. Is that because, in contrast to most other devices, userspace needs to initiate device creation? Are Android dynamic partitions better behaved in this respect? > The Android metadata (or something similar) > seems to be simple enough to implement in a bootloader. So, as we only need a > small subset of the full LVM functionality on embedded devices, perhaps > there's > space for a lightweight alternative? :) Agreed, I am not exactly thrilled about needing a parser for the LVM ASCII metadata format in Barebox :) Android dynamic partitions undoubtedly seem much better from that perspective. Here is my concern with it: wouldn't going this route mean that you have to either (a) build your own tooling for working with Android dynamic partitions, or (b) have some semi-automated way of extracting the existing tooling from the Android source tree? In contrast, the LVM2 package is just a config option away in both Buildroot, PTXdist, and Yocto. > Jan > -- > Pengutronix e.K. | | > Steuerwalder Str. 21 | http://www.pengutronix.de/ | > 31137 Hildesheim, Germany | Phone: +49-5121-206917-0 | > Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 |
