Re: [RAUC] Query regarding rauc

[Abhishek Kumar Rai <abhishekr@eximiusdesign.com>]

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Hi Team,

Please provide your valuable suggestion regarding the above query .

Regards,
Abhishek Rai

On Wed, Dec 5, 2018 at 12:15 PM Abhishek Kumar Rai <
abhishekr@eximiusdesign.com> wrote:

> Hi Enrico,
>
> Thanks for the detailed response. Helped change our perspective and
> understand rauc better.
>
> Please find our responses inline
>
> Regards,
> Abhishek Rai
>
> On Tue, Dec 4, 2018 at 6:20 PM Enrico Joerns <ejo@pengutronix.de> wrote:
> >
> > Hi Abhishek,
> >
> > On 12/4/18 1:06 PM, Abhishek Kumar Rai wrote:
> > > Hi Enrico,
> > >
> > > Thanks for the prompt response!
> > >
> > > Please find our responses inline (blue colored)
> >
> > you're lucky that I've a graphical mailer... ;)
> > Better use standard mail quoting.
> >
>
> Sure. Lesson learnt :)
>
> > >> Our understanding of rauc install suggests that it does the
> > >> following things:
> > >>
> > >> 1. Verify signature of the bundle 2. Run partition selection
> > >> algorithm 3. Extract the tar balls from the bundle 4. Create new
> > >> ext4 FS on the selected partition 5. Write appropriate tar ball to
> > >> the partition
> > >>
> > >>
> > >> Since "rauc install" would give us errors due to our configuration
> > >> we plan to achieve this using the steps below:
> > >>
> > >> 1. Verify signature of the bundle (rauc info ...) 2. Partition
> > >> selection algorithm (we would like to skip this) 3. Extract the tar
> > >> balls from the bundle (rauc extract ..) 4. Create new ext4 FS on
> > >> the selected partition + Write appropriate tar ball to the
> > >> partition (rauc write-slot ... ....)
> > >
> > > how do you trigger the custom installation? Do you use the
> > > full-custom RAUC install handler? No for now we have replaced the
> > > "rauc install" call with the calls to the commands "rauc info + rauc
> > > extract + rauc write-slot". We were thinking that we might not get
> > > control due to slot selection algorithm. But we will explore this
> > > further starting today. Get a feeling it would be what we want.
> > > Though we read in the documentation that the pre/post install hooks
> > > would not work with full custom install. We might need them. Not too
> > > sure though. We might be able to merge the "post-install" hook work
> > > with the "install" hook
> >
> > You want to have a look at this sections:
> >
> > https://rauc.readthedocs.io/en/latest/using.html#full-custom-update
> >
>
> Thanks!
>
> > > Extracting the tar's should not be required in all cases. With the
> > > full-custom handler you will already have it mounted, otherwise you
> > > can simply mount the bundle after verification as it is basically a
> > > squashfs. Sure..
> > >
> > > For rauc write-slot you also rely on parts of the system.conf, but
> > > not in the fixed scheme. If that is where your issue resides, you
> > > should be fine with that. Sure. We were also considering referring to
> > > the manifest file when the bundle gets mounted
> > >
> > > Could you give me a hint what forces you to do this kind of manual
> > > handling? Maybe then we can think about a possible solution more
> > > targeted.
> > >
> > > * For now, we have 4 partitions containing rfs.0, rfs.1, appfs.0 and
> > > appfs.1. We would like to have a scheme where only the partition that
> > > has been flashed with bundle data is  changed i.e lets say currently
> > > we are using rfs.0 and appfs.0. Now if we flash a bundle containing
> > > appfs, on next reboot, system should use rfs.0 and appfs.*1*.
> > > Similarly for rfs.
> > >
> > > * To achieve this we started without a parent child relationship in
> > > system.conf. So when we are executing from appfs.0 and rfs.0 and we
> > > try to flash a bundle containing appfs, it would try to write to
> > > appfs.0 which would already be in use and hence we would get errors.
> > > So we introduced the parent child relationship
> > >
> > > * Now _with_ parent child relationship the issue above would be
> > > resolved. Now when we boot from "rfs.0" and execute apps from
> > > "appfs.0" and flash a appfs bundle it would write to appfs.1. On
> > > reboot, as per our scheme we would boot from "rfs.0" and execute apps
> > > from "appfs.1". Now when we try to do a rauc install it would write
> > > to "appfs.1" as it would consider appfs.0 as active partition due to
> > > parent-child relationship.
> > >
> > > * Hence as we were running into all these issues we felt that it
> > > would help our cause if we had our own slot selection logic. Hence
> > > the deviation to rauc info + rauc extract + rauc write-slot.
> >
> > Ok, I think I got your base motivation.
> >
> > What do you do to assure that the right appfs is used?
> > Is that mechanism atomic? I.e. when you are interrupted between update
> > of appfs, does it still boot the valid one?
> >
>
> We have yet not reached a stage where we would start releasing out the
> app bundles. Probably we would do it in a month or two.
> Yes if we are interrupted between update of appfs we would not switch
> to using the target partition and continue using the same appfs
> partition
>
> > In general, as you might have read, our strict design case and
> > recommendation is that you only install well-tested sets of all pieces
> > of software. If you use it as an 'app store' maybe that is note a task
> > for RAUC?
> >
>
> Ohh. But we are able to achieve the appfs upgrades by mending rauc a
> little bit. Isnt that ok? Would you be able to provide more details as
> to why it might not be a good idea to use rauc for app-only upgrades?
> This would help us better design our update scheme. The core idea
> behind all the experiments is we wish to maintain symmetry and across
> reboots change only the partition that has been updated. So thats how
> the idea of having a rfs.0 + appfs.1 combination in place of rfs.1 +
> appfs.1 comes into the picture.
> For now, we have 3 use-cases (that might increase)
> - rfs only updates
> - appfs only updates
> - rfs + appfs updates
>
> > But, what speaks against having both rootfs and appfs updated together?
> > Is that installation time / bundle size?
> >
>
> Yes. Its mainly the bundle size. We would be updating our apps more
> frequently as compared to rfs. Hence we would want to release as small
> a bundle as we possibly can.
>
> > Note that RAUC will skip the actual update of the rootfs anyway if the
> > slot's hash matches the hash of the image to install. Thus if you do not
> > change the rootfs content across multiple instalations, it will skip
> > the rootfs writing, anyway.
> >
> >
>
> Ok..
>
> > Another concept to thinks about is (if you insist on updating the
> > appfs separately), if you do not move the switching point entirely to
> > be in the rootfs. Then RAUC would incorporate with the appfs-selection
> > logic you currently use. Might need some extension for using custom boot
> > selection scripts, but this is on our list anyway.
> >
>
> Yes. For now, we are planning to have that intelligence of
> appfs-selection in our boot script.
>
> > The open question would be if you also intend to update your rootfs and
> > if it is ok to never update the appfs and rootfs together, as this would
> > not work with my approach.
> >
> >
>
> Yes. For now we have 3 different target use-cases
> - rfs only : an update might happen once every 6 months or so
> - appfs only : an update might happen monthly to start with and then
> on a need basis
> - rfs + appfs : probably once every 6 months or so
>
> > Regards, Enrico
> >
> > --
> > Pengutronix e.K.                           | Enrico Jörns
> |
> > Industrial Linux Solutions                 | http://www.pengutronix.de/
> |
> > Peiner Str. 6-8, 31137 Hildesheim, Germany | Phone: +49-5121-206917-5080
> |
> > Amtsgericht Hildesheim, HRA 2686           | Fax:   +49-5121-206917-5555
> |
> >
>

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