Re: How is OSTree designed to be safe from power loss damage?

[Phil Wise <phil advancedtelematic com>]

Hi Leon,

On 09.01.2017 15:29, Leon Woestenberg wrote:
> +CC: Leon Anavi and Anton Gerasimov.
>
> I think discussions will happen here on the OSTree mailing list or
> OpenEmbedded (or Yocto) mailing list, depending on the core of the subject.
>
> The existing work is AGL related, this is where I saw Leon and Anton do
> what I was trying to do. :)

meta-updater is independent of AGL now, so it should work with any
OE-based project.  We've put together a simple example using poky and
the R-Pi here:

https://github.com/advancedtelematic/garage-quickstart-rpi

I'd be keen to get OSTree support upstreamed into Yocto/OE: is there
anything we can do to help that process?


Cheers,

Phil


> On Mon, Jan 9, 2017 at 3:12 PM, Colin Walters <walters verbum org
> <mailto:walters verbum org>> wrote:
>
>     __
>
>     On Mon, Jan 9, 2017, at 07:37 AM, Leon Woestenberg wrote:
> >     I would like to make OSTree a first class citizen in upstream
> >     Yocto/OpenEmbedded, a lot has been done already by Leon Anavi and
> >     Anton Gerasimov in meta-updater.
> >     (https://github.com/advancedtelematic/meta-updater
> >     <https://github.com/advancedtelematic/meta-updater>)
>
>     Awesome, happy to help with anything I can here.
>
> >     The question was not so much about the atomic swap, but more about
> >     what happens if the system was power-cycled or reset in the middle
> >     of pulling objects from a remote, or in the middle of deploying an OS?
> >     In other words, what happens if I reset the device halfway
> >     creating the hardlinks, on the next boot cycle?
>
>     Okay, so there are two phases here.  Downloading into the repo, and
>     creating deployments.
>
>     For downloads, the latest on this is:
>     https://github.com/ostreedev/ostree/commit/27a45e2edbd1c4551b801a957cafcb27b3417fd3
>     <https://github.com/ostreedev/ostree/commit/27a45e2edbd1c4551b801a957cafcb27b3417fd3>
>     Specifically:
>     
> https://github.com/ostreedev/ostree/commit/27a45e2edbd1c4551b801a957cafcb27b3417fd3#diff-23d4c8887c7dda91613c9451bf3fe7c0R1281
>     
> <https://github.com/ostreedev/ostree/commit/27a45e2edbd1c4551b801a957cafcb27b3417fd3#diff-23d4c8887c7dda91613c9451bf3fe7c0R1281>
>
>     Basically, pending objects (files) are staged in a directory per
>     kernel "boot id", which is
>     unique per boot.  Hence, if the power is lost any pending objects
>     will be discarded (
>     we currently do a time-based pruning of the tmpdir).
>     This is a bit conservative obviously - we could *try* resuming from
>     them and if the checksum doesn't match, redownload, but so far it
>     hasn't gone up in priority.
>
>     For deployments, it's a lot simpler - we're just making a hardlink
>     farm and copying
>     forward changes in /etc.  If the system crashes before, on the next
>     upgrade attempt,
>     we'll just garbage collect the pending hardlink farm and redo it.
>
>
>
>
>
> _______________________________________________
> ostree-list mailing list
> ostree-list gnome org
> https://mail.gnome.org/mailman/listinfo/ostree-list

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Phil Wise, ATS Advanced Telematic Systems GmbH
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