Re: Checksummed environments

[Daniel Kiper]

On Tue, Apr 10, 2018 at 11:09:33PM +0200, Daniel Kiper wrote:
> On Fri, Apr 06, 2018 at 03:08:23PM +0200, Kristian Amlie wrote:
> > On 06/04/18 14:35, Daniel Kiper wrote:
> > > On Fri, Apr 06, 2018 at 11:25:22AM +0200, Kristian Amlie wrote:
> > >> Hey, I work for Northern.tech, developing update software for embedded
> > >> Linux devices.
> > >>
> > >> I have a question about GRUB's environment block: This block is not
> > >
> > > I am not sure what exactly you mean by "GRUB's environment block".
> > > Could you send me some references to the code?
> >
> > Of course, sorry if the context wasn't clear. I'm talking about the
> > environment block mentioned here:
> > https://www.gnu.org/software/grub/manual/grub/grub.html#Environment-block,
> > which is used to store information from one boot to the next, using
> > save_env and load_env.
> >
> > >> checksummed, and hence I reckon it can become corrupt if power is lost
> > >> in the middle of a write.
> > >
> > > What about the other blocks?
> >
> > In theory, there is only one block, because it is written in-place,
> > directly on disk, without changing any other filesystem blocks. Is that
> > what you meant by "other blocks"?
> >
> > >> This is an important safety criterion for us, so we've been thinking of
> > >> developing environment block checksumming as an extension to the
> > >> existing save_env and load_env commands. The most likely approach will
> > >> be to grab X amount of bytes at the end of the block and use these for
> > >> the checksum.
> > >
> > > Could you tell us more about that?
> >
> > The idea comes from U-Boot [1], which uses a dedicated block on a
> > storage device to store data, and uses a CRC32 checksum to make sure it
> > is consistent. The motivation is to be able to detect that the block is
> > corrupt, rather than accepting a block of data that may have incorrect
> > data in if a write was interrupted midway by a powerloss. You can read
> > more about it in the link.
> >
> > [2] https://www.denx.de/wiki/DULG/UBootEnvVariables
>
> I am OK with the idea. However, I think that the feature should have
> a kind of switch to turn it off/on. At first sight it looks that new
> environment variable is sufficient for it.

And/Or an argument for save_env/load_env...

Daniel