[Dev] [RFC] Tizen system rollback

Aliaksei Katovich a.katovich at samsung.com
Tue Dec 3 07:36:33 GMT 2013


> It was <2013-12-02 pon 14:11>, when Artem Bityutskiy wrote:
> > On Mon, 2013-12-02 at 13:17 +0100, Łukasz Stelmach wrote:
> >> >> integration of snapshots with file-system code *may* (it is yet to
> >> be
> >> >> measured) bring better performance. It would also allow for
> >> snapshots
> >> >> for /boot (p. 11).
> >> >
> >> >       How? Teach bootloader to deal with snapshots?
> >> 
> >> Teach it btrfs. As far as I know btrfs snapshots are simply
> >> alternative
> >> root directories (or subvolumes? Is there anyone wiser than me to
> >> help?).  All you have to do is to tell the boot-loader which one to
> >> "mount".
> >
> > I wonder, what is the boot-loader(s) we discuss?
> 
> We talk about "a boot-loader" ;-)
> 
> > I am aware of 2 major types of boot-loaders.
> >
> > 1. simple ones, which do not know any FS, they simply read the kernel
> > from a special place where it is stored in a simple raw format. E.g.,
> > this may be a special partition, or a separate flash. There may be some
> > trivial format which allows for storing several kernels/initrd, may be
> > changing the boot parameters, etc.
> 
> Yet another option is to provide a list of blocks to read like lilo(1)
> does.
> 
> > 2. complex ones, which support file-systems.
> >
> > Which ones do we discuss? Dow we want to bind Tizen architecture to
> > either of these? Or we want to be agnostic?
> >
> > A couple of random thoughts...
> >
> > Type 2 bootloaders have own disadvantages. E.g., the FS driver teds to
> > quickly get out-of-date there. There is more complexity when we consider
> > corrupted FS handling.
> 
> In case of boot-loaders this isn't that bad because you need a read-only
> support and on-disk format does not change that often.
> 
> > It would be cool if the Aliaksei's architecture could be generalized so
> > that it would allow for btrfs as a special case...
> 
> This would be cool indeed.

	Giving that we leave kernel recovery w/o changes and snapshots are
	handled from initramfs we can support btrfs as alternative way to
	rollback system. But first things first.

--
Aliaksei

> 
> -- 
> Łukasz Stelmach
> Samsung R&D Institute Poland
> Samsung Electronics




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