Offtopic: ubifs and best practice for supporting browser based firmware upgrades

[Ricard Wanderlof]

On Wed, 26 Sep 2012, Artem Bityutskiy wrote:

> On Wed, 2012-09-26 at 13:42 +0800, Jaya Kumar wrote:
>> I think what this means is that after doing the rootfs upgrade using
>> ubiupdatevol, I must reboot into a 3rd partition running a minimal OS
>> to perform the ubirename of roofs_reserve and then reboot again. This
>> step seems expensive to have to boot into a 3rd partition to do the
>> rename operation.
>>
>> I see someone else also has encountered this,
>> http://comments.gmane.org/gmane.linux.drivers.mtd/39415 and solved by
>> having a initramfs. I guess I could do that. But still seems messy.
>
> Yes, the way it is currently implemented is:
>
> 1. ubirename /dev/ubi0 rootfs rootfs_reserve
> 2. UBI figures out that old 'rootfs' should be removed.
> 3. UBI changes the volume table and wipes old rootfs from there,
>   and changes name 'rootfs_reserve' to 'rootfs'.
>
>   Now if you have a power cut, you will no longer see the old rootfs
>   vloume, only the new one.
> 4. Then UBI actually deletes the old volume from all the in-memory
>   data structures. Obviously, you cannot use this volume at the same
>   time.
>
> But this can be improved, I did not think a lot about this, but I guess
> if you just skip step 4, it should work. The rename will succeed, but
> you will still see the old layout. And only when you reboot, you'll have
> the old rootfs deleted and the new one being in place.

But the problem is that the first step fails as the system is still 
running, and you can't unmount / while it is up.

> Also, I guess the rename path should not open the volume in the
> exclusive mode.

Yes, that would be a workable solution, if there weren't any other 
disadvantages (e.g. something getting confused by the volume name 
changing, like df).

/Ricard
-- 
Ricard Wolf Wanderlöf                           ricardw(at)axis.com
Axis Communications AB, Lund, Sweden            www.axis.com
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