[Sugar-devel] Hello, was Re: Hack to get a USB/SD to autologin to only "Sugar-desktop on a stick". from a F12-alpha live CD

[Douglas McClendon]

Douglas McClendon wrote:
> Martin Langhoff wrote:
>> On Wed, Sep 9, 2009 at 4:26 AM, Douglas
>> McClendon<dmc.sugar at filteredperception.org> wrote:
>>> My name is Douglas McClendon, and I created the ZyX-LiveInstaller which appears
>>>  on track to becoming part of SoaS.  I also can accept praise and blame for
>>> the LiveUSB persistence feature I implemented for fedora a couple years back,
>> Good to have you on board! One thing we've found is that the overlay
>> fs trick is neat but somewhat fragile. In brief - unclean shutdowns
>> and "oops, I pulled out the stick" cases very often leave the USB
>> stick unbootable.
>>
>> Of course, first step is fsck.vfat, but after that, we're completely
>> lost. Hints would be more than welcome. Ideally, something smarter can
>> be done during the boot itself or otherwise with a "repair" script.
> 
> Unfortunately I don't have any easy answers.  As someone who works on NDS 

Ok, more hints as various vague theories start percolating through my memory.
First disclaimer- I'm no fsck.vfat expert.  Maybe there are options and ways to
use it to more success than I've had, perhaps even targeted to the failure case
at hand.  But from a worst case perspective of assuming you always run grave
risk of completely corrupted fat due to simple write interruption, you could go
with an extra buffer layer in the devicemapper snapshot overlay.  I.e. a second
small overlay on a separate, intentionally 'volatile' partition.  Then
periodically (5min and/or user-tunable) write that back to main overlay on the
less volatile main partition.  And some amount of replication of those
files/slices.

Of course unionfs implemented LiveOSs are somewhat different, though actually I
think the above maps pretty well to both the same problem and solution for that
type of LiveOS.

Or maybe subtle features of btrfs that I don't completely grok yet make
this problem go away...

Dunno...

-dmc