Upgrading cramfs root file system while running (DENX wrote that is not possible)

[Tolunay Orkun]

If your bootloader is U-Boot and you are using standard bootm command to 
boot, U-Boot decompresses the initrd image to RAM before passing the 
file system to Linux. So, you are not working with flash copy and 
updating the flash copy is not a problem at all. This applies to ext2, 
cramfs or squashfs based initrd.

You can keep working as long as you like until it is time to reboot.

Antonio Di Bacco wrote:
> Yes, I also thought this too. Anything important should stay already in RAM 
> but there is a chance that something bad could happen. Probably the best 
> thing is what you suggested as second option but I have not so much ram. My 
> CGI writes the downloaded new software in RAM and then I should directly jump 
> to u-boot without leaving Linux the chance to mix things up and then u-boot  
> should copy the RAM to the flash. It seems a strange procedure but what else 
> could be done with 4MB flash and 16 MB ram? 
> 
> Bye,
> Antonio.
> 
> On Thursday 20 April 2006 22:18, White wrote:
>> make it easy: if you start an application which do the flash and after
>> this a reset.. nothing should happen. I do it that way.
>> the application resist completly in RAM .. and all important libs are
>> in RAm or in Filesystem Cache.
>> It's only important that you pretend any Application from accessing
>> Datafiles or start of new application ...
>>
>> Alternativly, you can put it in a reserved RAM Area ( mark it not
>> usable by Linux) and put a Flash Code in your Bootloader (U-boot?)
>> after a reset....
>>
>> But overwrite a cramfs works for me on >100 times without problems.
>>
>> Am Thu, 20 Apr 2006 21:54:45 +0200 schrieb Antonio Di Bacco
>>
>> <antonio.dibacco at aruba.it> :
>>> Yes you are right, it is not a good idea to overwrite working cramfs
>>> filesystem. But what happens if I download the new cramfs plus kernel in
>>> RAM, do a checksum and then, completely in kernel mode, disabling all the
>>> interrupts, I write to flash? No process could complain that I am
>>> overwriting because no one is executing.
>>>
>>> Bye,
>>> Antonio.
>>>
>>> On Wednesday 19 April 2006 09:42, Wojciech Kromer wrote:
>>>> Dnia 2006-04-06 22:38, Użytkownik Antonio Di Bacco napisał:
>>>>> Hi,
>>>>>
>>>>> how could I upgrade my cramfs rootfs? I have a CGI in the rootfs that
>>>>> receives the new rootfs from a web interface and then tries to write
>>>>> it in the flash. While overwriting the old cramfs, the CGI will
>>>>> continue to work? something weird could happen?
>>>> Generally it's not a good idea to override working filesystem ( I've
>>>> tried to do it once).
>>>>
>>>> You can have two separate copies of filesystem, one to work with, and
>>>> another to overwrite, it requires more flash.
>>>> Another way is working in initrd, it requires more RAM.
>>>> You can also use jffs2 or jffs3 (experimental) to have read-write
>>>> filesystem, and change applications only, not whole filesystem (be
>>>> carefull with changing busybox or libraries!)
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