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

Tolunay Orkun listmember at orkun.us
Sun Apr 23 04:50:26 EST 2006

Wolfgang Denk wrote:
> In message <44485B3F.8080308 at orkun.us> you wrote:
>> 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.
> But it makes no sense to use cramfs or squashfs on a ramdisk.
> You *want* to run these directly from flash.
> But then, of course, you need alternate images (or other tricks)
> for full image updates.
Well, we lose a couple of MB of RAM but squashfs as initrd has been 
reliable, very compact and since the file system is in RAM, it is faster 
and we can tune a bit for smaller cache etc. 

Image updates have been extremely easy as a result, we did not need to 
resort to alternate images and other tricks as a result. If you have 
more flexibility in RAM than in flash, our approach makes sense without 
complicating the matter much. I understand that not everyone might have 
this option.
> [Single file updates can be done using overlay file systems; see  the
> DULG for details.]
I know about the overlay fs. There is also unionfs that works similarly.

Best regards,

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