Does XIP_MTD really exist?

[Chris Brandt]

Hello Nicolas,

(I was wondering if you watched this mailing list)

On Thursday, June 15, 2017 1, Nicolas Pitre wrote:
> > Also, I don't really see of any mainline filesystem driver that would
> > make use of it.
> 
> Upon a time, the cramfs filesystem had the ability to flag some files
> that would not be compressed, aligned to a page boundary, and be mapped
> directly out of flash. I might have to revive that functionality in the
> near future if no longer available.

Yes, I think that was the only XIP file system left when I was looking 2
years ago. But I remember something about the method for marking the 
files for XIP was a bit of a hack, and maybe was broken??? After I decided
on AXFS (and forward ported it to the 3.14 kernel), I never went back 
and tried cramfs-XIP.

> > The NO_MMU + XIP_KERNEL people must be using something for a file
> > system....I'm just not sure what that is.
> 
> So far I've seen initramfs packaged with the kernel.

Oh, initramfs. That would explain it. Funny!


> The kernel is XIP
> but user space ends up living in RAM forever.

Hmm, that seems like a waste. Some big bloated open source packages use 
up lots of code pages that would be much better served XIP from ROM 
space. Qt comes to mind.

Anyway way, thank you for the info.
I might have another look at cramfs, but still end up forward porting 
AXFS to 4.x.

Thank you,
Chris