[Buildroot] [PATCH v2 2/2] axfs: add new filesystem type

[Yann E. MORIN <yann.morin.1998@free.fr>]

Arnout, Ariel, All,

On 2015-10-05 19:53 +0100, Arnout Vandecappelle spake thusly:
> On 05-10-15 17:55, Ariel D'Alessandro wrote:
> > The Advanced XIP File System is a Linux kernel filesystem driver that enables
> > files to be executed directly from flash or ROM memory rather than being copied
> > into RAM.
[--SNIP--]
>  It would be nice to add the axfs kernel side as a kernel extension as well. But
> that looks heavily non-trivial.

I had a quick and cursory look at the axfs sources, and I think this
could be quite easily achievable. Non-trivial, granted, but not too
complex either.

Ariel, are you interested in adding this as a kernel extension?
(Hint: it would be really great! ;-) )

Kernel extensions are a way to "modify" the kernel source tree with
patches provided by another package:
    http://buildroot.org/downloads/manual/manual.html#linux-kernel-ext

Basically, here's what you'd have to do in the axfs extension:

  - get the 'raw' version of the kernel with (but see notes below):
        AXFSUTILS_KVER = $(MAKE) -C $(LINUX_DIR) kernelversion

  - check that there is a patch directory for that kernel version:
        kernel/patches/v$(AXFSUTILS_KVER)/
    => if not, bail out
    => if yes, continue

  - copy $(@D)/kernel/fs/axfs to $(LINUX_DIR)/fs/axfs

  - copy $(@D)/include/linux/* to $(LINUX_DIR)/include/linux/

  - modify $(LINUX_DIR)/fs/Kconfig with (before last line):
        source "fs/axfs/Kconfig"

  - modify $(LINUX_DIR)/fs/Makefile with (as last line):
        obj-$(CONFIG_AXFS) += axfs

Obviously, entirely untested; adapt to Real Life (TM). ;-)

Notes: ideally, the kernel 'raw' version should be provided by
linux/linux.mk but we currently do not have it yet; we only have
'kernelrelease', not 'kernelversion'. It would be interesting if you
provided an initial patch that adds this.

Currently, 'kernelrelease' is in $(LINUX_VERSION_PROBED), so maybe you
could introduce LINUX_VERSION_RAW filled with the output of
'kernelversion' (see how it's done for 'kernelrelease').

Regards,
Yann E. MORIN.

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