[Buildroot] Creating JFFS2 rootfs to SPI flash, and mounting it from kernel

[Arnout Vandecappelle <arnout@mind.be>]

On 18/03/13 07:45, Juha Lumme wrote:
> 1) My board is described in dtb file, so is it correct to assume that I
> should also describe my flash layout there under the SPI section for the
> flash ?

  It's either in the DTB or you can pass it along as boot arguments, 
something like:
mtdparts=dataflash0:128k(u-boot),4m(kernel),12m(rootfs),-(home)

> My planned layout is something like this (please ignore the addresses
> themselves):
> 0x0 - 0x9 u-boot
> 0x10 - 0x19 kernel
> 0x20 - 0x29 root fs
> 0x30 - 0x39 /home
>
> 2) Currently I am passing the partition info on the memory card to the
> kernel from u-boot (noinitrd console=ttyAMA0,115200 root=/dev/mmcblk0p2
> rw rootwait).
> Can I now change this to: "noinitrd console=ttyAMA0,115200
> root=/dev/mtdblock2 rootfstype=jffs2 ro rootwait" ?
> I'm thinking the block2 is since block 0 is u-boot and 1 would be kernel
> ? ro instead of rw since I don't want to write to root fs.
> Or does that make any sense ? What would you recommend me to do ? Is
> JFFS2 a good idea ? Should I consider RAMFS for root file system ?

  JFFS2 as a read-only rootfs works perfectly. If you want to explore 
alternatives, consider UBI/UBIFS, but that's a bit more complex to set up.


> 3) Where can I tell my kernel to mount /home as a separate file system ?
> I would like that one to be read write, but I only rarely need to save
> configuration files there... What would be a good idea with this ?

  In /etc/fstab. Create a target rootfs overlay with a custom fstab that 
specifies to mount /dev/mtdblok3 on /home.

  Note that you'll have to manually create a (supposedly empty) jffs2 
filesystem on /dev/mtdblock3.


  Regards,
  Arnout

-- 
Arnout Vandecappelle                          arnout at mind be
Senior Embedded Software Architect            +32-16-286500
Essensium/Mind                                http://www.mind.be
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