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

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

[Juha Lumme]

Hi,

Sorry for asking not directly buildroot question, but I thought this forum
would have many members who knows answer to this one.
In my project, I'm trying to migrate my file system to spi flash from
memory card, and I seem to have created filesystem image successfully. I
want my rootfs to be read-only to avoid corruption issues, and only have
application files reside on a writable file system.
(Buildroot was creating a working filesystem for memory card, and I
reconfigured it also to create JFFS2-one, and it did as told).

My question is how to move forward from here, I seem to have several gaps
in my knowledge now.

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 ?
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 ?

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 ?

Thank you for any suggestions, and once again, sorry for using this mailing
list for kernel configuration related question, but I thought many people
here would be well versed in this type of configuration.

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

[Baruch Siach]

Hi Juha,

On Mon, Mar 18, 2013 at 03:45:49PM +0900, Juha Lumme wrote:
> 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 ?

You may also consider Squashfs which is a read-only filesystem, and should 
give better compression ratio than JFFS2.

baruch

-- 
     http://baruch.siach.name/blog/                  ~. .~   Tk Open Systems
=}------------------------------------------------ooO--U--Ooo------------{=
   - baruch at tkos.co.il - tel: +972.2.679.5364, http://www.tkos.co.il -

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

[Carlo Caione]

On Mon, Mar 18, 2013 at 7:45 AM, Juha Lumme <juha.lumme@gmail.com> wrote:
> Hi,
>
> Sorry for asking not directly buildroot question, but I thought this forum
> would have many members who knows answer to this one.
> In my project, I'm trying to migrate my file system to spi flash from memory
> card, and I seem to have created filesystem image successfully. I want my
> rootfs to be read-only to avoid corruption issues, and only have application
> files reside on a writable file system.
[cut]

For this point you can take a look to overlayfs:

http://lwn.net/Articles/447650/
http://wiki.openwrt.org/doc/techref/flash.layout

Best,

--
Carlo Caione

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

[Arnout Vandecappelle]

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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