Create multiple SquashFS partitions

Question

Hello

I'm working on embedded platform (Broadcom's bcm5358u processor with MIPS core), where I need extra partitions for the purpose of further upgrade procedure. The filesystem used is SquashFS, so I modified 'struct mtd_partition' accordingly, which is passed to MTD related code, and I ended up with this:

#cat /proc/partitions
major minor  #blocks  name

 - 31     0        128 mtdblock0
 - 31     0        128 mtdblock0
 - 31     1       6016 mtdblock1
 - 31     2       4573 mtdblock2
 - 31     3       6016 mtdblock3
 - 31     4       4445 mtdblock4
 - 31     5       4160 mtdblock5
 - 31     6         64 mtdblock6

Now I want to be able to mount /dev/mtdblock4 as a temporary storage during system upgrade, but I can't do this, because it appears that this partition mtdblock4 doesn't have any FS installed. The kernel image and FS are integrated in one image, which is flashed down the /dev/mtdblock2 (which is supplied as root_fs to kernel).

I see only one solution: create a empty squashFS image, write it on /dev/mtdblock4 and may be it will work as I want (?). Is there a way to, like, format the partition on the fly, whenever the kernel boots, or it violates the MTD concepts?

Thanks.

Answer 1

You can mount a JFFS2 filesystem on an empty (erased) flash. It will automatically "format" the flash partition at mount time. Squashfs is not a good candidate, because it is a read-only filesystem.

Answer 2

Is there a reason you can't create a mount a new FS on the fly?

You definitely do not want an empty squashFS image. If you want temporary writeable storage you can use something like a tmpfs volume. If you need to support a system reboot, you can use JFFS on a raw flash device. You should be able to format/mount the MTD devices just like any other block device.

Answer 3

Thanks for responses.

Yes, SquashFS is read-only, but nevertheless I'm able to update my system via Web interface provided by the platform vendor. The platform SDK provides API to directly access MTD from user space.