CONFIG_MTD_UBI=y
CONFIG_MTD_UBI_WL_THRESHOLD=4096
CONFIG_MTD_UBI_BEB_RESERVE=1
CONFIG_MTD_UBI_DEBUG=y
CONFIG_MTD_UBI_DEBUG_MSG=y
CONFIG_UBIFS_FS=y
CONFIG_UBIFS_FS_LZO=y
CONFIG_UBIFS_FS_ZLIB=y

Next I used a simple rootfs – basically busybox + mtd-utils – to create/format the partitions, suppose that you kernel divided the memory in the following parts:

# cat /proc/mtd
mtd0: 00300000 00020000 “bootloader” *
mtd1: 00500000 00020000 “nand.kernel” **
mtd2: 00100000 00020000 “nand.ramdisk”
mtd3: 06400000 00020000 “nand.system”

*,** The bootloader and nand.kernel I flashed via u-boot.

1. The first time

This is only needed when you create the partition for the first time. Steps are erasing the flash, detaching the UBI [if it was previously attached], format on UBI model, attach again, creating the volume (specifying a name) and finally mounting.

flash_eraseall /dev/mtd3

ubidetach /dev/ubi_ctrl -m 3
ubiformat /dev/mtd3 -y
ubiattach /dev/ubi_ctrl -m 3
ubimkvol /dev/ubi0 -N system -m
mount -t ubifs ubi0:system /mnt/ubi

[ copy your rootfs ]

umount /mnt/ubi

system is the name that I choose for partition, could be any.

2. Editing

Suppose that you need edit some files on your UBIFS , then you only need:

ubiattach /dev/ubi_ctrl -m 3
mount -t ubifs ubi0:system /mnt/ubi

3. Boot

In order to boot, you need add some parameters to u-boot.

setenv bootargs 'console=ttymxc0,115200 rootfstype=ubifs ubi.mtd=3 root=ubi0:system init=...'

32-bit: VmallocTotal:   122880 kB
64-bit: VmallocTotal:   34359738367 kB

Nandsim uses another design to access memory, it creates a slab allocation for an array to allow large chunks of memory, the following functions contains more information:

static int __init init_mtdram(void) in drivers/mtd/devices/mtdram.c
static int alloc_device(struct nandsim *ns) in drivers/mtd/nand/nandsim.c

Lets remember the “original” way (using mdtram) to mount an JFFS2 image:

modprobe mtd
modprobe mtdblock
modprobe mtdram total_size=10240 erase_size=16
dd if=image.jffs2 of=/dev/mtdblock0
mount -t jffs2 /dev/mtdblock0 /mount-point

And the new one with nandsim:

modprobe mtd
modprobe mtdblock
modprobe nandsim first_id_byte=0x20 second_id_byte=0x71
dd if=image.jffs2 of=/dev/mtdblock0
mount -t jffs2 /dev/mtdblock0 /mount-point

And check both:

cat /proc/mtd
dev:    size   erasesize  name
mtd0: 08000000 00004000 "NAND simulator partition 0"
mtd1: 00400000 00004000 "mtdram test device"

With mtdram you can define any value to erase_size but with nandsim you need pre-defined memory parameters found in manufacturer datasheet, to select the simulated flash type one should specify ID bytes of your flasher (I’ve tested with pages of 512 and 2048 bytes).  For more information click here.

You can use nandsim to mount another flash file systems, such as: YAFFS2, CramFS and UBIFS.

As described on first paragraph, nandsim is much more than just a “mount tool”. It can reproduce real condition of memory and lead developers make experiments without real hardware. I’m still learning the possibilities, if you would like to contribute leave an comment.

Endianess issue

If you need convert an image from big endian to little endian (specially on x86 systems) use jffs2dump.

jffs2dump -b big_endian.img -e new_little_endian.img