linux-mtd digest, Vol 1 #323 - 3 msgs

Sanjay Kumar sanjayk at
Fri Jan 4 14:51:24 EST 2002

Thanks Geoffrey. It solved my problem. 

-----Original Message-----
From: Geoffrey Espin [mailto:espin at]
Sent: Friday, January 04, 2002 10:21 PM
To: linux-mtd at
Subject: Re: linux-mtd digest, Vol 1 #323 - 3 msgs

> From: "Sanjay Kumar" <sankumar96 at>
> Subject: Problem in changing  the starting location of JFFS2 for AMD flash
> I am using AMD flash of 4M size and keeping starting 1/2 MB for RAW data.
Then for the remaining I want to use JFFS2. That is JFF2 will start from 0.5
MB to 4MB. For that I am making changes in super.c of JFFS2 for function
jffs2_read_super. The changes are -    
> c->free_size = c->mtd->size - jffs2_start_addr;
> c->flash_size = c->mtd->size - jffs2_start_addr;
> c->nr_blocks = c->flash_size / c->sector_size;
> c->blocks[i].offset = i * c->sector_size + jffs2_start_addr;
> where am keeping jffs2_start_addr = 0x80000.
> I am using linux 2.4.2.
> Now I am able to mount the jffs2 file system and able to create a empty
> But when I go for writing into the created empty file, it is crashing.

As someone already has replied, don't mess with sources like super.c.

In linux/.config, have these options on:


Under linux/drivers/mtd/maps/ you must create your myboard-flash.c
(and add to Makefile), which has the partition table in it, e.g.:

    #define WINDOW_ADDR 0xbfc00000  /* default 4M part */
    #define WINDOW_SIZE 0x00400000
    static struct mtd_partition myboard_partitions[] = {
		    name: "bootstrap and kernel",
		    size: WINDOW_SIZE / 4,  /* 0.5M */
		    offset: 0,
		    name: "filesystem",
		    size: MTDPART_SIZ_FULL, /* 2M */
		    offset: MTDPART_OFS_APPEND,

Then from shell you can:

    # mtd_debug erase /dev/mtd/0 ${OFFSET} ${SIZE}   # 0 is entire device
    # cp empty.jffs2 /dev/mtd/2                      # 2 is second partition
    # mount -t jffs2 /dev/mtdblock/2 /mnt

Where 'empty.jffs2' is a stub file created by mkfs.jffs2,
and OFFSET & SIZE are whatever boundaries you've setup.

You might need to drop in later mtd files into 2.4.2.

Geoffrey Espin
espin at

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