Title:   jffs2 howto
Subject: Use jffs2 in a simple way
Author: John Stile <john@stilen.com>
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What and why:
  #------------------------------------
  #  Ext2fs - optimized for 512 or 1024 block sizes, but flash varies
  #  Ext2fs - sector erase coppies whole sector to RAM, erased, then rewritten back (flash limits to 100,000 wirtes).
  #  Ext2fs - is not crash-proof
  #  Ext2   - does not support wear levelling
  #  Ext2fs - does not have particularly brilliant sector management,
  #------------------------------------
  #  JFFS - bad side-effect was boot time (5-10 minute pause)
  #  JFFS - higher cpu usage than other file systems.
  #------------------------------------
  #  JFFS2 - Performas wareleveling via an abstraction between logical file positions and physical memory location
  #  JFFS2 - Better performance than JFFS
  #------------------------------------
  #  MTD is broken into 2 secions User space, kernel spcace.
  #  1. MTD subsystem
  #  2. MTD_BLOCK projects the flash as a normal block device (like an IDE disk)
  #  devices associated with MTD_BLOCK are /dev/mtdblock0, mtdblock1 (etc).
  #  mtd block devices are normally formatted with JFFS2 or FTL, on top of emulcation device (/dev/mtdblock0).
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Kernel: I build blkmtd driver as a module, and other stuff as static.
  These are the relevent sections from the kernel 'make menuconfig'
      Device Drivers  --->
     	  Memory Technology Devices (MTD)  --->
     	      <*> Memory Technology Device (MTD) support
              [*]   MTD partitioning support    
              <*>   NFTL (NAND Flash Translation Layer) support
              [*]     Write support for NFTL
     	      Mapping drivers for chip access  --->
     		  [*] Support non-linear mappings of flash chips
     		  <*> PCI MTD driver
              Self-contained MTD device drivers  --->
                  <*> Physical system RAM
                  <M> MTD emulation using block device
                  <*> MTD using block device (rewrite)
     	      NAND Flash Device Drivers  --->
     		  <*> NAND Device Support
     		  [*]	Verify NAND page writes
       File Systems --->
     	   Miscellaneous filesystems  --->
               <*> Journalling Flash File System v2 (JFFS2) support 
               (0)   JFFS2 debugging verbosity (0 = quiet, 2 = noisy)
               [*]   JFFS2 write-buffering support 

  My .config now looks like this
    egrep 'MTD|JFFS' .config |egrep -v '^#|$#'
        CONFIG_MTD=y
        CONFIG_MTD_PARTITIONS=y
        CONFIG_MTD_MAP_BANK_WIDTH_1=y
        CONFIG_MTD_MAP_BANK_WIDTH_2=y
        CONFIG_MTD_MAP_BANK_WIDTH_4=y
        CONFIG_MTD_CFI_I1=y
        CONFIG_MTD_CFI_I2=y
        CONFIG_MTD_RAM=y
        CONFIG_MTD_COMPLEX_MAPPINGS=y
        CONFIG_MTD_PCI=y
        CONFIG_MTD_PHRAM=y
        CONFIG_MTD_BLKMTD=m
        CONFIG_MTD_BLOCK2MTD=y
        CONFIG_MTD_NAND=y
        CONFIG_MTD_NAND_VERIFY_WRITE=y
        CONFIG_MTD_NAND_IDS=y
        CONFIG_JFFS2_FS=y
        CONFIG_JFFS2_FS_DEBUG=0
        CONFIG_JFFS2_FS_WRITEBUFFER=y
        CONFIG_JFFS2_ZLIB=y
        CONFIG_JFFS2_RTIME=y

  I'm using gentoo, so now I rebuild my kernel
    genkernel --menuconfig --no-clean --gensplash=gentoo  all
    vi /boot/grub/menu.lst
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How: My compact flash card that shows up as hdc.
     This will put a 560Mb jffs2 image on partition hdc3

     #
     # 1. Create 560Mb image file
     #
     mkdir jffsfile
     rsync -avz /bin jffsfile/
     mkfs.jffs2 -r jffsfile -p -o jffs.image -e560MiB --pad

     #
     # 2. Write image file to the parition
     #
     dd if=jffs.image of=/dev/hdc3
   
     #
     # 3. Mount hdc3  as jffs2
     #
     modprobe blkmtd device=/dev/hdc3
     mknod /dev/mtd0 c 90 0
     mknod /dev/mtdblock0 b 31 0
     mount -t jffs2 /dev/mtdblock0 /mnt/floppy
     cat /proc/mtd
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