How to run customized ext4 under Linux 2.6.26

There are two difficulties:

1. How to build your own ext4 and jbd2 module without re-build the whole kernel.

2. How to enable ext4 support on old linux 2.6.26 kernel

My platform is centOS.

Solution:

0. Make a copy of your linux source code tree. Modify the ext4 and jbd2 source code as you need.

1. Modify the .config file in your linux kernel source code directory. Delete all the xxx=m line. Add the following line:

COFIG_CRC16=m //needed by ext4

CONFIG_EXT4DEV_FS=m

CONFIG_JBD=m

CONFIG_JBD2=m

2. do "make modules" under this directory. This will produce the needed kernel modules.

3. Check /etc/modprobe.conf, /etc/modules.conf, and /etc/modprobe.d/blacklist files, make sure ext4 and jbd2 module are not automatically loaded. This is to prevent the kernel from loading the some other version of these modules from a default place.

4. reboot the kernel. Do insmod on lib/crc_16.ko, fs/jbd2/jbd2.ko and fs/ext4/ext4dev.ko. Theses are the modules you modified. Note that crc_16.ko is needed by ext4dev.

5. yum install e4fsprogs. This will give you necessary utility support for ext4.

6. Choose a disk partition to mkfs: mkfs -t ext4dev /dev/sdc

7. Tune the fs to tag that it's a test filesystem (otherwise kernel will refuse to mount it): tune4fs -E test_fs /dev/sdc

8. mount -t ext4dev /dev/sdc /dir/you/want/to/mount. Note that you may need to mount with some especial flags (e.g. no extent support), since ext4 under 2.6.26 have some bugs.

Done.