i have configured a kernel without FAT fs support from a base kernel version 8.This new kernel has ext2 ,ext3 support.now if i copy the fat directory into the second kernel and try to configure it using
./config
error msg : " file/dir not found" appears

if i try to insmod the fat.o of the base kernel into the new kernel(configured from base kernel) the error msg appears
" cannot find kernel version for which module was compiled"

how do i get the fat dir working on my configured kernel?
please help....

When you configure the kernel, with make menuconfig or make xconfig, add the support for the fat filesystem as a module.
It should be in the filesystem section, under DOS/FAT filesystems

Then recompile your kernel.

--Rounan

could u plz explain a bit more....very very newbie to config....

Well, if you compiled your kernel, at some point you typed
"make menuconfig"
or
"make xconfig"

And got a list of all the options you could compile into the kernel, either directly (* in menuconfig), or as a module (M in menuconfig).
In the Filesystems section, you didn't specify that you wanted to use the fat filesystem. You need to either compile it into the kernel, in which case it's available all the time, or as a module,in which case it will be loaded as you need it.

For more info, read the kernel howto at:
http://www.linuxdocs.org/HOWTOs/Kernel-HOWTO.html

--Rounan

alright now if fat fs is built as a module....can i use the fat.o formed on another kernel configured without fat fs support configured from the same base kernel?

possibly, but probably not.

stumbling blocks would be:
The module might not have been compiled with the same specs (cpu optimization, etc) or the same version of GCC as the kernel. This can lead to strange behaviour, something you DEFINATELY don't want with a filesystem.

The kernel might not realise it has a fat module if you didn't put it in the config - in trying to read a fat filesystem, it might decide it can't do it because it wasn't compiled to recognize fat, even if you stick fat.o in /lib/modules/<kernelversion>. I don't know since i've never tried.

Especially since it's a filesystem, just recompile.

--Rounan

but if i recompile then the kernel wil just build the fat.o on its own....i cant even insmod it and see how it works......:-(

... if you build it as a module, then you'll get a fat.o built for your kernel. So it'll work with your kernel. I don't see the difference between that fat.o and the one you have now except that the new one will work, and this one might not.
You can still insmod and rmmod the module - it will just be the RIGHT module.

.. I don't think I understand the problem. Perhaps rephrase?

--Rounan