How to port a linux driver , which is compiled in 2.6 kernel ,without compiling in other new version of kernel

Thanks to every one,

This is the question asked in one of the interview i faced.

I have a Linux device driver which was compiled in Linux kernel version 2.6.I would like to port the same driver in a Linux PC which has kernel 3.X without compiling in new versions.

Is it possible ? If it is possible please let me know how. If it is not possible please let me know why not ?

Thanks & Regards Siva

Solution

No you cannot port module which is compiled for one version to other version.

The reason is as follows:

Modules are strongly tied to the data structures and function prototypes defined in a particular kernel version; the interface seen by a module can change significantly from one kernel version to the next. This is especially true of development kernels, of course.

The kernel does not just assume that a given module has been built against the proper kernel version. One of the steps in the build process is to link your module against a file (called vermagic.o) from the current kernel tree; this object contains a fair amount of information about the kernel the module was built for, including the target kernel version, compiler version, and the settings of a number of important configuration variables. When an attempt is made to load a module, this information can be tested for compatibility with the running kernel. If things don’t match, the module is not loaded; instead, you see something like:
# insmod hello.ko
Error inserting './hello.ko': -1 Invalid module format
A look in the system log file (/var/log/messages or whatever your system is configured to use) will reveal the specific problem that caused the module to fail to load.

-- Linux Device Drivers, 3rd ed. (2005), Corbet, Rubini & Kroah-Hartman (Chapter 2, Compiling and Loading, Version Dependency) (p. 26)

Kernel interfaces often change between releases. If you are writing a module that is intended to work with multiple versions of the kernel (especially if it must work across major releases), you likely have to make use of macros and #ifdef constructs to make your code build properly.