I'm trying to port a device driver from a 2.2.14 kernel to the latest
RedHat 7 release (2.2.16 kernel).  We did a fresh installation of RedHat 7
-- not an upgrade.

I didn't get very far with porting the driver... during debugging I ran
across a weird problem that can be reproduced using the following minimal
driver.

#include <linux/module.h>

extern void printk( const char *fmt, ... );

int init_module( void )
{
   printk( "<1>Hello, world!\n" );
   return 0;
}


void cleanup_module( void )
{
   printk( "<1>Goodbye, cruel world!\n" );
}




(1) When I build this minimal driver ("gcc -D__KERNEL -DMODULE -c drv.c") I
get
a weird assembler warning:

/tmp/ccWGbbyQ.s: Assembler messages:
/tmp/ccWGbbyQ.s:9: Warning: Ignoring changed section attributes for
.modinfo

(2) Since the above message is only a warning, not an error, I go ahead and
try to load the module.  When I do so ("insmod drv.o"), I get the following
error:

drv.o: kernel-module version mismatch
        drv.o was compiled for kernel version 2.4.0-0.26
        while this kernel is version 2.2.16-22.

(3) I've tracked it down... normally /usr/include/linux is a symbolic link
into the /usr/src/linux-x.y.zz/include/linux directory (where x.y.zz is the
currently installed kernel version).  With RedHat 7 this is not true...
/usr/include/linux is an actual directory rather than a symbolic link, and
it contains header files for kernel version 2.4!!!  At least that is what
is indicated in version.h.  Further, the pci_dev struct in pci.h has been
redefined in 2.4 (which is what started this mess, because our driver
wouldn't build because there is no more 'base_address' field defined).  So
I moved the /usr/include/linux directory into linux-2.4, then created a
symbolic link into the "normal" /usr/src/linux-2.2.16/include/linux
directory.  

(4) Unfortunately, I still get that weird assembler warning when compiling,
but I _am_ able to load the driver.  What does the assembler warning mean,
and how do I get rid of it?

(5) I need to know if my "fix" of redefining /usr/include/linux to point
into the kernel source code is okay, or if there's something more basic
that I'm missing.  We have a customer reporting the same problem... and
since RedHat 7 is the current release available in stores everywhere, we're
expecting a lot of calls on this issue.

(6) Another problem (?) I've encountered is that no matter what error value
I return in init_module(), I always get the same message displayed when I
try to load the driver:

drv.o: init_module: Device or resource busy
Hint: insmod errors can be caused by incorrect module parameters, including
invalid IO or IRQ parameters

Is this normal, i.e. to get the exact same message no matter what error
value is returned in init_module()?

Thank you very much for your time.