Re: How to write a kernel patch to expose a kernel-level function?

hzmonte@xxxxxxxxxxx wrote:
http://altlinux.org/index.php?module=sisyphus&package=cpuid 

Thx but no, it is not what I want.  This package displays the CPU spec
like who the manufacturer is and what model it is, etc.  What I want,
and what smp_processor_id() returns, is which logical processor the
calling thread is running on.  Is CPU0, CPU1, or CPU2, for example?

In both cases you need a piece of kernel code, a patch or a kernel module 

So my question is How to write a kernel patch?  Is it as simple as
adding a statement in the source like "EXPORT TO USER-SPACE
smp_processor_id"?  Any pointer to how to do it?  Ay more concrete
guideline?



The kernel runs in a private address space compared to
the user code. You cannot use the kernel internal
address for anything in user code, and it's not allowed
to even look at the contents of the address.

For details, get the books

  Understanding the Linux Kernel

and

  Linux Device Drivers

and read and understand them before attempting own
kernel coding.

Both books are published by O'Reilly.

IMHO, creating a /proc file is the easiest way of
reading the identifier.

A different story is that the result is probably
invalid at the time your user code gets it. There
is no guarantee that the process is running on
the reported processor anymore.

--

Tauno Voipio
tauno voipio (at) iki fi

.

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