current->mm cannot be NULL (else the kernel would
oops all over the place, since it would be dereferencing
a NULL pointer to get at the processes memory).
Most likely, you are either trying to use this from
inside an interrupt (outside of the context of a task),
or you tried to compile a module and install it in an
SMP kernel, but you forgot to define __SMP__. You can
do the latter by adding -D__SMP__:
gcc -D__SMP__ ....
Don't feel too bad. I had this same problem too :-)
>
>user program obtains memory using malloc()
>
>addr = malloc(size);
>
>then passes this to a kernel module for translation to physical addr
>
>pgd = pgd_offset(current->mm, addr);
>pmd = pmd_offset(pgd, addr);
>pte = pte_offset(pmd, addr);
>
>if (pte_present(*pte))
> page = pte_page(*pte);
>
>i have seen that always the current->mm is NULL.
This should be correct. In 2.2.9 there is a character
driver (bttv???) that have a static function uvirt_to_phys.
You might snag it. I think it does what you want to do.
virt_to_phys, AFAICT, converts a kernel virtual address
to a physical. There is a difference between kernel
virtual and user virtual, since with the latter, you have
to do a page table lookup. Make sure you mlock the buffer, as
it might not be present when you go to write/read on it ...
Hope this is helpful.
Regards,
Christopher Boyd
--- Chrisotopher W. Boyd <cboyd@pobox.com> Web Page: http://www.pobox.com/~cboyd/ University of Texas at Austin PGP Key ID 0x18037059 ICQ UIN# 13185314 My views don't necessarily reflect those of anybody else.
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