Nikolaus Rath <[email protected]> writes:
> On 02/05/2011 04:36 PM, Brice Goglin wrote:
>>> Is there an equivalent function to virt_to_page (and virt_to_phys) that
>>> works with userspace pointers? Or do I have to manually walk through the
>>> page tables? In the later case, are there any examples of this kind of
>>> search that I could use as a basis?
>>>
>>
>> You probably want get_user_pages() (or get_user_pages_fast()).
>
> Thanks for the pointer, that already helped a lot!
>
> I would, however, prefer a more primitive function that just gives me
> the struct page without locking it. And if the page is swapped out, I'd
> rather get a NULL pointer than having a page frame allocated. Is there
> anything like that?
After studying the source for get_user_pages(), I believe the following
should do what I want:
vma = find_extend_vma(current->mm, (unsigned long) data.vi_buf);
if(vma == NULL) {
err("find_extend_vma failed for VI.");
}
acq_dev->vi_pg = follow_page(vma, (unsigned long) data.vi_buf, 0);
if(acq_dev->vi_pg == NULL) {
err("follow_page failed for VI.");
}
Unfortunately, I'm getting into trouble at link time when using these
functions:
MODPOST 1 modules
WARNING: "follow_page" [/home/nikratio/control/acq196_hostdrv/acq200_hostdrv.ko] undefined!
WARNING: "find_extend_vma" [/home/nikratio/control/acq196_hostdrv/acq200_hostdrv.ko] undefined!
Can they only be used in the kernel itself, but not in kernel modules?
Thanks,
-Nikolaus
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