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From: Nikolaus Rath <>
Subject: Re: virt_to_page for userspace pointers
Date: Mon, 14 Feb 2011 17:46:30 -0500	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

Nikolaus Rath <> 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

  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?



 »Time flies like an arrow, fruit flies like a Banana.«

  PGP fingerprint: 5B93 61F8 4EA2 E279 ABF6  02CF A9AD B7F8 AE4E 425C

  parent reply	other threads:[~2011-02-14 23:08 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2011-02-03 20:50 Reversing a memory mapping? Nikolaus Rath
2011-02-05 21:04 ` virt_to_page for userspace pointers (was: Reversing a memory mapping?) Nikolaus Rath
2011-02-05 21:36   ` virt_to_page for userspace pointers Brice Goglin
2011-02-13 20:24     ` Nikolaus Rath
2011-02-13 20:37       ` Brice Goglin
2011-02-13 21:56         ` Nikolaus Rath
2011-02-13 22:06           ` Alan Cox
2011-02-13 22:11             ` Nikolaus Rath
2011-02-14 22:46       ` Nikolaus Rath [this message]
2011-07-26 12:03         ` Alexey Skidanov

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