Sharing memory between kernel and user space
Brian D. McGrew
kernel space.
Let's say I have a common structure;
struct counter {
u_long interrupt_counts;
bool saw_interupt;
}
And I need to be able to modify these elements from both the kernel and
user space. What is the best way to allocate this??? I've tried
several methods including __get_free_pages, alloc_pages, vmalloc and so
on; and thus far, I'm just confused myself.
Can someone help me out here with a quick example of some sort???
Thanks,
:b!
Brian D. McGrew { br...@visionpro.com || br...@doubledimension.com }
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H. Peter Anvin
By author: "Brian D. McGrew" <br...@visionpro.com>
In newsgroup: linux.dev.kernel
>
> I have a question about the best way to share memory between user and
> kernel space.
>
In general, allocate the memory in kernel space (via get_free_page et
al), and make accessible to userspace via mmap on a device node.
-hpa
Brian D. McGrew
trouble you for a snippet of code to do that? I've tried every
combination I can think of.
Thank you,
:b!
Brian D. McGrew { br...@visionpro.com || br...@doubledimension.com }
--
> This is a test. This is only a test!
Had this been an actual emergency, you would have been
told to cancel this test and seek professional assistance!
-----Original Message-----
From: linux-ker...@vger.kernel.org
[mailto:linux-ker...@vger.kernel.org] On Behalf Of H. Peter Anvin
Sent: Tuesday, May 30, 2006 3:46 PM
To: linux-...@vger.kernel.org
Subject: Re: Sharing memory between kernel and user space
Followup to:
<14CFC56C96D8554AA0B8...@chicken.machinevisionproducts.
Christopher Friesen
> I'm using the 2.6.16.16 kernel. Is there any chance that I could
> trouble you for a snippet of code to do that? I've tried every
> combination I can think of.
You could try looking at how /dev/kmem does it.
Also, be aware that the size of "unsigned long" can vary between the
kernel and userspace if you have a 64-bit machine.
Chris
Brian D. McGrew
user space I try and mmap the memory.
The mmap is successful but then when I go back and try and read from
that location I get a 'can't read of address 0xbf7c8000 (which is the
address the kernel gave me back).
???
:b!
Brian D. McGrew { br...@visionpro.com || br...@doubledimension.com }
--
> This is a test. This is only a test!
Had this been an actual emergency, you would have been
told to cancel this test and seek professional assistance!
-----Original Message-----
From: linux-ker...@vger.kernel.org
[mailto:linux-ker...@vger.kernel.org] On Behalf Of H. Peter Anvin
Sent: Tuesday, May 30, 2006 3:46 PM
To: linux-...@vger.kernel.org
Subject: Re: Sharing memory between kernel and user space
Followup to:
<14CFC56C96D8554AA0B8...@chicken.machinevisionproducts.
com>
By author: "Brian D. McGrew" <br...@visionpro.com>
In newsgroup: linux.dev.kernel
>
> I have a question about the best way to share memory between user and
> kernel space.
>
In general, allocate the memory in kernel space (via get_free_page et
al), and make accessible to userspace via mmap on a device node.
-hpa
Jonathan Corbet
> trouble you for a snippet of code to do that? I've tried every
> combination I can think of.
The memory mapping chapter of LDD3 (http://lwn.net/Kernel/LDD3/) has a
pretty thorough description of how to share both kernel- and user-space
memory, with code examples.
jon