[SOLVED] Questions on linux kernel

nakul.k1 · 07-20-2010, 08:18 PM

Hi all

i have few question relating to linux kernel memory here are the questions

1) Can Kernel space access user space memory yes or no ?
if no what happens when kernel space tries to access user space memory

2) Can Device memory(character device/chipset on the hardware board) be
mapped to user space ?

Cheers
NRK

paulsm4 · 07-21-2010, 01:11 PM

Hi -

Quote:

1) Can Kernel space access user space memory yes or no ?

A: Yes

Quote:

2) Can Device memory(character device/chipset on the hardware board) be
mapped to user space?

A: Yes
See "mmap()"

Here are a couple of good links:
http://tldp.org/LDP/tlk/mm/memory.html

http://people.ee.ethz.ch/~arkeller/l...ace_howto.html

I understand that Robert Love has come out with a new edition of his (Most Excellent!) book on Linux kernel internals, which you might be interested in:

http://www.amazon.com/Linux-Kernel-D...dp/0672329468/

'Hope that helps .. PSM

nakul.k1 · 07-22-2010, 10:32 AM

Thank you paul

1) I wanted to know can kernel space access user space pointer yes or no ?
if no then what happen when kernel tries to access user space pointer.

2) so you say in kernel if i need some memory from user space
then this function kmalloc(1024,GFP_USER); would work fine yes or no ?

Aquarius_Girl · 08-09-2010, 07:30 AM

Quote:

Originally Posted by nakul.k1

2) so you say in kernel if i need some memory from user space
then this function kmalloc(1024,GFP_USER); would work fine yes or no ?

Read the following manual carefully.
Kmalloc allocates only in kernel-space.
http://www.fiveanddime.net/man-pages/kmalloc.9.html

Moreover I didn't understand why would anyone want to allocate user space memory from kernel space ? In what kind of cases is this required ?

nakul.k1 · 08-09-2010, 09:25 AM

Thanks anisha

it was of great help from your end
that link you sent me clearly explains the Allocating and freeing dynamic kernel memory.

Nakul

Aquarius_Girl · 08-09-2010, 10:39 AM

You are most welcome