Editing
Paper
(section)
From Linix VServer
Jump to navigation
Jump to search
Warning:
You are not logged in. Your IP address will be publicly visible if you make any edits. If you
log in
or
create an account
, your edits will be attributed to your username, along with other benefits.
Anti-spam check. Do
not
fill this in!
=== Kernel and User Space === In Linux and similar Operating Systems, User and Kernel Space is separated, and address space is divided into two parts. Kernel space is where the kernel code resides, and user space is where the user programs live. Of course, a given user program can't write to kernel memory or to another program's memory area. Unfortunately, this is also the case for kernel code. Kernel code can't write to user space either. What does this mean? Well, when a given hardware driver wants to write data bytes to a program in user memory, it can't do it directly, but rather it must use specific kernel functions instead. Also, when parameters are passed by address to a kernel function, the kernel function can not read the parameters directly. It must use other kernel functions to read each byte of the parameters. Of course, there are some helpers which do the transfer to and from user space. <pre> copy_to_user(void *to, const void *from, long n); copy_from_user(void *to, const void *from, long n); </pre> get_user() and put_user() Get or put the given byte, word, or long from or to user memory. This is a macro, and it relies on the type of the argument to determine the number of bytes to transfer.
Summary:
Please note that all contributions to Linix VServer may be edited, altered, or removed by other contributors. If you do not want your writing to be edited mercilessly, then do not submit it here.
You are also promising us that you wrote this yourself, or copied it from a public domain or similar free resource (see
Linix VServer:Copyrights
for details).
Do not submit copyrighted work without permission!
Cancel
Editing help
(opens in new window)
Navigation menu
Page actions
Page
Discussion
Read
Edit
History
Page actions
Page
Discussion
More
Tools
Personal tools
Not logged in
Talk
Contributions
Create account
Log in
About
Overview
Paper
News
Developers
Donations
Search
Getting Started
Downloads
FAQs
Documentation
Support
Participate
How to participate
Report a Bug
Communicate
Teams/Projects
Hall of Fame
Resources
Archives
Recent Wiki Changes
Pastebin
Related Projects
VServer Hosting
Happy VServer Users
Tools
What links here
Related changes
Special pages
Page information