1. User-Space-to-Kernel Interface
Chapter 3
Presenter: Mojtaba Malekpour
Professor: Dr. Seyed Vahid Azhari

2. Introduction Application User Mode Implementation Abstraction Detail
Kernel
Hardware

3. A Question How a user application use kernel info? Example:
How can find number of CPU clock in a C++ application?
How can access ARP table in a application?

4. Mechanisms Kernel Interfaces Socket Based Ioctl Kernel System Calls
Sending Signals
Upcall
Mmap

5. Kernel Interfaces Kernel Interfaces Procfs Sysfs Sysctl Configfs
Debugfs

6. Procfs Procfs Located in /proc
Originally designed to export all kind of process information
Current status of the process
All open file descriptors to the user space

7. Procfs and other purposes
Provide information about the running system
CPU information
Interrupts information
Available memory
Version of kernel
Information about
"idle devices“
"scsi devices“
"tty's".
Networking information
Arp table
Network statistics
Lists of used sockets

8. Practical! Example: ls proc/ cat /proc/version cat cpuinfo
cat filesystem
cat /proc/looks
cat /proc/net/dev
cat /proc/net/arp
cat /proc/net/route
cat /proc/net/tcp

9. Practical!
Example:
Exe Read.c

10. Sysfs Represent the device model Contains information about
Devices
Drivers
Buses
Use for device
Heavily structured
A lot of links between the individual directories

11. Sysfs kernel 2.6.23 it contains the following 9 top-level directories
sys/block/ all known block devices such as hda/ ram/ sda/
sys/bus/ all registered buses
device/ for all devices attached to that bus
driver/ for all drivers assigned with that bus.
sys/class/ each device type have a subdirectory: for example /printer or /sound
sys/device/ all devices known by the kernel, connected by the bus
sys/firmware/ files in this directory handle the firmware of some hardware
sys/fs/ files to control a file system
sys/kernel/ holds directories (mount points) for other filesystems
sys/module/ each kernel module loaded is represented with a directory.
sys/power/ files to handle the power state of some hardware

12. Practical Example: cat sys/ cat sys/class/ieee80211/phy0/macaddress
cat sys/class/net/wlan0/phy80211/macaddress
cat sys/class/power_supply/BAT1/energy_now
cat class/block/sda1/size

13. Configfs The configfs is some what the counterpart of the sysfs
Full control by user
Difference between configfs and sysfs
Configfs all objects are created from user space with a call to mkdir
The kernel responds with creating the attributes (files)
Can be read and written by the user
Use rmdir to deleted
life cycle of a configfs object is fully controlled by user space

14. Debugfs To use RAM based file system
Especially designed for debugging purposes
Obtain some debugging information from their kernel code
Provide set or get a single value
Developer is also allowed to write its own read/write functions

15. Sysctl Designed to configure kernel parameters at run time
Heavily used by the Linux networking subsystem
It can be used to configure some core kernel parameters
Represented as files in /proc/sys/*
The values can be accessed by
cat
echo: set: only persists as long as the kernel is runningbut gets lost as soon as the machine is rebooted
sysctl

16. Sysctl Example cat /proc/sys/net/ipv4/ip_default_ttl
cat /proc/sys/net/ipv4/ipfrag_high_thresh

17. add a new file How can add a new file in /proc Exe jif.c
Show number of clock
cat /prog/jif

18. Ioctl Documentation/ioctl-number.txt
ifconfig command uses ioctl to communicate with the kernel
#include <sys/ioctl.h>
int ioctl(int d, int request, ...);

19. Practical
Exe iotcl.c
Turn on and off capslook

20. Netlink Sockets
Especially designed for the communication between the kernel space and the user space
Full-duplex communication link between the Linux kernel and user space

21. Tanks for your attention