Review Saranya

8/6/2019 Review Saranya

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PERFORMANCE REVIEW

By

G. Saranya


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Outline

Linux Booting Process

Compiling Linux Kernel

Linux Device Driver Storage Concepts

IPC Mechanisms

Memory Management


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Linux Booting Process


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Getthe Linuxlatest kernel code

eg:linux-x.y.z.tar.bz

To extracttar(.tar.bz) image

#tar- xjvflinux-x.y.z.tar.bz - C /usr/src

#cd /usr/src Conf igure kernel

$make menuconfig

Compile kernel

Start compiling to create a compressed kernelimage,enter

$make


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Start compiling to kernel modules

$make modules

Install Kernel modules(become a rootuser,use su

command).$su

#make modules_install

Install Kernel

#make install


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Create an initrd image

type the following command atthe shell prompt

#mkinitrd -o initrd.img-x.y.z x.y.z

Modify Grub configuartion file -/boot/grub/menu.lst

#vi /boot/grub/menu.lst


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save and close the file.

title ubuntu(x.y.z.fcl4.i686)

root (hd0,0)

kernel /boot/vmlinuz root=/dev/hdb1 r0initrd /boot/initrd.img-x.y.z

savedefault

boot


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try outupdate-grub command to update the lines for each

kernelin /boot/grub/menu.lst file.

update-grub

Reboot computer and update in to your kernel

#reboot


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Device driver

A device driveris a program that a computer's operating

system uses to control a particular hardware device thatisattached to a computer.


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Kernel and User Space Communication


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Kernel and User Space Communication


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Module

The modules can be dynamically linked to the running kernelby insmod cmd and can be unlinked by rmmod cmd.


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Device Driver Types

Char Device

Block Device

Network Device


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Character Device

Character device is one that can be accessed as a stream of

bytes(like a file).


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Major and Minor Numbers

Major numberidentifies the driver associated with the device

Minor numberidentifies a particularinstance of a device.


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Sample Code

static int eg_ioctl (structinode*,struct file *,unsigned

int,unsigned long) { }

static int eg_open (structinode*,struct file *) { }

static int eg_release (structinode *,struct file *) { }

struct file_operations={

.read:eg_read,

.write:eg_write,

.open:eg_open,

.release:eg_release,

.ioctl:eg_ioctl,

};


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Char Device Registration and Release

function to register a char device driveris with

register_chrdev(unsigned int major, const char name,struct

file_operations *fops);

function to remove your device(s) from the system is

unregister_chrdev(unsigned int major, const char *name);


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Debugging Techniques

Debugging by Printk

Using /proc Filesystem

gdb,kgdb


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Debugging by Printk

To add your own debug message to the kernel, you can place a

"printk()" in the kernel code.


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Debugging by Printk

When using printk a loglevel gets defined.

printk(KERN_WARNING "Help\n");. Valid loglevelsare:defined in the header

KERN_EMERG,KERN_ALERT,KERN_CRIT,KERN_ERR, KERN_WARNING,KERN_NOTICE, KERN_INFO,KERN_DEBUG

Changing the console_loglevel can be done by proc filesystem.

# cat /proc/sys/kernel/printk

7 4 1 7

So the easiest way to change the loglevelis simply:

#echo 8 > /proc/sys/kernel/printk


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Proc Filesystem

proc f ilesystem is a virtual filesystem thatis used to export

kernel related information to the user space.


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Proc Filesystem

To create a virtual file in the /proc filesystem, use the

create_proc_entry function. Struct proc_dir_entry

create_proc_entry( const char *name, mode_t mode, struct

proc_dir_entry *parent );

To remove_proc_entry function void remove_proc_entry(

const char *name, struct proc_dir_entry *parent );


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Proc Filesystem

The Wr ite Callback function:

You can write to a proc entry (from the userto the

kernel) by using a write_proc function.

int (*write_proc) ( struct file *filp, const

char __user *buff, unsigned long len, void *data );

The Read Callback function:

You can read data from a proc entry (from the kernelto

the user) by using the read_proc function.

int (*read_proc) ( char *page, char **start,

off_t off, int count, int *eof, void *data );


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Proc Filesystem

Reading from /proc using cat command

eg: #cat /proc/sys/net/ipv4/ip_forward

Writing to /proc using echo cmd

eg: #echo "1" > /proc/sys/net/ipv4/ip_forward

#cat /proc/sys/net/ipv4/ip_forward


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Interrupt Handling

Interrupt Handler

Top and Bottom Halves Task lets and Workqueues


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Storage Concepts

DAS

NAS

SAN RAID


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IPC Mechanisms

Pipes

Message Queues

Shared Memory

Synchronization Techniques:

semaphores and mutexes spin locks


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Memory Management

Virtual Memory

Paging

API's:

vmalloc

kmalloc get_free_pages

memset


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Current Event

implementing a code using msgqueues and threads


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Need to be Covered

Netlink

TCP/IP Socket-programming


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Documents

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