strace

trace system call and signals

linux multipath

load driver:

1. chkconfig boot.multipath on

2.chkconfig multipathd on

3. /etc/init.d/boot.multipath start

4. /etc/init.d/multipathd start

query multipath status:

multipath -l

stop multipath service:

1. /etc/init.d/boot.multipath stop

2. /etc/init.d/multipathd stop

/etc/scsi_id.config:

the info related to multipath

how to decide multipath:

the sds with the same uuid are combined into a dm

scsi_id -g -s /block/sda can get uuid

for red hat:

default multipath is not triggered

modify /etc/multipath.conf :

comment blacklist

remove dm:

multipath -F

multipath stop

iometer

In windows : GUI

In linux:  agent

Use windows iometer GUI to connect to linux iometer agent to get io information 

run iometer agent in linux:

./dynamo -i windows_gui_ip  -m linux_agent_ip

change log level & enable sysrq

echo 9 > /proc/sysrq-trigger

echo 1 >  /proc/sys/kernel/sysrq

alt + sysrq  +  p :  show cpu info

alt + sysrq  + t : show current task list

alt  + sysrq  + m : show memory info

redirect output from serial port

1. modify bios:

   (1)Change BIOS settings /Server/Serial Console Features/BIOS Redirection Port to

       [Serial port 1 or 2]

   (2)change direct to modem 

2.  modify /boot/grub/menu.lst for suse

     modify /boot/grub/grub.conf  for red hat

    console=ttyS0, 115200,vt100

3. modify /ect/inittab

    c0:2345:respawn:/sbin/agetty ttyS0 19200 vt100    

4. modify  /etc/securetty

    ttyS0

How to Scan new LUNs on Linux with QLogic driver

http://bash.cyberciti.biz/diskadmin/rescan-linux-scsi-bus/

line number

nl: number lines

cpu info

cat /proc/cpuinfo

interrupt context

1. can not relinquish cpu by calling sleep functions

GFP_KERNEL

allocate memory:

1. GFP_KERNEL:

    kmalloc() is allowed to go to sleep and wait for pages to get freed up.

2.GFP_ATOMIC:

   Used by interrupt context code to get hold of memory. In this mode, kmalloc() is not allowed to    sleep-wait for free pages, so the probability of successful allocation with GFP_ATOMIC is lower    than with GFP_KERNEL.

df

show disk space

ex: df  -h:

Filesystem            Size  Used Avail Use% Mounted on

/dev/hda3             9.9G  7.0G  2.4G  75% /

udev                  8.0G  132K  8.0G   1% /dev

objdump

show assembly of program:
ex:

objdump -D test.o

fsck

check file system

tethereal

ex:

tethereal -i eth7 host 192.168.5.41 -V > out

AF_UNSPEC

ai_family = AF_UNSPEC;
AF_UNSPEC: for IPv4 & IPv6

accept

#include
#include
int accept(int s, struct sockaddr *addr, socklen_t *addrlen);


return:
If successful, accept() returns a non-negative integer, which is a descriptor of the accepted socket.

chkconfig

insserv

scsi_execute_req

int scsi_execute_req(struct scsi_device *sdev, const unsigned char *cmd,

                     int data_direction, void *buffer, unsigned bufflen,

                     struct scsi_sense_hdr *sshdr, int timeout, int retries)

scsi command code

include/scsi/scsi.h

READ_6   0x08

WRITE_6  0x0a

READ_10   0x28

WRITE_10  0x2a

READ_16   0x88

WRITE_16   0x8a

website about block driver

http://www.geocities.com/ravikiran_uvs/articles/

proc

read_proc

struct dentry *proc_lookup(struct inode * dir, struct dentry *dentry)

drivers/scsi/sd.c

the problem related to struct scsi_cmnd

struct scsi_cmnd

 /* These elements define the operation we are about to perform */

 #define MAX_COMMAND_SIZE        16

  unsigned char cmnd[MAX_COMMAND_SIZE];

sd_mod

remove sd_mod will delete /dev/sd*

struct scsi_sense_hdr

scsi_en.h

struct scsi_sense_hdr {         /* See SPC-3 section 4.5 */

          u8 response_code;       /* permit: 0x0, 0x70, 0x71, 0x72, 0x73 */

          u8 sense_key;

          u8 asc;

          u8 ascq;

          u8 byte4;

          u8 byte5;

          u8 byte6;

          u8 additional_length;   /* always 0 for fixed sense format */

  };

random number in driver

get_random_bytes():

ex:

unsigned char uuid[16];

get_random_bytes(uuid, sizeof (uuid));

type definition

struct block_device:

linux/fs.h

dev_t:

linux/types.h

struct page:

linux/mm_types.h

struct gendisk:

linux/genhd.h

struct request_queue:

linux/blkdev.h

wait_queue_head_t:

linux/wait.h

spinlock_t:

linux/spinlock_types.h

struct semaphore:

linux/semaphore.h

dmesg

/var/log/messages

dhclient

get new ip

dm

 //The request function that just remaps the bio built up by dm_merge_bvec

static int dm_request(struct request_queue *q, struct bio *bio)

       call  __split_bio

// Split the bio into several clones.

static int __split_bio(struct mapped_device *md, struct bio *bio)

       call  __clone_and_map with parameter ci

       ( ci.sector_count= bio_sectors(bio)  )

static int __clone_and_map(struct clone_info *ci)

call  split_bvec

sector_t

typedef unsigned long sector_t;

mkfs

create filesystem

ex:

mkfs -v  /dev/hda3

struct bio

struct bio:

struct block_device  *bi_bdev;

struct bio_vec          *bi_io_vec;     /* the actual vec list */

unsigned short          bi_vcnt;        /* how many bio_vec's */

unsigned int            bi_size;        /* residual I/O count */

struct bio_vec:

  struct page     *bv_page;

  unsigned int    bv_len;

  unsigned int    bv_offset;

do I/O without request queue

three steps:

1. define a make_request function

ex:

static int sbull_make_request(request_queue_t *q, struct bio *bio) 

     in the make_request function, transfer bio & call bio_endio(struct bio *bio, unsigned int bytes, int error) to signal completion 

2. use blk_alloc_queue(GFP_KERNEL) to allocate a queue 

3. call blk_queue_make_request(request_queue_t *queue, make_request_fn *func)

when make_request function return non-zero:

the bio is submitted again. Hence, we can modify bi_bdev & starting sector to redirect bio to another device

split bio into multiple chunks:

bio_split

kthread

show kthread list

ps  -ef

interrupt

prevent interrupt entering critical section 

method 1:

 local_irq_disable();  /* Disable Interrupts in local CPU */

  /* ... Critical Section ...  */

  local_irq_enable();   /* Enable Interrupts in local CPU */

method 2:

unsigned long flags;

Point A:

  local_irq_save(flags);     /* Disable Interrupts */

  /* ... Critical Section ... */

  local_irq_restore(flags);  /* Restore state to what it was at point A */

spinlock & mutex

spinlock ensures only one thread can enter critical section

spinlock example:

#include

spinlock_t mylock = SPIN_LOCK_UNLOCKED; /* Initialize */

/* Acquire the spinlock. This is inexpensive if there

 * is no one inside the critical section. In the face of

 * contention, spinlock() has to busy-wait.

 */

spin_lock(&mylock);

/* ... Critical Section code ... */

spin_unlock(&mylock); /* Release the lock */

spinlock will busy-wait,  mutex will sleep

mutex example:

#include

/* Statically declare a mutex. To dynamically

   create a mutex, use mutex_init() */

static DEFINE_MUTEX(mymutex);

/* Acquire the mutex. This is inexpensive if there

 * is no one inside the critical section. In the face of

 * contention, mutex_lock() puts the calling thread to sleep.

 */

mutex_lock(&mymutex);

/* ... Critical Section code ... */

mutex_unlock(&mymutex);      /* Release the mutex */

linux開機設定

GRUB:

/boot/grub/grub.conf  or /boot/grub/menu.lst

grub.conf example:

default 0  #Boot the 2.6.23 kernel by default

timeout 5  #5 second to alter boot order or parameters

title kernel 2.6.23     #Boot Option 1

  #The boot image resides in the first partition of the first disk

  #under the /boot/ directory and is named vmlinuz-2.6.23. 'ro'

  #indicates that the root partition should be mounted read-only.

  kernel (hd0,0)/boot/vmlinuz-2.6.23 ro root=/dev/hda1

  #Look under section "Freeing initrd memory:387k freed"

  initrd (hd0,0)/boot/initrd

#...

LILO:

/etc/lilo.conf

compile driver

method 1:

Makefile:

      obj-m+=test.ko

make -C /usr/src/kernels/x.y.z/  M=`pwd`  modules

kernel source module

compile module:

1. cd  /usr/src/linux-x.y.z/

2. make modules

install module

1.  make modules_install

the generated module( ko)  is stored in /lib/modules/x.y.z/kernel/ 

patch

A patch is a text file containing source code differences between a development tree and the original snapshot from which the developer started work

apply patch:

ex:  if x.y.z-mm2.bz2 is a patch, go to the directory of linux source

      bzip2  -dc  ../x.y.z-mm2.bz2 |  patch -p1

create patch:

ex:

diff  -Nur   /path/originalKernal/    /path/newKernel  >  change changes.patch

global code browser

install:

http://www.gnu.org/software/global/global.html

run:

1. go to directory of source code

2. gtags

3. htags  ./codeTrace/

the generated html is in ./codeTrace/

find command

find  .  -name  "test.txt"

find text.txt under current directory

linux module location

/lib/modules/2.6.18-92.el5/kernel/drivers

HZ & jiffies

HZ是用來定義每一秒有幾次timer interrupts(time tick)

jiffies:

the number of time ticks since kernel start

ex:

unsigned long timeout=jiffies+ 3*HZ;

//  the time after 3 second

time_after(jiffies, timeout)

convert from jiffies to seconds

divide by HZ

time related methods:

time_after:  parameter is time tick 

time_before: parameter is time tick

schedule_timeout: parameter is time tick  

only schedule_timeout will give up processor

wait_event_timeout:

msleep: parameter is milliseconds

timer example( do something in the future):

#include

struct timer_list my_timer;

init_timer(&my_timer);            /* Also see setup_timer() */

my_timer.expire = jiffies + n*HZ; /* n is the timeout in number

                                     of seconds */

my_timer.function = timer_func;   /* Function to execute

                                     after n seconds */

my_timer.data = func_parameter;   /* Parameter to be passed

                                     to timer_func */

add_timer(&my_timer);             /* Start the timer */

smp

smp(多cpu)

rpm

remove rpm:

rpm -e test

query info about specific rpm

ex: 

rpm -q  test

rpm for red hat and cent os

Because red hat & cent os are related , we can get rpm for ret hat from rpm for cent os 

init network

開機網路設定:

/etc/sysconfig/network/

ifcfg-lo

ifcfg-eth0

blk_queue_make_request

 void blk_queue_make_request (request_queue_t * q, make_request_fn * mfn);

define an alternate make_request function for a device

ARGUMENTS

q

the request queue for the device to be affected

mfn

the alternate make_request function

linux driver command

lsmod 

顯示目前已經載入的模組清單

insmod 

load module into kernel

ex: insmod hello.ko

rmmod:

remove module

modprobe:

like insmod,  but also install dependent modules

(the module dependency is stored in /lib/modules/x.y.z/modules.dep)

modprobe -r:

remove module

modinfo:

show module info

linux kernel version

red hat enterprise linux 4 update 4

core_2.6.9-42.EL_i686  &  core_2.6.9-42.ELsmp_i686,  core_2.6.9-42.ELsmp_x86_64,  core_2.6.9-42.EL_x86_64

red hat enterprise linux 5 update 1

core_2.6.18-53.el5_i686  &  core_2.6.18-53.el5_x86_64

red hat enterprise linux 5 update 2

core_2.6.18-92.el5_i686  &  core_2.6.18-92.el5_x86_64

suse linux enterprise server 9

core_2.6.5-7.244-smp_x86_64

suse linux enterprise server 10 

core_2.6.16.21-0.8-smp_i686  & core_2.6.16.21-0.8-smp_x86_64

suse linux enterprise server 10 sp1

core_2.6.16.46-0.12-smp_x86_64  

suse linux enterprise server 10 sp2

core_2.6.16.60-0.21-default_i686   ,core_2.6.16.60-0.21-default_x86_64

LVM

(1) 實體磁碟 --> PV( physical volume)

1. change id to 8e

ex:

   (a) fdisk  /dev/hda

   (b) p

         show information of hda

   (c)  t -->  1 --> 8e

        modify partition 1 's id to 8e

   (d) w

         alter partition table

   (e) partprobe

         let kernel read newest partition table

2. create pv  

   (a)pvscan:

        show information of pv

   (b)pvcreate 

x11

設定開機進入X11

edit /etc/inittab

id:3:initdefault:

設定開機進入文字介面:

edit /etc/inittab

id:5:initdefault:

x11 problem:

method 1:

edit /etc/X11/xorg.conf

defaultdepth =8

iscsi-initiator-utils

start:

/etc/init.d/iscsi start

discovery lun

iscsiadm -m discovery -t sendtargets -p 192.168.5.122

192.168.5.122 is lun's ip

/etc/init.d/iscsi restart

connect to the lun 192.168.5.122,  there is a new disk , sdd( use fdisk -l to show)

Format & mount

fdisk /dev/sdd

mke2fs -j -m 0 -O dir_index /dev/sdd1

mkdir /mnt/iscsi

mount /dev/sdd1 /mnt/iscsi

yum

設定search path

/etc/yum.conf:

[main]

cachedir=/var/cache/yum

debuglevel=2

logfile=/var/log/yum.log

pkgpolicy=newest

distroverpkg=redhat-release

tolerant=1

exactarch=1

bsoletes=1

# PUT YOUR REPOS HERE OR IN separate files named file.repo

# in /etc/yum.repos.d

#[base]

#name=Red Hat Linux $releasever - $basearch - Base

#baseurl=http://mirror.dulug.duke.edu/pub/yum-repository/redhat/$releasever/$basearch/

#[updates]

#name=Red Hat Linux $releasever - Updates

#baseurl=http://mirror.dulug.duke.edu/pub/yum-repository/redhat/updates/$releasever/

[dag]

name=Dag RPM Repository for Red Hat Enterprise Linux

baseurl=http://apt.sw.be/redhat/el4/en/i386/dag/

gpgcheck=1

enabled=1

[freshrpms]

name=FreshRPMs

baseurl=http://dag.freshrpms.net/redhat/el4/en/i386/dag/

gpgcheck=1

enabled=1

[rpmfind]

name=RPMFind.net

baseurl=http://rpmfind.net/linux/dag/redhat/el4/en/i386/dag/

gpgcheck=1

enabled=1

[pdx.edu]

name=PDX.edu

baseurl=http://mirrors.cat.pdx.edu/dag/redhat/el4/en/i386/dag/

gpgcheck=1

enabled=1

Open-iSCSI

install  2.0-869.2

make

start:

rcopen-iscsi start

discovery:

iscsiadm -m discovery  -t st -p 192.168.4.123 

update chap information:

iscsiadm -m node -p 192.168.4.123 --op=update \   

--name=node.session.auth.authmethod --value=CHAP

iscsiadm -m node -p 192.168.4.123 --op=update \     --name=node.session.auth.username --value=andy

iscsiadm -m node -p 192.168.4.123 --op=update \     --name=node.session.auth.password --value=1234

login:

iscsiadm -m node -p 192.168.4.123 -l

or

iscsiadm -m node -r nodeId -l

the disk added after login is in /dev/sd*

delete record:

iscsiadm -m node -o delete

or

rm -rf /etc/iscsi/nodes/*

logout 

iscsiadm -m node -U all

daemon:

/etc/init.d/iscsi

increase iscsi ping time to prevent a lot of io error messages

node.conn[0].timeo.noop_out_interval = X

ode.conn[0].timeo.noop_out_timeout = X

open_by_devnum

struct block_device *open_by_devnum(dev_t dev, unsigned mode)

struct bio

struct bio {

    sector_t             bi_sector;  //  beginning sector

    struct bio          *bi_next;

    struct block_device *bi_bdev;

    unsigned short       bi_vcnt;

    unsigned short       bi_idx;  //  an offset into the bi_io_vec array

    struct bio_vec      *bi_io_vec;

    ...

};

generic_make_request

void generic_make_request (struct bio * bio);

make I/O requests of block devices. 

It is passed a &struct bio, which describes the I/O that needs to be done.

the success/failure status of the request, along with notification of completion,

is delivered asynchronously through the bio->bi_end_io function

The caller of generic_make_request must make sure that bi_io_vec are set to describe the memory buffer, and that bi_dev and bi_sector are set to describe the device address, and the bi_end_io and optionally bi_private are set to describe how completion notification should be signaled.

MKDEV

dev_t  a=  MKDEV( int major, int minor )

get major & minor

MIJOR( a )  &  MINOR( a)

struct gendisk

int major

int  first_minor

        first minor number associated with disk

int  minors

       range of minor numbers associated with disk. It control disk's max partition number 

char  disk_name[32]

struct gendisk *alloc_disk(int minors)

allocate gendisk 

system_utsname

add_disk

void add_disk(struct gendisk *disk);

add the disk to the list of active disks

the disk is active now

ioctl communication between kernel and user space

use block device as example:

user space program:

struct Test_info  test_info;

ioctl ( fd,  ADD,  &test_info);

driver:

1. define a function to deal with ioctl operation & assign this function 

    to struct block_device_operations

     ex: 

     define a function  test_ioctl

     struct block_device_operations test_ops;

     test_ops.ioctl = test_ioctl       

2.  define the function to deal with ioctl operation

     it will receive two important parameters.

     One is command, the other is argument.

     From out example,  the command received is ADD, the parameter received is &test_info

3.  copy data from user space to kernel space

     use copy_from_user

copy_from_user

copy_from_user(void *to, const void *from, long n);

to: point to kernel-space address

from :  point to user-space address

function stat

int  stat(const char *restrict path, struct stat *restrict buf);

get file status

struct stat {

dev_t st_dev;

ino_t st_ino;

mode_t st_mode;

nlink_t st_nlink;

uid_t st_uid;

gid_t st_gid;

dev_t st_rdev;

off_t st_size;

time_t st_atime;

time_t st_mtime;

time_t st_ctime;

blksize_t st_blksize;

blkcnt_t st_blocks;

mode_t st_attr;

}; 

structure sg_io_hdr_t

getopt

getopt(int argc, char * const argv[], const char *optstring)

get option character from command line argument list

ex:getopt(argc, argv, “bf:")

     options are b & f

strdup

char *  strdup(const char *s1); 

allocates sufficient memory for a copy of the string s1, 

does the copy, and returns a pointer to it.

strstr

strstr(const char *s1, const char *s2);

locate a substring in a string

struct utsname & uname

struct utsname

hold information returned by the uname function

uname(struct utsname *name)

store information identifying the current system in the structure pointed to by name.

vnc

start:

vncserver