Kernel printk printing level

 

To determine the kernel print level and prink parameter print level, add the following code to the LED driver initialization code [and exit.

Each time the insmod and rmmod LED modules are used, different print results are obtained based on the print level settings:

1. Static int _ init s3c24xx_leds_init ()
2. {
3. Int ret;
4. Int minor = 0;
5.  
6. Printk (kern_emerg "1111111 kern_emerg \ n ");
7. Printk (kern_alert "2222 kern_alert \ n ");
8. Printk (kern_crit "3333333 kern_crit \ n ");
9. Printk (kern_err "44444444 kern_err \ n ");
10. Printk (kern_warning "55555 kern_warning \ n ");
11. Printk (kern_notice "66666 kern_notice \ n ");
12. Printk (kern_info "77777 kern_info \ n ");
13. Printk (kern_debug "888888 kern_debug \ n ");
14. Printk ("9999 no_fix \ n ");
15. ...
16. }

 

Operation:

Set the default print level when compiling the kernel source code at one time: [they are defined in kernel/printk. C]

Echo 8 4 1 7>/proc/sys/kernel/printk

 

8. kern_debug

# Echo 8 4 1 7>/proc/sys/kernel/printk

# Insmod myleds_new.ko

1111111 kern_emerg

2222 kern_alert

3333333 kern_crit

44444444 kern_err

55555 kern_warning

66666 kern_notice

77777 kern_info

888888Kern_debug

9999 no_fix

 

7. Default

# Cat/proc/sys/kernel/printk

#7 4 1 7

Print result:

111111 kern_emerg

2222 kern_alert

3333333 kern_crit

44444444 kern_err

55555 kern_warning

66666 kern_notice

77777 kern_info

9999 no_fix

 

6.

# Echo 6 4 1 7>/proc/sys/kernel/printk

# Insmod myleds_new.ko

1111111 kern_emerg

2222 kern_alert

3333333 kern_crit

44444444 kern_err

55555 kern_warning

66666 kern_notice

9999 no_fix

 

5.

# Echo 5 1 4 7>/proc/sys/kernel/printk

# Rmmod myleds_new.ko

1111111 kern_emerg

2222 kern_alert

3333333 kern_crit

44444444 kern_err

55555 kern_warning

9999 no_fix

 

4.

# Echo 4 4 1 7>/proc/sys/kernel/printk

# Insmod myleds_new.ko

1111111 kern_emerg

2222 kern_alert

3333333 kern_crit

44444444 kern_err

 

3.

# Echo 3 4 1 7>/proc/sys/kernel/printk

# Rmmod myleds_new.ko

1111111 kern_emerg

2222 kern_alert

3333333 kern_crit

 

2.

# Echo 2 4 1 7>/proc/sys/kernel/printk

# Insmod myleds_new.ko

1111111 kern_emerg

2222 kern_alert

 

1.

# Echo 1 4 1 7>/proc/sys/kernel/printk

# Insmod myleds_new.ko

1111111 kern_emerg

Analysis:

When you manually set the print level to 5, 4, 7, or above (restart will fail), the printing information of kern_warning and printk without formatting parameters will be printed.

Kern_debug has the lowest priority.

Kern_emerg has the highest priority.

Otherwise, recursive by series.

 

Suppose you want to print printfk without a fix by default,

Kernel/printk. c

# Define default_lele_loglevel (XX); XX> = 5

Assume that the kern_debug information is printed by default.

# Define default_lele_loglevel (XX); xx = 8

// For the preceding operation, Echo XX 4 1 7>/proc/sys/kernel/printk can be used once.

 

Source code reference:

Kernel/printk. c

1. /* Printk's without a loglevel use this ..*/
2. # Define default_message_loglevel 4/* kern_warning */
3.  
4. /* We show everything that is more important than this ..*/
5. # Define minimum_console_loglevel 1/* Minimum loglevel we let people use */
6. # Define default_console_loglevel 7/* anything more serious than kern_debug */
7.  
8. Declare_wait_queue_head (log_wait );
9.  
10. Int console_printk [4] = {
11. Default_console_loglevel,/* console_loglevel */
12. Default_message_loglevel,/* default_message_loglevel */
13. Minimum_console_loglevel,/* minimum_console_loglevel */
14. Default_console_loglevel,/* default_console_loglevel */
15. };
16. ...

Include/Linux/kernel. h

1. # Define kern_emerg "<0>"/* system is unusable */
2. # Define kern_alert "<1>"/* action must be taken immediately */
3. # Define kern_crit "<2>"/* critical conditions */
4. # Define kern_err "<3>"/* error conditions */
5. # Define kern_warning "<4>"/* warning conditions */
6. # Define kern_notice "<5>"/* normal but significant condition */
7. # Define kern_info "<6>"/* informational */
8. # Define kern_debug "<7>"/* debug-level messages */

Kernel printk printing level