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Old 10-10-2005, 12:31 PM   #1
Registered: Sep 2005
Posts: 53

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Using printk


Can any one say me how to use printk for printing from the kernel. Where did the printed messages will be? How to display that on the konsole

Old 10-10-2005, 03:07 PM   #2
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Registered: Jul 2004
Distribution: Ubuntu 7.04
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int printk(const char *fmt, ) works very much like int printf(const char *fmt, ), with one notable exception.

The first parameter to printk can be replaced with an integer value, which is called the log level. This decides where the message goes, which can be to the kernel's log book (a 16kb memory block; see dmesg), or to the console.

The levels normally range from 0 (emergency; system unusable) to 7 (debugging), and are controlled by the constants KERN_EMERG, KERN_ALERT, KERN_CRIT, KERN_ERR, KERN_WARNING, KERN_NOTICE, KERN_INFO and KERN_DEBUG.

The compile-time flag CON_ENABLED is used when compiling the printk function to enable logging to the console. If set, and a console driver is loaded, then any message printed over the value of console_loglevel will be write()n to the console driver. The syslog() system call changes the console loglevel, which is normally done from user space when debugging a module; the default value is 7.

long sys_syslog(int type, char *buf, int len)
type can be 6 (sets the loglevel to 1), 7 (sets the loglevel to 7) or 8 (sets the loglevel to len, which must be between 0 and 9. Returns 0; I think buf is ignored (otherwise set it to log_start+log_size, which I think are globals).


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