whats the significance of __ and "<0>"

dogslayer · 03-13-2006, 02:32 PM

cud any one plz tell me the significance of __ in a #define statement eg #define __KERNEL__ or #define __LINUX_MAC_H and so on.....whats the point of __ prefix in these statements? Is it some kind of programing standard???

And also what does the following statement do?
#define KERN_EMERG "<0>"
#define KERN_ALERT "<1>" and so on.......
here what does "<0>" and "<1>"signify?????
for what purpose is "< >" keyword used???

Hko · 03-13-2006, 04:26 PM

Quote:

Originally Posted by dogslayer

cud any one plz tell me the significance of __ in a #define statement eg #define __KERNEL__ or #define __LINUX_MAC_H and so on.....whats the point of __ prefix in these statements? Is it some kind of programing standard???

Yes, it's done by convention. When you include the kernel-header in your program you can be sure not to accidentally #define a macro that already 'taken'. Just remember not to use macro-names that start with __.

Quote:

Originally Posted by dogslayer

And also what does the following statement do?
#define KERN_EMERG "<0>"
#define KERN_ALERT "<1>" and so on.......
here what does "<0>" and "<1>"signify?????
for what purpose is "< >" keyword used???

I have no idea.
Maybe they're just printed (logged) literally?

paulsm4 · 03-13-2006, 05:09 PM

KERN_EMERG, and friends are used to specify the error log level in stuff you write using "printk". For example:

Code:

printk (KERN_NOTICE "setup_cdev(devno= 0x%x, major= %d, minor= %d, err= %d)...\n", 
  devno, fbdev2_info.major, minor, err);