RFC - pr_info,warn,dbg,err and PREFIX

[Joe Perches <joe@perches.com>]

A number of local #defines or functions exist which merely
add a constant prefix to printks.  Perhaps it is better
to have these functions standardized.

Thoughts?

A method to prefix pr_info messages with an arbitrary prefix
(#define PREFIX "foo") could be:

--------------------------------

#define PRINTK_stringify_1(x) #x
#define PRINTK_stringify(x) PRINTK_stringify_1(x)

#define PRINTK_USEPREFIX (strcmp(PRINTK_stringify(PREFIX), "PREFIX"))

#define PRINTK_PREFIX(PREFIX) \
({const char *p = PRINTK_USEPREFIX(PREFIX) ? PRINTK_stringify(PREFIX) + 1 : ""; p;})

#define PRINTK_PREFIXLEN(PREFIX) \
({int len = PRINTK_USEPREFIX(PREFIX) ? strlen(PRINTK_stringify(PREFIX)) - 2 : 0; len;})

#define PRINTK_PREFIXSEPARATOR(PREFIX) \
({const char *p = PRINTK_USEPREFIX(PREFIX) ? ": " : ""; p;})

#define PRINTK_PREFIXFMT "%.*s%s"
#define PRINTK_PREFIXARG PRINTK_PREFIXLEN(PREFIX), PRINTK_PREFIX(PREFIX), PRINTK_PREFIXSEPARATOR(PREFIX)

#define pr_info(fmt, arg...) printk(KERN_INFO PRINTK_PREFIXFMT fmt, PRINTK_PREFIXARG, ##arg)
#define pr_warn(fmt, arg...) printk(KERN_WARNING PRINTK_PREFIXFMT fmt, PRINTK_PREFIXARG, ##arg)
#define pr_err(fmt, arg...) printk(KERN_ERR PRINTK_PREFIXFMT fmt, PRINTK_PREFIXARG, ##arg)

---------------

With a #define of PREFIX:
	#define PREFIX "abc"
	pr_info("msg\n")
output:
	<6>abc: msg

without a #define of PREFIX:
	pr_info("msg\n")
output:
	<6>msg

---------------