stapex

STAPEX(5)							    STAPEX(5)



NAME
       stapex - systemtap examples



LANGUAGE BASICS
       These  examples	give  a	 feel  for basic systemtap syntax and control
       structures.

	      global odds, evens

	      probe begin {
		# "no" and "ne" are local integers
		for (i=0; i<10; i++) {
		  if (i % 2) odds [no++] = i
		  else evens [ne++] = i
		}
		delete odds[2]
		delete evens[3]
		exit ()
	      }

	      probe end {
		foreach (x+ in odds) {
		  printf ("odds[%d] = %d0, x, odds[x])
		}
		foreach (x in evens-) {
		  printf ("evens[%d] = %d0, x, evens[x])
		}
	      }
       This prints:
	      odds[1] = 1
	      odds[3] = 5
	      odds[4] = 7
	      odds[5] = 9
	      evens[5] = 8
	      evens[4] = 6
	      evens[2] = 2
	      evens[1] = 0
       Note that all variables types are inferred, and that  all  locals  and
       globals are automatically initialized.


       This script prints the primes between 0 and 49.
	      function isprime (x) {
		if (x < 2) return 0
		for (i=2; i<x; i++) {
		  if (x % i == 0) return 0
		  if (i * i > x) break
		}
		return 1
	      }
	      probe begin {
		for (i=0; i<50; i++)
		  if (isprime (i)) printf("%d0, i)
		exit()
	      }


       This script demonstrates recursive functions.
	      function fibonacci(i) {
		if (i < 1) error ("bad number")
		if (i == 1) return 1
		if (i == 2) return 2
		return fibonacci (i-1) + fibonacci (i-2)
	      }
	      probe begin {
		printf ("11th fibonacci number: %d0, fibonacci (11))
		exit ()
	      }
       Any  larger  number may exceed the MAXACTION or MAXNESTING limits, and
       result in an error.



PROBING
       To trace entry and exit from a function, use a pair of probes:
	      probe kernel.function("sys_mkdir") { println ("enter") }
	      probe kernel.function("sys_mkdir").return { println ("exit") }

       To list the probeable functions in the kernel, use the  last-pass  op-
       tion to the translator.	That output needs to be filtered because each
       inlined function instance is listed separately.
	      % stap -p2 -e 'probe kernel.function("*") {}' | sort | uniq


SEE ALSO
       /usr/doc/systemtap*/examples stap(1) stapprobes(5) stapfuncs(5)




Red Hat				  2009-04-20			    STAPEX(5)