STAPEX(3stap)															     STAPEX(3stap)

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 listings mode.

	      % stap -l 'kernel.function("*")'

       To list the probeable functions and local variables in the kernel, use another listings mode.

	      % stap -L 'kernel.function("*")'

MORE EXAMPLES

       The directory to find more examples can be found in the stappaths(7) manual page, and online at http://sourceware.org/systemtap/examples/

SEE ALSO

       stap(1)
       stapprobes(3stap)
       stappaths(7)

																     STAPEX(3stap)