Reposting as I just had another problem pointed out to me, in that I
left variable-assign in the initial list of probes and forgot to add in
the new variable-set. Thanks Michael.
alan.
Alan Hargreaves wrote:
> As promised based on Darren's suggestion, I have updated the spec and
> included it below.
>
> Changes
> -------
> 1. The variable-assign probe has been renamed to variable-set.
> 2. Added the variable-unset probe
> 3. Corrected a typo in the probe list.
>
> In the light of adding variable-unset, it seems to m e that the name
> variable set is more consistent than variable-assign.
>
The sh provider makes available probes that can be used to observe the
behaviour of bourne shell scripts.
Probes
------
The sh provider makes available the following probes as exports:
builtin-entry Fires on entry to a shell builtin command.
builtin-return Fires on return from a shell builtin command.
command-entry Fires when the shell execs an external command.
command-return Fires on return from an external command.
function-entry Fires on entry into a shell function.
function-return Pires on return from a shell function.
line Fires before commands on a particular line of code are
executed.
subshell-entry Fires when the shell forks a subshell.
subshell-return Fires on return from a forked subshell.
script-start Fires before any commands in a script are executed.
script-done Fires on script exit.
variable-set Fires on assignment to a variable.
variable-unset Fires when a variable is unset.
The use of non-empty module or function names in a sh* probe is
undefined at this time.
Arguments
---------
builtin-entry,
command-entry,
function-entry
char * args[0] Script Name
char * args[1] Builtin/Command/Function Name
int args[2] Line Number
int args[3] # Arguments
char ** args[4] Pointer to argument list
builtin-return,
command-return,
function-return
char * args[0] Script Name
char * args[1] Builtin/Command/Function Name
int args[2] Return Value
subshell-entry
char * args[0] Script Name
pid_t args[1] Forked Process ID
subshell-return
char * args[0] Script Name
int args[1] Return Value
line
char * args[0] Script Name
int args[1] Line Number
script-start
char * args[0] Script Name
script-done
char * args[0] Script Name
int args[1] Exit Value
variable-set
char * args[0] Script Name
char * args[1] Variable Name
char * args[2] Value
variable-unset
char * args[0] Script Name
char * args[1] Variable Name
Examples
--------
1. Catching a variable assignment
Say we want to determine which line in the following script has
an assignment to WatchedVar:
#!/bin/sh
# starting script
WatchedVar=Value
unset WatchedVar
# ending script
We could use the following script
#!/usr/sbin/dtrace -s
#pragma D option quiet
sh$target:::line { self->line = arg1; }
sh$target:::variable-set /copyinstr(arg1) == "WatchedVar"/ {
printf("%d: %s=%s\n", self->line, copyinstr(arg1),
copyinstr(arg2))
}
sh$target:::variable-unset /copyinstr(arg1) == "WatchedVar"/ {
printf("%d: unset %s\n", self->line, copyinstr(arg1)); }
$ ./watch.d -c ./var.sh
4: WatchedVar=Value
2. Watching the time spent in functions
#!/usr/sbin/dtrace -s
#pragma D option quiet
sh$target:::function-entry { self->start = vtimestamp }
sh$target:::function-return {
@[copyinstr(arg1)] = quantize(vtimestamp - self->start)
}
Similar for the other entry/return probes, with the exception
of subshell as the probe name is unavailable.
3. Wasted time using external functions instead of builtins
This script is copied from the DTrace toolkit. It's function
and how it works should be relatively self explanatory.
#!/usr/sbin/dtrace -Zs
/*
* sh_wasted.d - measure Bourne shell elapsed times for "wasted" commands.
* Written for the sh DTrace provider.
*
* $Id: sh_wasted.d 25 2007-09-12 09:51:58Z brendan $
*
* USAGE: sh_wasted.d { -p PID | -c cmd } # hit Ctrl-C to end
*
* This script measures "wasted" commands - those which are called
externally
* but are in fact builtins to the shell. Ever seen a script which calls
* /usr/bin/echo needlessly? This script measures that cost.
*
* FIELDS:
* FILE Filename of the shell or shellscript
* NAME Name of call
* TIME Total elapsed time for calls (us)
*
* IDEA: Mike Shapiro
*
* Filename and call names are printed if available.
*
* COPYRIGHT: Copyright (c) 2007 Brendan Gregg.
*
* CDDL HEADER START
*
* The contents of this file are subject to the terms of the
* Common Development and Distribution License, Version 1.0 only
* (the "License"). You may not use this file except in compliance
* with the License.
*
* You can obtain a copy of the license at Docs/cddl1.txt
* or http://www.opensolaris.org/os/licensing.
* See the License for the specific language governing permissions
* and limitations under the License.
*
* CDDL HEADER END
*
* 09-Sep-2007 Brendan Gregg Created this.
*/
#pragma D option quiet
dtrace:::BEGIN
{
isbuiltin["echo"] = 1;
isbuiltin["test"] = 1;
/* add builtins here */
printf("Tracing... Hit Ctrl-C to end.\n");
self->start = timestamp;
}
sh$target:::command-entry
{
self->command = timestamp;
}
sh$target:::command-return
{
this->elapsed = timestamp - self->command;
this->path = copyinstr(arg1);
this->cmd = basename(this->path);
}
sh$target:::command-return
/self->command && !isbuiltin[this->cmd]/
{
@types_cmd[basename(copyinstr(arg0)), this->path] =
sum(this->elapsed);
self->command = 0;
}
sh$target:::command-return
/self->command/
{
@types_wasted[basename(copyinstr(arg0)), this->path] =
sum(this->elapsed);
self->command = 0;
}
proc:::exit
/pid == $target/
{
exit(0);
}
dtrace:::END
{
this->elapsed = (timestamp - self->start) / 1000;
printf("Script duration: %d us\n", this->elapsed);
normalize(@types_cmd, 1000);
printf("\nExternal command elapsed times,\n");
printf(" %-30s %-22s %8s\n", "FILE", "NAME", "TIME(us)");
printa(" %-30s %-22s %...@8d\n", @types_cmd);
normalize(@types_wasted, 1000);
printf("\nWasted command elapsed times,\n");
printf(" %-30s %-22s %8s\n", "FILE", "NAME", "TIME(us)");
printa(" %-30s %-22s %...@8d\n", @types_wasted);
}
Stability
---------
Element Name Class Data Class
------------------------------------------
Provider Uncommited Uncommited
Module Private Private
Function Private Private
Name Uncommited Uncommited
Arguments Uncommited Uncommited
------------------------------------------
--
Alan Hargreaves - http://blogs.sun.com/tpenta
Staff Engineer (Kernel/VOSJEC/Performance)
Systems Technical Support Centre
Sun Microsystems
