dtrace discuss - May 2006 - Reading external files with dtrace

I''d like to be able to dynamically read external configuration files
within a dtrace script.  I know dtrace allows inclusion of C header files but
only at the preprocessing stage.

What we need to do is dynamically enable/disable probes based on current
application settings.  I''d rather not have a bunch of independant
scripts running and being started and killed whenever the settings change.  I
believe that if we can read a configuration file, we can use those settings
within a predicate to enable/disable specific probes.  Problem is, I
don''t know how to directly read a file or otherwise affect a running
dtrace script on the fly.

Any help, insight or tricks would be greatly appreciated.

Thanks,

Stacy Maydew
 
 
This message posted from opensolaris.org

You could have something like:

BEGIN
{
	int a_variable_this_is = 0;
}

/* turn on change watch */
syscall::open*:entry
/stringof(copyinstr(arg0)) == "/tmp/settings_have_changed_on"/
{
	a_variable_this_is = 1;
}

/* turn off change watch */
syscall::open*:entry
/stringof(copyinstr(arg0)) == "/tmp/settings_have_changed_off"/
{
	a_variable_this_is = 0;
}

<some provider>::<some probefunc>:<some point>
/a_variable_this_is == 1/
{
	/* do this action if a_variable_this_is == 1 */
}

  So by touching /tmp/settings_have_changed_on you''d turn on watching
  extra probes and turn them off by touching /tmp/settings_have_changed_off

  Mind you the
''<provider>::<probefunc>:<point>'' would
always be enabled but the
  action wouldn''t be taken.

   Usual disclaimer applies, I haven''t tried this out..

Sean.
.
Stacy Maydew stated:
< I''d like to be able to dynamically read external configuration
files within a dtrace script.  I know dtrace allows inclusion of C header files
but only at the preprocessing stage.
< 
< What we need to do is dynamically enable/disable probes based on current
application settings.  I''d rather not have a bunch of independant
scripts running and being started and killed whenever the settings change.  I
believe that if we can read a configuration file, we can use those settings
within a predicate to enable/disable specific probes.  Problem is, I
don''t know how to directly read a file or otherwise affect a running
dtrace script on the fly.
< 
< Any help, insight or tricks would be greatly appreciated.
< 
< Thanks,
< 
< Stacy Maydew
<  
<  
< This message posted from opensolaris.org
< _______________________________________________
< dtrace-discuss mailing list
< dtrace-discuss at opensolaris.org

-- 
Sean.
.

Oops.  slight change, take the declaration of int a_variable_this_is outside
 the BEGIN clause.

 Works if I ''echo >
/tmp/settings_have_changed_on|settings_have_changed_off''

Regards,
Sean.
.

Sean McGrath - Sun Microsystems Ireland stated:
< 
<   You could have something like:
< 
< BEGIN
< {
< 	int a_variable_this_is = 0;
< }
< 
< /* turn on change watch */
< syscall::open*:entry
< /stringof(copyinstr(arg0)) == "/tmp/settings_have_changed_on"/
< {
< 	a_variable_this_is = 1;
< }
< 
< /* turn off change watch */
< syscall::open*:entry
< /stringof(copyinstr(arg0)) == "/tmp/settings_have_changed_off"/
< {
< 	a_variable_this_is = 0;
< }
< 
< <some provider>::<some probefunc>:<some point>
< /a_variable_this_is == 1/
< {
< 	/* do this action if a_variable_this_is == 1 */
< }
< 
<   So by touching /tmp/settings_have_changed_on you''d turn on
watching
<   extra probes and turn them off by touching /tmp/settings_have_changed_off
< 
<   Mind you the
''<provider>::<probefunc>:<point>'' would
always be enabled but the
<   action wouldn''t be taken.
< 
<    Usual disclaimer applies, I haven''t tried this out..
< 
< Sean.
< .
< Stacy Maydew stated:
< < I''d like to be able to dynamically read external
configuration files within a dtrace script.  I know dtrace allows inclusion of C
header files but only at the preprocessing stage.
< < 
< < What we need to do is dynamically enable/disable probes based on
current application settings.  I''d rather not have a bunch of
independant scripts running and being started and killed whenever the settings
change.  I believe that if we can read a configuration file, we can use those
settings within a predicate to enable/disable specific probes.  Problem is, I
don''t know how to directly read a file or otherwise affect a running
dtrace script on the fly.
< < 
< < Any help, insight or tricks would be greatly appreciated.
< < 
< < Thanks,
< < 
< < Stacy Maydew
< <  
< <  
< < This message posted from opensolaris.org
< < _______________________________________________
< < dtrace-discuss mailing list
< < dtrace-discuss at opensolaris.org
< 
< -- 
< Sean.
< .
< _______________________________________________
< dtrace-discuss mailing list
< dtrace-discuss at opensolaris.org

-- 
Sean.
.
-------------- next part --------------
int a_variable_this_is;

BEGIN
{   
        a_variable_this_is = 0;
}   
    
/* turn on change watch */
syscall::open*:entry
/stringof(copyinstr(arg0)) == "/tmp/settings_have_changed_on"/
{   
        a_variable_this_is = 1;
	printf("Turning on change watch\n");
}   
    
/* turn off change watch */
syscall::open*:entry
/stringof(copyinstr(arg0)) == "/tmp/settings_have_changed_off"/
{   
        a_variable_this_is = 0;
	printf("Turning off change watch\n");
}   
    
syscall::read*:entry
/a_variable_this_is == 1 && execname == "firefox-bin"/
{   
        printf(" got ya !\n");
}