D Literal Strings

The D language supports literal strings. DTrace represents strings as an array of characters terminated by a null byte. The visible part of the string varies in length depending on the location of the null byte. DTrace stores each string in a fixed-size array to ensure that each probe traces a consistent amount of data. Strings cannot exceed the length of the predefined string limit. The limit can be modified in your D program or on the dtrace command line by tuning the strsize option. Refer to Chapter 16, Options and Tunables, in Solaris Dynamic Tracing Guide for more information on tunable DTrace options. The default string limit is 256 bytes.

The D language provides an explicit string type rather than using the type char * to refer to strings. See Chapter 6, Strings, in Solaris Dynamic Tracing Guide for more information about D literal strings.

Example 3–2 Using D Literal Strings With The trace() Function

# cat string.d

#!/usr/sbin/dtrace -s

fbt::bdev_strategy:entry
{
   trace(execname);
   trace(" is initiating a disk I/O\n");
}

The \n symbol at the end of the literal string produces a new line. To run this script, enter the following command:

# dtrace -s string.d
dtrace: script 'string.d' matched 1 probes
CPU     ID                     FUNCTION:NAME
  0   9215               bdev_strategy:entry   bash is initiating a disk I/O

  0   9215               bdev_strategy:entry   vi is initiating a disk I/O

  0   9215               bdev_strategy:entry   vi is initiating a disk I/O

  0   9215               bdev_strategy:entry   sched is initiating a disk I/O

^C

The -q option of the dtrace command only records the actions that are explicitly stated in the script or command line invocation. This option suppresses the default output that the dtrace command normally produces.

# dtrace -q -s string.d
ls is initiating a disk I/O
cat is initiating a disk I/O
fsflush is initiating a disk I/O
vi is initiating a disk I/O
^C