D(7)

NAME
D - DTrace scripting language overview

SYNOPSIS
provider: module: function: name [ [ / predicate /] {action}]

DESCRIPTION
D is the dtrace(1) scripting language. This manual provides a brief reference of the D language and scripting.

This manual page serves as a short reference of the language. Refer to books listed in SEE ALSO for a complete reference.

MACRO VARIABLES
Name | Description
$1, $2, $3, ... | Macro arguments
$egid | Effective group ID (getegid(2))
$euid | Effective user ID (geteuid(2))
$gid | Real group ID (getgid(2))
$pid | Process ID (getpid(2))
$pgid | Process group ID (getpgrp(2))
$ppid | Parent process ID (getppid(2))
$sid | Session ID (getsid(2))
$target | Target process ID of the process
specified via the -p flag or created via the -c flag.
$uid | Real user ID (getuid(2))

The macro arguments correspond to the command-line operands. They expand to an integer, identifier, or string depending on the context. Prepending a macro argument with an extra dollar sign (‘$’) forces string expansion.

For example,
    dtrace -n 'syscall::fstatat: /execname == $$1/ {}' -- ls

uses $$1 instead of $1 to expand to a string instead rather than to a global variable identifier.

PROBE'S DESCRIPTION
A probe's description consists of four elements:
    provider:module:function:name

The exact meaning of module, function, and name depends on provider.

USER-DEFINED VARIABLE TYPES
Type | Syntax
global | variable_name
aggregate | @variable_name
thread-local | self->variable_name
clause-local | this->variable_name

Tips:
-   Always use the variable type with the smallest scope to minimize processing overhead.
-   Use aggregate variables instead of global variables when possible. Aggregate variables are multi-CPU safe in contrast to global variables.

BUILT-IN VARIABLES

  Probe Arguments

args[]
    The array of typed probe arguments.

arg0, ..., arg9
    The untyped probe arguments represented as 64-bit unsigned integers. Only the first ten arguments are available this way.

  Probe Information

epid
    The enabled probe ID which uniquely identifies an enabled probe. An enabled probe is defined by its probe ID, its predicates, and its actions.

id  The probe ID which uniquely identifies a probe available to DTrace.

probeprov
    The provider in the probe's description (provider:module:function:name)

probemod
    The module in the probe's description (provider:module:function:name)

probefunc
    The function in the probe's description (provider:module:function:name)

probename
    The name in the probe's description (provider:module:function:name)

  Process Information

execargs
    The process arguments. Effectively, ‘curthread->td_proc->p_args’.

execname
    The name of the current process. Effectively, ‘curthread->td_proc->p_comm’.

gid The group ID of the current process.

pid The process ID of the current process.

ppid
    The parent process ID of the current process.

uid The user ID of the current process.

  Thread Information

uregs[]
    The saved user-mode register values.

cpu The ID of the current CPU.

stackdepth
    The kernel stack frame depth.

ustackdepth
    The userspace counterpart of stackdepth.

tid The thread ID. Depending on the context, this can be either the ID of a kernel thread or a thread in a user process.

errno
    The errno(2) value of the last system call performed by the current thread.

curlwpsinfo
    A pointer to the lwpsinfo_t representation of the current thread. Refer to dtrace_proc(4) for more details.

curpsinfo
    A pointer to the psinfo_t representation of the current process. Refer to dtrace_proc(4) for more details.

curthread
    A pointer to the thread struct that is currently on-CPU. E.g., ‘curthread->td_name’ returns the thread name. The <sys/proc.h> header documents all members of struct thread.

caller
    The address of the kernel thread instruction at the time of execution of the current probe.

ucaller
    The userspace counterpart of caller.

  Timestamps

timestamp
    The number of nanoseconds since boot. Suitable for calculating relative time differences of elapsed time and latency.

vtimestamp
    The number of nanoseconds that the current thread spent on CPU. The counter is not increased during handling of a fired DTrace probe. Suitable for calculating relative time differences of on-CPU time.

walltimestamp
    The number of nanoseconds since the Epoch (1970-01-01T00+00:00). Suitable for timestamping logs.

BUILT-IN FUNCTIONS

string strchr(string s, char c)
    Return a substring of s starting at the first occurrence of c in s. Return NULL if c does not occur in s.

    For example,
        strchr("abc", 'b');

    returns ‘bc’ and
        strchr("abc", 'd');

    returns NULL.

string strjoin(string s1, string s2)
    Return a string resulting from concatenating s1 and s2.

    For example,
        strjoin("abc", "def")

    returns ‘abcdef’.

string strrchr(string s, char c)
    Return a substring of s starting at the last occurrence of c in s. Similar to strchr().

string strstr(string haystack, string needle)
    Return a substring of haystack starting at the first occurrence of needle. Return NULL if needle is not a substring of haystack.

    For example,
        strstr("abc1bc2", "bc")

    returns ‘bc1bc2’ and
        strstr("abc", "xy")

    returns NULL.

string strtok(string s, string separators)
    Tokenize s with separators.

    For example,
        strtok("abcdefg", "xyzd")

    returns ‘abc’.

size_t strlen(string s)
    Return the length of string s.

string substr(string s, int position, [int length])
    Return a substring of string s starting at position. The substring will be at most length-long. If length is not specified, use the rest of the string. If position is greater than the size of s, return an empty string.

    For example,
        substr("abcd", 2)

    returns ‘cd’,
        substr("abcd", 2, 1)

    returns ‘c’, and
        substr("abcd", 99)

    returns an empty string.

  Aggregation Functions
avg(value)
    Average
count()
    Count
llquantize(value, factor, low, high, nsteps)
    Log-linear quantization
lquantize(value, low, high, nsteps)
    Linear quantization
max(value)
    Maximum
min(value)
    Minimum
quantize(value)
    Power-of-two frequency distribution
stddev(value)
    Standard deviation
sum(value)
    Sum

  Kernel Destructive Functions
By default, dtrace(1) does not permit the use of destructive actions.

breakpoint()
    Set a kernel breakpoint and transfer control to the ddb(4) kernel debugger.

chill(nanoseconds)
    Spin on the CPU for the specified number of nanoseconds.

panic()
    Panic the kernel.

FILES

/usr/share/dtrace
    DTrace scripts shipped with FreeBSD base.

SEE ALSO
awk(1), dtrace(1), tracing(7) The illumos Dynamic Tracing Guide, 2008, https://illumos.org/books/dtrace/. Brendan Gregg, Jim Mauro, DTrace: Dynamic Tracing in Oracle Solaris, Mac OS X and FreeBSD, Prentice Hall, 2011, https://www.brendangregg.com/dtracebook/. George Neville-Neil, Jonathan Anderson, Graeme Jenkinson, Brian Kidney, Domagoj Stolfa, Arun Thomas, Robert N. M. Watson, Cambridge, United Kingdom, August 2018, University of Cambridge Computer Laboratory, OpenDTrace Specification version 1.0, https://www.cl.cam.ac.uk/techreports/UCAM-CL-TR-924.pdf.

HISTORY
This manual page first appeared in FreeBSD 15.0.

AUTHORS
-nosplit This manual page was written by Mateusz Piotrowski <0mp@FreeBSD.org>.

BUGS
The cwd variable which typically provides the current working directory is not supported on FreeBSD at the moment.

Macro variables $projid and $taskid are always 0 on FreeBSD.

Functions ddi_pathname(), getmajor(), and getminor() are not supported on FreeBSD.