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 |
| $uid | Real user ID (getuid(2)) |
The macro arguments correspond to the command-line operands. They expand to an integer, identifier, or string depending on the context. Prepending a macro argument with an extra dollar sign (‘$’) 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 and 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, and Robert N. M. Watson, University of Cambridge Computer Laboratory, OpenDTrace Specification version 1.0, Cambridge, United Kingdom, August 2018, https://www.cl.cam.ac.uk/techreports/UCAM-CL-TR-924.pdf.
HISTORY
This manual page first appeared in FreeBSD 15.0.
AUTHORS
This manual page was written by Mateusz Piotrowski ⟨[email protected]⟩.
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.