Documentation/trace/tracepoints.rst

16 A tracepoint placed in code provides a hook to call a function (probe)
17 that you can provide at runtime. A tracepoint can be "on" (a probe is
18 connected to it) or "off" (no probe is attached). When a tracepoint is
22 and adds a data structure in a separate section).  When a tracepoint
23 is "on", the function you provide is called each time the tracepoint
26 the tracepoint site).
30 which prototypes are described in a tracepoint declaration placed in a
40 - A tracepoint definition, placed in a header file.
41 - The tracepoint statement, in C code.
43 In order to use tracepoints, you should include linux/tracepoint.h.
53 	#include <linux/tracepoint.h>
85     function called by this tracepoint.
93 Connecting a function (probe) to a tracepoint is done by providing a
94 probe (function to call) for the specific tracepoint through
103 The tracepoint mechanism supports inserting multiple instances of the
104 same tracepoint, but a single definition must be made of a given
105 tracepoint name over all the kernel to make sure no type conflict will
117 If the tracepoint has to be used in kernel modules, an
121 If you need to do a bit of work for a tracepoint parameter, and
122 that work is only used for the tracepoint, that work can be encapsulated
135 All trace_<tracepoint>() calls have a matching trace_<tracepoint>_enabled()
136 function defined that returns true if the tracepoint is enabled and
137 false otherwise. The trace_<tracepoint>() should always be within the
138 block of the if (trace_<tracepoint>_enabled()) to prevent races between
139 the tracepoint being enabled and the check being seen.
141 The advantage of using the trace_<tracepoint>_enabled() is that it uses
142 the static_key of the tracepoint to allow the if statement to be implemented
150 If you require calling a tracepoint from a header file, it is not
151 recommended to call one directly or to use the trace_<tracepoint>_enabled()
154 well as the trace_<tracepoint>() is not that small of an inline
156 include tracepoint-defs.h and use tracepoint_enabled().