Provided by: liblttng-ust-dev_2.10.5-1_amd64 bug

NAME

       lttng-ust - LTTng user space tracing

SYNOPSIS

       #include <lttng/tracepoint.h>

       #define TRACEPOINT_ENUM(prov_name, enum_name, mappings)
       #define TRACEPOINT_EVENT(prov_name, t_name, args, fields)
       #define TRACEPOINT_EVENT_CLASS(prov_name, class_name, args, fields)
       #define TRACEPOINT_EVENT_INSTANCE(prov_name, class_name, t_name, args)
       #define TRACEPOINT_LOGLEVEL(prov_name, t_name, level)
       #define ctf_array(int_type, field_name, expr, count)
       #define ctf_array_nowrite(int_type, field_name, expr, count)
       #define ctf_array_hex(int_type, field_name, expr, count)
       #define ctf_array_nowrite_hex(int_type, field_name, expr, count)
       #define ctf_array_network(int_type, field_name, expr, count)
       #define ctf_array_network_nowrite(int_type, field_name, expr, count)
       #define ctf_array_network_hex(int_type, field_name, expr, count)
       #define ctf_array_network_nowrite_hex(int_type, field_name, expr, count)
       #define ctf_array_text(char, field_name, expr, count)
       #define ctf_array_text_nowrite(char, field_name, expr, count)
       #define ctf_enum(prov_name, enum_name, int_type, field_name, expr)
       #define ctf_enum_nowrite(prov_name, enum_name, int_type, field_name,
                                expr)
       #define ctf_enum_value(label, value)
       #define ctf_enum_range(label, start, end)
       #define ctf_float(float_type, field_name, expr)
       #define ctf_float_nowrite(float_type, field_name, expr)
       #define ctf_integer(int_type, field_name, expr)
       #define ctf_integer_hex(int_type, field_name, expr)
       #define ctf_integer_network(int_type, field_name, expr)
       #define ctf_integer_network_hex(int_type, field_name, expr)
       #define ctf_integer_nowrite(int_type, field_name, expr)
       #define ctf_sequence(int_type, field_name, expr, len_type, len_expr)
       #define ctf_sequence_nowrite(int_type, field_name, expr, len_type,
                                    len_expr)
       #define ctf_sequence_hex(int_type, field_name, expr, len_type,
                                len_expr)
       #define ctf_sequence_nowrite_hex(int_type, field_name, expr, len_type,
                                        len_expr)
       #define ctf_sequence_network(int_type, field_name, expr, len_type,
                                    len_expr)
       #define ctf_sequence_network_nowrite(int_type, field_name, expr,
                                            len_type, len_expr)
       #define ctf_sequence_network_hex(int_type, field_name, expr, len_type,
                                        len_expr)
       #define ctf_sequence_network_nowrite_hex(int_type, field_name, expr,
                                                len_type, len_expr)
       #define ctf_sequence_text(char, field_name, expr, len_type, len_expr)
       #define ctf_sequence_text_nowrite(char, field_name, expr, len_type,
                                         len_expr)
       #define ctf_string(field_name, expr)
       #define ctf_string_nowrite(field_name, expr)
       #define do_tracepoint(prov_name, t_name, ...)
       #define tracepoint(prov_name, t_name, ...)
       #define tracepoint_enabled(prov_name, t_name)

       Link with -llttng-ust -ldl, following this man page.

DESCRIPTION

       The Linux Trace Toolkit: next generation <http://lttng.org/> is an open source software
       package used for correlated tracing of the Linux kernel, user applications, and user
       libraries.

       LTTng-UST is the user space tracing component of the LTTng project. It is a port to user
       space of the low-overhead tracing capabilities of the LTTng Linux kernel tracer. The
       liblttng-ust library is used to trace user applications and libraries.

           Note
           This man page is about the liblttng-ust library. The LTTng-UST project also provides
           Java and Python packages to trace applications written in those languages. How to
           instrument and trace Java and Python applications is documented in the online LTTng
           documentation <http://lttng.org/docs/>.

       There are three ways to use liblttng-ust:

       ·   Using the tracef(3) API, which is similar to printf(3).

       ·   Using the tracelog(3) API, which is tracef(3) with a log level parameter.

       ·   Defining your own tracepoints. See the Creating a tracepoint provider section below.

   Creating a tracepoint provider
       Creating a tracepoint provider is the first step of using liblttng-ust. The next steps
       are:

       ·   Instrumenting your application with tracepoint() calls

       ·   Building your application with LTTng-UST support, either statically or dynamically.

       A tracepoint provider is a compiled object containing the event probes corresponding to
       your custom tracepoint definitions. A tracepoint provider contains the code to get the
       size of an event and to serialize it, amongst other things.

       To create a tracepoint provider, start with the following tracepoint provider header
       template:

           #undef TRACEPOINT_PROVIDER
           #define TRACEPOINT_PROVIDER my_provider

           #undef TRACEPOINT_INCLUDE
           #define TRACEPOINT_INCLUDE "./tp.h"

           #if !defined(_TP_H) || defined(TRACEPOINT_HEADER_MULTI_READ)
           #define _TP_H

           #include <lttng/tracepoint.h>

           /*
            * TRACEPOINT_EVENT(), TRACEPOINT_EVENT_CLASS(),
            * TRACEPOINT_EVENT_INSTANCE(), TRACEPOINT_LOGLEVEL(),
            * and `TRACEPOINT_ENUM()` are used here.
            */

           #endif /* _TP_H */

           #include <lttng/tracepoint-event.h>

       In this template, the tracepoint provider is named my_provider (TRACEPOINT_PROVIDER
       definition). The file needs to bear the name of the TRACEPOINT_INCLUDE definition (tp.h in
       this case). Between #include <lttng/tracepoint.h> and #endif go the invocations of the
       TRACEPOINT_EVENT(), TRACEPOINT_EVENT_CLASS(), TRACEPOINT_EVENT_INSTANCE(),
       TRACEPOINT_LOGLEVEL(), and TRACEPOINT_ENUM() macros.

           Note
           You can avoid writing the prologue and epilogue boilerplate in the template file above
           by using the lttng-gen-tp(1) tool shipped with LTTng-UST.

       The tracepoint provider header file needs to be included in a source file which looks like
       this:

           #define TRACEPOINT_CREATE_PROBES

           #include "tp.h"

       Together, those two files (let’s call them tp.h and tp.c) form the tracepoint provider
       sources, ready to be compiled.

       You can create multiple tracepoint providers to be used in a single application, but each
       one must have its own header file.

       The TRACEPOINT_EVENT() usage section below shows how to use the TRACEPOINT_EVENT() macro
       to define the actual tracepoints in the tracepoint provider header file.

       See the EXAMPLE section below for a complete example.

   TRACEPOINT_EVENT() usage
       The TRACEPOINT_EVENT() macro is used in a template provider header file (see the Creating
       a tracepoint provider section above) to define LTTng-UST tracepoints.

       The TRACEPOINT_EVENT() usage template is as follows:

           TRACEPOINT_EVENT(
               /* Tracepoint provider name */
               my_provider,

               /* Tracepoint/event name */
               my_tracepoint,

               /* List of tracepoint arguments (input) */
               TP_ARGS(
                   ...
               ),

               /* List of fields of eventual event (output) */
               TP_FIELDS(
                   ...
               )
           )

       The TP_ARGS() macro contains the input arguments of the tracepoint. Those arguments can be
       used in the argument expressions of the output fields defined in TP_FIELDS().

       The format of the TP_ARGS() parameters is: C type, then argument name; repeat as needed,
       up to ten times. For example:

           TP_ARGS(
               int, my_int,
               const char *, my_string,
               FILE *, my_file,
               double, my_float,
               struct my_data *, my_data
           )

       The TP_FIELDS() macro contains the output fields of the tracepoint, that is, the actual
       data that can be recorded in the payload of an event emitted by this tracepoint.

       The TP_FIELDS() macro contains a list of ctf_*() macros NOT separated by commas. The
       available macros are documented in the Available ctf_*() field type macros section below.

   Available ctf_*() field type macros
       This section documents the available ctf_*() macros that can be inserted in the
       TP_FIELDS() macro of the TRACEPOINT_EVENT() macro.

       Standard integer, displayed in base 10:

           ctf_integer(int_type, field_name, expr)
           ctf_integer_nowrite(int_type, field_name, expr)

       Standard integer, displayed in base 16:

           ctf_integer_hex(int_type, field_name, expr)

       Integer in network byte order (big endian), displayed in base 10:

           ctf_integer_network(int_type, field_name, expr)

       Integer in network byte order, displayed in base 16:

           ctf_integer_network_hex(int_type, field_name, expr)

       Floating point number:

           ctf_float(float_type, field_name, expr)
           ctf_float_nowrite(float_type, field_name, expr)

       Null-terminated string:

           ctf_string(field_name, expr)
           ctf_string_nowrite(field_name, expr)

       Statically-sized array of integers (_hex versions displayed in hexadecimal, _network
       versions in network byte order):

           ctf_array(int_type, field_name, expr, count)
           ctf_array_nowrite(int_type, field_name, expr, count)
           ctf_array_hex(int_type, field_name, expr, count)
           ctf_array_nowrite_hex(int_type, field_name, expr, count)
           ctf_array_network(int_type, field_name, expr, count)
           ctf_array_network_nowrite(int_type, field_name, expr, count)
           ctf_array_network_hex(int_type, field_name, expr, count)
           ctf_array_network_nowrite_hex(int_type, field_name, expr, count)

       Statically-sized array, printed as text; no need to be null-terminated:

           ctf_array_text(char, field_name, expr, count)
           ctf_array_text_nowrite(char, field_name, expr, count)

       Dynamically-sized array of integers (_hex versions displayed in hexadecimal, _network
       versions in network byte order):

           ctf_sequence(int_type, field_name, expr, len_type, len_expr)
           ctf_sequence_nowrite(int_type, field_name, expr, len_type, len_expr)
           ctf_sequence_hex(int_type, field_name, expr, len_type, len_expr)
           ctf_sequence_nowrite_hex(int_type, field_name, expr, len_type,
                                    len_expr)
           ctf_sequence_network(int_type, field_name, expr, len_type, len_expr)
           ctf_sequence_network_nowrite(int_type, field_name, expr, len_type,
                                        len_expr)
           ctf_sequence_network_hex(int_type, field_name, expr, len_type,
                                    len_expr)
           ctf_sequence_network_nowrite_hex(int_type, field_name, expr,
                                            len_type, len_expr)

       Dynamically-sized array, displayed as text; no need to be null-terminated:

           ctf_sequence_text(char, field_name, expr, len_type, len_expr)
           ctf_sequence_text_nowrite(char, field_name, expr, len_type, len_expr)

       Enumeration. The enumeration field must be defined before using this macro with the
       TRACEPOINT_ENUM() macro. See the TRACEPOINT_ENUM() usage section for more information.

           ctf_enum(prov_name, enum_name, int_type, field_name, expr)
           ctf_enum_nowrite(prov_name, enum_name, int_type, field_name, expr)

       The parameters are:

       count
           Number of elements in array/sequence. This must be known at compile time.

       enum_name
           Name of an enumeration field previously defined with the TRACEPOINT_ENUM() macro. See
           the TRACEPOINT_ENUM() usage section for more information.

       expr
           C expression resulting in the field’s value. This expression can use one or more
           arguments passed to the tracepoint. The arguments of a given tracepoint are defined in
           the TP_ARGS() macro (see the Creating a tracepoint provider section above).

       field_name
           Event field name (C identifier syntax, NOT a literal string).

       float_type
           Float C type (float or double). The size of this type determines the size of the
           floating point number field.

       int_type
           Integer C type. The size of this type determines the size of the integer/enumeration
           field.

       len_expr
           C expression resulting in the sequence’s length. This expression can use one or more
           arguments passed to the tracepoint.

       len_type
           Unsigned integer C type of sequence’s length.

       prov_name
           Tracepoint provider name. This must be the same as the tracepoint provider name used
           in a previous field definition.

       The _nowrite versions omit themselves from the recorded trace, but are otherwise
       identical. Their primary purpose is to make some of the event context available to the
       event filters without having to commit the data to sub-buffers. See lttng-enable-event(1)
       to learn more about dynamic event filtering.

       See the EXAMPLE section below for a complete example.

   TRACEPOINT_ENUM() usage
       An enumeration field is a list of mappings between an integers, or a range of integers,
       and strings (sometimes called labels or enumerators). Enumeration fields can be used to
       have a more compact trace when the possible values for a field are limited.

       An enumeration field is defined with the TRACEPOINT_ENUM() macro:

           TRACEPOINT_ENUM(
               /* Tracepoint provider name */
               my_provider,

               /* Enumeration name (unique in the whole tracepoint provider) */
               my_enum,

               /* Enumeration mappings */
               TP_ENUM_VALUES(
                   ...
               )
           )

       TP_ENUM_VALUES() contains a list of enumeration mappings, NOT separated by commas. Two
       macros can be used in the TP_ENUM_VALUES(): ctf_enum_value() and ctf_enum_range().

       ctf_enum_value() is a single value mapping:

           ctf_enum_value(label, value)

       This macro maps the given label string to the value value.

       ctf_enum_range() is a range mapping:

           ctf_enum_range(label, start, end)

       This macro maps the given label string to the range of integers from start to end,
       inclusively. Range mappings may overlap, but the behaviour is implementation-defined: each
       trace reader handles overlapping ranges as it wishes.

       See the EXAMPLE section below for a complete example.

   TRACEPOINT_EVENT_CLASS() usage
       A tracepoint class is a class of tracepoints sharing the same field types and names. A
       tracepoint instance is one instance of such a declared tracepoint class, with its own
       event name.

       LTTng-UST creates one event serialization function per tracepoint class. Using
       TRACEPOINT_EVENT() creates one tracepoint class per tracepoint definition, whereas using
       TRACEPOINT_EVENT_CLASS() and TRACEPOINT_EVENT_INSTANCE() creates one tracepoint class, and
       one or more tracepoint instances of this class. In other words, many tracepoints can reuse
       the same serialization code. Reusing the same code, when possible, can reduce cache
       pollution, thus improve performance.

       The TRACEPOINT_EVENT_CLASS() macro accepts the same parameters as the TRACEPOINT_EVENT()
       macro, except that instead of an event name, its second parameter is the tracepoint class
       name:

           TRACEPOINT_EVENT_CLASS(
               /* Tracepoint provider name */
               my_provider,

               /* Tracepoint class name */
               my_tracepoint_class,

               /* List of tracepoint arguments (input) */
               TP_ARGS(
                   ...
               ),

               /* List of fields of eventual event (output) */
               TP_FIELDS(
                   ...
               )
           )

       Once the tracepoint class is defined, you can create as many tracepoint instances as
       needed:

           TRACEPOINT_EVENT_INSTANCE(
               /* Tracepoint provider name */
               my_provider,

               /* Tracepoint class name */
               my_tracepoint_class,

               /* Tracepoint/event name */
               my_tracepoint,

               /* List of tracepoint arguments (input) */
               TP_ARGS(
                   ...
               )
           )

       As you can see, the TRACEPOINT_EVENT_INSTANCE() does not contain the TP_FIELDS() macro,
       because they are defined at the TRACEPOINT_EVENT_CLASS() level.

       See the EXAMPLE section below for a complete example.

   TRACEPOINT_LOGLEVEL() usage
       Optionally, a log level can be assigned to a defined tracepoint. Assigning different
       levels of severity to tracepoints can be useful: when controlling tracing sessions, you
       can choose to only enable events falling into a specific log level range using the
       --loglevel and --loglevel-only options of the lttng-enable-event(1) command.

       Log levels are assigned to tracepoints that are already defined using the
       TRACEPOINT_LOGLEVEL() macro. The latter must be used after having used TRACEPOINT_EVENT()
       or TRACEPOINT_EVENT_INSTANCE() for a given tracepoint. The TRACEPOINT_LOGLEVEL() macro is
       used as follows:

           TRACEPOINT_LOGLEVEL(
               /* Tracepoint provider name */
               my_provider,

               /* Tracepoint/event name */
               my_tracepoint,

               /* Log level */
               TRACE_INFO
           )

       The available log level definitions are:

       TRACE_EMERG
           System is unusable.

       TRACE_ALERT
           Action must be taken immediately.

       TRACE_CRIT
           Critical conditions.

       TRACE_ERR
           Error conditions.

       TRACE_WARNING
           Warning conditions.

       TRACE_NOTICE
           Normal, but significant, condition.

       TRACE_INFO
           Informational message.

       TRACE_DEBUG_SYSTEM
           Debug information with system-level scope (set of programs).

       TRACE_DEBUG_PROGRAM
           Debug information with program-level scope (set of processes).

       TRACE_DEBUG_PROCESS
           Debug information with process-level scope (set of modules).

       TRACE_DEBUG_MODULE
           Debug information with module (executable/library) scope (set of units).

       TRACE_DEBUG_UNIT
           Debug information with compilation unit scope (set of functions).

       TRACE_DEBUG_FUNCTION
           Debug information with function-level scope.

       TRACE_DEBUG_LINE
           Debug information with line-level scope (default log level).

       TRACE_DEBUG
           Debug-level message.

       See the EXAMPLE section below for a complete example.

   Instrumenting your application
       Once the tracepoint provider is created (see the Creating a tracepoint provider section
       above), you can instrument your application with the defined tracepoints thanks to the
       tracepoint() macro:

           #define tracepoint(prov_name, t_name, ...)

       With:

       prov_name
           Tracepoint provider name.

       t_name
           Tracepoint/event name.

       ...
           Tracepoint arguments, if any.

       Make sure to include the tracepoint provider header file anywhere you use tracepoint() for
       this provider.

           Note
           Even though LTTng-UST supports tracepoint() call site duplicates having the same
           provider and tracepoint names, it is recommended to use a provider/tracepoint name
           pair only once within the application source code to help map events back to their
           call sites when analyzing the trace.

       Sometimes, arguments to the tracepoint are expensive to compute (take call stack, for
       example). To avoid the computation when the tracepoint is disabled, you can use the
       tracepoint_enabled() and do_tracepoint() macros:

           #define tracepoint_enabled(prov_name, t_name)
           #define do_tracepoint(prov_name, t_name, ...)

       tracepoint_enabled() returns a non-zero value if the tracepoint named t_name from the
       provider named prov_name is enabled at run time.

       do_tracepoint() is like tracepoint(), except that it doesn’t check if the tracepoint is
       enabled. Using tracepoint() with tracepoint_enabled() is dangerous since tracepoint() also
       contains the tracepoint_enabled() check, thus a race condition is possible in this
       situation:

           if (tracepoint_enabled(my_provider, my_tracepoint)) {
               stuff = prepare_stuff();
           }

           tracepoint(my_provider, my_tracepoint, stuff);

       If the tracepoint is enabled after the condition, then stuff is not prepared: the emitted
       event will either contain wrong data, or the whole application could crash (segmentation
       fault, for example).

           Note
           Neither tracepoint_enabled() nor do_tracepoint() have a STAP_PROBEV() call, so if you
           need it, you should emit this call yourself.

   Statically linking the tracepoint provider
       With the static linking method, compiled tracepoint providers are copied into the target
       application.

       Define TRACEPOINT_DEFINE definition below the TRACEPOINT_CREATE_PROBES definition in the
       tracepoint provider source:

           #define TRACEPOINT_CREATE_PROBES
           #define TRACEPOINT_DEFINE

           #include "tp.h"

       Create the tracepoint provider object file:

           $ cc -c -I. tp.c

           Note
           Although an application instrumented with LTTng-UST tracepoints can be compiled with a
           C++ compiler, tracepoint probes should be compiled with a C compiler.

       At this point, you can archive this tracepoint provider object file, possibly with other
       object files of your application or with other tracepoint provider object files, as a
       static library:

           $ ar rc tp.a tp.o

       Using a static library does have the advantage of centralising the tracepoint providers
       objects so they can be shared between multiple applications. This way, when the tracepoint
       provider is modified, the source code changes don’t have to be patched into each
       application’s source code tree. The applications need to be relinked after each change,
       but need not to be otherwise recompiled (unless the tracepoint provider’s API changes).

       Then, link your application with this object file (or with the static library containing
       it) and with liblttng-ust and libdl (libc on a BSD system):

           $ cc -o app tp.o app.o -llttng-ust -ldl

   Dynamically loading the tracepoint provider
       The second approach to package the tracepoint provider is to use the dynamic loader: the
       library and its member functions are explicitly sought, loaded at run time.

       In this scenario, the tracepoint provider is compiled as a shared object.

       The process to create the tracepoint provider shared object is pretty much the same as the
       static linking method, except that:

       ·   Since the tracepoint provider is not part of the application, TRACEPOINT_DEFINE must
           be defined, for each tracepoint provider, in exactly one source file of the
           application

       ·   TRACEPOINT_PROBE_DYNAMIC_LINKAGE must be defined next to TRACEPOINT_DEFINE

       Regarding TRACEPOINT_DEFINE and TRACEPOINT_PROBE_DYNAMIC_LINKAGE, the recommended practice
       is to use a separate C source file in your application to define them, then include the
       tracepoint provider header files afterwards. For example, as tp-define.c:

           #define TRACEPOINT_DEFINE
           #define TRACEPOINT_PROBE_DYNAMIC_LINKAGE

           #include "tp.h"

       The tracepoint provider object file used to create the shared library is built like it is
       using the static linking method, but with the -fpic option:

           $ cc -c -fpic -I. tp.c

       It is then linked as a shared library like this:

           $ cc -shared -Wl,--no-as-needed -o tp.so tp.o -llttng-ust

       This tracepoint provider shared object isn’t linked with the user application: it must be
       loaded manually. This is why the application is built with no mention of this tracepoint
       provider, but still needs libdl:

           $ cc -o app app.o tp-define.o -ldl

       There are two ways to dynamically load the tracepoint provider shared object:

       ·   Load it manually from the application using dlopen(3)

       ·   Make the dynamic loader load it with the LD_PRELOAD environment variable (see
           ld.so(8))

       If the application does not dynamically load the tracepoint provider shared object using
       one of the methods above, tracing is disabled for this application, and the events are not
       listed in the output of lttng-list(1).

       Note that it is not safe to use dlclose(3) on a tracepoint provider shared object that is
       being actively used for tracing, due to a lack of reference counting from LTTng-UST to the
       shared object.

       For example, statically linking a tracepoint provider to a shared object which is to be
       dynamically loaded by an application (a plugin, for example) is not safe: the shared
       object, which contains the tracepoint provider, could be dynamically closed (dlclose(3))
       at any time by the application.

       To instrument a shared object, either:

       ·   Statically link the tracepoint provider to the application, or

       ·   Build the tracepoint provider as a shared object (following the procedure shown in
           this section), and preload it when tracing is needed using the LD_PRELOAD environment
           variable.

   Using LTTng-UST with daemons
       Some extra care is needed when using liblttng-ust with daemon applications that call
       fork(2), clone(2), or BSD’s rfork(2) without a following exec(3) family system call. The
       library liblttng-ust-fork.so needs to be preloaded before starting the application with
       the LD_PRELOAD environment variable (see ld.so(8)).

       To use liblttng-ust with a daemon application which closes file descriptors that were not
       opened by it, preload the liblttng-ust-fd.so library before you start the application.
       Typical use cases include daemons closing all file descriptors after fork(2), and buggy
       applications doing “double-closes”.

   Context information
       Context information can be prepended by the LTTng-UST tracer before each event, or before
       specific events.

       Context fields can be added to specific channels using lttng-add-context(1).

       The following context fields are supported by LTTng-UST:

       cpu_id
           CPU ID.

               Note
               This context field is always enabled, and it cannot be added with lttng-add-
               context(1). Its main purpose is to be used for dynamic event filtering. See lttng-
               enable-event(1) for more information about event filtering.

       ip
           Instruction pointer: enables recording the exact address from which an event was
           emitted. This context field can be used to reverse-lookup the source location that
           caused the event to be emitted.

       perf:thread:COUNTER
           perf counter named COUNTER. Use lttng add-context --list to list the available perf
           counters.

           Only available on IA-32 and x86-64 architectures.

       perf:thread:raw:rN:NAME
           perf counter with raw ID N and custom name NAME. See lttng-add-context(1) for more
           details.

       pthread_id
           POSIX thread identifier. Can be used on architectures where pthread_t maps nicely to
           an unsigned long type.

       procname
           Thread name, as set by exec(3) or prctl(2). It is recommended that programs set their
           thread name with prctl(2) before hitting the first tracepoint for that thread.

       vpid
           Virtual process ID: process ID as seen from the point of view of the process
           namespace.

       vtid
           Virtual thread ID: thread ID as seen from the point of view of the process namespace.

   LTTng-UST state dump
       If an application that uses liblttng-ust becomes part of a tracing session, information
       about its currently loaded shared objects, their build IDs, and their debug link
       information are emitted as events by the tracer.

       The following LTTng-UST state dump events exist and must be enabled to record application
       state dumps. Note that, during the state dump phase, LTTng-UST can also emit shared
       library load/unload events (see Shared library load/unload tracking below).

       lttng_ust_statedump:start
           Emitted when the state dump begins.

           This event has no fields.

       lttng_ust_statedump:end
           Emitted when the state dump ends. Once this event is emitted, it is guaranteed that,
           for a given process, the state dump is complete.

           This event has no fields.

       lttng_ust_statedump:bin_info
           Emitted when information about a currently loaded executable or shared object is
           found.

           Fields:

           ┌───────────────┬──────────────────────────────────┐
           │Field nameDescription                      │
           ├───────────────┼──────────────────────────────────┤
           │baddr          │ Base address of loaded           │
           │               │ executable.                      │
           ├───────────────┼──────────────────────────────────┤
           │memsz          │ Size of loaded executable in     │
           │               │ memory.                          │
           ├───────────────┼──────────────────────────────────┤
           │path           │ Path to loaded executable file.  │
           ├───────────────┼──────────────────────────────────┤
           │is_pic         │ Whether or not the executable is │
           │               │ position-independent code.       │
           ├───────────────┼──────────────────────────────────┤
           │has_build_id   │ Whether or not the executable    │
           │               │ has a build ID. If this field is │
           │               │ 1, you can expect that an        │
           │               │ lttng_ust_statedump:build_id     │
           │               │ event record follows this one    │
           │               │ (not necessarily immediately     │
           │               │ after).                          │
           ├───────────────┼──────────────────────────────────┤
           │has_debug_link │ Whether or not the executable    │
           │               │ has debug link information. If   │
           │               │ this field is 1, you can expect  │
           │               │ that an                          │
           │               │ lttng_ust_statedump:debug_link   │
           │               │ event record follows this one    │
           │               │ (not necessarily immediately     │
           │               │ after).                          │
           └───────────────┴──────────────────────────────────┘

       lttng_ust_statedump:build_id
           Emitted when a build ID is found in a currently loaded shared library. See Debugging
           Information in Separate Files <https://sourceware.org/gdb/onlinedocs/gdb/Separate-
           Debug-Files.html> for more information about build IDs.

           Fields:

           ┌───────────┬─────────────────────────────────┐
           │Field nameDescription                     │
           ├───────────┼─────────────────────────────────┤
           │baddr      │ Base address of loaded library. │
           ├───────────┼─────────────────────────────────┤
           │build_id   │ Build ID.                       │
           └───────────┴─────────────────────────────────┘

       lttng_ust_statedump:debug_link
           Emitted when debug link information is found in a currently loaded shared library. See
           Debugging Information in Separate Files
           <https://sourceware.org/gdb/onlinedocs/gdb/Separate-Debug-Files.html> for more
           information about debug links.

           Fields:

           ┌───────────┬─────────────────────────────────┐
           │Field nameDescription                     │
           ├───────────┼─────────────────────────────────┤
           │baddr      │ Base address of loaded library. │
           ├───────────┼─────────────────────────────────┤
           │crc        │ Debug link file’s CRC.          │
           ├───────────┼─────────────────────────────────┤
           │filename   │ Debug link file name.           │
           └───────────┴─────────────────────────────────┘

   Shared library load/unload tracking
       The LTTng-UST state dump and the LTTng-UST helper library to instrument the dynamic linker
       (see liblttng-ust-dl(3)) can emit shared library load/unload tracking events.

       The following shared library load/unload tracking events exist and must be enabled to
       track the loading and unloading of shared libraries:

       lttng_ust_lib:load
           Emitted when a shared library (shared object) is loaded.

           Fields:

           ┌───────────────┬──────────────────────────────────┐
           │Field nameDescription                      │
           ├───────────────┼──────────────────────────────────┤
           │baddr          │ Base address of loaded library.  │
           ├───────────────┼──────────────────────────────────┤
           │memsz          │ Size of loaded library in        │
           │               │ memory.                          │
           ├───────────────┼──────────────────────────────────┤
           │path           │ Path to loaded library file.     │
           ├───────────────┼──────────────────────────────────┤
           │has_build_id   │ Whether or not the library has a │
           │               │ build ID. If this field is 1,    │
           │               │ you can expect that an           │
           │               │ lttng_ust_lib:build_id event     │
           │               │ record follows this one (not     │
           │               │ necessarily immediately after).  │
           ├───────────────┼──────────────────────────────────┤
           │has_debug_link │ Whether or not the library has   │
           │               │ debug link information. If this  │
           │               │ field is 1, you can expect that  │
           │               │ an lttng_ust_lib:debug_link      │
           │               │ event record follows this one    │
           │               │ (not necessarily immediately     │
           │               │ after).                          │
           └───────────────┴──────────────────────────────────┘

       lttng_ust_lib:unload
           Emitted when a shared library (shared object) is unloaded.

           Fields:

           ┌───────────┬──────────────────────────┐
           │Field nameDescription              │
           ├───────────┼──────────────────────────┤
           │baddr      │ Base address of unloaded │
           │           │ library.                 │
           └───────────┴──────────────────────────┘

       lttng_ust_lib:build_id
           Emitted when a build ID is found in a loaded shared library (shared object). See
           Debugging Information in Separate Files
           <https://sourceware.org/gdb/onlinedocs/gdb/Separate-Debug-Files.html> for more
           information about build IDs.

           Fields:

           ┌───────────┬─────────────────────────────────┐
           │Field nameDescription                     │
           ├───────────┼─────────────────────────────────┤
           │baddr      │ Base address of loaded library. │
           ├───────────┼─────────────────────────────────┤
           │build_id   │ Build ID.                       │
           └───────────┴─────────────────────────────────┘

       lttng_ust_lib:debug_link
           Emitted when debug link information is found in a loaded shared library (shared
           object). See Debugging Information in Separate Files
           <https://sourceware.org/gdb/onlinedocs/gdb/Separate-Debug-Files.html> for more
           information about debug links.

           Fields:

           ┌───────────┬─────────────────────────────────┐
           │Field nameDescription                     │
           ├───────────┼─────────────────────────────────┤
           │baddr      │ Base address of loaded library. │
           ├───────────┼─────────────────────────────────┤
           │crc        │ Debug link file’s CRC.          │
           ├───────────┼─────────────────────────────────┤
           │filename   │ Debug link file name.           │
           └───────────┴─────────────────────────────────┘

   Detect if LTTng-UST is loaded
       To detect if liblttng-ust is loaded from an application:

        1. Define the lttng_ust_loaded weak symbol globally:

               int lttng_ust_loaded __attribute__((weak));

           This weak symbol is set by the constructor of liblttng-ust.

        2. Test lttng_ust_loaded where needed:

               /* ... */

               if (lttng_ust_loaded) {
                   /* LTTng-UST is loaded */
               } else {
                   /* LTTng-UST is NOT loaded */
               }

               /* ... */

EXAMPLE

           Note
           A few examples are available in the doc/examples <https://github.com/lttng/lttng-
           ust/tree/master/doc/examples> directory of LTTng-UST’s source tree.

       This example shows all the features documented in the previous sections. The static
       linking method is chosen here to link the application with the tracepoint provider.

       You can compile the source files and link them together statically like this:

           $ cc -c -I. tp.c
           $ cc -c app.c
           $ cc -o app tp.o app.o -llttng-ust -ldl

       Using the lttng(1) tool, create an LTTng tracing session, enable all the events of this
       tracepoint provider, and start tracing:

           $ lttng create my-session
           $ lttng enable-event --userspace 'my_provider:*'
           $ lttng start

       You may also enable specific events:

           $ lttng enable-event --userspace my_provider:big_event
           $ lttng enable-event --userspace my_provider:event_instance2

       Run the application:

           $ ./app some arguments

       Stop the current tracing session and inspect the recorded events:

           $ lttng stop
           $ lttng view

   Tracepoint provider header file
       tp.h:

           #undef TRACEPOINT_PROVIDER
           #define TRACEPOINT_PROVIDER my_provider

           #undef TRACEPOINT_INCLUDE
           #define TRACEPOINT_INCLUDE "./tp.h"

           #if !defined(_TP_H) || defined(TRACEPOINT_HEADER_MULTI_READ)
           #define _TP_H

           #include <lttng/tracepoint.h>
           #include <stdio.h>

           #include "app.h"

           TRACEPOINT_EVENT(
               my_provider,
               simple_event,
               TP_ARGS(
                   int, my_integer_arg,
                   const char *, my_string_arg
               ),
               TP_FIELDS(
                   ctf_string(argc, my_string_arg)
                   ctf_integer(int, argv, my_integer_arg)
               )
           )

           TRACEPOINT_ENUM(
               my_provider,
               my_enum,
               TP_ENUM_VALUES(
                   ctf_enum_value("ZERO", 0)
                   ctf_enum_value("ONE", 1)
                   ctf_enum_value("TWO", 2)
                   ctf_enum_range("A RANGE", 52, 125)
                   ctf_enum_value("ONE THOUSAND", 1000)
               )
           )

           TRACEPOINT_EVENT(
               my_provider,
               big_event,
               TP_ARGS(
                   int, my_integer_arg,
                   const char *, my_string_arg,
                   FILE *, stream,
                   double, flt_arg,
                   int *, array_arg
               ),
               TP_FIELDS(
                   ctf_integer(int, int_field1, my_integer_arg * 2)
                   ctf_integer_hex(long int, stream_pos, ftell(stream))
                   ctf_float(double, float_field, flt_arg)
                   ctf_string(string_field, my_string_arg)
                   ctf_array(int, array_field, array_arg, 7)
                   ctf_array_text(char, array_text_field, array_arg, 5)
                   ctf_sequence(int, seq_field, array_arg, int,
                                my_integer_arg / 10)
                   ctf_sequence_text(char, seq_text_field, array_arg,
                                     int, my_integer_arg / 5)
                   ctf_enum(my_provider, my_enum, int,
                            enum_field, array_arg[1])
               )
           )

           TRACEPOINT_LOGLEVEL(my_provider, big_event, TRACE_WARNING)

           TRACEPOINT_EVENT_CLASS(
               my_provider,
               my_tracepoint_class,
               TP_ARGS(
                   int, my_integer_arg,
                   struct app_struct *, app_struct_arg
               ),
               TP_FIELDS(
                   ctf_integer(int, a, my_integer_arg)
                   ctf_integer(unsigned long, b, app_struct_arg->b)
                   ctf_string(c, app_struct_arg->c)
               )
           )

           TRACEPOINT_EVENT_INSTANCE(
               my_provider,
               my_tracepoint_class,
               event_instance1,
               TP_ARGS(
                   int, my_integer_arg,
                   struct app_struct *, app_struct_arg
               )
           )

           TRACEPOINT_EVENT_INSTANCE(
               my_provider,
               my_tracepoint_class,
               event_instance2,
               TP_ARGS(
                   int, my_integer_arg,
                   struct app_struct *, app_struct_arg
               )
           )

           TRACEPOINT_LOGLEVEL(my_provider, event_instance2, TRACE_INFO)

           TRACEPOINT_EVENT_INSTANCE(
               my_provider,
               my_tracepoint_class,
               event_instance3,
               TP_ARGS(
                   int, my_integer_arg,
                   struct app_struct *, app_struct_arg
               )
           )

           #endif /* _TP_H */

           #include <lttng/tracepoint-event.h>

   Tracepoint provider source file
       tp.c:

           #define TRACEPOINT_CREATE_PROBES
           #define TRACEPOINT_DEFINE

           #include "tp.h"

   Application header file
       app.h:

           #ifndef _APP_H
           #define _APP_H

           struct app_struct {
               unsigned long b;
               const char *c;
               double d;
           };

           #endif /* _APP_H */

   Application source file
       app.c:

           #include <stdlib.h>
           #include <stdio.h>

           #include "tp.h"
           #include "app.h"

           static int array_of_ints[] = {
               100, -35, 1, 23, 14, -6, 28, 1001, -3000,
           };

           int main(int argc, char* argv[])
           {
               FILE *stream;
               struct app_struct app_struct;

               tracepoint(my_provider, simple_event, argc, argv[0]);
               stream = fopen("/tmp/app.txt", "w");

               if (!stream) {
                   fprintf(stderr,
                           "Error: Cannot open /tmp/app.txt for writing\n");
                   return EXIT_FAILURE;
               }

               if (fprintf(stream, "0123456789") != 10) {
                   fclose(stream);
                   fprintf(stderr, "Error: Cannot write to /tmp/app.txt\n");
                   return EXIT_FAILURE;
               }

               tracepoint(my_provider, big_event, 35, "hello tracepoint",
                          stream, -3.14, array_of_ints);
               fclose(stream);
               app_struct.b = argc;
               app_struct.c = "[the string]";
               tracepoint(my_provider, event_instance1, 23, &app_struct);
               app_struct.b = argc * 5;
               app_struct.c = "[other string]";
               tracepoint(my_provider, event_instance2, 17, &app_struct);
               app_struct.b = 23;
               app_struct.c = "nothing";
               tracepoint(my_provider, event_instance3, -52, &app_struct);

               return EXIT_SUCCESS;
           }

ENVIRONMENT VARIABLES

       LTTNG_HOME
           Alternative user’s home directory. This variable is useful when the user running the
           instrumented application has a non-writable home directory.

           Unix sockets used for the communication between liblttng-ust and the LTTng session and
           consumer daemons (part of the LTTng-tools project) are located in a specific directory
           under $LTTNG_HOME (or $HOME if $LTTNG_HOME is not set).

       LTTNG_UST_ALLOW_BLOCKING
           If set, allow the application to retry event tracing when there’s no space left for
           the event record in the sub-buffer, therefore effectively blocking the application
           until space is made available or the configured timeout is reached.

           To allow an application to block during tracing, you also need to specify a blocking
           timeout when you create a channel with the --blocking-timeout option of the lttng-
           enable-channel(1) command.

           This option can be useful in workloads generating very large trace data throughput,
           where blocking the application is an acceptable trade-off to prevent discarding event
           records.

               Warning
               Setting this environment variable may significantly affect application timings.

       LTTNG_UST_CLOCK_PLUGIN
           Path to the shared object which acts as the clock override plugin. An example of such
           a plugin can be found in the LTTng-UST documentation under examples/clock-override
           <https://github.com/lttng/lttng-ust/tree/master/doc/examples/clock-override>.

       LTTNG_UST_DEBUG
           If set, enable liblttng-ust's debug and error output.

       LTTNG_UST_GETCPU_PLUGIN
           Path to the shared object which acts as the getcpu() override plugin. An example of
           such a plugin can be found in the LTTng-UST documentation under examples/getcpu-
           override <https://github.com/lttng/lttng-ust/tree/master/doc/examples/getcpu-
           override>.

       LTTNG_UST_REGISTER_TIMEOUT
           Waiting time for the registration done session daemon command before proceeding to
           execute the main program (milliseconds).

           The value 0 means do not wait. The value -1 means wait forever. Setting this
           environment variable to 0 is recommended for applications with time constraints on the
           process startup time.

           Default: 3000.

       LTTNG_UST_WITHOUT_BADDR_STATEDUMP
           If set, prevents liblttng-ust from performing a base address state dump (see the
           LTTng-UST state dump section above).

BUGS

       If you encounter any issue or usability problem, please report it on the LTTng bug tracker
       <https://bugs.lttng.org/projects/lttng-ust>.

RESOURCES

       ·   LTTng project website <http://lttng.org>

       ·   LTTng documentation <http://lttng.org/docs>

       ·   Git repositories <http://git.lttng.org>

       ·   GitHub organization <http://github.com/lttng>

       ·   Continuous integration <http://ci.lttng.org/>

       ·   Mailing list <http://lists.lttng.org> for support and development: lttng-
           dev@lists.lttng.org

       ·   IRC channel <irc://irc.oftc.net/lttng>: #lttng on irc.oftc.net

COPYRIGHTS

       This library is part of the LTTng-UST project.

       This library is distributed under the GNU Lesser General Public License, version 2.1
       <http://www.gnu.org/licenses/old-licenses/lgpl-2.1.en.html>. See the COPYING
       <https://github.com/lttng/lttng-ust/blob/master/COPYING> file for more details.

THANKS

       Thanks to Ericsson for funding this work, providing real-life use cases, and testing.

       Special thanks to Michel Dagenais and the DORSAL laboratory
       <http://www.dorsal.polymtl.ca/> at École Polytechnique de Montréal for the LTTng journey.

AUTHORS

       LTTng-UST was originally written by Mathieu Desnoyers, with additional contributions from
       various other people. It is currently maintained by Mathieu Desnoyers
       <mailto:mathieu.desnoyers@efficios.com>.

SEE ALSO

       tracef(3), tracelog(3), lttng-gen-tp(1), lttng-ust-dl(3), lttng-ust-cyg-profile(3),
       lttng(1), lttng-enable-event(1), lttng-list(1), lttng-add-context(1), babeltrace(1),
       dlopen(3), ld.so(8)