)
.fi
+.SH "ASSIGNING LOGLEVEL TO EVENTS"
+
+.nf
+
+Optionally, a loglevel can be assigned to a TRACEPOINT_EVENT using the
+following construct:
+
+ TRACEPOINT_LOGLEVEL(< [com_company_]project[_component] >,
+ < event >, < loglevel_name >)
+
+ The first field is the provider name, the second field is the name of
+the tracepoint, and the third field is the loglevel name. A
+TRACEPOINT_EVENT should be declared prior to the the TRACEPOINT_LOGLEVEL
+for a given tracepoint name. The TRACEPOINT_PROVIDER must be already
+declared before declaring a TRACEPOINT_LOGLEVEL.
+
+The loglevels go from 0 to 14. Higher numbers imply the most verbosity
+(higher event throughput expected.
+
+Loglevels 0 through 6, and loglevel 14, match syslog(3) loglevels
+semantic. Loglevels 7 through 13 offer more fine-grained selection of
+debug information.
+
+ TRACE_EMERG 0
+ system is unusable
+
+ TRACE_ALERT 1
+ action must be taken immediately
+
+ TRACE_CRIT 2
+ critical conditions
+
+ TRACE_ERR 3
+ error conditions
+
+ TRACE_WARNING 4
+ warning conditions
+
+ TRACE_NOTICE 5
+ normal, but significant, condition
+
+ TRACE_INFO 6
+ informational message
+
+ TRACE_DEBUG_SYSTEM 7
+ debug information with system-level scope (set of programs)
+
+ TRACE_DEBUG_PROGRAM 8
+ debug information with program-level scope (set of processes)
+
+ TRACE_DEBUG_PROCESS 9
+ debug information with process-level scope (set of modules)
+
+ TRACE_DEBUG_MODULE 10
+ debug information with module (executable/library) scope (set of
+ units)
+
+ TRACE_DEBUG_UNIT 11
+ debug information with compilation unit scope (set of functions)
+
+ TRACE_DEBUG_FUNCTION 12
+ debug information with function-level scope
+
+ TRACE_DEBUG_LINE 13
+ debug information with line-level scope (TRACEPOINT_EVENT default)
+
+ TRACE_DEBUG 14
+ debug-level message (trace_printf default)
+
+See lttng(1) for information on how to use LTTng-UST loglevels.
+
+.fi
+
.SH "ADDING TRACEPOINTS TO YOUR CODE"
.nf
As a call to the tracepoint. It will only be activated when requested by
lttng(1) through lttng-sessiond(8).
+Even though LTTng-UST supports tracepoint() call site duplicates having
+the same provider and event name, it is recommended to use a
+provider event name pair only once within the source code to help
+mapping events back to their call sites when analyzing the trace.
.fi
.SH "BUILDING/LINKING THE TRACEPOINT PROVIDER"
directly or through a static library (.a):
- Into exactly one object of your application: define
"TRACEPOINT_DEFINE" and include the tracepoint provider.
- - Use "-I." for the compilation unit containing the tracepoint
+ - Use "\-I." for the compilation unit containing the tracepoint
provider include (e.g. tp.c).
- - Link application with "-ldl".
+ - Link application with "\-ldl".
- If building the provider directly into the application,
- link the application with "-llttng-ust".
+ link the application with "\-llttng-ust".
- If building a static library for the provider, link the static
- library with "-lllttng-ust".
+ library with "\-llttng-ust".
- Include the tracepoint provider header into all C files using
the provider.
- Example:
- tests/hello/ hello.c tp.c ust_tests_hello.h Makefile.example
+ - tests/hello/ hello.c tp.c ust_tests_hello.h Makefile.example
2) Compile the Tracepoint Provider separately from the application,
using dynamic linking:
provider header.
- Include the tracepoint provider header into all instrumented C
files that use the provider.
- - Compile the tracepoint provider with "-I.".
- - Link the tracepoint provider with "-llttng-ust".
- - Link application with "-ldl".
+ - Compile the tracepoint provider with "\-I.".
+ - Link the tracepoint provider with "\-llttng-ust".
+ - Link application with "\-ldl".
- Set a LD_PRELOAD environment to preload the tracepoint provider
shared object before starting the application when tracing is
- needed.
+ needed. Another way is to dlopen the tracepoint probe when needed
+ by the application.
- Example:
- tests/demo/ demo.c tp*.c ust_tests_demo*.h demo-trace
- - Note about dlopen() usage: due to locking side-effects due to the
- way libc lazily resolves Thread-Local Storage (TLS) symbols when a
- library is dlopen'd, linking the tracepoint probe or liblttng-ust
- with dlopen() is discouraged. They should be linked with the
- application using "-llibname" or loaded with LD_PRELOAD.
+ - Note about dlclose() usage: it is not safe to use dlclose on a
+ provider shared object that is being actively used for tracing due
+ to a lack of reference counting from lttng-ust to the used shared
+ object.
- Enable instrumentation and control tracing with the "lttng" command
from lttng-tools. See lttng-tools doc/quickstart.txt.
+ - Note for C++ support: although an application instrumented with
+ tracepoints can be compiled with g++, tracepoint probes should be
+ compiled with gcc (only tested with gcc so far).
+
+.fi
+
+.SH "USING LTTNG UST WITH DAEMONS"
+
+.nf
+Some extra care is needed when using liblttng-ust with daemon
+applications that call fork(), clone(), or BSD rfork() without a
+following exec() family system call. The library "liblttng-ust-fork.so"
+needs to be preloaded for the application (launch with e.g.
+LD_PRELOAD=liblttng-ust-fork.so appname).
.fi
+.SH "CONTEXT"
+
+.PP
+Context information can be prepended by the tracer before each, or some,
+events. The following context information is supported by LTTng-UST:
+.PP
+
+.PP
+.IP "vtid"
+Virtual thread ID: thread ID as seen from the point of view of the
+process namespace.
+.PP
+
+.PP
+.IP "vpid"
+Virtual process ID: process ID as seen from the point of view of the
+process namespace.
+.PP
+
+.PP
+.IP "procname"
+Thread name, as set by exec() or prctl(). It is recommended that
+programs set their thread name with prctl() before hitting the first
+tracepoint for that thread.
+.PP
+
+.PP
+.IP "pthread_id"
+Pthread identifier. Can be used on architectures where pthread_t maps
+nicely to an unsigned long type.
+.PP
+
.SH "ENVIRONMENT VARIABLES"
.PP
"registration done" command before proceeding to execute the main
program. The default is 3000ms (3 seconds). The timeout value is
specified in milliseconds. The value 0 means "don't wait". The value
--1 means "wait forever". Setting this environment variable to 0 is
+\-1 means "wait forever". Setting this environment variable to 0 is
recommended for applications with time constraints on the process
startup time.
.PP
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