README.md

   1 LTTng-modules
   2 =============
   3
   4 _by [Mathieu Desnoyers](mailto:mathieu.desnoyers@efficios.com)_
   5
   6
   7 LTTng kernel modules are Linux kernel modules which make
   8 [LTTng](http://lttng.org/) kernel tracing possible. They include
   9 essential control modules and many probes which instrument numerous
  10 interesting parts of Linux. LTTng-modules builds against a vanilla or
  11 distribution kernel, with no need for additional patches.
  12
  13 Other notable features:
  14
  15   - Produces [CTF](http://www.efficios.com/ctf)
  16     (Common Trace Format) natively,
  17   - Tracepoints, function tracer, CPU Performance Monitoring Unit (PMU)
  18     counters, kprobes, and kretprobes support,
  19   - Have the ability to attach _context_ information to events in the
  20     trace (e.g., any PMU counter, PID, PPID, TID, command name, etc).
  21     All the extra information fields to be collected with events are
  22     optional, specified on a per-tracing-session basis (except for
  23     timestamp and event ID, which are mandatory).
  24
  25
  26 Building
  27 --------
  28
  29 To build and install LTTng-modules, you will need to have your kernel
  30 headers available (or access to your full kernel source tree), and do:
  31
  32     make
  33     sudo make modules_install
  34     sudo depmod -a
  35
  36 The above commands will build LTTng-modules against your
  37 current kernel. If you need to build LTTng-modules against a custom
  38 kernel, do:
  39
  40     make KERNELDIR=/path/to/custom/kernel
  41     sudo make KERNELDIR=/path/to/custom/kernel modules_install
  42     sudo depmod -a kernel_version
  43
  44
  45 ### Kernel built-in support
  46
  47 It is also possible to build these modules as part of a kernel image. Simply
  48 run the [`scripts/built-in.sh`](scripts/built-in.sh) script with the path to
  49 your kernel source directory as an argument.  It will symlink the
  50 lttng-modules directory in the kernel sources and add an include in the kernel
  51 Makefile.
  52
  53 Then configure your kernel as usual and enable the `CONFIG_LTTNG` option.
  54
  55
  56 ### Required kernel config options
  57
  58 Make sure your target kernel has the following config options enabled:
  59
  60   - `CONFIG_MODULES`: loadable module support (not strictly required
  61      when built into the kernel),
  62   - `CONFIG_KALLSYMS`: see files in [`wrapper`](wrapper); this is
  63      necessary until the few required missing symbols are exported to GPL
  64      modules from mainline,
  65   - `CONFIG_HIGH_RES_TIMERS`: needed for LTTng 2.x clock source,
  66   - `CONFIG_TRACEPOINTS`: kernel tracepoint instrumentation
  67      (enabled as a side-effect of any of the perf/ftrace/blktrace
  68      instrumentation features).
  69
  70
  71 ### Supported (optional) kernel config options
  72
  73 The following kernel configuration options will affect the features
  74 available from LTTng:
  75
  76   - `CONFIG_HAVE_SYSCALL_TRACEPOINTS`: system call tracing:
  77
  78         lttng enable-event -k --syscall
  79         lttng enable-event -k -a
  80
  81   - `CONFIG_PERF_EVENTS`: performance counters:
  82
  83         lttng add-context -t perf:*
  84
  85   - `CONFIG_EVENT_TRACING`: needed to allow block layer tracing
  86   - `CONFIG_KPROBES`: dynamic probes:
  87
  88         lttng enable-event -k --probe ...
  89
  90   - `CONFIG_KRETPROBES`: dynamic function entry/return probes:
  91
  92         lttng enable-event -k --function ...
  93
  94   - `CONFIG_KALLSYMS_ALL`: state dump of mapping between block device
  95     number and name
  96
  97 Customization/Extension
  98 -----------------------
  99
 100 The lttng-modules source includes definitions for the actual callback
 101 functions that will be attached to the kernel tracepoints by lttng.
 102 The lttng-modules project implements its own macros generating these
 103 callbacks: the LTTNG_TRACEPOINT_EVENT macro family found in
 104 instrumentation/events/lttng-module/. In order to show up in a
 105 lttng-modules trace, a kernel tracepoint must be defined within the
 106 kernel tree, and also defined within lttng-modules with the
 107 LTTNG_TRACEPOINT_EVENT macro family. Customizations or extensions must
 108 be done by modifying instances of these macros within the lttng-modules
 109 source.
 110
 111 Usage
 112 -----
 113
 114 Use [LTTng-tools](https://lttng.org/download) to control the tracer.
 115 The session daemon of LTTng-tools should automatically load the LTTng
 116 kernel modules when needed. Use [Babeltrace](https://lttng.org/babeltrace)
 117 to print traces as a human-readable text log.
 118
 119
 120 Support
 121 -------
 122
 123 Linux kernels >= 3.0 are supported.
 124
 125
 126 Notes
 127 -----
 128
 129 ### About perf PMU counters support
 130
 131 Each PMU counter has its zero value set when it is attached to a context with
 132 add-context. Therefore, it is normal that the same counters attached to both the
 133 stream context and event context show different values for a given event; what
 134 matters is that they increment at the same rate.