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   - `CONFIG_KPROBES` (5.7+): use kallsyms for kernel 5.7 and newer.
  70
  71
  72 ### Supported (optional) kernel config options
  73
  74 The following kernel configuration options will affect the features
  75 available from LTTng:
  76
  77   - `CONFIG_HAVE_SYSCALL_TRACEPOINTS`: system call tracing:
  78
  79         lttng enable-event -k --syscall
  80         lttng enable-event -k -a
  81
  82   - `CONFIG_PERF_EVENTS`: performance counters:
  83
  84         lttng add-context -t perf:*
  85
  86   - `CONFIG_EVENT_TRACING`: needed to allow block layer tracing
  87   - `CONFIG_KPROBES`: dynamic probes:
  88
  89         lttng enable-event -k --probe ...
  90
  91   - `CONFIG_KRETPROBES`: dynamic function entry/return probes:
  92
  93         lttng enable-event -k --function ...
  94
  95   - `CONFIG_KALLSYMS_ALL`: state dump of mapping between block device
  96     number and name
  97
  98 Customization/Extension
  99 -----------------------
 100
 101 The lttng-modules source includes definitions for the actual callback
 102 functions that will be attached to the kernel tracepoints by lttng.
 103 The lttng-modules project implements its own macros generating these
 104 callbacks: the LTTNG_TRACEPOINT_EVENT macro family found in
 105 instrumentation/events/lttng-module/. In order to show up in a
 106 lttng-modules trace, a kernel tracepoint must be defined within the
 107 kernel tree, and also defined within lttng-modules with the
 108 LTTNG_TRACEPOINT_EVENT macro family. Customizations or extensions must
 109 be done by modifying instances of these macros within the lttng-modules
 110 source.
 111
 112 Usage
 113 -----
 114
 115 Use [LTTng-tools](https://lttng.org/download) to control the tracer.
 116 The session daemon of LTTng-tools should automatically load the LTTng
 117 kernel modules when needed. Use [Babeltrace](https://lttng.org/babeltrace)
 118 to print traces as a human-readable text log.
 119
 120
 121 Support
 122 -------
 123
 124 Linux kernels >= 3.0 are supported.
 125
 126
 127 Notes
 128 -----
 129
 130 ### About perf PMU counters support
 131
 132 Each PMU counter has its zero value set when it is attached to a context with
 133 add-context. Therefore, it is normal that the same counters attached to both the
 134 stream context and event context show different values for a given event; what
 135 matters is that they increment at the same rate.