doc/man/tracef-tracelog-limitations.txt

   1 :macro-name: lttng_ust_{macro-suffix}
   2 :vmacro-name: lttng_ust_v{macro-suffix}
   3
   4 The +{macro-name}()+ and +{vmacro-name}()+ utility macros were
   5 developed to make user space tracing super simple, albeit with notable
   6 disadvantages compared to custom, full-fledged tracepoint providers:
   7
   8   * All generated events have the same provider/event names.
   9   * There's no static type checking.
  10   * The only event field with user data you actually get, named `msg`,
  11     is a string potentially containing the values you passed to the
  12     macro using your own format. This also means that you cannot use
  13     filtering using a custom expression at run time because there are no
  14     isolated fields.
  15   * Since +{macro-name}()+ and +{vmacro-name}()+ use C standard
  16     library's man:vasprintf(3) function in the background to format the
  17     strings at run time, their expected performance is lower than using
  18     custom tracepoint providers with typed fields, which do not require
  19     a conversion to a string.
  20   * Generally, a string containing the textual representation of the
  21     user data fields is not as compact as binary fields in the resulting
  22     trace.
  23
  24 Thus, +{macro-name}()+/+{vmacro-name}()+ are useful for quick
  25 prototyping and debugging, but should not be considered for any
  26 permanent/serious application instrumentation.
  27
  28 +{vmacro-name}()+ does not have a `STAP_PROBEV()` call, because
  29 `STAP_PROBEV()` does not support `va_list`. If you need it, you should
  30 emit this call yourself.
  31
  32 See man:lttng-ust(3) to learn more about custom tracepoint providers.