TODO

   1 - support multiple simultaneous traces
   2 - fix FIXME's in the code
   3 - add compilation tests
   4 - test with smaller subbuffer sizes
   5 - add option to usttrace to select subbuffer size/count
   6 - correctly destroy buffers at trace destroy
   7 - add option to see subbuffer size and count
   8 - performance testing tool (in progress by Rafik Fahem)
   9 - profile with oprofile or similar to check for perf bottlenecks
  10 - improve support for combined kernel/userspace tracing
  11 - document API
  12 - make sure the proper structures are cacheline aligned, and test performance, including multi-threaded
  13 - fix header/lib priority problem at compilation
  14 - port changes from recent versions of lttng kernel
  15 - make cli interface for flight recorder
  16 - save_registers: save them only when the marker is active (complicated because we need to know their value at the address that is put in struct marker)
  17 - make streaming work, including periodical flush
  18 - make a system (signal-based?) that allow the listener thread to not be started initially
  19 - ustd should work as a pool of threads
  20 - support more than one marker with the same channel and name on the same line?
  21 - make a mode where the listener thread can poll buffers to check if they are ready to be collected
  22   This is to guarantee there will never be a system call in the tracing path. Currently there is a system
  23   call when the buffer is full to notify the listener it can be collected.
  24 - In early tracing mode, the only channels that can be used reliably are "metadata" and "ust". The "usttrace" tool always uses early tracing and is hence subject to this limitation. Traces setup with the "ustctl" tool ("manual mode") are not subject to this limitation and can contain channels that have any name. Also, when loading a library with dlopen(), in order for markers in the library to generate events in the trace, these markers must be in the same channel as an event that was in the executable or its dynamically linked libraries that were loaded at start time. If using early tracing, only the "ust" channel can be used. Fix this. (RCU locking of channel structures in progress by Mathieu Desnoyers)