[Qemu-devel] [PATCH v3 00/18] Refactor trace to allow modular build

[Daniel P. Berrange]

These patches were previously posted as part of my giant
trace events modular build series

  v1: https://lists.gnu.org/archive/html/qemu-devel/2016-08/msg01714.html
  v2: https://lists.gnu.org/archive/html/qemu-devel/2016-09/msg03335.html

This series does all the refactoring required to support a fully
modular build of the trace probe points, but does not actually
convert anything to use it. The 40+ patches to convert each subdir
to use modular build will only be posted again, once the refactoring
is reviewed & queued, in order to avoid patch-bombing the list
more than is needed. The full series is visible at

   https://github.com/berrange/qemu/tree/trace-events-3

The key problem being tackled by this series is the assumption
that there is a single statically declared enum which provides
globally unique event IDs. Inside QEMU the event IDs were used
as list indexes into the 'trace_events' array, while the event
VCPU IDs were used as bitmap indexes in trace_dstate against
the CPUState struct.  Externally to QEMU, the event IDs were
also written in the simpletrace binary data format and used
to lookup the entry in the trace-events file afterwards.

Inside QEMU the refactoring work managed to remove all need
for event IDs for purposes of 'trace_events' array lookups.
Instead we now have global variables per-event which can be
referenced directly.

When QEMU starts up and the various event groups are registered,
we now dynamically assign event IDs and VCPU IDs to each event.
This removes the limitation in the v1 posting that all vCPU
events had to be in one file. We also removed the limitation
on the total number of vCPU events. So there is no regression
in functionality of VCPU event support compared to current
GIT master.

Since the event IDs are allocated dynamically at runtime,
the simpletrace.py script cannot assume they map directly
to the 'trace-events' file entries. Thus, the simpletrace
binary format is extended to include a record type that
maps trace event IDs to trace event names. While it would
be possible to take this even further and make the
simpletrace binary format 100% self-describing this is left
as an exercise for future developers, as it is not a
pre-requisite for this modular build.

While some of the intermediate patches may seem pointless
on their own, they exist in order to facilitate the review
of later patches by ensuring each patch does the minimum
possible refactoring work.

Changed in v3:

 - Change simpletrace format to write a mapping of
   IDs to names
 - Declare a TraceEvent variable per event, instead
   of just an array
 - Make 'trace_events' array be 'TraceEvent **'
   instead of 'TraceEvent *'
 - Fix infinite loop in iterators due to bad
   fix in v2 posting.
 - Dynamically allocate the trace_dstate variable
   in CPUState based on actual number of vcpu events
   registered at runtime
 - Push logic for determining group name into the
   tracetool program
 - Fix to ftrace to make it more practical for users
   who sometimes run QEMU as non-root.
 - Get rid of TraceEventID/VCPUID enums entirely

Changed in v2:

 - Fixed filtering of events on first call of
   iterator_next (Stefan)
 - Switch from size_t to uint32_t for event ID
   type (Paolo/Stefan)
 - Replace global 'dstate' array with individual
   variables (Lluís)



Daniel P. Berrange (18):
  trace: add trace event iterator APIs
  trace: convert code to use event iterators
  trace: remove some now unused functions
  trace: remove global 'uint16 dstate[]' array
  trace: remove duplicate control.h includes in generated-tracers.h
  trace: break circular dependancy in event-internal.h
  trace: give each trace event a named TraceEvent struct
  trace: remove the TraceEventID and TraceEventVCPUID enums
  trace: emit name <-> ID mapping in simpletrace header
  trace: don't abort qemu if ftrace can't be initialized
  trace: provide mechanism for registering trace events
  trace: dynamically allocate trace_dstate in CPUState
  trace: dynamically allocate event IDs at runtime
  trace: get rid of generated-events.h/generated-events.c
  trace: rename _read_events to read_events
  trace: push reading of events up a level to tracetool main
  trace: pass trace-events to tracetool as a positional param
  trace: introduce a formal group name for trace events

 Makefile                                         |   3 -
 Makefile.target                                  |   6 +-
 include/qemu/module.h                            |   2 +
 include/qom/cpu.h                                |   7 +-
 include/trace-tcg.h                              |   1 -
 include/trace.h                                  |   1 -
 monitor.c                                        |  26 +++--
 qemu-img.c                                       |   1 +
 qemu-io.c                                        |   1 +
 qemu-nbd.c                                       |   1 +
 qom/cpu.c                                        |   7 +-
 scripts/simpletrace.py                           |  55 ++++++---
 scripts/tracetool.py                             |  29 ++++-
 scripts/tracetool/__init__.py                    |  27 +++--
 scripts/tracetool/backend/__init__.py            |  12 +-
 scripts/tracetool/backend/dtrace.py              |   4 +-
 scripts/tracetool/backend/ftrace.py              |   6 +-
 scripts/tracetool/backend/log.py                 |   7 +-
 scripts/tracetool/backend/simple.py              |  10 +-
 scripts/tracetool/backend/syslog.py              |   5 +-
 scripts/tracetool/backend/ust.py                 |   4 +-
 scripts/tracetool/format/__init__.py             |   4 +-
 scripts/tracetool/format/c.py                    |  57 +++++++--
 scripts/tracetool/format/d.py                    |   2 +-
 scripts/tracetool/format/events_c.py             |  37 ++++--
 scripts/tracetool/format/events_h.py             |  24 +---
 scripts/tracetool/format/h.py                    |  36 ++++--
 scripts/tracetool/format/simpletrace_stap.py     |  25 +++-
 scripts/tracetool/format/stap.py                 |   2 +-
 scripts/tracetool/format/tcg_h.py                |   2 +-
 scripts/tracetool/format/tcg_helper_c.py         |   2 +-
 scripts/tracetool/format/tcg_helper_h.py         |   2 +-
 scripts/tracetool/format/tcg_helper_wrapper_h.py |   2 +-
 scripts/tracetool/format/ust_events_c.py         |   2 +-
 scripts/tracetool/format/ust_events_h.py         |   8 +-
 stubs/trace-control.c                            |   9 +-
 trace/Makefile.objs                              |  46 +++-----
 trace/control-internal.h                         |  45 +++-----
 trace/control-target.c                           |  22 ++--
 trace/control.c                                  | 141 +++++++++++++++--------
 trace/control.h                                  | 110 ++++++------------
 trace/event-internal.h                           |  17 ++-
 trace/ftrace.c                                   |   6 +
 trace/qmp.c                                      |  16 ++-
 trace/simple.c                                   |  38 +++++-
 trace/simple.h                                   |   6 +-
 vl.c                                             |   2 +
 47 files changed, 520 insertions(+), 358 deletions(-)

-- 
2.7.4