Trace events outside the global mutex cannot be used with the simple
trace backend since it is not thread-safe.  There is no check to prevent
them being enabled so people sometimes learn this the hard way.

This patch restructures the simple trace backend with a ring buffer
suitable for multiple concurrent writers.  A writeout thread empties the
trace buffer when threshold fill levels are reached.  Should the
writeout thread be unable to keep up with trace generation, records will
simply be dropped.

Each time events are dropped a special record is written to the trace
file indicating how many events were dropped.  The event ID is
0xfffffffffffffffe and its signature is dropped(uint32_t count).
Signed-off-by: NStefan Hajnoczi <stefanha@linux.vnet.ibm.com>

The simpletrace.py script pretty-prints a binary trace file.  Most of
the code can be reused by trace file analysis scripts, so turn it into a
module.

Here is an example script that uses the new simpletrace module:

  #!/usr/bin/env python
  # Print virtqueue elements that were never returned to the guest.

  import simpletrace

  class VirtqueueRequestTracker(simpletrace.Analyzer):
      def __init__(self):
          self.elems = set()

      def virtqueue_pop(self, vq, elem, in_num, out_num):
          self.elems.add(elem)

      def virtqueue_fill(self, vq, elem, length, idx):
          self.elems.remove(elem)

      def end(self):
          for elem in self.elems:
              print hex(elem)

  simpletrace.run(VirtqueueRequestTracker())

The simpletrace API is based around the Analyzer class.  Users implement
an analyzer subclass and add methods for trace events they want to
process.  A catchall() method is invoked for trace events which do not
have dedicated methods.  Finally, there are also begin() and end()
methods like in sed that can be used to perform setup or print
statistics at the end.

A binary trace file is processed either with:

  simpletrace.run(analyzer) # uses command-line args

or with:

  simpletrace.process('path/to/trace-events',
                      'path/to/trace-file',
                      analyzer)
Signed-off-by: NStefan Hajnoczi <stefanha@linux.vnet.ibm.com>
Signed-off-by: NAurelien Jarno <aurelien@aurel32.net>

Move build and user scripts into scripts directory.
Signed-off-by: NBlue Swirl <blauwirbel@gmail.com>

The regular expression to parse trace event definitions assumed the
format string would be a simple double-quoted string.  However, we now
use PRI?64 for portability which splits string literals.  The regular
expression can disregard the format string entirely since simpletrace.py
never needs to use it.
Signed-off-by: NStefan Hajnoczi <stefanha@linux.vnet.ibm.com>
Signed-off-by: NBlue Swirl <blauwirbel@gmail.com>

This patch adds a simple tracer which produces binary trace files.  To
try out the simple backend:

$ ./configure --trace-backend=simple
$ make

After running QEMU you can pretty-print the trace:

$ ./simpletrace.py trace-events trace.log

The output of simpletrace.py looks like this:

  qemu_realloc 0.699 ptr=0x24363f0 size=0x3 newptr=0x24363f0
  qemu_free 0.768 ptr=0x24363f0
  ^           ^---- timestamp delta (us)
  |____ trace event name
Signed-off-by: NStefan Hajnoczi <stefanha@linux.vnet.ibm.com>

trace: Make trace record fields 64-bit

Explicitly use 64-bit fields in trace records so that timestamps and
magic numbers work for 32-bit host builds.

Includes fixes from Prerna Saxena <prerna@linux.vnet.ibm.com>.
Signed-off-by: NPrerna Saxena <prerna@linux.vnet.ibm.com>
Signed-off-by: NStefan Hajnoczi <stefanha@linux.vnet.ibm.com>