trace: Add user documentation

[mirror_qemu.git] / trace-events

# Trace events for debugging and performance instrumentation
#
# This file is processed by the tracetool script during the build.
#
# To add a new trace event:
#
# 1. Choose a name for the trace event.  Declare its arguments and format
#    string.
#
# 2. Call the trace event from code using trace_##name, e.g. multiwrite_cb() ->
#    trace_multiwrite_cb().  The source file must #include "trace.h".
#
# Format of a trace event:
#
# [disable] <name>(<type1> <arg1>[, <type2> <arg2>] ...) "<format-string>"
#
# Example: qemu_malloc(size_t size) "size %zu"
#
# The "disable" keyword will build without the trace event.
# In case of 'simple' trace backend, it will allow the trace event to be
# compiled, but this would be turned off by default. It can be toggled on via
# the monitor.
#
# The <name> must be a valid as a C function name.
#
# Types should be standard C types.  Use void * for pointers because the trace
# system may not have the necessary headers included.
#
# The <format-string> should be a sprintf()-compatible format string.