Sometimes it is useful to disable a trace event. Removing the event
from trace-events is not enough since source code will call the
trace_*() function for the event.
This patch makes it easy to build without specific trace events by
marking them disabled in trace-events:
disable multiwrite_cb(void *mcb, int ret) "mcb %p ret %d"
This builds without the multiwrite_cb trace event.
Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
trace: Allow bulk enabling/disabling of trace events at compile time
For 'simple' trace backend, allow bulk enabling/disabling of trace
events at compile time. Trace events that are preceded by 'disable'
keyword are compiled in, but turned off by default. These can
individually be turned on using the monitor. All other trace events are
enabled by default.
TODO :
This could be enhanced when the trace-event namespace is partitioned into a
group and an ID within that group. In such a case, marking a group as enabled
would automatically enable all trace-events listed under it.
Signed-off-by: Prerna Saxena <prerna@linux.vnet.ibm.com>
Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
This patch introduces the trace-events file where trace events can be
declared like so:
qemu_malloc(size_t size) "size %zu"
qemu_free(void *ptr) "ptr %p"
These trace event declarations are processed by a new tool called
tracetool to generate code for the trace events. Trace event
declarations are independent of the backend tracing system (LTTng User
Space Tracing, ftrace markers, DTrace).
The default "nop" backend generates empty trace event functions.
Therefore trace events are disabled by default.
The trace-events file serves two purposes:
1. Adding trace events is easy. It is not necessary to understand the
details of a backend tracing system. The trace-events file is a
single location where trace events can be declared without code
duplication.
2. QEMU is not tightly coupled to one particular backend tracing system.
In order to support tracing across QEMU host platforms and to
anticipate new backend tracing systems that are currently maturing,
it is important to be flexible and not tied to one system.
This commit includes fixes from Prerna Saxena
<prerna@linux.vnet.ibm.com> and Blue Swirl <blauwirbel@gmail.com>.
Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
