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trace: Provide a detailed event control interface

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This interface decouples event obtaining from interaction.

Events can be obtained through three different methods:

* identifier
* name
* simple wildcard pattern

Signed-off-by: Lluís Vilanova <vilanova@ac.upc.edu>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
This commit is contained in:
Lluís Vilanova 2013-03-05 14:47:38 +01:00 • committed by Stefan Hajnoczi
parent 45be2f5d0d
commit b1bae816c4
4 changed files with 350 additions and 59 deletions
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44
docs/tracing.txt
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@ -100,49 +100,37 @@ respectively. This ensures portability between 32- and 64-bit platforms.
== Generic interface and monitor commands ==
You can programmatically query and control the dynamic state of trace events
through a backend-agnostic interface:
You can programmatically query and control the state of trace events through a
backend-agnostic interface provided by the header "trace/control.h".
* trace_print_events
Note that some of the backends do not provide an implementation for some parts
of this interface, in which case QEMU will just print a warning (please refer to
header "trace/control.h" to see which routines are backend-dependent).
* trace_event_set_state
Enables or disables trace events at runtime inside QEMU.
The function returns "true" if the state of the event has been successfully
changed, or "false" otherwise:
#include "trace/control.h"
trace_event_set_state("virtio_irq", true); /* enable */
[...]
trace_event_set_state("virtio_irq", false); /* disable */
Note that some of the backends do not provide an implementation for this
interface, in which case QEMU will just print a warning.
This functionality is also provided through monitor commands:
The state of events can also be queried and modified through monitor commands:
* info trace-events
View available trace events and their state. State 1 means enabled, state 0
means disabled.
* trace-event NAME on|off
Enable/disable a given trace event or a group of events having common prefix
through wildcard.
Enable/disable a given trace event or a group of events (using wildcards).
The "-trace events=<file>" command line argument can be used to enable the
events listed in <file> from the very beginning of the program. This file must
contain one event name per line.
A basic wildcard matching is supported in both the monitor command "trace
-event" and the events list file. That means you can enable/disable the events
having a common prefix in a batch. For example, virtio-blk trace events could
be enabled using:
trace-event virtio_blk_* on
If a line in the "-trace events=<file>" file begins with a '-', the trace event
will be disabled instead of enabled. This is useful when a wildcard was used
to enable an entire family of events but one noisy event needs to be disabled.
Wildcard matching is supported in both the monitor command "trace-event" and the
events list file. That means you can enable/disable the events having a common
prefix in a batch. For example, virtio-blk trace events could be enabled using
the following monitor command:
trace-event virtio_blk_* on
== Trace backends ==
The "tracetool" script automates tedious trace event code generation and also
@ -263,3 +251,7 @@ guard such computations and avoid its compilation when the event is disabled:
}
return ptr;
}
You can check both if the event has been disabled and is dynamically enabled at
the same time using the 'trace_event_get_state' routine (see header
"trace/control.h" for more information).