trace: Multi-backend tracing

Adds support to compile QEMU with multiple tracing backends at the same time.

For example, you can compile QEMU with:

  $ ./configure --enable-trace-backends=ftrace,dtrace

Where 'ftrace' can be handy for having an in-flight record of events, and 'dtrace' can be later used to extract more information from the system.

This patch allows having both available without recompiling QEMU.

Signed-off-by: Lluís Vilanova <vilanova@ac.upc.edu>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

2 files changed, 19 insertions, 20 deletions

diff --git a/scripts/tracetool/__init__.py b/scripts/tracetool/__init__.py
index eccf552..e8e8edc 100644
--- a/scripts/tracetool/__init__.py
+++ b/scripts/tracetool/__init__.py
@@ -233,9 +233,9 @@ def try_import(mod_name, attr_name=None, attr_default=None):
         return False, None
 
 
-def generate(fevents, format, backend,
+def generate(fevents, format, backends,
              binary=None, probe_prefix=None):
-    """Generate the output for the given (format, backend) pair.
+    """Generate the output for the given (format, backends) pair.
 
     Parameters
     ----------
@@ -243,8 +243,8 @@ def generate(fevents, format, backend,
         Event description file.
     format : str
         Output format name.
-    backend : str
-        Output backend name.
+    backends : list
+        Output backend names.
     binary : str or None
         See tracetool.backend.dtrace.BINARY.
     probe_prefix : str or None
@@ -258,15 +258,13 @@ def generate(fevents, format, backend,
         raise TracetoolError("format not set")
     if not tracetool.format.exists(format):
         raise TracetoolError("unknown format: %s" % format)
-    format = format.replace("-", "_")
-
-    backend = str(backend)
-    if len(backend) is 0:
-        raise TracetoolError("backend not set")
-    if not tracetool.backend.exists(backend):
-        raise TracetoolError("unknown backend: %s" % backend)
-    backend = backend.replace("-", "_")
-    backend = tracetool.backend.Wrapper(backend, format)
+
+    if len(backends) is 0:
+        raise TracetoolError("no backends specified")
+    for backend in backends:
+        if not tracetool.backend.exists(backend):
+            raise TracetoolError("unknown backend: %s" % backend)
+    backend = tracetool.backend.Wrapper(backends, format)
 
     import tracetool.backend.dtrace
     tracetool.backend.dtrace.BINARY = binary
diff --git a/scripts/tracetool/backend/__init__.py b/scripts/tracetool/backend/__init__.py
index 5e36f04..5bfa1ef 100644
--- a/scripts/tracetool/backend/__init__.py
+++ b/scripts/tracetool/backend/__init__.py
@@ -99,17 +99,18 @@ def exists(name):
 
 
 class Wrapper:
-    def __init__(self, backend, format):
-        self._backend = backend.replace("-", "_")
+    def __init__(self, backends, format):
+        self._backends = [backend.replace("-", "_") for backend in backends]
         self._format = format.replace("-", "_")
-        assert exists(self._backend)
+        assert all(exists(backend) for backend in self._backends)
         assert tracetool.format.exists(self._format)
 
     def _run_function(self, name, *args, **kwargs):
-        func = tracetool.try_import("tracetool.backend." + self._backend,
-                                    name % self._format, None)[1]
-        if func is not None:
-            func(*args, **kwargs)
+        for backend in self._backends:
+            func = tracetool.try_import("tracetool.backend." + backend,
+                                        name % self._format, None)[1]
+            if func is not None:
+                func(*args, **kwargs)
 
     def generate_begin(self, events):
         self._run_function("generate_%s_begin", events)