tracetool: add output filename command-line argument

The tracetool.py script writes to stdout. This means the output filename
is not available to the script. Add the output filename to the
command-line so that the script has access to the filename.

This also simplifies the tracetool.py invocation. It's no longer
necessary to use meson's custom_build(capture : true) to save output.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Message-Id: <20200827142915.108730-2-stefanha@redhat.com>

2 files changed, 23 insertions, 7 deletions

diff --git a/scripts/tracetool.py b/scripts/tracetool.py
index 31146242b7..ab7653a5ce 100755
--- a/scripts/tracetool.py
+++ b/scripts/tracetool.py
@@ -16,7 +16,7 @@ __email__      = "stefanha@redhat.com"
 import sys
 import getopt
 
-from tracetool import error_write, out
+from tracetool import error_write, out, out_open
 import tracetool.backend
 import tracetool.format
 
@@ -32,7 +32,7 @@ def error_opt(msg = None):
     format_descr = "\n".join([ "    %-15s %s" % (n, d)
                                for n,d in tracetool.format.get_list() ])
     error_write("""\
-Usage: %(script)s --format=<format> --backends=<backends> [<options>]
+Usage: %(script)s --format=<format> --backends=<backends> [<options>] <trace-events> ... <output>
 
 Backends:
 %(backends)s
@@ -135,13 +135,15 @@ def main(args):
         if probe_prefix is None:
             probe_prefix = ".".join(["qemu", target_type, target_name])
 
-    if len(args) < 1:
-        error_opt("missing trace-events filepath")
+    if len(args) < 2:
+        error_opt("missing trace-events and output filepaths")
     events = []
-    for arg in args:
+    for arg in args[:-1]:
         with open(arg, "r") as fh:
             events.extend(tracetool.read_events(fh, arg))
 
+    out_open(args[-1])
+
     try:
         tracetool.generate(events, arg_group, arg_format, arg_backends,
                            binary=binary, probe_prefix=probe_prefix)
diff --git a/scripts/tracetool/__init__.py b/scripts/tracetool/__init__.py
index 3ee54be223..a6013389a0 100644
--- a/scripts/tracetool/__init__.py
+++ b/scripts/tracetool/__init__.py
@@ -31,14 +31,28 @@ def error(*lines):
     sys.exit(1)
 
 
+out_filename = '<none>'
+out_fobj = sys.stdout
+
+def out_open(filename):
+    global out_filename, out_fobj
+    out_filename = filename
+    out_fobj = open(filename, 'wt')
+
 def out(*lines, **kwargs):
     """Write a set of output lines.
 
     You can use kwargs as a shorthand for mapping variables when formatting all
     the strings in lines.
+
+    The 'out_filename' kwarg is automatically added with the output filename.
     """
-    lines = [ l % kwargs for l in lines ]
-    sys.stdout.writelines("\n".join(lines) + "\n")
+    output = []
+    for l in lines:
+        kwargs['out_filename'] = out_filename
+        output.append(l % kwargs)
+
+    out_fobj.writelines("\n".join(output) + "\n")
 
 # We only want to allow standard C types or fixed sized
 # integer types. We don't want QEMU specific types