From d74daa8fceca8785c72a449f370225ee137bb8d3 Mon Sep 17 00:00:00 2001 From: Markus Armbruster Date: Fri, 9 Mar 2018 08:51:12 -0500 Subject: [PATCH] qapi: Touch generated files only when they change A massive number of objects depends on QAPI-generated headers. In my "build everything" tree, it's roughly 4800 out of 5100. This is particularly annoying when only some of the generated files change, say for a doc fix. Improve qapi-gen.py to touch its output files only if they actually change. Rebuild time for a QAPI doc fix drops from many minutes to a few seconds. Rebuilds get faster for certain code changes, too. For instance, adding a simple QMP event now recompiles less than 200 instead of 4800 objects. But adding a QAPI type is as bad as ever; we've clearly got more work to do. Backports commit 907b846653fb3757bf2ab98d6d66f92df34d875f from qemu --- qemu/scripts/qapi/common.py | 11 +++++++++-- 1 file changed, 9 insertions(+), 2 deletions(-) diff --git a/qemu/scripts/qapi/common.py b/qemu/scripts/qapi/common.py index 00746a9c..24eb558e 100644 --- a/qemu/scripts/qapi/common.py +++ b/qemu/scripts/qapi/common.py @@ -1956,9 +1956,16 @@ class QAPIGen(object): except os.error as e: if e.errno != errno.EEXIST: raise - f = open(os.path.join(output_dir, fname), 'w') - f.write(self._top(fname) + self._preamble + self._body + fd = os.open(os.path.join(output_dir, fname), + os.O_RDWR | os.O_CREAT, 0o666) + f = os.fdopen(fd, 'r+') + text = (self._top(fname) + self._preamble + self._body + self._bottom(fname)) + oldtext = f.read(len(text) + 1) + if text != oldtext: + f.seek(0) + f.truncate(0) + f.write(text) f.close()