From 473fda75dd6cfc7a637a1e63c0295bd09a44fe23 Mon Sep 17 00:00:00 2001
From: Bryan Drewery <bdrewery@FreeBSD.org>
Date: Thu, 14 Apr 2016 22:00:33 +0000
Subject: [PATCH] META_MODE+filemon: Default -DNO_CLEAN enabled.

When using meta mode with filemon, the build is reliably incremental
safe.  Bmake will use the meta files, along with filemon information,
to rebuild targets when their dependencies change, commands change,
or files they generate are missing.

Sponsored by:	EMC / Isilon Storage Division
---
 Makefile.inc1          |  9 +++++++++
 share/man/man7/build.7 | 10 +++++++++-
 2 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/Makefile.inc1 b/Makefile.inc1
index 28dc8fbfc4e5..65b0ebc0ab92 100644
--- a/Makefile.inc1
+++ b/Makefile.inc1
@@ -144,6 +144,15 @@ CLEANDIR=	clean cleandepend
 CLEANDIR=	cleandir
 .endif
 
+.if ${MK_META_MODE} == "yes"
+# If filemon is used then we can rely on the build being incremental-safe.
+# The .meta files will also track the build command and rebuild should
+# it change.
+.if empty(.MAKE.MODE:Mnofilemon)
+NO_CLEAN=	t
+.endif
+.endif
+
 LOCAL_TOOL_DIRS?=
 PACKAGEDIR?=	${DESTDIR}/${DISTDIR}
 
diff --git a/share/man/man7/build.7 b/share/man/man7/build.7
index 36603dac5ac3..a605c2846bd2 100644
--- a/share/man/man7/build.7
+++ b/share/man/man7/build.7
@@ -24,7 +24,7 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd March 29, 2016
+.Dd April 14, 2016
 .Dt BUILD 7
 .Os
 .Sh NAME
@@ -539,6 +539,14 @@ instead of
 .Dq make cleandir .
 .It Va NO_CLEAN
 If set, no object tree files are cleaned at all.
+This is the default when
+.Va WITH_META_MODE
+is used with
+.Xr filemon 4
+loaded.
+See
+.Xr src.conf 5
+for more details.
 Setting
 .Va NO_CLEAN
 implies