From 210ecc00213aca4682de305caa8cd84c834fa431 Mon Sep 17 00:00:00 2001
From: Bryan Drewery <bdrewery@FreeBSD.org>
Date: Thu, 22 Jun 2017 05:34:41 +0000
Subject: [PATCH] Rework logic for skipping .depend/.meta file
 read/stat/writes.

- Rename _SKIP_READ_DEPEND to _SKIP_DEPEND since it also avoids writing.
- This now uses .NOMETA to avoid reading any .meta files related to
  DEPENDOBJS.  Objects not in OBJS/DEPENDOBJS may still have their .meta
  files read in if they are in the dependency graph.
- This also avoids statting .meta and .depend files in the META_MODE +
  -DNO_FILEMON case.

MFC after:	2 weeks
Sponsored by:	Dell EMC Isilon
---
 share/mk/bsd.dep.mk   | 22 +++++++++++++++++-----
 sys/conf/kern.post.mk | 18 ++++++++++++++----
 2 files changed, 31 insertions(+), 9 deletions(-)

diff --git a/share/mk/bsd.dep.mk b/share/mk/bsd.dep.mk
index 3ed0857724a0..de23ac09833d 100644
--- a/share/mk/bsd.dep.mk
+++ b/share/mk/bsd.dep.mk
@@ -86,10 +86,13 @@ _meta_filemon=	1
 # Skip reading .depend when not needed to speed up tree-walks and simple
 # lookups.  See _SKIP_BUILD logic in bsd.init.mk for more details.
 # Also skip generating or including .depend.* files if in meta+filemon mode
-# since it will track dependencies itself.  OBJS_DEPEND_GUESS is still used.
-.if defined(_SKIP_BUILD) || defined(_meta_filemon)
-_SKIP_READ_DEPEND=	1
+# since it will track dependencies itself.  OBJS_DEPEND_GUESS is still used
+# for _meta_filemon but not for _SKIP_DEPEND.
+.if defined(_SKIP_BUILD)
+_SKIP_DEPEND=	1
+.endif
 .if ${MK_DIRDEPS_BUILD} == "no"
+.if defined(_SKIP_DEPEND) || defined(_meta_filemon)
 .MAKE.DEPENDFILE=	/dev/null
 .endif
 .endif
@@ -180,6 +183,15 @@ DEPENDSRCS=	${SRCS:M*.[cSC]} ${SRCS:M*.cxx} ${SRCS:M*.cpp} ${SRCS:M*.cc}
 DEPENDOBJS+=	${DEPENDSRCS:R:S,$,.o,}
 .endif
 DEPENDFILES_OBJS=	${DEPENDOBJS:O:u:${DEPEND_FILTER}:C/^/${DEPENDFILE}./}
+.if defined(_SKIP_DEPEND)
+# Don't bother statting any .meta files for .depend*
+${DEPENDOBJS}:	.NOMETA
+${DEPENDFILE}:	.NOMETA
+# Unset these to avoid looping/statting on them later.
+.undef DEPENDSRCS
+.undef DEPENDOBJS
+.undef DEPENDFILES_OBJS
+.endif	# defined(_SKIP_DEPEND)
 DEPEND_CFLAGS+=	-MD ${DEPEND_MP} -MF${DEPENDFILE}.${.TARGET:${DEPEND_FILTER}}
 DEPEND_CFLAGS+=	-MT${.TARGET}
 .if !defined(_meta_filemon)
@@ -191,7 +203,6 @@ CFLAGS+=	${${DEPEND_CFLAGS_CONDITION}:?${DEPEND_CFLAGS}:}
 .else
 CFLAGS+=	${DEPEND_CFLAGS}
 .endif
-.if !defined(_SKIP_READ_DEPEND)
 .for __depend_obj in ${DEPENDFILES_OBJS}
 .if ${MAKE_VERSION} < 20160220
 .sinclude "${.OBJDIR}/${__depend_obj}"
@@ -199,7 +210,6 @@ CFLAGS+=	${DEPEND_CFLAGS}
 .dinclude "${.OBJDIR}/${__depend_obj}"
 .endif
 .endfor
-.endif	# !defined(_SKIP_READ_DEPEND)
 .endif	# !defined(_meta_filemon)
 .endif	# defined(SRCS)
 
@@ -266,12 +276,14 @@ DPSRCS+= ${SRCS}
 # targets are kept as they be used for generating something.  The target is
 # kept to allow 'make depend' to generate files.
 ${DEPENDFILE}: ${DPSRCS}
+.if !defined(_SKIP_DEPEND)
 .if exists(${.OBJDIR}/${DEPENDFILE}) || \
     ((commands(beforedepend) || \
     (!defined(_meta_filemon) && commands(_EXTRADEPEND)) || \
     commands(afterdepend)) && !empty(.MAKE.MODE:Mmeta))
 	rm -f ${DEPENDFILE}
 .endif
+.endif
 .if !defined(_meta_filemon) && target(_EXTRADEPEND)
 _EXTRADEPEND: .USE
 ${DEPENDFILE}: _EXTRADEPEND
diff --git a/sys/conf/kern.post.mk b/sys/conf/kern.post.mk
index 5f12952c85eb..b131b72d6ac7 100644
--- a/sys/conf/kern.post.mk
+++ b/sys/conf/kern.post.mk
@@ -199,12 +199,15 @@ _meta_filemon=	1
 # Skip reading .depend when not needed to speed up tree-walks and simple
 # lookups.  For install, only do this if no other targets are specified.
 # Also skip generating or including .depend.* files if in meta+filemon mode
-# since it will track dependencies itself.  OBJS_DEPEND_GUESS is still used.
+# since it will track dependencies itself.  OBJS_DEPEND_GUESS is still used
+# for _meta_filemon but not for _SKIP_DEPEND.
 .if !empty(.MAKEFLAGS:M-V${_V_READ_DEPEND}) || make(*obj) || \
     ${.TARGETS:M*clean*} == ${.TARGETS} || \
     ${.TARGETS:M*install*} == ${.TARGETS} || \
     defined(_meta_filemon)
-_SKIP_READ_DEPEND=	1
+_SKIP_DEPEND=	1
+.endif
+.if defined(_SKIP_DEPEND) || defined(_meta_filemon)
 .MAKE.DEPENDFILE=	/dev/null
 .endif
 
@@ -218,6 +221,15 @@ DEPENDFILES_OBJS=	${DEPENDOBJS:O:u:C/^/.depend./}
 .if ${MAKE_VERSION} < 20160220
 DEPEND_MP?=	-MP
 .endif
+.if defined(_SKIP_DEPEND)
+# Don't bother reading any .meta files
+${DEPENDOBJS}:	.NOMETA
+.depend:	.NOMETA
+# Unset these to avoid looping/statting on them later.
+.undef DEPENDSRCS
+.undef DEPENDOBJS
+.undef DEPENDFILES_OBJS
+.endif	# defined(_SKIP_DEPEND)
 DEPEND_CFLAGS+=	-MD ${DEPEND_MP} -MF.depend.${.TARGET}
 DEPEND_CFLAGS+=	-MT${.TARGET}
 .if !defined(_meta_filemon)
@@ -229,7 +241,6 @@ CFLAGS+=	${${DEPEND_CFLAGS_CONDITION}:?${DEPEND_CFLAGS}:}
 .else
 CFLAGS+=	${DEPEND_CFLAGS}
 .endif
-.if !defined(_SKIP_READ_DEPEND)
 .for __depend_obj in ${DEPENDFILES_OBJS}
 .if ${MAKE_VERSION} < 20160220
 .sinclude "${.OBJDIR}/${__depend_obj}"
@@ -237,7 +248,6 @@ CFLAGS+=	${DEPEND_CFLAGS}
 .dinclude "${.OBJDIR}/${__depend_obj}"
 .endif
 .endfor
-.endif	# !defined(_SKIP_READ_DEPEND)
 .endif	# !defined(_meta_filemon)
 
 # Always run 'make depend' to generate dependencies early and to avoid the