WITH_META_MODE: Lessen the filemon(4) requirement scope.

- Move the sys.mk filemon requirement to bsd.init.mk as a warning.
  This is intended only to show when building directly in a subdirectory
  without filemon loaded.
- Move the error into Makefile and only apply it when building
  from the META_TGT_WHITELIST target list.

-DNO_FILEMON can be used to suppress both the warning and the error but
makes WITH_META_MODE less useful.  It will only compare build commands
in this mode rather than track all dependencies.

This fixes installing from a jail which doesn't need filemon in this
phase [1].

Reported by:	Nikolai Lifanov <lifanov@mail.lifanov.com> [1]
Approved by:	re (implicit)
Sponsored by:	EMC / Isilon Storage Division

4 files changed, 23 insertions, 6 deletions

diff --git a/Makefile b/Makefile
index 5e2f951..b829916 100644
--- a/Makefile
+++ b/Makefile
@@ -219,6 +219,13 @@ _CAN_USE_META_MODE?= yes
 .if !defined(_CAN_USE_META_MODE)
 _MAKE+=	MK_META_MODE=no
 .unexport META_MODE
+.elif ${MK_META_MODE} == "yes"
+.if !exists(/dev/filemon) && !defined(NO_FILEMON) && !make(showconfig)
+# Require filemon be loaded to provide a working incremental build
+.error ${.newline}ERROR: The filemon module (/dev/filemon) is not loaded. \
+    ${.newline}ERROR: WITH_META_MODE is enabled but requires filemon for an incremental build. \
+    ${.newline}ERROR: 'kldload filemon' or pass -DNO_FILEMON to suppress this error.
+.endif	# !exists(/dev/filemon) && !defined(NO_FILEMON)
 .endif	# !defined(_CAN_USE_META_MODE)
 
 # Guess machine architecture from machine type, and vice versa.
diff --git a/share/mk/bsd.init.mk b/share/mk/bsd.init.mk
index d00b9e5..01d5c47 100644
--- a/share/mk/bsd.init.mk
+++ b/share/mk/bsd.init.mk
@@ -28,4 +28,14 @@ _SKIP_BUILD = not building at level 0
 .warning ${_SKIP_BUILD}
 .endif
 
+.if ${MK_META_MODE} == "yes"
+.if !exists(/dev/filemon) && \
+    ${UPDATE_DEPENDFILE:Uyes:tl} != "no" && !defined(NO_FILEMON) && \
+    !make(showconfig)
+.warning The filemon module (/dev/filemon) is not loaded.
+.warning META_MODE is less useful for incremental builds without filemon.
+.warning 'kldload filemon' or pass -DNO_FILEMON to suppress this warning.
+.endif
+.endif	# ${MK_META_MODE} == "yes"
+
 .endif	# !target(__<bsd.init.mk>__)
diff --git a/share/mk/sys.mk b/share/mk/sys.mk
index e103fdd..cccc543 100644
--- a/share/mk/sys.mk
+++ b/share/mk/sys.mk
@@ -60,10 +60,6 @@ META_MODE+=	missing-meta=yes
 META_MODE+=	silent=yes
 .endif
 .if !exists(/dev/filemon)
-.if ${UPDATE_DEPENDFILE:Uyes:tl} != "no" && !defined(NO_FILEMON) && \
-    !make(showconfig)
-.error ${.newline}ERROR: The filemon module (/dev/filemon) is not loaded.
-.endif
 META_MODE+= nofilemon
 .endif
 # Require filemon data with bmake
diff --git a/tools/build/options/WITH_META_MODE b/tools/build/options/WITH_META_MODE
index 775ab01..65595ac 100644
--- a/tools/build/options/WITH_META_MODE
+++ b/tools/build/options/WITH_META_MODE
@@ -7,9 +7,13 @@ using
 The meta file is created in the OBJDIR as
 .Pa target.meta .
 These meta files track the command ran, its output, and the current directory.
-When the
+The
 .Xr filemon 4
-module is loaded, any files used by the commands executed will be tracked as
+module is required unless
+.Va NO_FILEMON
+is defined.
+When the module is loaded, any files used by the commands executed will be
+tracked as
 dependencies for the target in its meta file.
 The target will be considered out-of-date and rebuilt if any of the following
 are true compared to the last build: