kbuild: add CONFIG_HEADERS_INSTALL and loosen the dependency of samples

Commit 5318321d367c ("samples: disable CONFIG_SAMPLES for UML") used
a big hammer to fix the build errors under the samples/ directory.
Only some samples actually include uapi headers from usr/include.

Introduce CONFIG_HEADERS_INSTALL since 'depends on HEADERS_INSTALL' is
clearer than 'depends on !UML'. If this option is enabled, uapi headers
are installed before starting directory descending.

I added 'depends on HEADERS_INSTALL' to per-sample CONFIG options.
This allows UML to compile some samples.

$ make ARCH=um allmodconfig samples/
  [ snip ]
  CC [M]  samples/configfs/configfs_sample.o
  CC [M]  samples/kfifo/bytestream-example.o
  CC [M]  samples/kfifo/dma-example.o
  CC [M]  samples/kfifo/inttype-example.o
  CC [M]  samples/kfifo/record-example.o
  CC [M]  samples/kobject/kobject-example.o
  CC [M]  samples/kobject/kset-example.o
  CC [M]  samples/trace_events/trace-events-sample.o
  CC [M]  samples/trace_printk/trace-printk.o
  AR      samples/vfio-mdev/built-in.a
  AR      samples/built-in.a

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

1 files changed, 4 insertions, 4 deletions

diff --git a/Makefile b/Makefile
index 4bc9c708bcdd..f3fd2a549970 100644
--- a/Makefile
+++ b/Makefile
@@ -1053,9 +1053,6 @@ vmlinux: scripts/link-vmlinux.sh autoksyms_recursive $(vmlinux-deps) FORCE
 
 targets := vmlinux
 
-# Some samples need headers_install.
-samples: headers_install
-
 # The actual objects are generated when descending,
 # make sure no implicit rule kicks in
 $(sort $(vmlinux-deps)): $(vmlinux-dirs) ;
@@ -1199,6 +1196,10 @@ headers_check: headers_install
         $(Q)$(MAKE) $(hdr-inst)=include/uapi dst=include HDRCHECK=1
         $(Q)$(MAKE) $(hdr-inst)=arch/$(SRCARCH)/include/uapi dst=include HDRCHECK=1
 
+ifdef CONFIG_HEADERS_INSTALL
+prepare: headers_install
+endif
+
 ifdef CONFIG_HEADERS_CHECK
 all: headers_check
 endif
@@ -1744,7 +1745,6 @@ build-dir = $(patsubst %/,%,$(dir $(build-target)))
 PHONY += /
 /: ./
 
-samples/: headers_install
 %/: prepare FORCE
         $(Q)$(MAKE) KBUILD_MODULES=1 $(build)=$(build-dir)