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, 11 insertions, 3 deletions

diff --git a/samples/Kconfig b/samples/Kconfig
index d63cc8a3e0df..71b5e833dd9e 100644
--- a/samples/Kconfig
+++ b/samples/Kconfig
@@ -1,7 +1,6 @@
 # SPDX-License-Identifier: GPL-2.0-only
 menuconfig SAMPLES
         bool "Sample kernel code"
-        depends on !UML
         help
           You can build and test sample kernel code here.
 
@@ -95,16 +94,24 @@ config SAMPLE_CONFIGFS
 
 config SAMPLE_CONNECTOR
         tristate "Build connector sample -- loadable modules only"
-        depends on CONNECTOR && m
+        depends on CONNECTOR && HEADERS_INSTALL && m
         help
           When enabled, this builds both a sample kernel module for
           the connector interface and a user space tool to communicate
           with it.
           See also Documentation/connector/connector.txt
 
+config SAMPLE_HIDRAW
+        bool "hidraw sample"
+        depends on HEADERS_INSTALL
+
+config SAMPLE_PIDFD
+        bool "pidfd sample"
+        depends on HEADERS_INSTALL
+
 config SAMPLE_SECCOMP
         bool "Build seccomp sample code"
-        depends on SECCOMP_FILTER
+        depends on SECCOMP_FILTER && HEADERS_INSTALL
         help
           Build samples of seccomp filters using various methods of
           BPF filter construction.
@@ -156,6 +163,7 @@ config SAMPLE_ANDROID_BINDERFS
 
 config SAMPLE_VFS
         bool "Build example programs that use new VFS system calls"
+        depends on HEADERS_INSTALL
         help
           Build example userspace programs that use new VFS system calls such
           as mount API and statx().  Note that this is restricted to the x86