Even after commit c624adc9cb6e ("samples: fix binderfs sample"), this
sample is never compiled.
'hostprogs' teaches Kbuild that this is a host program, but not enough
to order to compile it. You must add it to 'always-y' to really compile
it.
Since this sample has never been compiled in upstream, various issues
are left unnoticed.
[1] compilers without <linux/android/binderfs.h> are still widely used
<linux/android/binderfs.h> is only available since commit c13295ad219d
("binderfs: rename header to binderfs.h"), i.e., Linux 5.0
If your compiler is based on UAPI headers older than Linux 5.0, you
will see the following error:
samples/binderfs/binderfs_example.c:16:10: fatal error: linux/android/binderfs.h: No such file or directory
#include <linux/android/binderfs.h>
^~~~~~~~~~~~~~~~~~~~~~~~~~
compilation terminated.
You cannot rely on compilers to have such a new header.
The common approach is to install UAPI headers of this kernel into
usr/include, and then add it to the header include path.
I added 'depends on HEADERS_INSTALL' in Kconfig, and '-I usr/include'
compiler flag in Makefile.
[2] compile the sample for target architecture
Since headers_install works for the target architecture, only the native
build was able to build sample code that requires '-I usr/include'.
Commit 7f3a59db274c ("kbuild: add infrastructure to build userspace
programs") added the new syntax 'userprogs' to compile user-space
programs for the target architecture.
Use it, and 'ifndef CROSS_COMPILE' will go away.
I added 'depends on CC_CAN_LINK' because $(CC) is not necessarily capable
of linking user-space programs.
[3] use subdir-y to descend into samples/binderfs/
Since this directory does not contain any kernel-space code, it has no
point to generate built-in.a or modules.order.
Replace obj-$(CONFIG_...) with subdir-$(CONFIG_...).
[4] -Wunused-variable warning
If I compile this, I see the following warning.
samples/binderfs/binderfs_example.c: In function 'main':
samples/binderfs/binderfs_example.c:21:9: warning: unused variable 'len' [-Wunused-variable]
21 | size_t len;
| ^~~
I removed the unused 'len'.
[5] CONFIG_ANDROID_BINDERFS is not required
Since this is a user-space standalone program, it is independent of
the kernel configuration.
Remove 'depends on ANDROID_BINDERFS'.
Fixes: 9762dc1432e1 ("samples: add binderfs sample program")
Fixes: c624adc9cb6e ("samples: fix binderfs sample")
Signed-off-by: Masahiro Yamada <masahiroy@xxxxxxxxxx>
---
samples/Kconfig | 2 +-
samples/Makefile | 2 +-
samples/binderfs/Makefile | 9 ++++-----
samples/binderfs/binderfs_example.c | 1 -
4 files changed, 6 insertions(+), 8 deletions(-)
diff --git a/samples/Kconfig b/samples/Kconfig
index 0cbb6146f3cf..953abbdebf7b 100644
--- a/samples/Kconfig
+++ b/samples/Kconfig
@@ -185,7 +185,7 @@ config SAMPLE_VFIO_MDEV_MBOCHS
config SAMPLE_ANDROID_BINDERFS
bool "Build Android binderfs example"
- depends on ANDROID_BINDERFS
+ depends on CC_CAN_LINK && HEADERS_INSTALL
help
Builds a sample program to illustrate the use of the Android binderfs
filesystem.
diff --git a/samples/Makefile b/samples/Makefile
index 29c66aadd954..4029d207cebb 100644
--- a/samples/Makefile
+++ b/samples/Makefile
@@ -2,7 +2,7 @@
# Makefile for Linux samples code
subdir-$(CONFIG_SAMPLE_AUXDISPLAY) += auxdisplay
-obj-$(CONFIG_SAMPLE_ANDROID_BINDERFS) += binderfs/
+subdir-$(CONFIG_SAMPLE_ANDROID_BINDERFS) += binderfs
obj-$(CONFIG_SAMPLE_CONFIGFS) += configfs/
obj-$(CONFIG_SAMPLE_CONNECTOR) += connector/
subdir-$(CONFIG_SAMPLE_HIDRAW) += hidraw
diff --git a/samples/binderfs/Makefile b/samples/binderfs/Makefile
index a3ac5476338a..989e4badaee2 100644
--- a/samples/binderfs/Makefile
+++ b/samples/binderfs/Makefile
@@ -1,6 +1,5 @@
# SPDX-License-Identifier: GPL-2.0-only
-ifndef CROSS_COMPILE
-ifdef CONFIG_SAMPLE_ANDROID_BINDERFS
-hostprogs := binderfs_example
-endif
-endif
+userprogs := binderfs_example
+always-y := $(userprogs)
+
+userccflags += -I usr/include
diff --git a/samples/binderfs/binderfs_example.c b/samples/binderfs/binderfs_example.c
index 5bbd2ebc0aea..0fd92cdda460 100644
--- a/samples/binderfs/binderfs_example.c
+++ b/samples/binderfs/binderfs_example.c
@@ -18,7 +18,6 @@
int main(int argc, char *argv[])
{
int fd, ret, saved_errno;
- size_t len;
struct binderfs_device device = { 0 };
ret = unshare(CLONE_NEWNS);
--
2.25.1
