fca5e94921
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 having 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 search path.
I added 'depends on HEADERS_INSTALL' in Kconfig, and '-I usr/include'
compiler flag in Makefile.
[2] compile the sample for target architecture
Because headers_install works for the target architecture, only the
native compiler 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 then 'ifndef CROSS_COMPILE' will go away.
I added 'depends on CC_CAN_LINK' because $(CC) is not necessarily
capable of linking user-space programs.
[3] use subdir-y to descend into samples/binderfs
Since this directory does not contain any kernel-space code, it has no
point in generating built-in.a or modules.order.
Replace obj-$(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@kernel.org>
Acked-by: Christian Brauner <christian.brauner@ubuntu.com>
83 lines
1.9 KiB
C
83 lines
1.9 KiB
C
// SPDX-License-Identifier: GPL-2.0
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#define _GNU_SOURCE
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#include <errno.h>
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#include <fcntl.h>
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#include <sched.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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#include <sys/ioctl.h>
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#include <sys/mount.h>
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#include <sys/stat.h>
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#include <sys/types.h>
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#include <unistd.h>
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#include <linux/android/binder.h>
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#include <linux/android/binderfs.h>
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int main(int argc, char *argv[])
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{
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int fd, ret, saved_errno;
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struct binderfs_device device = { 0 };
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ret = unshare(CLONE_NEWNS);
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if (ret < 0) {
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fprintf(stderr, "%s - Failed to unshare mount namespace\n",
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strerror(errno));
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exit(EXIT_FAILURE);
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}
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ret = mount(NULL, "/", NULL, MS_REC | MS_PRIVATE, 0);
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if (ret < 0) {
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fprintf(stderr, "%s - Failed to mount / as private\n",
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strerror(errno));
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exit(EXIT_FAILURE);
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}
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ret = mkdir("/dev/binderfs", 0755);
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if (ret < 0 && errno != EEXIST) {
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fprintf(stderr, "%s - Failed to create binderfs mountpoint\n",
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strerror(errno));
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exit(EXIT_FAILURE);
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}
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ret = mount(NULL, "/dev/binderfs", "binder", 0, 0);
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if (ret < 0) {
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fprintf(stderr, "%s - Failed to mount binderfs\n",
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strerror(errno));
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exit(EXIT_FAILURE);
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}
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memcpy(device.name, "my-binder", strlen("my-binder"));
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fd = open("/dev/binderfs/binder-control", O_RDONLY | O_CLOEXEC);
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if (fd < 0) {
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fprintf(stderr, "%s - Failed to open binder-control device\n",
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strerror(errno));
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exit(EXIT_FAILURE);
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}
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ret = ioctl(fd, BINDER_CTL_ADD, &device);
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saved_errno = errno;
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close(fd);
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errno = saved_errno;
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if (ret < 0) {
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fprintf(stderr, "%s - Failed to allocate new binder device\n",
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strerror(errno));
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exit(EXIT_FAILURE);
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}
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printf("Allocated new binder device with major %d, minor %d, and name %s\n",
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device.major, device.minor, device.name);
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ret = unlink("/dev/binderfs/my-binder");
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if (ret < 0) {
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fprintf(stderr, "%s - Failed to delete binder device\n",
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strerror(errno));
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exit(EXIT_FAILURE);
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}
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/* Cleanup happens when the mount namespace dies. */
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exit(EXIT_SUCCESS);
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}
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