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samples: add binderfs sample program

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This adds a simple sample program mounting binderfs and adding, then
removing a binder device.  Hopefully, it will be helpful to users who want
to know how binderfs is supposed to be used.

Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
This commit is contained in:
Christian Brauner 2019-01-11 14:41:00 +01:00 committed by Jonathan Corbet
parent 35283f5662
commit 9762dc1432
4 changed files with 92 additions and 1 deletions
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7
samples/Kconfig
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@ -147,6 +147,13 @@ config SAMPLE_VFIO_MDEV_MBOCHS
Specifically it does *not* include any legacy vga stuff.
Device looks a lot like "qemu -device secondary-vga".
config SAMPLE_ANDROID_BINDERFS
bool "Build Android binderfs example"
depends on CONFIG_ANDROID_BINDERFS
help
Builds a sample program to illustrate the use of the Android binderfs
filesystem.
config SAMPLE_STATX
bool "Build example extended-stat using code"
depends on BROKEN

2
samples/Makefile
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@ -3,4 +3,4 @@
obj-$(CONFIG_SAMPLES) += kobject/ kprobes/ trace_events/ livepatch/ \
hw_breakpoint/ kfifo/ kdb/ hidraw/ rpmsg/ seccomp/ \
configfs/ connector/ v4l/ trace_printk/ \
vfio-mdev/ statx/ qmi/
vfio-mdev/ statx/ qmi/ binderfs/

1
samples/binderfs/Makefile Normal file
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@ -0,0 +1 @@
obj-$(CONFIG_SAMPLE_ANDROID_BINDERFS) += binderfs_example.o

83
samples/binderfs/binderfs_example.c Normal file
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@ -0,0 +1,83 @@
// SPDX-License-Identifier: GPL-2.0
#define _GNU_SOURCE
#include <errno.h>
#include <fcntl.h>
#include <sched.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/ioctl.h>
#include <sys/mount.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <unistd.h>
#include <linux/android/binder.h>
#include <linux/android/binderfs.h>
int main(int argc, char *argv[])
{
int fd, ret, saved_errno;
size_t len;
struct binderfs_device device = { 0 };
ret = unshare(CLONE_NEWNS);
if (ret < 0) {
fprintf(stderr, "%s - Failed to unshare mount namespace\n",
strerror(errno));
exit(EXIT_FAILURE);
}
ret = mount(NULL, "/", NULL, MS_REC | MS_PRIVATE, 0);
if (ret < 0) {
fprintf(stderr, "%s - Failed to mount / as private\n",
strerror(errno));
exit(EXIT_FAILURE);
}
ret = mkdir("/dev/binderfs", 0755);
if (ret < 0 && errno != EEXIST) {
fprintf(stderr, "%s - Failed to create binderfs mountpoint\n",
strerror(errno));
exit(EXIT_FAILURE);
}
ret = mount(NULL, "/dev/binderfs", "binder", 0, 0);
if (ret < 0) {
fprintf(stderr, "%s - Failed to mount binderfs\n",
strerror(errno));
exit(EXIT_FAILURE);
}
memcpy(device.name, "my-binder", strlen("my-binder"));
fd = open("/dev/binderfs/binder-control", O_RDONLY | O_CLOEXEC);
if (fd < 0) {
fprintf(stderr, "%s - Failed to open binder-control device\n",
strerror(errno));
exit(EXIT_FAILURE);
}
ret = ioctl(fd, BINDER_CTL_ADD, &device);
saved_errno = errno;
close(fd);
errno = saved_errno;
if (ret < 0) {
fprintf(stderr, "%s - Failed to allocate new binder device\n",
strerror(errno));
exit(EXIT_FAILURE);
}
printf("Allocated new binder device with major %d, minor %d, and name %s\n",
device.major, device.minor, device.name);
ret = unlink("/dev/binderfs/my-binder");
if (ret < 0) {
fprintf(stderr, "%s - Failed to delete binder device\n",
strerror(errno));
exit(EXIT_FAILURE);
}
/* Cleanup happens when the mount namespace dies. */
exit(EXIT_SUCCESS);
}