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Subject[PATCH v1 2/2] samples: add binderfs sample program
Date
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>
---
/* Changelog */
v1:
- patch introduced

v0:
- patch not present
---
samples/Kconfig | 7 +++
samples/Makefile | 2 +-
samples/binderfs/Makefile | 1 +
samples/binderfs/binderfs_example.c | 83 +++++++++++++++++++++++++++++
4 files changed, 92 insertions(+), 1 deletion(-)
create mode 100644 samples/binderfs/Makefile
create mode 100644 samples/binderfs/binderfs_example.c

diff --git a/samples/Kconfig b/samples/Kconfig
index ad1ec7016d4c..d19754ccad08 100644
--- a/samples/Kconfig
+++ b/samples/Kconfig
@@ -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
diff --git a/samples/Makefile b/samples/Makefile
index bd601c038b86..b1142a958811 100644
--- a/samples/Makefile
+++ b/samples/Makefile
@@ -3,4 +3,4 @@
obj-$(CONFIG_SAMPLES) += kobject/ kprobes/ trace_events/ livepatch/ \
hw_breakpoint/ kfifo/ kdb/ hidraw/ rpmsg/ seccomp/ \
configfs/ connector/ v4l/ trace_printk/ \
- vfio-mdev/ statx/ qmi/
+ vfio-mdev/ statx/ qmi/ binderfs/
diff --git a/samples/binderfs/Makefile b/samples/binderfs/Makefile
new file mode 100644
index 000000000000..01ca9f2529a7
--- /dev/null
+++ b/samples/binderfs/Makefile
@@ -0,0 +1 @@
+obj-$(CONFIG_SAMPLE_ANDROID_BINDERFS) += binderfs_example.o
diff --git a/samples/binderfs/binderfs_example.c b/samples/binderfs/binderfs_example.c
new file mode 100644
index 000000000000..5bbd2ebc0aea
--- /dev/null
+++ b/samples/binderfs/binderfs_example.c
@@ -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);
+}
--
2.19.1
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