samples/binderfs/binderfs_example.c

0001 // SPDX-License-Identifier: GPL-2.0
0002
0003 #define _GNU_SOURCE
0004 #include <errno.h>
0005 #include <fcntl.h>
0006 #include <sched.h>
0007 #include <stdio.h>
0008 #include <stdlib.h>
0009 #include <string.h>
0010 #include <sys/ioctl.h>
0011 #include <sys/mount.h>
0012 #include <sys/stat.h>
0013 #include <sys/types.h>
0014 #include <unistd.h>
0015 #include <linux/android/binder.h>
0016 #include <linux/android/binderfs.h>
0017
0018 int main(int argc, char *argv[])
0019 {
0020     int fd, ret, saved_errno;
0021     struct binderfs_device device = { 0 };
0022
0023     ret = unshare(CLONE_NEWNS);
0024     if (ret < 0) {
0025         fprintf(stderr, "%s - Failed to unshare mount namespace\n",
0026             strerror(errno));
0027         exit(EXIT_FAILURE);
0028     }
0029
0030     ret = mount(NULL, "/", NULL, MS_REC | MS_PRIVATE, 0);
0031     if (ret < 0) {
0032         fprintf(stderr, "%s - Failed to mount / as private\n",
0033             strerror(errno));
0034         exit(EXIT_FAILURE);
0035     }
0036
0037     ret = mkdir("/dev/binderfs", 0755);
0038     if (ret < 0 && errno != EEXIST) {
0039         fprintf(stderr, "%s - Failed to create binderfs mountpoint\n",
0040             strerror(errno));
0041         exit(EXIT_FAILURE);
0042     }
0043
0044     ret = mount(NULL, "/dev/binderfs", "binder", 0, 0);
0045     if (ret < 0) {
0046         fprintf(stderr, "%s - Failed to mount binderfs\n",
0047             strerror(errno));
0048         exit(EXIT_FAILURE);
0049     }
0050
0051     memcpy(device.name, "my-binder", strlen("my-binder"));
0052
0053     fd = open("/dev/binderfs/binder-control", O_RDONLY | O_CLOEXEC);
0054     if (fd < 0) {
0055         fprintf(stderr, "%s - Failed to open binder-control device\n",
0056             strerror(errno));
0057         exit(EXIT_FAILURE);
0058     }
0059
0060     ret = ioctl(fd, BINDER_CTL_ADD, &device);
0061     saved_errno = errno;
0062     close(fd);
0063     errno = saved_errno;
0064     if (ret < 0) {
0065         fprintf(stderr, "%s - Failed to allocate new binder device\n",
0066             strerror(errno));
0067         exit(EXIT_FAILURE);
0068     }
0069
0070     printf("Allocated new binder device with major %d, minor %d, and name %s\n",
0071            device.major, device.minor, device.name);
0072
0073     ret = unlink("/dev/binderfs/my-binder");
0074     if (ret < 0) {
0075         fprintf(stderr, "%s - Failed to delete binder device\n",
0076             strerror(errno));
0077         exit(EXIT_FAILURE);
0078     }
0079
0080     /* Cleanup happens when the mount namespace dies. */
0081     exit(EXIT_SUCCESS);
0082 }