samples/binderfs/binderfs_example.c

   1 // SPDX-License-Identifier: GPL-2.0
   2
   3 #define _GNU_SOURCE
   4 #include <errno.h>
   5 #include <fcntl.h>
   6 #include <sched.h>
   7 #include <stdio.h>
   8 #include <stdlib.h>
   9 #include <string.h>
  10 #include <sys/ioctl.h>
  11 #include <sys/mount.h>
  12 #include <sys/stat.h>
  13 #include <sys/types.h>
  14 #include <unistd.h>
  15 #include <linux/android/binder.h>
  16 #include <linux/android/binderfs.h>
  17
  18 int main(int argc, char *argv[])
  19 {
  20         int fd, ret, saved_errno;
  21         struct binderfs_device device = { 0 };
  22
  23         ret = unshare(CLONE_NEWNS);
  24         if (ret < 0) {
  25                 fprintf(stderr, "%s - Failed to unshare mount namespace\n",
  26                         strerror(errno));
  27                 exit(EXIT_FAILURE);
  28         }
  29
  30         ret = mount(NULL, "/", NULL, MS_REC | MS_PRIVATE, 0);
  31         if (ret < 0) {
  32                 fprintf(stderr, "%s - Failed to mount / as private\n",
  33                         strerror(errno));
  34                 exit(EXIT_FAILURE);
  35         }
  36
  37         ret = mkdir("/dev/binderfs", 0755);
  38         if (ret < 0 && errno != EEXIST) {
  39                 fprintf(stderr, "%s - Failed to create binderfs mountpoint\n",
  40                         strerror(errno));
  41                 exit(EXIT_FAILURE);
  42         }
  43
  44         ret = mount(NULL, "/dev/binderfs", "binder", 0, 0);
  45         if (ret < 0) {
  46                 fprintf(stderr, "%s - Failed to mount binderfs\n",
  47                         strerror(errno));
  48                 exit(EXIT_FAILURE);
  49         }
  50
  51         memcpy(device.name, "my-binder", strlen("my-binder"));
  52
  53         fd = open("/dev/binderfs/binder-control", O_RDONLY | O_CLOEXEC);
  54         if (fd < 0) {
  55                 fprintf(stderr, "%s - Failed to open binder-control device\n",
  56                         strerror(errno));
  57                 exit(EXIT_FAILURE);
  58         }
  59
  60         ret = ioctl(fd, BINDER_CTL_ADD, &device);
  61         saved_errno = errno;
  62         close(fd);
  63         errno = saved_errno;
  64         if (ret < 0) {
  65                 fprintf(stderr, "%s - Failed to allocate new binder device\n",
  66                         strerror(errno));
  67                 exit(EXIT_FAILURE);
  68         }
  69
  70         printf("Allocated new binder device with major %d, minor %d, and name %s\n",
  71                device.major, device.minor, device.name);
  72
  73         ret = unlink("/dev/binderfs/my-binder");
  74         if (ret < 0) {
  75                 fprintf(stderr, "%s - Failed to delete binder device\n",
  76                         strerror(errno));
  77                 exit(EXIT_FAILURE);
  78         }
  79
  80         /* Cleanup happens when the mount namespace dies. */
  81         exit(EXIT_SUCCESS);
  82 }