samples/vfs/test-fsmount.c

   1 // SPDX-License-Identifier: GPL-2.0-or-later
   2 /* fd-based mount test.
   3  *
   4  * Copyright (C) 2017 Red Hat, Inc. All Rights Reserved.
   5  * Written by David Howells (dhowells@redhat.com)
   6  */
   7
   8 #include <stdio.h>
   9 #include <stdlib.h>
  10 #include <unistd.h>
  11 #include <errno.h>
  12 #include <fcntl.h>
  13 #include <sys/prctl.h>
  14 #include <sys/wait.h>
  15 #include <linux/mount.h>
  16 #include <linux/unistd.h>
  17
  18 #define E(x) do { if ((x) == -1) { perror(#x); exit(1); } } while(0)
  19
  20 static void check_messages(int fd)
  21 {
  22         char buf[4096];
  23         int err, n;
  24
  25         err = errno;
  26
  27         for (;;) {
  28                 n = read(fd, buf, sizeof(buf));
  29                 if (n < 0)
  30                         break;
  31                 n -= 2;
  32
  33                 switch (buf[0]) {
  34                 case 'e':
  35                         fprintf(stderr, "Error: %*.*s\n", n, n, buf + 2);
  36                         break;
  37                 case 'w':
  38                         fprintf(stderr, "Warning: %*.*s\n", n, n, buf + 2);
  39                         break;
  40                 case 'i':
  41                         fprintf(stderr, "Info: %*.*s\n", n, n, buf + 2);
  42                         break;
  43                 }
  44         }
  45
  46         errno = err;
  47 }
  48
  49 static __attribute__((noreturn))
  50 void mount_error(int fd, const char *s)
  51 {
  52         check_messages(fd);
  53         fprintf(stderr, "%s: %m\n", s);
  54         exit(1);
  55 }
  56
  57 /* Hope -1 isn't a syscall */
  58 #ifndef __NR_fsopen
  59 #define __NR_fsopen -1
  60 #endif
  61 #ifndef __NR_fsmount
  62 #define __NR_fsmount -1
  63 #endif
  64 #ifndef __NR_fsconfig
  65 #define __NR_fsconfig -1
  66 #endif
  67 #ifndef __NR_move_mount
  68 #define __NR_move_mount -1
  69 #endif
  70
  71
  72 static inline int fsopen(const char *fs_name, unsigned int flags)
  73 {
  74         return syscall(__NR_fsopen, fs_name, flags);
  75 }
  76
  77 static inline int fsmount(int fsfd, unsigned int flags, unsigned int ms_flags)
  78 {
  79         return syscall(__NR_fsmount, fsfd, flags, ms_flags);
  80 }
  81
  82 static inline int fsconfig(int fsfd, unsigned int cmd,
  83                            const char *key, const void *val, int aux)
  84 {
  85         return syscall(__NR_fsconfig, fsfd, cmd, key, val, aux);
  86 }
  87
  88 static inline int move_mount(int from_dfd, const char *from_pathname,
  89                              int to_dfd, const char *to_pathname,
  90                              unsigned int flags)
  91 {
  92         return syscall(__NR_move_mount,
  93                        from_dfd, from_pathname,
  94                        to_dfd, to_pathname, flags);
  95 }
  96
  97 #define E_fsconfig(fd, cmd, key, val, aux)                              \
  98         do {                                                            \
  99                 if (fsconfig(fd, cmd, key, val, aux) == -1)             \
 100                         mount_error(fd, key ?: "create");               \
 101         } while (0)
 102
 103 int main(int argc, char *argv[])
 104 {
 105         int fsfd, mfd;
 106
 107         /* Mount a publically available AFS filesystem */
 108         fsfd = fsopen("afs", 0);
 109         if (fsfd == -1) {
 110                 perror("fsopen");
 111                 exit(1);
 112         }
 113
 114         E_fsconfig(fsfd, FSCONFIG_SET_STRING, "source", "#grand.central.org:root.cell.", 0);
 115         E_fsconfig(fsfd, FSCONFIG_CMD_CREATE, NULL, NULL, 0);
 116
 117         mfd = fsmount(fsfd, 0, MOUNT_ATTR_RDONLY);
 118         if (mfd < 0)
 119                 mount_error(fsfd, "fsmount");
 120         E(close(fsfd));
 121
 122         if (move_mount(mfd, "", AT_FDCWD, "/mnt", MOVE_MOUNT_F_EMPTY_PATH) < 0) {
 123                 perror("move_mount");
 124                 exit(1);
 125         }
 126
 127         E(close(mfd));
 128         exit(0);
 129 }