LXR linux/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
  20static 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
  49static __attribute__((noreturn))
  50void 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
  72static inline int fsopen(const char *fs_name, unsigned int flags)
  73{
  74        return syscall(__NR_fsopen, fs_name, flags);
  75}
  76
  77static inline int fsmount(int fsfd, unsigned int flags, unsigned int ms_flags)
  78{
  79        return syscall(__NR_fsmount, fsfd, flags, ms_flags);
  80}
  81
  82static 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
  88static 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
 103int 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}
 130