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 } 130