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}