mergerfs/libfuse/util/fusermount.c

/*
  FUSE: Filesystem in Userspace
  Copyright (C) 2001-2007  Miklos Szeredi <miklos@szeredi.hu>

  This program can be distributed under the terms of the GNU GPL.
  See the file COPYING.
*/
/* This program does the mounting and unmounting of FUSE filesystems */

#define _GNU_SOURCE /* for clone */
#include <config.h>

#include "mount_util.h"
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
#include <unistd.h>
#include <getopt.h>
#include <errno.h>
#include <fcntl.h>
#include <pwd.h>
#include <paths.h>
#include <mntent.h>
#include <sys/wait.h>
#include <sys/stat.h>
#include <sys/mount.h>
#include <sys/fsuid.h>
#include <sys/socket.h>
#include <sys/utsname.h>
#include <sched.h>

#define FUSE_COMMFD_ENV		"_FUSE_COMMFD"

#define FUSE_DEV_OLD "/proc/fs/fuse/dev"
#define FUSE_DEV_NEW "/dev/fuse"
#define FUSE_VERSION_FILE_OLD "/proc/fs/fuse/version"
#define FUSE_CONF "/etc/fuse.conf"

#ifndef MS_DIRSYNC
#define MS_DIRSYNC 128
#endif
#ifndef MS_REC
#define MS_REC 16384
#endif
#ifndef MS_PRIVATE
#define MS_PRIVATE (1<<18)
#endif

#ifndef UMOUNT_DETACH
#define UMOUNT_DETACH	0x00000002	/* Just detach from the tree */
#endif
#ifndef UMOUNT_NOFOLLOW
#define UMOUNT_NOFOLLOW	0x00000008	/* Don't follow symlink on umount */
#endif
#ifndef UMOUNT_UNUSED
#define UMOUNT_UNUSED	0x80000000	/* Flag guaranteed to be unused */
#endif

static const char *progname;

static int user_allow_other = 0;
static int mount_max = 1000;

static int auto_unmount = 0;

static const char *get_user_name(void)
{
  struct passwd *pw = getpwuid(getuid());
  if (pw != NULL && pw->pw_name != NULL)
    return pw->pw_name;
  else {
    fprintf(stderr, "%s: could not determine username\n", progname);
    return NULL;
  }
}

static uid_t oldfsuid;
static gid_t oldfsgid;

static void drop_privs(void)
{
  if (getuid() != 0) {
    oldfsuid = setfsuid(getuid());
    oldfsgid = setfsgid(getgid());
  }
}

static void restore_privs(void)
{
  if (getuid() != 0) {
    setfsuid(oldfsuid);
    setfsgid(oldfsgid);
  }
}

#ifndef IGNORE_MTAB
/*
 * Make sure that /etc/mtab is checked and updated atomically
 */
static int lock_umount(void)
{
  const char *mtab_lock = _PATH_MOUNTED ".fuselock";
  int mtablock;
  int res;
  struct stat mtab_stat;

  /* /etc/mtab could be a symlink to /proc/mounts */
  if (lstat(_PATH_MOUNTED, &mtab_stat) == 0 && S_ISLNK(mtab_stat.st_mode))
    return -1;

  mtablock = open(mtab_lock, O_RDWR | O_CREAT, 0600);
  if (mtablock == -1) {
    fprintf(stderr, "%s: unable to open fuse lock file: %s\n",
            progname, strerror(errno));
    return -1;
  }
  res = lockf(mtablock, F_LOCK, 0);
  if (res < 0) {
    fprintf(stderr, "%s: error getting lock: %s\n", progname,
            strerror(errno));
    close(mtablock);
    return -1;
  }

  return mtablock;
}

static void unlock_umount(int mtablock)
{
  if (mtablock >= 0) {
    int res;

    res = lockf(mtablock, F_ULOCK, 0);
    if (res < 0) {
      fprintf(stderr, "%s: error releasing lock: %s\n",
              progname, strerror(errno));
    }
    close(mtablock);
  }
}

static int add_mount(const char *source, const char *mnt, const char *type,
		     const char *opts)
{
  return fuse_mnt_add_mount(progname, source, mnt, type, opts);
}

static int may_unmount(const char *mnt, int quiet)
{
  struct mntent *entp;
  FILE *fp;
  const char *user = NULL;
  char uidstr[32];
  unsigned uidlen = 0;
  int found;
  const char *mtab = _PATH_MOUNTED;

  user = get_user_name();
  if (user == NULL)
    return -1;

  fp = setmntent(mtab, "r");
  if (fp == NULL) {
    fprintf(stderr, "%s: failed to open %s: %s\n", progname, mtab,
            strerror(errno));
    return -1;
  }

  uidlen = sprintf(uidstr, "%u", getuid());

  found = 0;
  while ((entp = getmntent(fp)) != NULL) {
    if (!found && strcmp(entp->mnt_dir, mnt) == 0 &&
        (strcmp(entp->mnt_type, "fuse") == 0 ||
         strncmp(entp->mnt_type, "fuse.", 5) == 0)) {
      char *p = strstr(entp->mnt_opts, "user=");
      if (p &&
          (p == entp->mnt_opts || *(p-1) == ',') &&
          strcmp(p + 5, user) == 0) {
        found = 1;
        break;
      }
      /* /etc/mtab is a link pointing to
         /proc/mounts: */
      else if ((p =
                strstr(entp->mnt_opts, "user_id=")) &&
               (p == entp->mnt_opts ||
                *(p-1) == ',') &&
               strncmp(p + 8, uidstr, uidlen) == 0 &&
               (*(p+8+uidlen) == ',' ||
                *(p+8+uidlen) == '\0')) {
        found = 1;
        break;
      }
    }
  }
  endmntent(fp);

  if (!found) {
    if (!quiet)
      fprintf(stderr,
              "%s: entry for %s not found in %s\n",
              progname, mnt, mtab);
    return -1;
  }

  return 0;
}

/*
 * Check whether the file specified in "fusermount -u" is really a
 * mountpoint and not a symlink.  This is necessary otherwise the user
 * could move the mountpoint away and replace it with a symlink
 * pointing to an arbitrary mount, thereby tricking fusermount into
 * unmounting that (umount(2) will follow symlinks).
 *
 * This is the child process running in a separate mount namespace, so
 * we don't mess with the global namespace and if the process is
 * killed for any reason, mounts are automatically cleaned up.
 *
 * First make sure nothing is propagated back into the parent
 * namespace by marking all mounts "private".
 *
 * Then bind mount parent onto a stable base where the user can't move
 * it around.
 *
 * Finally check /proc/mounts for an entry matching the requested
 * mountpoint.  If it's found then we are OK, and the user can't move
 * it around within the parent directory as rename() will return
 * EBUSY.  Be careful to ignore any mounts that existed before the
 * bind.
 */
static int check_is_mount_child(void *p)
{
  const char **a = p;
  const char *last = a[0];
  const char *mnt = a[1];
  int res;
  const char *procmounts = "/proc/mounts";
  int found;
  FILE *fp;
  struct mntent *entp;
  int count;

  res = mount("", "/", "", MS_PRIVATE | MS_REC, NULL);
  if (res == -1) {
    fprintf(stderr, "%s: failed to mark mounts private: %s\n",
            progname, strerror(errno));
    return 1;
  }

  fp = setmntent(procmounts, "r");
  if (fp == NULL) {
    fprintf(stderr, "%s: failed to open %s: %s\n", progname,
            procmounts, strerror(errno));
    return 1;
  }

  count = 0;
  while (getmntent(fp) != NULL)
    count++;
  endmntent(fp);

  fp = setmntent(procmounts, "r");
  if (fp == NULL) {
    fprintf(stderr, "%s: failed to open %s: %s\n", progname,
            procmounts, strerror(errno));
    return 1;
  }

  res = mount(".", "/", "", MS_BIND | MS_REC, NULL);
  if (res == -1) {
    fprintf(stderr, "%s: failed to bind parent to /: %s\n",
            progname, strerror(errno));
    return 1;
  }

  found = 0;
  while ((entp = getmntent(fp)) != NULL) {
    if (count > 0) {
      count--;
      continue;
    }
    if (entp->mnt_dir[0] == '/' &&
        strcmp(entp->mnt_dir + 1, last) == 0) {
      found = 1;
      break;
    }
  }
  endmntent(fp);

  if (!found) {
    fprintf(stderr, "%s: %s not mounted\n", progname, mnt);
    return 1;
  }

  return 0;
}

static pid_t clone_newns(void *a)
{
  char buf[131072];
  char *stack = buf + (sizeof(buf) / 2 - ((size_t) buf & 15));

#ifdef __ia64__
  extern int __clone2(int (*fn)(void *),
                      void *child_stack_base, size_t stack_size,
                      int flags, void *arg, pid_t *ptid,
                      void *tls, pid_t *ctid);

  return __clone2(check_is_mount_child, stack, sizeof(buf) / 2,
                  CLONE_NEWNS, a, NULL, NULL, NULL);
#else
  return clone(check_is_mount_child, stack, CLONE_NEWNS, a);
#endif
}

static int check_is_mount(const char *last, const char *mnt)
{
  pid_t pid, p;
  int status;
  const char *a[2] = { last, mnt };

  pid = clone_newns((void *) a);
  if (pid == (pid_t) -1) {
    fprintf(stderr, "%s: failed to clone namespace: %s\n",
            progname, strerror(errno));
    return -1;
  }
  p = waitpid(pid, &status, __WCLONE);
  if (p == (pid_t) -1) {
    fprintf(stderr, "%s: waitpid failed: %s\n",
            progname, strerror(errno));
    return -1;
  }
  if (!WIFEXITED(status)) {
    fprintf(stderr, "%s: child terminated abnormally (status %i)\n",
            progname, status);
    return -1;
  }
  if (WEXITSTATUS(status) != 0)
    return -1;

  return 0;
}

static int chdir_to_parent(char *copy, const char **lastp)
{
  char *tmp;
  const char *parent;
  char buf[65536];
  int res;

  tmp = strrchr(copy, '/');
  if (tmp == NULL || tmp[1] == '\0') {
    fprintf(stderr, "%s: internal error: invalid abs path: <%s>\n",
            progname, copy);
    return -1;
  }
  if (tmp != copy) {
    *tmp = '\0';
    parent = copy;
    *lastp = tmp + 1;
  } else if (tmp[1] != '\0') {
    *lastp = tmp + 1;
    parent = "/";
  } else {
    *lastp = ".";
    parent = "/";
  }

  res = chdir(parent);
  if (res == -1) {
    fprintf(stderr, "%s: failed to chdir to %s: %s\n",
            progname, parent, strerror(errno));
    return -1;
  }

  if (getcwd(buf, sizeof(buf)) == NULL) {
    fprintf(stderr, "%s: failed to obtain current directory: %s\n",
            progname, strerror(errno));
    return -1;
  }
  if (strcmp(buf, parent) != 0) {
    fprintf(stderr, "%s: mountpoint moved (%s -> %s)\n", progname,
            parent, buf);
    return -1;

  }

  return 0;
}

/* Check whether the kernel supports UMOUNT_NOFOLLOW flag */
static int umount_nofollow_support(void)
{
  int res = umount2("", UMOUNT_UNUSED);
  if (res != -1 || errno != EINVAL)
    return 0;

  res = umount2("", UMOUNT_NOFOLLOW);
  if (res != -1 || errno != ENOENT)
    return 0;

  return 1;
}

static int unmount_fuse_locked(const char *mnt, int quiet, int lazy)
{
  int res;
  char *copy;
  const char *last;
  int umount_flags = lazy ? UMOUNT_DETACH : 0;

  if (getuid() != 0) {
    res = may_unmount(mnt, quiet);
    if (res == -1)
      return -1;
  }

  copy = strdup(mnt);
  if (copy == NULL) {
    fprintf(stderr, "%s: failed to allocate memory\n", progname);
    return -1;
  }

  res = chdir_to_parent(copy, &last);
  if (res == -1)
    goto out;

  if (umount_nofollow_support()) {
    umount_flags |= UMOUNT_NOFOLLOW;
  } else {
    res = check_is_mount(last, mnt);
    if (res == -1)
      goto out;
  }

  res = umount2(last, umount_flags);
  if (res == -1 && !quiet) {
    fprintf(stderr, "%s: failed to unmount %s: %s\n",
            progname, mnt, strerror(errno));
  }

 out:
  if (res == -1)
    return -1;

  res = chdir("/");
  if (res == -1) {
    fprintf(stderr, "%s: failed to chdir to '/'\n", progname);
    return -1;
  }

  return fuse_mnt_remove_mount(progname, mnt);
}

static int unmount_fuse(const char *mnt, int quiet, int lazy)
{
  int res;
  int mtablock = lock_umount();

  res = unmount_fuse_locked(mnt, quiet, lazy);
  unlock_umount(mtablock);

  return res;
}

static int count_fuse_fs(void)
{
  struct mntent *entp;
  int count = 0;
  const char *mtab = _PATH_MOUNTED;
  FILE *fp = setmntent(mtab, "r");
  if (fp == NULL) {
    fprintf(stderr, "%s: failed to open %s: %s\n", progname, mtab,
            strerror(errno));
    return -1;
  }
  while ((entp = getmntent(fp)) != NULL) {
    if (strcmp(entp->mnt_type, "fuse") == 0 ||
        strncmp(entp->mnt_type, "fuse.", 5) == 0)
      count ++;
  }
  endmntent(fp);
  return count;
}


#else /* IGNORE_MTAB */
static int count_fuse_fs()
{
  return 0;
}

static int add_mount(const char *source, const char *mnt, const char *type,
		     const char *opts)
{
  (void) source;
  (void) mnt;
  (void) type;
  (void) opts;
  return 0;
}

static int unmount_fuse(const char *mnt, int quiet, int lazy)
{
  return fuse_mnt_umount(progname, mnt, mnt, lazy);
}
#endif /* IGNORE_MTAB */

static void strip_line(char *line)
{
  char *s = strchr(line, '#');
  if (s != NULL)
    s[0] = '\0';
  for (s = line + strlen(line) - 1;
       s >= line && isspace((unsigned char) *s); s--);
  s[1] = '\0';
  for (s = line; isspace((unsigned char) *s); s++);
  if (s != line)
    memmove(line, s, strlen(s)+1);
}

static void parse_line(char *line, int linenum)
{
  int tmp;
  if (strcmp(line, "user_allow_other") == 0)
    user_allow_other = 1;
  else if (sscanf(line, "mount_max = %i", &tmp) == 1)
    mount_max = tmp;
  else if(line[0])
    fprintf(stderr,
            "%s: unknown parameter in %s at line %i: '%s'\n",
            progname, FUSE_CONF, linenum, line);
}

static void read_conf(void)
{
  FILE *fp = fopen(FUSE_CONF, "r");
  if (fp != NULL) {
    int linenum = 1;
    char line[256];
    int isnewline = 1;
    while (fgets(line, sizeof(line), fp) != NULL) {
      if (isnewline) {
        if (line[strlen(line)-1] == '\n') {
          strip_line(line);
          parse_line(line, linenum);
        } else {
          isnewline = 0;
        }
      } else if(line[strlen(line)-1] == '\n') {
        fprintf(stderr, "%s: reading %s: line %i too long\n", progname, FUSE_CONF, linenum);

        isnewline = 1;
      }
      if (isnewline)
        linenum ++;
    }
    if (!isnewline) {
      fprintf(stderr, "%s: reading %s: missing newline at end of file\n", progname, FUSE_CONF);

    }
    fclose(fp);
  } else if (errno != ENOENT) {
    fprintf(stderr, "%s: failed to open %s: %s\n",
            progname, FUSE_CONF, strerror(errno));
  }
}

static int begins_with(const char *s, const char *beg)
{
  if (strncmp(s, beg, strlen(beg)) == 0)
    return 1;
  else
    return 0;
}

struct mount_flags {
  const char *opt;
  unsigned long flag;
  int on;
  int safe;
};

static struct mount_flags mount_flags[] = {
  {"rw",	    MS_RDONLY,	    0, 1},
  {"ro",	    MS_RDONLY,	    1, 1},
  {"suid",    MS_NOSUID,	    0, 0},
  {"nosuid",  MS_NOSUID,	    1, 1},
  {"dev",	    MS_NODEV,	    0, 0},
  {"nodev",   MS_NODEV,	    1, 1},
  {"exec",    MS_NOEXEC,	    0, 1},
  {"noexec",  MS_NOEXEC,	    1, 1},
  {"async",   MS_SYNCHRONOUS, 0, 1},
  {"sync",    MS_SYNCHRONOUS, 1, 1},
  {"atime",   MS_NOATIME,	    0, 1},
  {"noatime", MS_NOATIME,	    1, 1},
  {"dirsync", MS_DIRSYNC,	    1, 1},
  {NULL,	    0,		    0, 0}
};

static int find_mount_flag(const char *s, unsigned len, int *on, int *flag)
{
  int i;

  for (i = 0; mount_flags[i].opt != NULL; i++) {
    const char *opt = mount_flags[i].opt;
    if (strlen(opt) == len && strncmp(opt, s, len) == 0) {
      *on = mount_flags[i].on;
      *flag = mount_flags[i].flag;
      if (!mount_flags[i].safe && getuid() != 0) {
        *flag = 0;
        fprintf(stderr,
                "%s: unsafe option %s ignored\n",
                progname, opt);
      }
      return 1;
    }
  }
  return 0;
}

static int add_option(char **optsp, const char *opt, unsigned expand)
{
  char *newopts;
  if (*optsp == NULL)
    newopts = strdup(opt);
  else {
    unsigned oldsize = strlen(*optsp);
    unsigned newsize = oldsize + 1 + strlen(opt) + expand + 1;
    newopts = (char *) realloc(*optsp, newsize);
    if (newopts)
      sprintf(newopts + oldsize, ",%s", opt);
  }
  if (newopts == NULL) {
    fprintf(stderr, "%s: failed to allocate memory\n", progname);
    return -1;
  }
  *optsp = newopts;
  return 0;
}

static int get_mnt_opts(int flags, char *opts, char **mnt_optsp)
{
  int i;
  int l;

  if (!(flags & MS_RDONLY) && add_option(mnt_optsp, "rw", 0) == -1)
    return -1;

  for (i = 0; mount_flags[i].opt != NULL; i++) {
    if (mount_flags[i].on && (flags & mount_flags[i].flag) &&
        add_option(mnt_optsp, mount_flags[i].opt, 0) == -1)
      return -1;
  }

  if (add_option(mnt_optsp, opts, 0) == -1)
    return -1;
  /* remove comma from end of opts*/
  l = strlen(*mnt_optsp);
  if ((*mnt_optsp)[l-1] == ',')
    (*mnt_optsp)[l-1] = '\0';
  if (getuid() != 0) {
    const char *user = get_user_name();
    if (user == NULL)
      return -1;

    if (add_option(mnt_optsp, "user=", strlen(user)) == -1)
      return -1;
    strcat(*mnt_optsp, user);
  }
  return 0;
}

static int opt_eq(const char *s, unsigned len, const char *opt)
{
  if(strlen(opt) == len && strncmp(s, opt, len) == 0)
    return 1;
  else
    return 0;
}

static int get_string_opt(const char *s, unsigned len, const char *opt,
			  char **val)
{
  int i;
  unsigned opt_len = strlen(opt);
  char *d;

  if (*val)
    free(*val);
  *val = (char *) malloc(len - opt_len + 1);
  if (!*val) {
    fprintf(stderr, "%s: failed to allocate memory\n", progname);
    return 0;
  }

  d = *val;
  s += opt_len;
  len -= opt_len;
  for (i = 0; i < len; i++) {
    if (s[i] == '\\' && i + 1 < len)
      i++;
    *d++ = s[i];
  }
  *d = '\0';
  return 1;
}

static int do_mount(const char *mnt, char **typep, mode_t rootmode,
		    int fd, const char *opts, const char *dev, char **sourcep,
		    char **mnt_optsp, off_t rootsize)
{
  int res;
  int flags = MS_NOSUID | MS_NODEV;
  char *optbuf;
  char *mnt_opts = NULL;
  const char *s;
  char *d;
  char *fsname = NULL;
  char *subtype = NULL;
  char *source = NULL;
  char *type = NULL;
  int check_empty = 1;

  optbuf = (char *) malloc(strlen(opts) + 128);
  if (!optbuf) {
    fprintf(stderr, "%s: failed to allocate memory\n", progname);
    return -1;
  }

  for (s = opts, d = optbuf; *s;) {
    unsigned len;
    const char *fsname_str = "fsname=";
    const char *subtype_str = "subtype=";
    for (len = 0; s[len]; len++) {
      if (s[len] == '\\' && s[len + 1])
        len++;
      else if (s[len] == ',')
        break;
    }
    if (begins_with(s, fsname_str)) {
      if (!get_string_opt(s, len, fsname_str, &fsname))
        goto err;
    } else if (begins_with(s, subtype_str)) {
      if (!get_string_opt(s, len, subtype_str, &subtype))
        goto err;
    } else if (opt_eq(s, len, "nonempty")) {
      check_empty = 0;
    } else if (opt_eq(s, len, "auto_unmount")) {
      auto_unmount = 1;
    } else if (!begins_with(s, "fd=") &&
               !begins_with(s, "rootmode=") &&
               !begins_with(s, "user_id=") &&
               !begins_with(s, "group_id=")) {
      int on;
      int flag;
      int skip_option = 0;
      if (opt_eq(s, len, "large_read")) {
        struct utsname utsname;
        unsigned kmaj, kmin;
        res = uname(&utsname);
        if (res == 0 &&
            sscanf(utsname.release, "%u.%u",
                   &kmaj, &kmin) == 2 &&
            (kmaj > 2 || (kmaj == 2 && kmin > 4))) {
          fprintf(stderr, "%s: note: 'large_read' mount option is deprecated for %i.%i kernels\n", progname, kmaj, kmin);
          skip_option = 1;
        }
      }
      if (getuid() != 0 && !user_allow_other &&
          (opt_eq(s, len, "allow_other") ||
           opt_eq(s, len, "allow_root"))) {
        fprintf(stderr, "%s: option %.*s only allowed if 'user_allow_other' is set in /etc/fuse.conf\n", progname, len, s);
        goto err;
      }
      if (!skip_option) {
        if (find_mount_flag(s, len, &on, &flag)) {
          if (on)
            flags |= flag;
          else
            flags  &= ~flag;
        } else {
          memcpy(d, s, len);
          d += len;
          *d++ = ',';
        }
      }
    }
    s += len;
    if (*s)
      s++;
  }
  *d = '\0';
  res = get_mnt_opts(flags, optbuf, &mnt_opts);
  if (res == -1)
    goto err;

  sprintf(d, "fd=%i,rootmode=%o,user_id=%u,group_id=%u",
          fd, rootmode, getuid(), getgid());

  if (check_empty &&
      fuse_mnt_check_empty(progname, mnt, rootmode, rootsize) == -1)
    goto err;

  source = malloc((fsname ? strlen(fsname) : 0) +
                  (subtype ? strlen(subtype) : 0) + strlen(dev) + 32);

  type = malloc((subtype ? strlen(subtype) : 0) + 32);
  if (!type || !source) {
    fprintf(stderr, "%s: failed to allocate memory\n", progname);
    goto err;
  }

  if (subtype)
    sprintf(type, "%s.%s", "fuse", subtype);
  else
    strcpy(type, "fuse");

  if (fsname)
    strcpy(source, fsname);
  else
    strcpy(source, subtype ? subtype : dev);

  res = mount(source, mnt, type, flags, optbuf);
  if (res == -1 && errno == ENODEV && subtype) {
    /* Probably missing subtype support */
    strcpy(type, "fuse");
    if (fsname) {
      sprintf(source, "%s#%s", subtype, fsname);
    } else {
      strcpy(source, type);
    }

    res = mount(source, mnt, type, flags, optbuf);
  }
  if (res == -1 && errno == EINVAL) {
    /* It could be an old version not supporting group_id */
    sprintf(d, "fd=%i,rootmode=%o,user_id=%u",
            fd, rootmode, getuid());
    res = mount(source, mnt, type, flags, optbuf);
  }
  if (res == -1) {
    int errno_save = errno;
    fprintf(stderr,
            "%s: mount failed: %s\n", progname,
            strerror(errno_save));
    goto err;
  }
  *sourcep = source;
  *typep = type;
  *mnt_optsp = mnt_opts;
  free(fsname);
  free(optbuf);

  return 0;

 err:
  free(fsname);
  free(subtype);
  free(source);
  free(type);
  free(mnt_opts);
  free(optbuf);
  return -1;
}

static int check_version(const char *dev)
{
  int res;
  int majorver;
  int minorver;
  const char *version_file;
  FILE *vf;

  if (strcmp(dev, FUSE_DEV_OLD) != 0)
    return 0;

  version_file = FUSE_VERSION_FILE_OLD;
  vf = fopen(version_file, "r");
  if (vf == NULL) {
    fprintf(stderr, "%s: kernel interface too old\n", progname);
    return -1;
  }
  res = fscanf(vf, "%i.%i", &majorver, &minorver);
  fclose(vf);
  if (res != 2) {
    fprintf(stderr, "%s: error reading %s\n", progname,
            version_file);
    return -1;
  }
  if (majorver < 3) {
    fprintf(stderr, "%s: kernel interface too old\n", progname);
    return -1;
  }
  return 0;
}

static int check_perm(const char **mntp, struct stat *stbuf, int *mountpoint_fd)
{
  int res;
  const char *mnt = *mntp;
  const char *origmnt = mnt;

  res = lstat(mnt, stbuf);
  if (res == -1) {
    fprintf(stderr, "%s: failed to access mountpoint %s: %s\n",
            progname, mnt, strerror(errno));
    return -1;
  }

  /* No permission checking is done for root */
  if (getuid() == 0)
    return 0;

  if (S_ISDIR(stbuf->st_mode)) {
    res = chdir(mnt);
    if (res == -1) {
      fprintf(stderr,
              "%s: failed to chdir to mountpoint: %s\n",
              progname, strerror(errno));
      return -1;
    }
    mnt = *mntp = ".";
    res = lstat(mnt, stbuf);
    if (res == -1) {
      fprintf(stderr,
              "%s: failed to access mountpoint %s: %s\n",
              progname, origmnt, strerror(errno));
      return -1;
    }

    if ((stbuf->st_mode & S_ISVTX) && stbuf->st_uid != getuid()) {
      fprintf(stderr, "%s: mountpoint %s not owned by user\n",
              progname, origmnt);
      return -1;
    }

    res = access(mnt, W_OK);
    if (res == -1) {
      fprintf(stderr, "%s: user has no write access to mountpoint %s\n",
              progname, origmnt);
      return -1;
    }
  } else if (S_ISREG(stbuf->st_mode)) {
    static char procfile[256];
    *mountpoint_fd = open(mnt, O_WRONLY);
    if (*mountpoint_fd == -1) {
      fprintf(stderr, "%s: failed to open %s: %s\n",
              progname, mnt, strerror(errno));
      return -1;
    }
    res = fstat(*mountpoint_fd, stbuf);
    if (res == -1) {
      fprintf(stderr,
              "%s: failed to access mountpoint %s: %s\n",
              progname, mnt, strerror(errno));
      return -1;
    }
    if (!S_ISREG(stbuf->st_mode)) {
      fprintf(stderr,
              "%s: mountpoint %s is no longer a regular file\n",
              progname, mnt);
      return -1;
    }

    sprintf(procfile, "/proc/self/fd/%i", *mountpoint_fd);
    *mntp = procfile;
  } else {
    fprintf(stderr,
            "%s: mountpoint %s is not a directory or a regular file\n",
            progname, mnt);
    return -1;
  }


  return 0;
}

static int try_open(const char *dev, char **devp, int silent)
{
  int fd = open(dev, O_RDWR);
  if (fd != -1) {
    *devp = strdup(dev);
    if (*devp == NULL) {
      fprintf(stderr, "%s: failed to allocate memory\n",
              progname);
      close(fd);
      fd = -1;
    }
  } else if (errno == ENODEV ||
             errno == ENOENT)/* check for ENOENT too, for the udev case */
    return -2;
  else if (!silent) {
    fprintf(stderr, "%s: failed to open %s: %s\n", progname, dev,
            strerror(errno));
  }
  return fd;
}

static int try_open_fuse_device(char **devp)
{
  int fd;
  int err;

  drop_privs();
  fd = try_open(FUSE_DEV_NEW, devp, 0);
  restore_privs();
  if (fd >= 0)
    return fd;

  err = fd;
  fd = try_open(FUSE_DEV_OLD, devp, 1);
  if (fd >= 0)
    return fd;

  return err;
}

static int open_fuse_device(char **devp)
{
  int fd = try_open_fuse_device(devp);
  if (fd >= -1)
    return fd;

  fprintf(stderr,
          "%s: fuse device not found, try 'modprobe fuse' first\n",
          progname);

  return -1;
}


static int mount_fuse(const char *mnt, const char *opts)
{
  int res;
  int fd;
  char *dev;
  struct stat stbuf;
  char *type = NULL;
  char *source = NULL;
  char *mnt_opts = NULL;
  const char *real_mnt = mnt;
  int mountpoint_fd = -1;

  fd = open_fuse_device(&dev);
  if (fd == -1)
    return -1;

  drop_privs();
  read_conf();

  if (getuid() != 0 && mount_max != -1) {
    int mount_count = count_fuse_fs();
    if (mount_count >= mount_max) {
      fprintf(stderr, "%s: too many FUSE filesystems mounted; mount_max=N can be set in /etc/fuse.conf\n", progname);
      goto fail_close_fd;
    }
  }

  res = check_version(dev);
  if (res != -1) {
    res = check_perm(&real_mnt, &stbuf, &mountpoint_fd);
    restore_privs();
    if (res != -1)
      res = do_mount(real_mnt, &type, stbuf.st_mode & S_IFMT,
                     fd, opts, dev, &source, &mnt_opts,
                     stbuf.st_size);
  } else
    restore_privs();

  if (mountpoint_fd != -1)
    close(mountpoint_fd);

  if (res == -1)
    goto fail_close_fd;

  res = chdir("/");
  if (res == -1) {
    fprintf(stderr, "%s: failed to chdir to '/'\n", progname);
    goto fail_close_fd;
  }

  if (geteuid() == 0) {
    res = add_mount(source, mnt, type, mnt_opts);
    if (res == -1) {
      /* Can't clean up mount in a non-racy way */
      goto fail_close_fd;
    }
  }

 out_free:
  free(source);
  free(type);
  free(mnt_opts);
  free(dev);

  return fd;

 fail_close_fd:
  close(fd);
  fd = -1;
  goto out_free;
}

static int send_fd(int sock_fd, int fd)
{
  int retval;
  struct msghdr msg;
  struct cmsghdr *p_cmsg;
  struct iovec vec;
  size_t cmsgbuf[CMSG_SPACE(sizeof(fd)) / sizeof(size_t)];
  int *p_fds;
  char sendchar = 0;

  msg.msg_control = cmsgbuf;
  msg.msg_controllen = sizeof(cmsgbuf);
  p_cmsg = CMSG_FIRSTHDR(&msg);
  p_cmsg->cmsg_level = SOL_SOCKET;
  p_cmsg->cmsg_type = SCM_RIGHTS;
  p_cmsg->cmsg_len = CMSG_LEN(sizeof(fd));
  p_fds = (int *) CMSG_DATA(p_cmsg);
  *p_fds = fd;
  msg.msg_controllen = p_cmsg->cmsg_len;
  msg.msg_name = NULL;
  msg.msg_namelen = 0;
  msg.msg_iov = &vec;
  msg.msg_iovlen = 1;
  msg.msg_flags = 0;
  /* "To pass file descriptors or credentials you need to send/read at
   * least one byte" (man 7 unix) */
  vec.iov_base = &sendchar;
  vec.iov_len = sizeof(sendchar);
  while ((retval = sendmsg(sock_fd, &msg, 0)) == -1 && errno == EINTR);
  if (retval != 1) {
    perror("sending file descriptor");
    return -1;
  }
  return 0;
}

static void usage(void)
{
  fprintf(stderr,
          "%s: [options] mountpoint\n"
          "Options:\n"
          " -h		    print help\n"
          " -V		    print version\n"
          " -o opt[,opt...]   mount options\n"
          " -u		    unmount\n"
          " -q		    quiet\n"
          " -z		    lazy unmount\n",
          progname);
  exit(1);
}

static void show_version(void)
{
  printf("fusermount version: %s\n", PACKAGE_VERSION);
  exit(0);
}

int main(int argc, char *argv[])
{
  sigset_t sigset;
  int ch;
  int fd;
  int res;
  char *origmnt;
  char *mnt;
  static int unmount = 0;
  static int lazy = 0;
  static int quiet = 0;
  char *commfd;
  int cfd;
  const char *opts = "";

  static const struct option long_opts[] = {
    {"unmount", no_argument, NULL, 'u'},
    {"lazy",    no_argument, NULL, 'z'},
    {"quiet",   no_argument, NULL, 'q'},
    {"help",    no_argument, NULL, 'h'},
    {"version", no_argument, NULL, 'V'},
    {0, 0, 0, 0}};

  progname = strdup(argv[0]);
  if (progname == NULL) {
    fprintf(stderr, "%s: failed to allocate memory\n", argv[0]);
    exit(1);
  }

  while ((ch = getopt_long(argc, argv, "hVo:uzq", long_opts,
                           NULL)) != -1) {
    switch (ch) {
    case 'h':
      usage();
      break;

    case 'V':
      show_version();
      break;

    case 'o':
      opts = optarg;
      break;

    case 'u':
      unmount = 1;
      break;

    case 'z':
      lazy = 1;
      break;

    case 'q':
      quiet = 1;
      break;

    default:
      exit(1);
    }
  }

  if (lazy && !unmount) {
    fprintf(stderr, "%s: -z can only be used with -u\n", progname);
    exit(1);
  }

  if (optind >= argc) {
    fprintf(stderr, "%s: missing mountpoint argument\n", progname);
    exit(1);
  } else if (argc > optind + 1) {
    fprintf(stderr, "%s: extra arguments after the mountpoint\n",
            progname);
    exit(1);
  }

  origmnt = argv[optind];

  drop_privs();
  mnt = fuse_mnt_resolve_path(progname, origmnt);
  if (mnt != NULL) {
    res = chdir("/");
    if (res == -1) {
      fprintf(stderr, "%s: failed to chdir to '/'\n", progname);
      exit(1);
    }
  }
  restore_privs();
  if (mnt == NULL)
    exit(1);

  umask(033);
  if (unmount)
    goto do_unmount;

  commfd = getenv(FUSE_COMMFD_ENV);
  if (commfd == NULL) {
    fprintf(stderr, "%s: old style mounting not supported\n",
            progname);
    exit(1);
  }

  fd = mount_fuse(mnt, opts);
  if (fd == -1)
    exit(1);

  cfd = atoi(commfd);
  res = send_fd(cfd, fd);
  if (res == -1)
    exit(1);
  close(fd);

  if (!auto_unmount)
    return 0;

  /* Become a daemon and wait for the parent to exit or die.
     ie For the control socket to get closed.
     btw We don't want to use daemon() function here because
     it forks and messes with the file descriptors. */
  setsid();
  res = chdir("/");
  if (res == -1) {
    fprintf(stderr, "%s: failed to chdir to '/'\n", progname);
    exit(1);
  }

  sigfillset(&sigset);
  sigprocmask(SIG_BLOCK, &sigset, NULL);

  lazy  = 1;
  quiet = 1;

  while (1) {
    unsigned char buf[16];
    int n = recv(cfd, buf, sizeof(buf), 0);
    if (!n)
      break;

    if (n < 0) {
      if (errno == EINTR)
        continue;
      break;
    }
  }

 do_unmount:
  if (geteuid() == 0)
    res = unmount_fuse(mnt, quiet, lazy);
  else {
    res = umount2(mnt, lazy ? UMOUNT_DETACH : 0);
    if (res == -1 && !quiet)
      fprintf(stderr,
              "%s: failed to unmount %s: %s\n",
              progname, mnt, strerror(errno));
  }
  if (res == -1)
    exit(1);
  return 0;
}