This "filesystem" provides only a single file. The mountpoint needs to be a file rather than a directory. All writes to the file will be discarded, and reading the file always returns \0.
#define FUSE_USE_VERSION 31
#ifdef HAVE_CONFIG_H
#include <config.h>
#endif
#define _GNU_SOURCE
#include <fuse.h>
#ifdef HAVE_LIBULOCKMGR
#include <ulockmgr.h>
#endif
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/stat.h>
#include <dirent.h>
#include <errno.h>
#include <sys/time.h>
#ifdef HAVE_SETXATTR
#include <sys/xattr.h>
#endif
#include <sys/file.h> 
{
        (void) conn;
        
        return NULL;
}
static int xmp_getattr(const char *path, struct stat *stbuf,
{
        int res;
        (void) path;
        if(fi)
                res = fstat(fi->
fh, stbuf);
        else
                res = lstat(path, stbuf);
        if (res == -1)
                return -errno;
        return 0;
}
static int xmp_access(const char *path, int mask)
{
        int res;
        if (res == -1)
                return -errno;
        return 0;
}
static int xmp_readlink(const char *path, char *buf, size_t size)
{
        int res;
        if (res == -1)
                return -errno;
        buf[res] = '\0';
        return 0;
}
struct xmp_dirp {
        DIR *dp;
        struct dirent *entry;
        off_t offset;
};
{
        int res;
        struct xmp_dirp *d = malloc(sizeof(struct xmp_dirp));
        if (d == NULL)
                return -ENOMEM;
        d->dp = opendir(path);
        if (d->dp == NULL) {
                res = -errno;
                free(d);
                return res;
        }
        d->offset = 0;
        d->entry = NULL;
        fi->
fh = (
unsigned long) d;
        return 0;
}
{
        return (
struct xmp_dirp *) (uintptr_t) fi->
fh;
 }
static int xmp_readdir(
const char *path, 
void *buf, 
fuse_fill_dir_t filler,
 {
        struct xmp_dirp *d = get_dirp(fi);
        (void) path;
        if (offset != d->offset) {
#ifndef __FreeBSD__
                seekdir(d->dp, offset);
#else
                
                seekdir(d->dp, offset-1);
#endif
                d->entry = NULL;
                d->offset = offset;
        }
        while (1) {
                struct stat st;
                off_t nextoff;
                if (!d->entry) {
                        d->entry = readdir(d->dp);
                        if (!d->entry)
                                break;
                }
#ifdef HAVE_FSTATAT
                if (flags & FUSE_READDIR_PLUS) {
                        int res;
                        res = fstatat(dirfd(d->dp), d->entry->d_name, &st,
                                      AT_SYMLINK_NOFOLLOW);
                        if (res != -1)
                }
#endif
                if (!(fill_flags & FUSE_FILL_DIR_PLUS)) {
                        memset(&st, 0, sizeof(st));
                        st.st_ino = d->entry->d_ino;
                        st.st_mode = d->entry->d_type << 12;
                }
                nextoff = telldir(d->dp);
#ifdef __FreeBSD__              
                
                nextoff++;
#endif
                if (filler(buf, d->entry->d_name, &st, nextoff, fill_flags))
                        break;
                d->entry = NULL;
                d->offset = nextoff;
        }
        return 0;
}
static int xmp_releasedir(
const char *path, 
struct fuse_file_info *fi)
 {
        struct xmp_dirp *d = get_dirp(fi);
        (void) path;
        closedir(d->dp);
        free(d);
        return 0;
}
static int xmp_mknod(const char *path, mode_t mode, dev_t rdev)
{
        int res;
        if (S_ISFIFO(mode))
                res = mkfifo(path, mode);
        else
                res = mknod(path, mode, rdev);
        if (res == -1)
                return -errno;
        return 0;
}
static int xmp_mkdir(const char *path, mode_t mode)
{
        int res;
        res = mkdir(path, mode);
        if (res == -1)
                return -errno;
        return 0;
}
static int xmp_unlink(const char *path)
{
        int res;
        res = unlink(path);
        if (res == -1)
                return -errno;
        return 0;
}
static int xmp_rmdir(const char *path)
{
        int res;
        res = rmdir(path);
        if (res == -1)
                return -errno;
        return 0;
}
static int xmp_symlink(const char *from, const char *to)
{
        int res;
        res = symlink(from, to);
        if (res == -1)
                return -errno;
        return 0;
}
static int xmp_rename(const char *from, const char *to, unsigned int flags)
{
        int res;
        
        if (flags)
                return -EINVAL;
        res = rename(from, to);
        if (res == -1)
                return -errno;
        return 0;
}
static int xmp_link(const char *from, const char *to)
{
        int res;
        res = link(from, to);
        if (res == -1)
                return -errno;
        return 0;
}
static int xmp_chmod(const char *path, mode_t mode,
{
        int res;
        if(fi)
                res = fchmod(fi->
fh, mode);
        else
                res = chmod(path, mode);
        if (res == -1)
                return -errno;
        return 0;
}
static int xmp_chown(const char *path, uid_t uid, gid_t gid,
{
        int res;
        if (fi)
                res = fchown(fi->
fh, uid, gid);
        else
                res = lchown(path, uid, gid);
        if (res == -1)
                return -errno;
        return 0;
}
static int xmp_truncate(const char *path, off_t size,
{
        int res;
        if(fi)
                res = ftruncate(fi->
fh, size);
        else
                res = truncate(path, size);
        if (res == -1)
                return -errno;
        return 0;
}
#ifdef HAVE_UTIMENSAT
static int xmp_utimens(const char *path, const struct timespec ts[2],
{
        int res;
        
        if (fi)
                res = futimens(fi->
fh, ts);
        else
                res = utimensat(0, path, ts, AT_SYMLINK_NOFOLLOW);
        if (res == -1)
                return -errno;
        return 0;
}
#endif
static int xmp_create(
const char *path, mode_t mode, 
struct fuse_file_info *fi)
 {
        int fd;
        fd = open(path, fi->
flags, mode);
        if (fd == -1)
                return -errno;
        return 0;
}
{
        int fd;
        fd = open(path, fi->
flags);
        if (fd == -1)
                return -errno;
        return 0;
}
static int xmp_read(const char *path, char *buf, size_t size, off_t offset,
{
        int res;
        (void) path;
        res = pread(fi->
fh, buf, size, offset);
        if (res == -1)
                res = -errno;
        return res;
}
static int xmp_read_buf(
const char *path, 
struct fuse_bufvec **bufp,
 {
        (void) path;
        if (src == NULL)
                return -ENOMEM;
        *src = FUSE_BUFVEC_INIT(size);
        *bufp = src;
        return 0;
}
static int xmp_write(const char *path, const char *buf, size_t size,
{
        int res;
        (void) path;
        res = pwrite(fi->
fh, buf, size, offset);
        if (res == -1)
                res = -errno;
        return res;
}
static int xmp_write_buf(
const char *path, 
struct fuse_bufvec *buf,
 {
        (void) path;
}
static int xmp_statfs(const char *path, struct statvfs *stbuf)
{
        int res;
        res = statvfs(path, stbuf);
        if (res == -1)
                return -errno;
        return 0;
}
{
        int res;
        (void) path;
        
        res = close(dup(fi->
fh));
        if (res == -1)
                return -errno;
        return 0;
}
{
        (void) path;
        return 0;
}
static int xmp_fsync(const char *path, int isdatasync,
{
        int res;
        (void) path;
#ifndef HAVE_FDATASYNC
        (void) isdatasync;
#else
        if (isdatasync)
        else
#endif
        if (res == -1)
                return -errno;
        return 0;
}
#ifdef HAVE_POSIX_FALLOCATE
static int xmp_fallocate(const char *path, int mode,
{
        (void) path;
        if (mode)
                return -EOPNOTSUPP;
        return -posix_fallocate(fi->
fh, offset, length);
 }
#endif
#ifdef HAVE_SETXATTR
static int xmp_setxattr(const char *path, const char *name, const char *value,
                        size_t size, int flags)
{
        int res = lsetxattr(path, name, value, size, flags);
        if (res == -1)
                return -errno;
        return 0;
}
static int xmp_getxattr(const char *path, const char *name, char *value,
                        size_t size)
{
        int res = lgetxattr(path, name, value, size);
        if (res == -1)
                return -errno;
        return res;
}
static int xmp_listxattr(const char *path, char *list, size_t size)
{
        int res = llistxattr(path, list, size);
        if (res == -1)
                return -errno;
        return res;
}
static int xmp_removexattr(const char *path, const char *name)
{
        int res = lremovexattr(path, name);
        if (res == -1)
                return -errno;
        return 0;
}
#endif 
#ifdef HAVE_LIBULOCKMGR
static int xmp_lock(
const char *path, 
struct fuse_file_info *fi, 
int cmd,
                     struct flock *lock)
{
        (void) path;
}
#endif
static int xmp_flock(
const char *path, 
struct fuse_file_info *fi, 
int op)
 {
        int res;
        (void) path;
        if (res == -1)
                return -errno;
        return 0;
}
#ifdef HAVE_COPY_FILE_RANGE
static ssize_t xmp_copy_file_range(const char *path_in,
                                   off_t off_in, const char *path_out,
                                   off_t off_out, size_t len, int flags)
{
        ssize_t res;
        (void) path_in;
        (void) path_out;
        res = copy_file_range(fi_in->
fh, &off_in, fi_out->
fh, &off_out, len,
                              flags);
        if (res == -1)
                return -errno;
        return res;
}
#endif
        .getattr        = xmp_getattr,
        .access         = xmp_access,
        .readlink       = xmp_readlink,
        .opendir        = xmp_opendir,
        .readdir        = xmp_readdir,
        .releasedir     = xmp_releasedir,
        .mknod          = xmp_mknod,
        .mkdir          = xmp_mkdir,
        .symlink        = xmp_symlink,
        .unlink         = xmp_unlink,
        .rmdir          = xmp_rmdir,
        .rename         = xmp_rename,
        .link           = xmp_link,
        .chmod          = xmp_chmod,
        .chown          = xmp_chown,
        .truncate       = xmp_truncate,
#ifdef HAVE_UTIMENSAT
        .utimens        = xmp_utimens,
#endif
        .create         = xmp_create,
        .open           = xmp_open,
        .read           = xmp_read,
        .read_buf       = xmp_read_buf,
        .write          = xmp_write,
        .write_buf      = xmp_write_buf,
        .statfs         = xmp_statfs,
        .flush          = xmp_flush,
        .release        = xmp_release,
        .fsync          = xmp_fsync,
#ifdef HAVE_POSIX_FALLOCATE
        .fallocate      = xmp_fallocate,
#endif
#ifdef HAVE_SETXATTR
        .setxattr       = xmp_setxattr,
        .getxattr       = xmp_getxattr,
        .listxattr      = xmp_listxattr,
        .removexattr    = xmp_removexattr,
#endif
#ifdef HAVE_LIBULOCKMGR
        .lock           = xmp_lock,
#endif
        .flock          = xmp_flock,
#ifdef HAVE_COPY_FILE_RANGE
        .copy_file_range = xmp_copy_file_range,
#endif
};
int main(int argc, char *argv[])
{
        umask(0);
        return fuse_main(argc, argv, &xmp_oper, NULL);
 }