libfuse

null.c File Reference
`#include <fuse.h>`
`#include <fuse_lowlevel.h>`
`#include <stdio.h>`
`#include <stdlib.h>`
`#include <string.h>`
`#include <unistd.h>`
`#include <time.h>`
`#include <errno.h>`

Go to the source code of this file.

## Detailed Description

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.

Compile with:

    gcc -Wall null.c `pkg-config fuse3 --cflags --libs` -o null

## Source code

/*
FUSE: Filesystem in Userspace
Copyright (C) 2001-2007 Miklos Szeredi <miklos@szeredi.hu>
Copyright (C) 2011 Sebastian Pipping <sebastian@pipping.org>
This program can be distributed under the terms of the GNU GPLv2.
See the file COPYING.
*/
#define FUSE_USE_VERSION 31
#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> /* flock(2) */
static void *xmp_init(struct fuse_conn_info *conn,
struct fuse_config *cfg)
{
(void) conn;
cfg->use_ino = 1;
cfg->nullpath_ok = 1;
/* parallel_direct_writes feature depends on direct_io features.
To make parallel_direct_writes valid, need either set cfg->direct_io
in current function (recommended in high level API) or set fi->direct_io
in xmp_create() or xmp_open(). */
// cfg->direct_io = 1;
cfg->parallel_direct_writes = 1;
/* Pick up changes from lower filesystem right away. This is
also necessary for better hardlink support. When the kernel
calls the unlink() handler, it does not know the inode of
the to-be-removed entry and can therefore not invalidate
the cache of the associated inode - resulting in an
incorrect st_nlink value being reported for any remaining
hardlinks to this inode. */
cfg->entry_timeout = 0;
cfg->attr_timeout = 0;
cfg->negative_timeout = 0;
return NULL;
}
static int xmp_getattr(const char *path, struct stat *stbuf,
struct fuse_file_info *fi)
{
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;
res = access(path, mask);
if (res == -1)
return -errno;
return 0;
}
static int xmp_readlink(const char *path, char *buf, size_t size)
{
int res;
res = readlink(path, buf, size - 1);
if (res == -1)
return -errno;
buf[res] = '\0';
return 0;
}
struct xmp_dirp {
DIR *dp;
struct dirent *entry;
off_t offset;
};
static int xmp_opendir(const char *path, struct fuse_file_info *fi)
{
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;
}
static inline struct xmp_dirp *get_dirp(struct fuse_file_info *fi)
{
return (struct xmp_dirp *) (uintptr_t) fi->fh;
}
static int xmp_readdir(const char *path, void *buf, fuse_fill_dir_t filler,
off_t offset, struct fuse_file_info *fi,
enum fuse_readdir_flags flags)
{
struct xmp_dirp *d = get_dirp(fi);
(void) path;
if (offset != d->offset) {
#ifndef __FreeBSD__
seekdir(d->dp, offset);
#else
/* Subtract the one that we add when calling
telldir() below */
seekdir(d->dp, offset-1);
#endif
d->entry = NULL;
d->offset = offset;
}
while (1) {
struct stat st;
off_t nextoff;
enum fuse_fill_dir_flags fill_flags = FUSE_FILL_DIR_DEFAULTS;
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)
fill_flags |= FUSE_FILL_DIR_PLUS;
}
#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__
/* Under FreeBSD, telldir() may return 0 the first time
it is called. But for libfuse, an offset of zero
means that offsets are not supported, so we shift
everything by one. */
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;
/* When we have renameat2() in libc, then we can implement flags */
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,
struct fuse_file_info *fi)
{
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,
struct fuse_file_info *fi)
{
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,
struct fuse_file_info *fi)
{
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],
struct fuse_file_info *fi)
{
int res;
/* don't use utime/utimes since they follow symlinks */
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;
fi->fh = fd;
return 0;
}
static int xmp_open(const char *path, struct fuse_file_info *fi)
{
int fd;
fd = open(path, fi->flags);
if (fd == -1)
return -errno;
/* Enable direct_io when open has flags O_DIRECT to enjoy the feature
parallel_direct_writes (i.e., to get a shared lock, not exclusive lock,
for writes to the same file). */
if (fi->flags & O_DIRECT) {
fi->direct_io = 1;
fi->parallel_direct_writes = 1;
}
fi->fh = fd;
return 0;
}
static int xmp_read(const char *path, char *buf, size_t size, off_t offset,
struct fuse_file_info *fi)
{
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,
size_t size, off_t offset, struct fuse_file_info *fi)
{
struct fuse_bufvec *src;
(void) path;
src = malloc(sizeof(struct fuse_bufvec));
if (src == NULL)
return -ENOMEM;
*src = FUSE_BUFVEC_INIT(size);
src->buf[0].flags = FUSE_BUF_IS_FD | FUSE_BUF_FD_SEEK;
src->buf[0].fd = fi->fh;
src->buf[0].pos = offset;
*bufp = src;
return 0;
}
static int xmp_write(const char *path, const char *buf, size_t size,
off_t offset, struct fuse_file_info *fi)
{
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,
off_t offset, struct fuse_file_info *fi)
{
struct fuse_bufvec dst = FUSE_BUFVEC_INIT(fuse_buf_size(buf));
(void) path;
dst.buf[0].flags = FUSE_BUF_IS_FD | FUSE_BUF_FD_SEEK;
dst.buf[0].fd = fi->fh;
dst.buf[0].pos = offset;
return fuse_buf_copy(&dst, buf, FUSE_BUF_SPLICE_NONBLOCK);
}
static int xmp_statfs(const char *path, struct statvfs *stbuf)
{
int res;
res = statvfs(path, stbuf);
if (res == -1)
return -errno;
return 0;
}
static int xmp_flush(const char *path, struct fuse_file_info *fi)
{
int res;
(void) path;
/* This is called from every close on an open file, so call the
close on the underlying filesystem. But since flush may be
called multiple times for an open file, this must not really
close the file. This is important if used on a network
filesystem like NFS which flush the data/metadata on close() */
res = close(dup(fi->fh));
if (res == -1)
return -errno;
return 0;
}
static int xmp_release(const char *path, struct fuse_file_info *fi)
{
(void) path;
close(fi->fh);
return 0;
}
static int xmp_fsync(const char *path, int isdatasync,
struct fuse_file_info *fi)
{
int res;
(void) path;
#ifndef HAVE_FDATASYNC
(void) isdatasync;
#else
if (isdatasync)
res = fdatasync(fi->fh);
else
#endif
res = fsync(fi->fh);
if (res == -1)
return -errno;
return 0;
}
#ifdef HAVE_POSIX_FALLOCATE
static int xmp_fallocate(const char *path, int mode,
off_t offset, off_t length, struct fuse_file_info *fi)
{
(void) path;
if (mode)
return -EOPNOTSUPP;
return -posix_fallocate(fi->fh, offset, length);
}
#endif
#ifdef HAVE_SETXATTR
/* xattr operations are optional and can safely be left unimplemented */
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 /* HAVE_SETXATTR */
#ifdef HAVE_LIBULOCKMGR
static int xmp_lock(const char *path, struct fuse_file_info *fi, int cmd,
struct flock *lock)
{
(void) path;
return ulockmgr_op(fi->fh, cmd, lock, &fi->lock_owner,
sizeof(fi->lock_owner));
}
#endif
static int xmp_flock(const char *path, struct fuse_file_info *fi, int op)
{
int res;
(void) path;
res = flock(fi->fh, op);
if (res == -1)
return -errno;
return 0;
}
#ifdef HAVE_COPY_FILE_RANGE
static ssize_t xmp_copy_file_range(const char *path_in,
struct fuse_file_info *fi_in,
off_t off_in, const char *path_out,
struct fuse_file_info *fi_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
static off_t xmp_lseek(const char *path, off_t off, int whence, struct fuse_file_info *fi)
{
off_t res;
(void) path;
res = lseek(fi->fh, off, whence);
if (res == -1)
return -errno;
return res;
}
static const struct fuse_operations xmp_oper = {
.init = xmp_init,
.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
.lseek = xmp_lseek,
};
int main(int argc, char *argv[])
{
umask(0);
return fuse_main(argc, argv, &xmp_oper, NULL);
}
fuse_fill_dir_t
int(* fuse_fill_dir_t)(void *buf, const char *name, const struct stat *stbuf, off_t off, enum fuse_fill_dir_flags flags)
Definition fuse.h:87
fuse_fill_dir_flags
fuse_fill_dir_flags
Definition fuse.h:58
FUSE_FILL_DIR_DEFAULTS
@ FUSE_FILL_DIR_DEFAULTS
Definition fuse.h:68
fuse_readdir_flags
fuse_readdir_flags
Definition fuse.h:42
fuse_buf_size
size_t fuse_buf_size(const struct fuse_bufvec *bufv)
Definition buffer.c:22
FUSE_BUF_FD_SEEK
@ FUSE_BUF_FD_SEEK
Definition fuse_common.h:833
FUSE_BUF_IS_FD
@ FUSE_BUF_IS_FD
Definition fuse_common.h:824
fuse_buf_copy
ssize_t fuse_buf_copy(struct fuse_bufvec *dst, struct fuse_bufvec *src, enum fuse_buf_copy_flags flags)
Definition buffer.c:284
FUSE_BUF_SPLICE_NONBLOCK
@ FUSE_BUF_SPLICE_NONBLOCK
Definition fuse_common.h:884
fuse_buf::flags
enum fuse_buf_flags flags
Definition fuse_common.h:902
fuse_buf::fd
int fd
Definition fuse_common.h:916
fuse_buf::pos
off_t pos
Definition fuse_common.h:923
fuse_bufvec
Definition fuse_common.h:942
fuse_bufvec::off
size_t off
Definition fuse_common.h:956
fuse_bufvec::buf
struct fuse_buf buf[1]
Definition fuse_common.h:961
fuse_config
Definition fuse.h:101
fuse_config::nullpath_ok
int32_t nullpath_ok
Definition fuse.h:273
fuse_config::parallel_direct_writes
int32_t parallel_direct_writes
Definition fuse.h:312
fuse_config::use_ino
int32_t use_ino
Definition fuse.h:198
fuse_config::entry_timeout
double entry_timeout
Definition fuse.h:127
fuse_config::negative_timeout
double negative_timeout
Definition fuse.h:137
fuse_config::attr_timeout
double attr_timeout
Definition fuse.h:143
fuse_conn_info
Definition fuse_common.h:555
fuse_file_info
Definition fuse_common.h:58
fuse_file_info::lock_owner
uint64_t lock_owner
Definition fuse_common.h:118
fuse_file_info::fh
uint64_t fh
Definition fuse_common.h:115
fuse_file_info::parallel_direct_writes
uint32_t parallel_direct_writes
Definition fuse_common.h:105
fuse_file_info::direct_io
uint32_t direct_io
Definition fuse_common.h:71
fuse_file_info::flags
int32_t flags
Definition fuse_common.h:60
fuse_operations
Definition fuse.h:349
fuse_operations::init
void *(* init)(struct fuse_conn_info *conn, struct fuse_config *cfg)
Definition fuse.h:641

Definition in file null.c.