|
HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
|
|
NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | STANDARDS | HISTORY | CAVEATS | SEE ALSO | COLOPHON |
|
|
|
FICLONE(2const) FICLONE(2const)
FICLONE, FICLONERANGE - share some the data of one file with
another file
Standard C library (libc, -lc)
#include <linux/fs.h> /* Definition of FICLONE* constants */
#include <sys/ioctl.h>
int ioctl(int dest_fd, FICLONERANGE, struct file_clone_range *arg);
int ioctl(int dest_fd, FICLONE, int src_fd);
If a filesystem supports files sharing physical storage between
multiple files ("reflink"), this ioctl(2) operation can be used to
make some of the data in the src_fd file appear in the dest_fd
file by sharing the underlying storage, which is faster than
making a separate physical copy of the data. Both files must
reside within the same filesystem. If a file write should occur
to a shared region, the filesystem must ensure that the changes
remain private to the file being written. This behavior is
commonly referred to as "copy on write".
This ioctl reflinks up to src_length bytes from file descriptor
src_fd at offset src_offset into the file dest_fd at offset
dest_offset, provided that both are files. If src_length is zero,
the ioctl reflinks to the end of the source file. This
information is conveyed in a structure of the following form:
struct file_clone_range {
__s64 src_fd;
__u64 src_offset;
__u64 src_length;
__u64 dest_offset;
};
Clones are atomic with regards to concurrent writes, so no locks
need to be taken to obtain a consistent cloned copy.
The FICLONE ioctl clones entire files.
On error, -1 is returned, and errno is set to indicate the error.
Error codes can be one of, but are not limited to, the following:
EBADF src_fd is not open for reading; dest_fd is not open for
writing or is open for append-only writes; or the
filesystem which src_fd resides on does not support
reflink.
EINVAL The filesystem does not support reflinking the ranges of
the given files. This error can also appear if either file
descriptor represents a device, FIFO, or socket. Disk
filesystems generally require the offset and length
arguments to be aligned to the fundamental block size. XFS
and Btrfs do not support overlapping reflink ranges in the
same file.
EISDIR One of the files is a directory and the filesystem does not
support shared regions in directories.
EOPNOTSUPP
This can appear if the filesystem does not support
reflinking either file descriptor, or if either file
descriptor refers to special inodes.
EPERM dest_fd is immutable.
ETXTBSY
One of the files is a swap file. Swap files cannot share
storage.
EXDEV dest_fd and src_fd are not on the same mounted filesystem.
Linux.
Linux 4.5.
They were previously known as BTRFS_IOC_CLONE and
BTRFS_IOC_CLONE_RANGE, and were private to Btrfs.
Because a copy-on-write operation requires the allocation of new
storage, the fallocate(2) operation may unshare shared blocks to
guarantee that subsequent writes will not fail because of lack of
disk space.
ioctl(2)
This page is part of the man-pages (Linux kernel and C library
user-space interface documentation) project. Information about
the project can be found at
⟨http://www.kernel.org/doc/man-pages/⟩. If you have a bug report
for this manual page, see
⟨http://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.
This page was obtained from the tarball man-pages-6.15.tar.gz
fetched from
⟨http://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on
2025-08-11. If you discover any rendering problems in this HTML
version of the page, or you believe there is a better or more up-
to-date source for the page, or you have corrections or
improvements to the information in this COLOPHON (which is not
part of the original manual page), send a mail to
man-pages@man7.org
Linux man-pages 6.15 2025-05-17 FICLONE(2const)
Pages that refer to this page: ioctl_fs(2)
|
HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
|