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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | VERSIONS | CONFORMING TO | NOTES | SEE ALSO | COLOPHON |
IOCTL-FICLONERANGE(2) Linux Programmer's Manual IOCTL-FICLONERANGE(2)
ioctl_ficlonerange, ioctl_ficlone - share some the data of one file
with another file
#include <sys/ioctl.h>
#include <linux/fs.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.
These ioctl operations first appeared in Linux 4.5. They were
previously known as BTRFS_IOC_CLONE and BTRFS_IOC_CLONE_RANGE, and
were private to Btrfs.
This API is Linux-specific.
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 release 4.12 of the Linux man-pages project. A
description of the project, information about reporting bugs, and the
latest version of this page, can be found at
https://www.kernel.org/doc/man-pages/.
Linux 2016-12-12 IOCTL-FICLONERANGE(2)
Pages that refer to this page: ioctl(2)