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ioctl_ficlonerange(2) System Calls Manual ioctl_ficlonerange(2)
NAME
ioctl_ficlonerange, ioctl_ficlone - share some the data of one file
with another file
LIBRARY
Standard C library (libc, -lc)
SYNOPSIS
#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);
DESCRIPTION
If a filesystem supports files sharing physical storage between multi-
ple 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, pro-
vided 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.
RETURN VALUE
On error, -1 is returned, and errno is set to indicate the error.
ERRORS
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 descrip-
tor represents a device, FIFO, or socket. Disk filesystems gen-
erally require the offset and length arguments to be aligned to
the fundamental block size. XFS and Btrfs do not support over-
lapping reflink ranges in the same file.
EISDIR One of the files is a directory and the filesystem does not sup-
port 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 stor-
age.
EXDEV dest_fd and src_fd are not on the same mounted filesystem.
STANDARDS
Linux.
HISTORY
Linux 4.5.
They were previously known as BTRFS_IOC_CLONE and
BTRFS_IOC_CLONE_RANGE, and were private to Btrfs.
NOTES
Because a copy-on-write operation requires the allocation of new stor-
age, the fallocate(2) operation may unshare shared blocks to guarantee
that subsequent writes will not fail because of lack of disk space.
SEE ALSO
ioctl(2)
Linux man-pages 6.04 2023-03-30 ioctl_ficlonerange(2)
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