ioctl_ficlone(2) — Linux manual page


IOCTL_FICLONERANGE(2)     Linux Programmer's Manual    IOCTL_FICLONERANGE(2)

NAME         top

       ioctl_ficlonerange,  ioctl_ficlone  - share some the data of one file
       with another file

SYNOPSIS         top

       #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);

DESCRIPTION         top

       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.

RETURN VALUE         top

       On error, -1 is returned, and errno is set to indicate the error.

ERRORS         top

       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.

              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.

              One of the files is a swap file.  Swap files cannot share

       EXDEV  dest_fd and src_fd are not on the same mounted filesystem.

VERSIONS         top

       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.

CONFORMING TO         top

       This API is Linux-specific.

NOTES         top

       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.

SEE ALSO         top


COLOPHON         top

       This page is part of release 5.08 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

Linux                            2017-09-15            IOCTL_FICLONERANGE(2)