ioctl_ficlonerange(2) — Linux manual page


ioctl_ficlonerange(2)      System Calls Manual     ioctl_ficlonerange(2)

NAME         top

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

LIBRARY         top

       Standard C library (libc, -lc)

SYNOPSIS         top

       #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         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

       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.

STANDARDS         top


HISTORY         top

       Linux 4.5.

       They were previously known as BTRFS_IOC_CLONE and
       BTRFS_IOC_CLONE_RANGE, and were private to Btrfs.

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


Linux man-pages (unreleased)     (date)            ioctl_ficlonerange(2)

Pages that refer to this page: ioctl(2)