plucky (2) FICLONERANGE.2const.gz

NAME

       FICLONE, FICLONERANGE - 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 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

       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 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.

STANDARDS

       Linux.

HISTORY

       Linux 4.5.

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

CAVEATS

       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

       ioctl(2)