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   ioctl_ficlonerange    ( 2 )

поделиться данными одного файла с другим файлом (share some the data of one file with another file)

Имя (Name)

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

Синопсис (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);


Описание (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.


Возвращаемое значение (Return value)

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

Ошибки (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.


Версии (Versions)

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.

Стандарты (Conforming to)

This API is Linux-specific.

Примечание (Note)

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.

Смотри также (See also)

ioctl(2)