2016-06-09 17:36:58 +00:00
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.\" Copyright (c) 2016, Oracle. All rights reserved.
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ldd.1, localedef.1, add_key.2, chroot.2, clone.2, fork.2, futex.2, get_mempolicy.2, get_robust_list.2, getitimer.2, getpriority.2, ioctl.2, ioctl_ficlonerange.2, ioctl_fideduperange.2, kcmp.2, kill.2, lookup_dcookie.2, mmap.2, mount.2, open.2, pciconfig_read.2, perf_event_open.2, prctl.2, process_vm_readv.2, ptrace.2, quotactl.2, recv.2, setfsgid.2, setfsuid.2, sysinfo.2, umask.2, umount.2, unshare.2, utimensat.2, wait.2, assert.3, fmax.3, fmin.3, getauxval.3, inet_pton.3, malloc_hook.3, memmem.3, mkdtemp.3, mktemp.3, printf.3, strcasecmp.3, strcat.3, strtoul.3, strxfrm.3, console_codes.4, console_ioctl.4, lirc.4, tty.4, vcs.4, charmap.5, elf.5, locale.5, proc.5, repertoiremap.5, utmp.5, capabilities.7, cgroup_namespaces.7, cgroups.7, charsets.7, cp1251.7, cp1252.7, credentials.7, feature_test_macros.7, iso_8859-1.7, iso_8859-15.7, iso_8859-5.7, koi8-r.7, koi8-u.7, man-pages.7, mount_namespaces.7, namespaces.7, netlink.7, pid_namespaces.7, unix.7, user_namespaces.7, utf-8.7: tstamp
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
2016-07-17 16:07:58 +00:00
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.TH IOCTL-FICLONERANGE 2 2016-07-17 "Linux" "Linux Programmer's Manual"
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.SH NAME
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ioctl_ficlonerange, ioctl_ficlone \- share some the data of one file with another file
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.SH SYNOPSIS
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.br
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.B #include <sys/ioctl.h>
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.br
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.B #include <linux/fs.h>
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.sp
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.BI "int ioctl(int " dest_fd ", FICLONERANGE, struct file_clone_range * " arg );
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.br
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.BI "int ioctl(int " dest_fd ", FICLONE, int " src_fd );
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.SH DESCRIPTION
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If a filesystem supports files sharing physical storage between multiple
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files ("reflink"), this
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.BR ioctl (2)
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operation can be used to make some of the data in the
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.I src_fd
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file appear in the
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.I dest_fd
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file by sharing the underlying storage, which is faster than making a separate
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physical copy of the data.
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Both files must reside within the same filesystem.
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If a file write should occur to a shared region,
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the filesystem must ensure that the changes remain private to the file being
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written.
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This behavior is commonly referred to as "copy on write".
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This ioctl reflinks up to
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.IR src_length
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bytes from file descriptor
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.IR src_fd
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at offset
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.IR src_offset
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into the file
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.IR dest_fd
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at offset
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.IR dest_offset ",
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provided that both are files.
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If
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.IR src_length
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is zero, the ioctl reflinks to the end of the source file.
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This information is conveyed in a structure of
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the following form:
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.in +4n
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.nf
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struct file_clone_range {
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__s64 src_fd;
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__u64 src_offset;
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__u64 src_length;
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__u64 dest_offset;
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};
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.fi
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.in
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Clones are atomic with regards to concurrent writes, so no locks need to be
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taken to obtain a consistent cloned copy.
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The
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.B FICLONE
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ioctl clones entire files.
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.SH RETURN VALUE
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On error, \-1 is returned, and
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.I errno
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is set to indicate the error.
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.PP
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.SH ERRORS
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Error codes can be one of, but are not limited to, the following:
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.TP
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.B EXDEV
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.IR dest_fd " and " src_fd
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are not on the same mounted filesystem.
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.TP
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.B EISDIR
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One of the files is a directory and the filesystem does not support shared
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regions in directories.
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.TP
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.B EINVAL
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The filesystem does not support reflinking the ranges of the given files.
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This error can also appear if either file descriptor represents
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a device, FIFO, or socket.
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Disk filesystems generally require the offset and length arguments
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to be aligned to the fundamental block size.
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XFS and Btrfs do not support
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overlapping reflink ranges in the same file.
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.TP
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.B EBADF
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.IR src_fd
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is not open for reading;
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.IR dest_fd
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is not open for writing or is open for append-only writes;
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or the filesystem which
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.IR src_fd
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resides on does not support reflink.
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.TP
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.B EPERM
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.IR dest_fd
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is immutable.
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.TP
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.B ETXTBSY
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One of the files is a swap file.
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Swap files cannot share storage.
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.TP
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.B EOPNOTSUPP
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This can appear if the filesystem does not support reflinking either file
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descriptor.
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2016-06-08 10:19:19 +00:00
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.SH VERSIONS
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These ioctl operations first appeared in Linux 4.5.
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They were previously known as
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.B BTRFS_IOC_CLONE
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and
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.BR BTRFS_IOC_CLONE_RANGE ,
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and were private to Btrfs.
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.SH CONFORMING TO
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This API is Linux-specific.
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.SH NOTES
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Because a copy-on-write operation requires the allocation of new storage, the
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.BR fallocate (2)
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operation may unshare shared blocks to guarantee that subsequent writes will
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not fail because of lack of disk space.
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.SH SEE ALSO
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.BR ioctl (2)
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