On 03/15/2016 05:48 PM, Darrick J. Wong wrote:
> Document the FIDEDUPERANGE ioctl, formerly known as BTRFS_IOC_EXTENT_SAME.
Again, thanks for the nice page, Darrick. Applied!
Cheers,
Michael
> Signed-off-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
> ---
> man2/ioctl_fideduperange.2 | 168 ++++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 168 insertions(+)
> create mode 100644 man2/ioctl_fideduperange.2
>
>
> diff --git a/man2/ioctl_fideduperange.2 b/man2/ioctl_fideduperange.2
> new file mode 100644
> index 0000000..0fbc388
> --- /dev/null
> +++ b/man2/ioctl_fideduperange.2
> @@ -0,0 +1,168 @@
> +.\" Copyright (C) 2016 Oracle. All rights reserved.
> +.\"
> +.\" %%%LICENSE_START(VERBATIM)
> +.\" This program is free software; you can redistribute it and/or
> +.\" modify it under the terms of the GNU General Public License as
> +.\" published by the Free Software Foundation.
> +.\"
> +.\" This program is distributed in the hope that it would be useful,
> +.\" but WITHOUT ANY WARRANTY; without even the implied warranty of
> +.\" MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
> +.\" GNU General Public License for more details.
> +.\"
> +.\" You should have received a copy of the GNU General Public License
> +.\" along with this program; if not, write the Free Software Foundation,
> +.\" Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
> +.\" %%%LICENSE_END
> +.TH IOCTL-FIDEDUPERANGE 2 2016-02-10 "Linux" "Linux Programmer's Manual"
> +.SH NAME
> +ioctl_fideduperange \- share some the data of one file with another file
> +.SH SYNOPSIS
> +.br
> +.B #include <sys/ioctl.h>
> +.br
> +.B #include <linux/fs.h>
> +.sp
> +.BI "int ioctl(int " src_fd ", FIDEDUPERANGE, struct file_dedupe_range * " arg );
> +.SH DESCRIPTION
> +If a filesystem supports files sharing physical storage between multiple
> +files, this
> +.BR ioctl (2)
> +system call can be used to make some of the data in the
> +.B src_fd
> +file appear in the
> +.B dest_fd
> +file by sharing the underlying storage if the file data is identical
> +("deduplication"). This reduces storage consumption by allowing the filesystem
> +to store one shared copy of the data. 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 performs the "compare and share if identical" operation on up to
> +.IR src_length
> +bytes from file descriptor
> +.IR src_fd
> +at offset
> +.IR src_offset ".
> +This information is conveyed in a structure of the following form:
> +.in +4n
> +.nf
> +
> +struct file_dedupe_range {
> + __u64 src_offset;
> + __u64 src_length;
> + __u16 dest_count;
> + __u16 reserved1;
> + __u32 reserved2;
> + struct file_dedupe_range_info info[0];
> +};
> +.fi
> +.in
> +Deduplication is atomic with regards to concurrent writes, so no locks need to
> +be taken to obtain a consistent deduplicated copy.
> +
> +The fields
> +.IR reserved1 " and " reserved2
> +must be zero.
> +
> +Destinations for the deduplication operation are conveyed in the array at the
> +end of the structure. The number of destinations is given in
> +.IR dest_count ",
> +and the destination information is conveyed in the following form:
> +
> +.in +4n
> +.nf
> +struct file_dedupe_range_info {
> + __s64 dest_fd;
> + __u64 dest_offset;
> + __u64 bytes_deduped;
> + __s32 status;
> + __u32 reserved;
> +};
> +
> +.fi
> +.in
> +
> +Each deduplication operation targets
> +.IR length
> +bytes in file descriptor
> +.IR dest_fd
> +at offset
> +.IR logical_offset ".
> +The field
> +.IR reserved
> +must be zero.
> +
> +Upon successful completion of this ioctl, the number of bytes successfully
> +deduplicated is returned in
> +.IR bytes_deduped
> +and a status code for the deduplication operation is returned in
> +.IR status ".
> +
> +The
> +.IR status
> +code is set to
> +.B 0
> +for success, a negative error code in case of error, or
> +.B FILE_DEDUPE_RANGE_DIFFERS
> +if the data did not match.
> +
> +.SH RETURN VALUE
> +On error, \-1 is returned, and
> +.I errno
> +is set to indicate the error.
> +.PP
> +.SH ERRORS
> +Error codes can be one of, but are not limited to, the following:
> +.TP
> +.B EXDEV
> +.IR dest_fd " and " src_fd
> +are not on the same mounted filesystem.
> +.TP
> +.B EISDIR
> +One of the files is a directory and the filesystem does not support shared
> +regions in directories.
> +.TP
> +.B EINVAL
> +The filesystem does not support deduplicating 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. Neither btrfs nor XFS support
> +overlapping deduplication ranges in the same file.
> +.TP
> +.B EBADF
> +.IR src_fd
> +is not open for reading;
> +.IR dest_fd
> +is not open for writing or is open for append-only writes; or the filesystem
> +which
> +.IR src_fd
> +resides on does not support deduplication.
> +.TP
> +.B EPERM
> +.IR dest_fd
> +is immutable.
> +.TP
> +.B ETXTBSY
> +One of the files is a swap file. Swap files cannot share storage.
> +.TP
> +.B EOPNOTSUPP
> +This can appear if the filesystem does not support deduplicating either file
> +descriptor.
> +.SH NOTES
> +Because a copy on write operation requires the allocation of new storage, the
> +.B fallocate (2)
> +operation may un-share shared blocks to guarantee that subsequent writes will
> +not fail because of lack of disk space.
> +
> +Some filesystems may limit the amount of data that can be deduplicated in a
> +single call.
> +
> +.SH CONFORMING TO
> +This API is Linux-specific. This ioctl was previously known as
> +.B BTRFS_IOC_FILE_EXTENT_SAME
> +and was private to btrfs.
> +.fi
> +.in
> +.SH SEE ALSO
> +.BR ioctl (2)
>
>
--
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/
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