[v3,10/9] copy_file_range.2: New page documenting copy_file_range()

Commit Message

Schumaker, Anna Sept. 25, 2015, 8:48 p.m. UTC

copy_file_range() is a new system call for copying ranges of data
completely in the kernel.  This gives filesystems an opportunity to
implement some kind of "copy acceleration", such as reflinks or
server-side-copy (in the case of NFS).

Signed-off-by: Anna Schumaker <[e-mail]>
---
v3:
- Added license information
- Updated splice(2)
- Various other edits after mailing list discussion
---
 man2/copy_file_range.2 | 211 +++++++++++++++++++++++++++++++++++++++++++++++++
 man2/splice.2          |   1 +
 2 files changed, 212 insertions(+)
 create mode 100644 man2/copy_file_range.2

Comments

Darrick J. Wong Sept. 28, 2015, 6:40 p.m. UTC | #1

On Fri, Sep 25, 2015 at 04:48:16PM -0400, Anna Schumaker wrote:
> copy_file_range() is a new system call for copying ranges of data
> completely in the kernel.  This gives filesystems an opportunity to
> implement some kind of "copy acceleration", such as reflinks or
> server-side-copy (in the case of NFS).
> 
> Signed-off-by: Anna Schumaker <[e-mail]>
> ---
> v3:
> - Added license information
> - Updated splice(2)
> - Various other edits after mailing list discussion
> ---
>  man2/copy_file_range.2 | 211 +++++++++++++++++++++++++++++++++++++++++++++++++
>  man2/splice.2          |   1 +
>  2 files changed, 212 insertions(+)
>  create mode 100644 man2/copy_file_range.2
> 
> diff --git a/man2/copy_file_range.2 b/man2/copy_file_range.2
> new file mode 100644
> index 0000000..6d66d4a
> --- /dev/null
> +++ b/man2/copy_file_range.2
> @@ -0,0 +1,211 @@
> +.\"This manpage is Copyright (C) 2015 Anna Schumaker <[e-mail]>
> +.\"
> +.\" %%%LICENSE_START(VERBATIM)
> +.\" Permission is granted to make and distribute verbatim copies of this
> +.\" manual provided the copyright notice and this permission notice are
> +.\" preserved on all copies.
> +.\"
> +.\" Permission is granted to copy and distribute modified versions of
> +.\" this manual under the conditions for verbatim copying, provided that
> +.\" the entire resulting derived work is distributed under the terms of
> +.\" a permission notice identical to this one.
> +.\"
> +.\" Since the Linux kernel and libraries are constantly changing, this
> +.\" manual page may be incorrect or out-of-date.  The author(s) assume.
> +.\" no responsibility for errors or omissions, or for damages resulting.
> +.\" from the use of the information contained herein.  The author(s) may.
> +.\" not have taken the same level of care in the production of this.
> +.\" manual, which is licensed free of charge, as they might when working.
> +.\" professionally.
> +.\"
> +.\" Formatted or processed versions of this manual, if unaccompanied by
> +.\" the source, must acknowledge the copyright and authors of this work.
> +.\" %%%LICENSE_END
> +.\"
> +.TH COPY 2 2015-08-31 "Linux" "Linux Programmer's Manual"
> +.SH NAME
> +copy_file_range \- Copy a range of data from one file to another
> +.SH SYNOPSIS
> +.nf
> +.B #include <linux/copy.h>
> +.B #include <sys/syscall.h>
> +.B #include <unistd.h>
> +
> +.BI "ssize_t copy_file_range(int " fd_in ", loff_t *" off_in ", int " fd_out ",
> +.BI "                        loff_t *" off_out ", size_t " len \
> +", unsigned int " flags );
> +.fi
> +.SH DESCRIPTION
> +The
> +.BR copy_file_range ()
> +system call performs an in-kernel copy between two file descriptors
> +without the additional cost of transferring data from the kernel to userspace
> +and then back into the kernel.
> +It copies up to
> +.I len
> +bytes of data from file descriptor
> +.I fd_in
> +to file descriptor
> +.IR fd_out ,
> +overwriting any data that exists within the requested range of the target file.
> +
> +The following semantics apply for
> +.IR off_in ,
> +and similar statements apply to
> +.IR off_out :
> +.IP * 3
> +If
> +.I off_in
> +is NULL, then bytes are read from
> +.I fd_in
> +starting from the current file offset, and the offset is
> +adjusted by the number of bytes copied.
> +.IP *
> +If
> +.I off_in
> +is not NULL, then
> +.I off_in
> +must point to a buffer that specifies the starting
> +offset where bytes from
> +.I fd_in
> +will be read.  The current file offset of
> +.I fd_in
> +is not changed, but
> +.I off_in
> +is adjusted appropriately.
> +.PP
> +
> +The
> +.I flags
> +argument can have one of the following flags set:
> +.TP 1.9i
> +.B COPY_FR_COPY
> +Copy all the file data in the requested range.
> +Some filesystems might be able to accelerate this copy
> +to avoid unnecessary data transfers.
> +.TP
> +.B COPY_FR_REFLINK
> +Create a lightweight "reflink", where data is not copied until
> +one of the files is modified.

.TP
.B COPY_FR_DEDUPE
Create a lightweight "reflink" with the same operational behavior as
COPY_FR_REFLINK, but only perform the reflink if the contents of both files'
byte ranges are identical.  This flag cannot be specified with COPY_FR_COPY or
COPY_FR_REFLINK.  If the ranges do not match, EILSEQ will be returned.

> +.PP
> +The default behavior
> +.RI ( flags
> +== 0) is to try creating a reflink,
> +and if reflinking fails
> +.BR copy_file_range ()
> +will fall back to performing a full data copy.
> +.SH RETURN VALUE
> +Upon successful completion,
> +.BR copy_file_range ()
> +will return the number of bytes copied between files.
> +This could be less than the length originally requested.
> +
> +On error,
> +.BR copy_file_range ()
> +returns \-1 and
> +.I errno
> +is set to indicate the error.
> +.SH ERRORS
> +.TP
> +.B EBADF
> +One or more file descriptors are not valid; or
> +.I fd_in
> +is not open for reading; or
> +.I fd_out
> +is not open for writing.
> +.TP
> +.B EINVAL
> +Requested range extends beyond the end of the source file; or the
> +.I flags
> +argument is set to an invalid value.

.TP
.B EILSEQ
The contents of both files' byte ranges did not match.

> +.TP
> +.B EIO
> +A low level I/O error occurred while copying.
> +.TP
> +.B ENOMEM
> +Out of memory.
> +.TP
> +.B ENOSPC
> +There is not enough space on the target filesystem to complete the copy.
> +.TP
> +.B EOPNOTSUPP
> +.B COPY_REFLINK

.B COPY_FR_REFLINK
or
.B COPY_FR_DEDUPE

> +was specified in
> +.IR flags ,
> +but the target filesystem does not support reflinks.

"does not support the given operation."

Otherwise you can add,
Reviewed-by: Darrick J. Wong <[e-mail]>

--D

> +.TP
> +.B EXDEV
> +Target filesystem doesn't support cross-filesystem copies.
> +.SH VERSIONS
> +The
> +.BR copy_file_range ()
> +system call first appeared in Linux 4.4.
> +.SH CONFORMING TO
> +The
> +.BR copy_file_range ()
> +system call is a nonstandard Linux extension.
> +.SH EXAMPLE
> +.nf
> +#define _GNU_SOURCE
> +#include <fcntl.h>
> +#include <linux/copy.h>
> +#include <stdio.h>
> +#include <stdlib.h>
> +#include <sys/stat.h>
> +#include <sys/syscall.h>
> +#include <unistd.h>
> +
> +loff_t copy_file_range(int fd_in, loff_t *off_in, int fd_out,
> +                       loff_t *off_out, size_t len, unsigned int flags)
> +{
> +    return syscall(__NR_copy_file_range, fd_in, off_in, fd_out,
> +                   off_out, len, flags);
> +}
> +
> +int main(int argc, char **argv)
> +{
> +    int fd_in, fd_out;
> +    struct stat stat;
> +    loff_t len, ret;
> +    char buf[2];
> +
> +    if (argc != 3) {
> +        fprintf(stderr, "Usage: %s <source> <destination>\\n", argv[0]);
> +        exit(EXIT_FAILURE);
> +    }
> +
> +    fd_in = open(argv[1], O_RDONLY);
> +    if (fd_in == \-1) {
> +        perror("open (argv[1])");
> +        exit(EXIT_FAILURE);
> +    }
> +
> +    if (fstat(fd_in, &stat) == \-1) {
> +        perror("fstat");
> +        exit(EXIT_FAILURE);
> +    }
> +    len = stat.st_size;
> +
> +    fd_out = open(argv[2], O_CREAT|O_WRONLY|O_TRUNC, 0644);
> +    if (fd_out == \-1) {
> +        perror("open (argv[2])");
> +        exit(EXIT_FAILURE);
> +    }
> +
> +    do {
> +        ret = copy_file_range(fd_in, NULL, fd_out, NULL, len, COPY_FR_COPY);
> +        if (ret == \-1) {
> +            perror("copy_file_range");
> +            exit(EXIT_FAILURE);
> +        }
> +
> +        len \-= ret;
> +    } while (len > 0);
> +
> +    close(fd_in);
> +    close(fd_out);
> +    exit(EXIT_SUCCESS);
> +}
> +.fi
> +.SH SEE ALSO
> +.BR splice (2)
> diff --git a/man2/splice.2 b/man2/splice.2
> index b9b4f42..5c162e0 100644
> --- a/man2/splice.2
> +++ b/man2/splice.2
> @@ -238,6 +238,7 @@ only pointers are copied, not the pages of the buffer.
>  See
>  .BR tee (2).
>  .SH SEE ALSO
> +.BR copy_file_range (2),
>  .BR sendfile (2),
>  .BR tee (2),
>  .BR vmsplice (2)
> -- 
> 2.5.3
> 
> --
> To unsubscribe from this list: send the line "unsubscribe linux-api" in
> the body of a message to [e-mail]
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
--
To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in
the body of a message to [e-mail]
More majordomo info at  http://vger.kernel.org/majordomo-info.html

Schumaker, Anna Sept. 28, 2015, 8:42 p.m. UTC | #2

On 09/28/2015 02:40 PM, Darrick J. Wong wrote:
> On Fri, Sep 25, 2015 at 04:48:16PM -0400, Anna Schumaker wrote:
>> copy_file_range() is a new system call for copying ranges of data
>> completely in the kernel.  This gives filesystems an opportunity to
>> implement some kind of "copy acceleration", such as reflinks or
>> server-side-copy (in the case of NFS).
>>
>> Signed-off-by: Anna Schumaker <[e-mail]>
>> ---
>> v3:
>> - Added license information
>> - Updated splice(2)
>> - Various other edits after mailing list discussion
>> ---
>>  man2/copy_file_range.2 | 211 +++++++++++++++++++++++++++++++++++++++++++++++++
>>  man2/splice.2          |   1 +
>>  2 files changed, 212 insertions(+)
>>  create mode 100644 man2/copy_file_range.2
>>
>> diff --git a/man2/copy_file_range.2 b/man2/copy_file_range.2
>> new file mode 100644
>> index 0000000..6d66d4a
>> --- /dev/null
>> +++ b/man2/copy_file_range.2
>> @@ -0,0 +1,211 @@
>> +.\"This manpage is Copyright (C) 2015 Anna Schumaker <[e-mail]>
>> +.\"
>> +.\" %%%LICENSE_START(VERBATIM)
>> +.\" Permission is granted to make and distribute verbatim copies of this
>> +.\" manual provided the copyright notice and this permission notice are
>> +.\" preserved on all copies.
>> +.\"
>> +.\" Permission is granted to copy and distribute modified versions of
>> +.\" this manual under the conditions for verbatim copying, provided that
>> +.\" the entire resulting derived work is distributed under the terms of
>> +.\" a permission notice identical to this one.
>> +.\"
>> +.\" Since the Linux kernel and libraries are constantly changing, this
>> +.\" manual page may be incorrect or out-of-date.  The author(s) assume.
>> +.\" no responsibility for errors or omissions, or for damages resulting.
>> +.\" from the use of the information contained herein.  The author(s) may.
>> +.\" not have taken the same level of care in the production of this.
>> +.\" manual, which is licensed free of charge, as they might when working.
>> +.\" professionally.
>> +.\"
>> +.\" Formatted or processed versions of this manual, if unaccompanied by
>> +.\" the source, must acknowledge the copyright and authors of this work.
>> +.\" %%%LICENSE_END
>> +.\"
>> +.TH COPY 2 2015-08-31 "Linux" "Linux Programmer's Manual"
>> +.SH NAME
>> +copy_file_range \- Copy a range of data from one file to another
>> +.SH SYNOPSIS
>> +.nf
>> +.B #include <linux/copy.h>
>> +.B #include <sys/syscall.h>
>> +.B #include <unistd.h>
>> +
>> +.BI "ssize_t copy_file_range(int " fd_in ", loff_t *" off_in ", int " fd_out ",
>> +.BI "                        loff_t *" off_out ", size_t " len \
>> +", unsigned int " flags );
>> +.fi
>> +.SH DESCRIPTION
>> +The
>> +.BR copy_file_range ()
>> +system call performs an in-kernel copy between two file descriptors
>> +without the additional cost of transferring data from the kernel to userspace
>> +and then back into the kernel.
>> +It copies up to
>> +.I len
>> +bytes of data from file descriptor
>> +.I fd_in
>> +to file descriptor
>> +.IR fd_out ,
>> +overwriting any data that exists within the requested range of the target file.
>> +
>> +The following semantics apply for
>> +.IR off_in ,
>> +and similar statements apply to
>> +.IR off_out :
>> +.IP * 3
>> +If
>> +.I off_in
>> +is NULL, then bytes are read from
>> +.I fd_in
>> +starting from the current file offset, and the offset is
>> +adjusted by the number of bytes copied.
>> +.IP *
>> +If
>> +.I off_in
>> +is not NULL, then
>> +.I off_in
>> +must point to a buffer that specifies the starting
>> +offset where bytes from
>> +.I fd_in
>> +will be read.  The current file offset of
>> +.I fd_in
>> +is not changed, but
>> +.I off_in
>> +is adjusted appropriately.
>> +.PP
>> +
>> +The
>> +.I flags
>> +argument can have one of the following flags set:
>> +.TP 1.9i
>> +.B COPY_FR_COPY
>> +Copy all the file data in the requested range.
>> +Some filesystems might be able to accelerate this copy
>> +to avoid unnecessary data transfers.
>> +.TP
>> +.B COPY_FR_REFLINK
>> +Create a lightweight "reflink", where data is not copied until
>> +one of the files is modified.
> 
> .TP
> .B COPY_FR_DEDUPE
> Create a lightweight "reflink" with the same operational behavior as
> COPY_FR_REFLINK, but only perform the reflink if the contents of both files'
> byte ranges are identical.  This flag cannot be specified with COPY_FR_COPY or
> COPY_FR_REFLINK.  If the ranges do not match, EILSEQ will be returned.
> 
>> +.PP
>> +The default behavior
>> +.RI ( flags
>> +== 0) is to try creating a reflink,
>> +and if reflinking fails
>> +.BR copy_file_range ()
>> +will fall back to performing a full data copy.
>> +.SH RETURN VALUE
>> +Upon successful completion,
>> +.BR copy_file_range ()
>> +will return the number of bytes copied between files.
>> +This could be less than the length originally requested.
>> +
>> +On error,
>> +.BR copy_file_range ()
>> +returns \-1 and
>> +.I errno
>> +is set to indicate the error.
>> +.SH ERRORS
>> +.TP
>> +.B EBADF
>> +One or more file descriptors are not valid; or
>> +.I fd_in
>> +is not open for reading; or
>> +.I fd_out
>> +is not open for writing.
>> +.TP
>> +.B EINVAL
>> +Requested range extends beyond the end of the source file; or the
>> +.I flags
>> +argument is set to an invalid value.
> 
> .TP
> .B EILSEQ
> The contents of both files' byte ranges did not match.
> 
>> +.TP
>> +.B EIO
>> +A low level I/O error occurred while copying.
>> +.TP
>> +.B ENOMEM
>> +Out of memory.
>> +.TP
>> +.B ENOSPC
>> +There is not enough space on the target filesystem to complete the copy.
>> +.TP
>> +.B EOPNOTSUPP
>> +.B COPY_REFLINK
> 
> .B COPY_FR_REFLINK
> or
> .B COPY_FR_DEDUPE
> 
>> +was specified in
>> +.IR flags ,
>> +but the target filesystem does not support reflinks.
> 
> "does not support the given operation."
> 
> Otherwise you can add,
> Reviewed-by: Darrick J. Wong <[e-mail]>

Thanks, Darrick!

I've added in your suggestions (and also renamed COPY_FR_DEDUPE -> COPY_FR_DEDUP). I'll send out a v4 tomorrow morning, once I see if any other comments trickle in.

Anna

> 
> --D
> 
>> +.TP
>> +.B EXDEV
>> +Target filesystem doesn't support cross-filesystem copies.
>> +.SH VERSIONS
>> +The
>> +.BR copy_file_range ()
>> +system call first appeared in Linux 4.4.
>> +.SH CONFORMING TO
>> +The
>> +.BR copy_file_range ()
>> +system call is a nonstandard Linux extension.
>> +.SH EXAMPLE
>> +.nf
>> +#define _GNU_SOURCE
>> +#include <fcntl.h>
>> +#include <linux/copy.h>
>> +#include <stdio.h>
>> +#include <stdlib.h>
>> +#include <sys/stat.h>
>> +#include <sys/syscall.h>
>> +#include <unistd.h>
>> +
>> +loff_t copy_file_range(int fd_in, loff_t *off_in, int fd_out,
>> +                       loff_t *off_out, size_t len, unsigned int flags)
>> +{
>> +    return syscall(__NR_copy_file_range, fd_in, off_in, fd_out,
>> +                   off_out, len, flags);
>> +}
>> +
>> +int main(int argc, char **argv)
>> +{
>> +    int fd_in, fd_out;
>> +    struct stat stat;
>> +    loff_t len, ret;
>> +    char buf[2];
>> +
>> +    if (argc != 3) {
>> +        fprintf(stderr, "Usage: %s <source> <destination>\\n", argv[0]);
>> +        exit(EXIT_FAILURE);
>> +    }
>> +
>> +    fd_in = open(argv[1], O_RDONLY);
>> +    if (fd_in == \-1) {
>> +        perror("open (argv[1])");
>> +        exit(EXIT_FAILURE);
>> +    }
>> +
>> +    if (fstat(fd_in, &stat) == \-1) {
>> +        perror("fstat");
>> +        exit(EXIT_FAILURE);
>> +    }
>> +    len = stat.st_size;
>> +
>> +    fd_out = open(argv[2], O_CREAT|O_WRONLY|O_TRUNC, 0644);
>> +    if (fd_out == \-1) {
>> +        perror("open (argv[2])");
>> +        exit(EXIT_FAILURE);
>> +    }
>> +
>> +    do {
>> +        ret = copy_file_range(fd_in, NULL, fd_out, NULL, len, COPY_FR_COPY);
>> +        if (ret == \-1) {
>> +            perror("copy_file_range");
>> +            exit(EXIT_FAILURE);
>> +        }
>> +
>> +        len \-= ret;
>> +    } while (len > 0);
>> +
>> +    close(fd_in);
>> +    close(fd_out);
>> +    exit(EXIT_SUCCESS);
>> +}
>> +.fi
>> +.SH SEE ALSO
>> +.BR splice (2)
>> diff --git a/man2/splice.2 b/man2/splice.2
>> index b9b4f42..5c162e0 100644
>> --- a/man2/splice.2
>> +++ b/man2/splice.2
>> @@ -238,6 +238,7 @@ only pointers are copied, not the pages of the buffer.
>>  See
>>  .BR tee (2).
>>  .SH SEE ALSO
>> +.BR copy_file_range (2),
>>  .BR sendfile (2),
>>  .BR tee (2),
>>  .BR vmsplice (2)
>> -- 
>> 2.5.3
>>
>> --
>> To unsubscribe from this list: send the line "unsubscribe linux-api" in
>> the body of a message to [e-mail]
>> More majordomo info at  http://vger.kernel.org/majordomo-info.html

--
To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in
the body of a message to [e-mail]
More majordomo info at  http://vger.kernel.org/majordomo-info.html

Patch

diff --git a/man2/copy_file_range.2 b/man2/copy_file_range.2
new file mode 100644
index 0000000..6d66d4a
--- /dev/null
+++ b/man2/copy_file_range.2
@@ -0,0 +1,211 @@ 
+.\"This manpage is Copyright (C) 2015 Anna Schumaker <[e-mail]>
+.\"
+.\" %%%LICENSE_START(VERBATIM)
+.\" Permission is granted to make and distribute verbatim copies of this
+.\" manual provided the copyright notice and this permission notice are
+.\" preserved on all copies.
+.\"
+.\" Permission is granted to copy and distribute modified versions of
+.\" this manual under the conditions for verbatim copying, provided that
+.\" the entire resulting derived work is distributed under the terms of
+.\" a permission notice identical to this one.
+.\"
+.\" Since the Linux kernel and libraries are constantly changing, this
+.\" manual page may be incorrect or out-of-date.  The author(s) assume.
+.\" no responsibility for errors or omissions, or for damages resulting.
+.\" from the use of the information contained herein.  The author(s) may.
+.\" not have taken the same level of care in the production of this.
+.\" manual, which is licensed free of charge, as they might when working.
+.\" professionally.
+.\"
+.\" Formatted or processed versions of this manual, if unaccompanied by
+.\" the source, must acknowledge the copyright and authors of this work.
+.\" %%%LICENSE_END
+.\"
+.TH COPY 2 2015-08-31 "Linux" "Linux Programmer's Manual"
+.SH NAME
+copy_file_range \- Copy a range of data from one file to another
+.SH SYNOPSIS
+.nf
+.B #include <linux/copy.h>
+.B #include <sys/syscall.h>
+.B #include <unistd.h>
+
+.BI "ssize_t copy_file_range(int " fd_in ", loff_t *" off_in ", int " fd_out ",
+.BI "                        loff_t *" off_out ", size_t " len \
+", unsigned int " flags );
+.fi
+.SH DESCRIPTION
+The
+.BR copy_file_range ()
+system call performs an in-kernel copy between two file descriptors
+without the additional cost of transferring data from the kernel to userspace
+and then back into the kernel.
+It copies up to
+.I len
+bytes of data from file descriptor
+.I fd_in
+to file descriptor
+.IR fd_out ,
+overwriting any data that exists within the requested range of the target file.
+
+The following semantics apply for
+.IR off_in ,
+and similar statements apply to
+.IR off_out :
+.IP * 3
+If
+.I off_in
+is NULL, then bytes are read from
+.I fd_in
+starting from the current file offset, and the offset is
+adjusted by the number of bytes copied.
+.IP *
+If
+.I off_in
+is not NULL, then
+.I off_in
+must point to a buffer that specifies the starting
+offset where bytes from
+.I fd_in
+will be read.  The current file offset of
+.I fd_in
+is not changed, but
+.I off_in
+is adjusted appropriately.
+.PP
+
+The
+.I flags
+argument can have one of the following flags set:
+.TP 1.9i
+.B COPY_FR_COPY
+Copy all the file data in the requested range.
+Some filesystems might be able to accelerate this copy
+to avoid unnecessary data transfers.
+.TP
+.B COPY_FR_REFLINK
+Create a lightweight "reflink", where data is not copied until
+one of the files is modified.
+.PP
+The default behavior
+.RI ( flags
+== 0) is to try creating a reflink,
+and if reflinking fails
+.BR copy_file_range ()
+will fall back to performing a full data copy.
+.SH RETURN VALUE
+Upon successful completion,
+.BR copy_file_range ()
+will return the number of bytes copied between files.
+This could be less than the length originally requested.
+
+On error,
+.BR copy_file_range ()
+returns \-1 and
+.I errno
+is set to indicate the error.
+.SH ERRORS
+.TP
+.B EBADF
+One or more file descriptors are not valid; or
+.I fd_in
+is not open for reading; or
+.I fd_out
+is not open for writing.
+.TP
+.B EINVAL
+Requested range extends beyond the end of the source file; or the
+.I flags
+argument is set to an invalid value.
+.TP
+.B EIO
+A low level I/O error occurred while copying.
+.TP
+.B ENOMEM
+Out of memory.
+.TP
+.B ENOSPC
+There is not enough space on the target filesystem to complete the copy.
+.TP
+.B EOPNOTSUPP
+.B COPY_REFLINK
+was specified in
+.IR flags ,
+but the target filesystem does not support reflinks.
+.TP
+.B EXDEV
+Target filesystem doesn't support cross-filesystem copies.
+.SH VERSIONS
+The
+.BR copy_file_range ()
+system call first appeared in Linux 4.4.
+.SH CONFORMING TO
+The
+.BR copy_file_range ()
+system call is a nonstandard Linux extension.
+.SH EXAMPLE
+.nf
+#define _GNU_SOURCE
+#include <fcntl.h>
+#include <linux/copy.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <sys/stat.h>
+#include <sys/syscall.h>
+#include <unistd.h>
+
+loff_t copy_file_range(int fd_in, loff_t *off_in, int fd_out,
+                       loff_t *off_out, size_t len, unsigned int flags)
+{
+    return syscall(__NR_copy_file_range, fd_in, off_in, fd_out,
+                   off_out, len, flags);
+}
+
+int main(int argc, char **argv)
+{
+    int fd_in, fd_out;
+    struct stat stat;
+    loff_t len, ret;
+    char buf[2];
+
+    if (argc != 3) {
+        fprintf(stderr, "Usage: %s <source> <destination>\\n", argv[0]);
+        exit(EXIT_FAILURE);
+    }
+
+    fd_in = open(argv[1], O_RDONLY);
+    if (fd_in == \-1) {
+        perror("open (argv[1])");
+        exit(EXIT_FAILURE);
+    }
+
+    if (fstat(fd_in, &stat) == \-1) {
+        perror("fstat");
+        exit(EXIT_FAILURE);
+    }
+    len = stat.st_size;
+
+    fd_out = open(argv[2], O_CREAT|O_WRONLY|O_TRUNC, 0644);
+    if (fd_out == \-1) {
+        perror("open (argv[2])");
+        exit(EXIT_FAILURE);
+    }
+
+    do {
+        ret = copy_file_range(fd_in, NULL, fd_out, NULL, len, COPY_FR_COPY);
+        if (ret == \-1) {
+            perror("copy_file_range");
+            exit(EXIT_FAILURE);
+        }
+
+        len \-= ret;
+    } while (len > 0);
+
+    close(fd_in);
+    close(fd_out);
+    exit(EXIT_SUCCESS);
+}
+.fi
+.SH SEE ALSO
+.BR splice (2)
diff --git a/man2/splice.2 b/man2/splice.2
index b9b4f42..5c162e0 100644
--- a/man2/splice.2
+++ b/man2/splice.2
@@ -238,6 +238,7 @@  only pointers are copied, not the pages of the buffer.
 See
 .BR tee (2).
 .SH SEE ALSO
+.BR copy_file_range (2),
 .BR sendfile (2),
 .BR tee (2),
 .BR vmsplice (2)