Return-Path: Received: from mx141.netapp.com ([216.240.21.12]:56128 "EHLO mx141.netapp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S935320AbbI2SFi (ORCPT ); Tue, 29 Sep 2015 14:05:38 -0400 From: Anna Schumaker To: , , , , , , , , , , Subject: [PATCH v4 10/9] copy_file_range.2: New page documenting copy_file_range() Date: Tue, 29 Sep 2015 14:05:13 -0400 Message-ID: <1443549913-8091-11-git-send-email-Anna.Schumaker@Netapp.com> In-Reply-To: <1443549913-8091-1-git-send-email-Anna.Schumaker@Netapp.com> References: <1443549913-8091-1-git-send-email-Anna.Schumaker@Netapp.com> MIME-Version: 1.0 Content-Type: text/plain Sender: linux-nfs-owner@vger.kernel.org List-ID: 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 Reviewed-by: Darrick J. Wong --- v4: - Updates for COPY_FR_DEDUP --- man2/copy_file_range.2 | 224 +++++++++++++++++++++++++++++++++++++++++++++++++ man2/splice.2 | 1 + 2 files changed, 225 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..23e3875 --- /dev/null +++ b/man2/copy_file_range.2 @@ -0,0 +1,224 @@ +.\"This manpage is Copyright (C) 2015 Anna Schumaker +.\" +.\" %%%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 +.\" +.\" Since the Linux kernel and libraries are constantly changing, this +.\" manual page may be incorrect or out-of-date.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 2015-09-29 "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 +.B #include +.B #include + +.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_DEDUP +Create a reflink, but only if the contents of +both files' byte ranges are identical. +If ranges do not match, +.B 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 EILSEQ +The contents of both files' byte ranges did not match. +.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 +or +.B COPY_DEDUP +was specified in +.IR flags , +but the target filesystem does not support the given operation. +.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 +#include +#include +#include +#include +#include +#include + +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 \\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