From patchwork Fri Sep 25 20:48:16 2015 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Schumaker, Anna" X-Patchwork-Id: 7267791 Return-Path: X-Original-To: patchwork-linux-nfs@patchwork.kernel.org Delivered-To: patchwork-parsemail@patchwork1.web.kernel.org Received: from mail.kernel.org (mail.kernel.org [198.145.29.136]) by patchwork1.web.kernel.org (Postfix) with ESMTP id 322059F380 for ; Fri, 25 Sep 2015 20:48:57 +0000 (UTC) Received: from mail.kernel.org (localhost [127.0.0.1]) by mail.kernel.org (Postfix) with ESMTP id 2297320961 for ; Fri, 25 Sep 2015 20:48:56 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 79C6A2095F for ; Fri, 25 Sep 2015 20:48:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933363AbbIYUss (ORCPT ); Fri, 25 Sep 2015 16:48:48 -0400 Received: from mx143.netapp.com ([216.240.21.24]:59082 "EHLO mx143.netapp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933301AbbIYUsj (ORCPT ); Fri, 25 Sep 2015 16:48:39 -0400 X-IronPort-AV: E=Sophos;i="5.17,588,1437462000"; d="scan'208";a="68724517" Received: from vmwexchts03-prd.hq.netapp.com ([10.122.105.31]) by mx143-out.netapp.com with ESMTP; 25 Sep 2015 13:48:39 -0700 Received: from smtp2.corp.netapp.com (10.57.159.114) by VMWEXCHTS03-PRD.hq.netapp.com (10.122.105.31) with Microsoft SMTP Server id 15.0.1104.5; Fri, 25 Sep 2015 13:48:39 -0700 Received: from davros.com ([10.63.229.98]) by smtp2.corp.netapp.com (8.13.1/8.13.1/NTAP-1.6) with ESMTP id t8PKmH9r028144; Fri, 25 Sep 2015 13:48:37 -0700 (PDT) From: Anna Schumaker To: , , , , , , , , , , Subject: [PATCH v3 10/9] copy_file_range.2: New page documenting copy_file_range() Date: Fri, 25 Sep 2015 16:48:16 -0400 Message-ID: <1443214096-12769-11-git-send-email-Anna.Schumaker@Netapp.com> X-Mailer: git-send-email 2.5.3 In-Reply-To: <1443214096-12769-1-git-send-email-Anna.Schumaker@Netapp.com> References: <1443214096-12769-1-git-send-email-Anna.Schumaker@Netapp.com> MIME-Version: 1.0 Sender: linux-nfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-nfs@vger.kernel.org X-Spam-Status: No, score=-6.9 required=5.0 tests=BAYES_00, RCVD_IN_DNSWL_HI, RP_MATCHES_RCVD, UNPARSEABLE_RELAY autolearn=unavailable version=3.3.1 X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on mail.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP 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 --- 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 +.\" +.\" %%%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 +.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. +.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 +#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)