Return-Path: Received: from mx144.netapp.com ([216.240.21.25]:49777 "EHLO mx144.netapp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754118AbbIKUaq (ORCPT ); Fri, 11 Sep 2015 16:30:46 -0400 From: Anna Schumaker To: , , , , , , , , , , Subject: [PATCH v2 10/9] copy_file_range.2: New page documenting copy_file_range() Date: Fri, 11 Sep 2015 16:30:23 -0400 Message-ID: <1442003423-6884-11-git-send-email-Anna.Schumaker@Netapp.com> In-Reply-To: <1442003423-6884-1-git-send-email-Anna.Schumaker@Netapp.com> References: <1442003423-6884-1-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 --- man2/copy_file_range.2 | 188 +++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 188 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..84912b5 --- /dev/null +++ b/man2/copy_file_range.2 @@ -0,0 +1,188 @@ +.\"This manpage is Copyright (C) 2015 Anna Schumaker +.TH COPY 2 2015-8-31 "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 syscall(__NR_copy_file_range, int " fd_in ", loff_t * " off_in ", +.BI " int " fd_out ", loff_t * " off_out ", size_t " len ", +.BI " unsigned int " flags ); +.fi +.SH DESCRIPTION +The +.BR copy_file_range () +system call performs an in-kernel copy between two file descriptors +without all that tedious mucking about in userspace. +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. + +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 current +file offset is adjusted appropriately. +.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 is a bit mask composed by OR-ing together zero +or more of the following flags: +.TP 1.9i +.B COPY_FR_COPY +Copy all the file data in the requested range. +Some filesystems, like NFS, 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 on performing a full data copy. +This is equivalent to setting +.I flags +equal to +.RB ( COPY_FR_COPY | COPY_FR_REFLINK ). +.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 do not have proper read-write mode; +.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 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 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 + + +int main(int argc, char **argv) +{ + int fd_in, fd_out; + struct stat stat; + loff_t len, ret; + + 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 = creat(argv[2], 0644); + if (fd_out == -1) { + perror("creat (argv[2])"); + exit(EXIT_FAILURE); + } + + do { + ret = syscall(__NR_copy_file_range, fd_in, NULL, + fd_out, NULL, len, 0); + 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) -- 2.5.1