1.\" $NetBSD: dofileread.9,v 1.9 2010/12/02 12:54:13 wiz Exp $ 2.\" 3.\" Copyright (c) 2002 The NetBSD Foundation, Inc. 4.\" All rights reserved. 5.\" 6.\" This code is derived from software contributed to The NetBSD Foundation 7.\" by Gregory McGarry. 8.\" 9.\" Redistribution and use in source and binary forms, with or without 10.\" modification, are permitted provided that the following conditions 11.\" are met: 12.\" 1. Redistributions of source code must retain the above copyright 13.\" notice, this list of conditions and the following disclaimer. 14.\" 2. Redistributions in binary form must reproduce the above copyright 15.\" notice, this list of conditions and the following disclaimer in the 16.\" documentation and/or other materials provided with the distribution. 17.\" 18.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS 19.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED 20.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 21.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS 22.\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 23.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF 24.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS 25.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN 26.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 27.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 28.\" POSSIBILITY OF SUCH DAMAGE. 29.\" 30.Dd December 20, 2005 31.Dt DOFILEREAD 9 32.Os 33.Sh NAME 34.Nm dofileread , 35.Nm dofilereadv , 36.Nm dofilewrite , 37.Nm dofilewritev 38.Nd high-level file operations 39.Sh SYNOPSIS 40.In sys/file.h 41.Ft int 42.Fn dofileread "struct lwp *l" "int fd" "struct file *fp" "void *buf" \ 43"size_t nbyte" "off_t *offset" "int flags" "register_t *retval" 44.Ft int 45.Fn dofilewrite "struct lwp *l" "int fd" "struct file *fp" \ 46"const void *buf" "size_t nbyte" "off_t *offset" "int flags" \ 47"register_t *retval" 48.Ft int 49.Fn dofilereadv "struct lwp *l" "int fd" "struct file *fp" \ 50"const struct iovec *iovp" "int iovcnt" "off_t *offset" "int flags" \ 51"register_t *retval" 52.Ft int 53.Fn dofilewritev "struct lwp *l" "int fd" "struct file *fp" \ 54"const struct iovec *iovp" "int iovcnt" "off_t *offset" "int flags" \ 55"register_t *retval" 56.Sh DESCRIPTION 57The functions implement the underlying functionality of the 58.Xr read 2 , 59.Xr write 2 , 60.Xr readv 2 , 61and 62.Xr writev 2 63system calls. 64They are also used throughout the kernel as high-level access routines 65for file I/O. 66.Pp 67The 68.Fn dofileread 69function attempts to read 70.Fa nbytes 71of data from the object referenced by file entry 72.Fa fp 73into the buffer pointed to by 74.Fa buf . 75The 76.Fn dofilewrite 77function attempts to write 78.Fa nbytes 79of data to the object referenced by file entry 80.Fa fp 81from the buffer pointed to by 82.Fa buf . 83.Pp 84The 85.Fn dofilereadv 86and 87.Fn dofilewritev 88functions perform the same operations, but scatter the data with the 89.Fa iovcnt 90buffers specified by the members of the 91.Fa iov 92array. 93.Pp 94The offset of the file operations is explicitly specified by 95.Fa *offset . 96The new file offset after the file operation is returned in 97.Fa *offset . 98If the FOF_UPDATE_OFFSET flag is specified in the 99.Fa flags 100argument, the file offset in the file entry 101.Fa fp 102is updated to reflect the new file offset, otherwise it remains 103unchanged after the operation. 104.Pp 105The file descriptor 106.Fa fd 107is largely unused except for use by the ktrace framework for reporting 108to userlevel the process's file descriptor. 109.Pp 110Upon successful completion the number of bytes which were transferred 111is returned in 112.Fa *retval . 113.Sh RETURN VALUES 114Upon successful completion zero is returned, otherwise an appropriate 115error is returned. 116.Sh CODE REFERENCES 117The framework for these file operations is implemented within the file 118.Pa sys/kern/sys_generic.c . 119.Sh SEE ALSO 120.Xr file 9 121