1.\" 2.\" Copyright (c) 1997 Joerg Wunsch 3.\" 4.\" All rights reserved. 5.\" 6.\" Redistribution and use in source and binary forms, with or without 7.\" modification, are permitted provided that the following conditions 8.\" are met: 9.\" 1. Redistributions of source code must retain the above copyright 10.\" notice, this list of conditions and the following disclaimer. 11.\" 2. Redistributions in binary form must reproduce the above copyright 12.\" notice, this list of conditions and the following disclaimer in the 13.\" documentation and/or other materials provided with the distribution. 14.\" 15.\" THIS SOFTWARE IS PROVIDED BY THE DEVELOPERS ``AS IS'' AND ANY EXPRESS OR 16.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 17.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 18.\" IN NO EVENT SHALL THE DEVELOPERS BE LIABLE FOR ANY DIRECT, INDIRECT, 19.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 20.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 21.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 22.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 23.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF 24.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 25.\" 26.\" $FreeBSD: src/share/man/man9/uio.9,v 1.5.2.4 2001/12/17 11:30:19 ru Exp $ 27.\" 28.Dd February 2, 1997 29.Os 30.Dt UIO 9 31.Sh NAME 32.Nm uio , 33.Nm uiomove 34.Nd device driver I/O routines 35.Sh SYNOPSIS 36.In sys/types.h 37.In sys/uio.h 38.Pp 39.Bd -literal 40struct uio { 41 struct iovec *uio_iov; 42 int uio_iovcnt; 43 off_t uio_offset; 44 int uio_resid; 45 enum uio_seg uio_segflg; 46 enum uio_rw uio_rw; 47 struct proc *uio_procp; 48}; 49.Ed 50.Ft int 51.Fn uiomove "caddr_t buf" "int howmuch" "struct uio *uiop" 52.Sh DESCRIPTION 53The function 54.Fn uiomove 55is used to handle transfer of data between buffers and I/O vectors 56that might possibly also cross the user/kernel space boundary. 57.Pp 58As a result of any 59.Xr read 2 , 60.Xr write 2 , 61.Xr readv 2 , 62or 63.Xr writev 2 64system call that is being passed to a character-device driver, the 65appropriate driver 66.Va d_read 67or 68.Va d_write 69entry will be called with a pointer to a 70.Vt "struct uio" 71being passed. 72The transfer request is encoded in this structure. 73The driver itself should use 74.Fn uiomove 75to get at the data in this structure. 76.Pp 77The fields in the 78.Vt uio 79structure are: 80.Bl -tag -width ".Va uio_iovcnt" 81.It Va uio_iov 82The array of I/O vectors to be processed. 83In the case of scatter/gather 84I/O, this will be more than one vector. 85.It Va uio_iovcnt 86The number of I/O vectors present. 87.It Va uio_offset 88The offset into the device. 89.It Va uio_resid 90The number of bytes to process. 91.It Va uio_segflg 92One of the following flags: 93.Bl -tag -width ".Dv UIO_USERISPACE" 94.It Dv UIO_USERSPACE 95The I/O vector points into a process's address space. 96.It Dv UIO_SYSSPACE 97The I/O vector points into the kernel address space. 98.It Dv UIO_USERISPACE 99The I/O vector points into the instruction area of a process's address 100space. 101.It Dv UIO_NOCOPY 102Don't copy, already in object. 103.El 104.It Va uio_rw 105The direction of the desired transfer, either 106.Dv UIO_READ , 107or 108.Dv UIO_WRITE . 109.It Va uio_td 110The pointer to a 111.Vt "struct thread" 112for the associated thread; used if 113.Va uio_segflg 114indicates that the transfer is to be made from/to a process's address 115space. 116.El 117.Sh EXAMPLES 118The idea is that the driver maintains a private buffer for its data, 119and processes the request in chunks of maximal the size of this 120buffer. 121Note that the buffer handling below is very simplified and 122won't work (the buffer pointer is not being advanced in case of a 123partial read), it's just here to demonstrate the 124.Nm 125handling. 126.Bd -literal 127/* MIN() can be found there: */ 128#include <sys/param.h> 129 130#define BUFSIZE 512 131static char buffer[BUFSIZE]; 132 133static int data_available; /* amount of data that can be read */ 134 135static int 136fooread(dev_t dev, struct uio *uio, int flag) 137{ 138 int rv, amnt; 139 140 while (uio->uio_resid > 0) { 141 if (data_available > 0) { 142 amnt = MIN(uio->uio_resid, data_available); 143 if ((rv = uiomove((caddr_t)buffer, amnt, uio)) 144 != 0) 145 goto error; 146 data_available -= amnt; 147 } else { 148 tsleep(...); /* wait for a better time */ 149 } 150 } 151 return 0; 152error: 153 /* do error cleanup here */ 154 return rv; 155} 156.Ed 157.Sh RETURN VALUES 158.Fn uiomove 159can return 160.Er EFAULT 161from the invoked 162.Xr copyin 9 163or 164.Xr copyout 9 165in case the transfer was to/from a process's address space. 166.Sh SEE ALSO 167.Xr read 2 , 168.Xr readv 2 , 169.Xr write 2 , 170.Xr writev 2 , 171.Xr copyin 9 , 172.Xr copyout 9 , 173.Xr sleep 9 174.Sh HISTORY 175The 176.Nm 177mechanism appeared in some early version of 178.Ux . 179.Sh AUTHORS 180This man page was written by 181.An J\(:org Wunsch . 182