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.\" $DragonFly: src/share/man/man9/uio.9,v 1.2 2003/06/17 04:37:01 dillon Exp $ 28.\" 29.Dd February 2, 1997 30.Os 31.Dt UIO 9 32.Sh NAME 33.Nm uio , 34.Nm uiomove 35.Nd device driver I/O routines 36.Sh SYNOPSIS 37.In sys/types.h 38.In sys/uio.h 39.Pp 40.Bd -literal 41struct uio { 42 struct iovec *uio_iov; 43 int uio_iovcnt; 44 off_t uio_offset; 45 int uio_resid; 46 enum uio_seg uio_segflg; 47 enum uio_rw uio_rw; 48 struct proc *uio_procp; 49}; 50.Ed 51.Ft int 52.Fn uiomove "caddr_t buf" "int howmuch" "struct uio *uiop" 53.Sh DESCRIPTION 54The function 55.Fn uiomove 56is used to handle transfer of data between buffers and I/O vectors 57that might possibly also cross the user/kernel space boundary. 58.Pp 59As a result of any 60.Xr read 2 , 61.Xr write 2 , 62.Xr readv 2 , 63or 64.Xr writev 2 65system call that is being passed to a character-device driver, the 66appropriate driver 67.Va d_read 68or 69.Va d_write 70entry will be called with a pointer to a 71.Vt "struct uio" 72being passed. 73The transfer request is encoded in this structure. 74The driver itself should use 75.Fn uiomove 76to get at the data in this structure. 77.Pp 78The fields in the 79.Vt uio 80structure are: 81.Bl -tag -width ".Va uio_iovcnt" 82.It Va uio_iov 83The array of I/O vectors to be processed. 84In the case of scatter/gather 85I/O, this will be more than one vector. 86.It Va uio_iovcnt 87The number of I/O vectors present. 88.It Va uio_offset 89The offset into the device. 90.It Va uio_resid 91The number of bytes to process. 92.It Va uio_segflg 93One of the following flags: 94.Bl -tag -width ".Dv UIO_USERISPACE" 95.It Dv UIO_USERSPACE 96The I/O vector points into a process's address space. 97.It Dv UIO_SYSSPACE 98The I/O vector points into the kernel address space. 99.It Dv UIO_USERISPACE 100The I/O vector points into the instruction area of a process's address 101space. 102.It Dv UIO_NOCOPY 103Don't copy, already in object. 104.El 105.It Va uio_rw 106The direction of the desired transfer, either 107.Dv UIO_READ , 108or 109.Dv UIO_WRITE . 110.It Va uio_td 111The pointer to a 112.Vt "struct thread" 113for the associated thread; used if 114.Va uio_segflg 115indicates that the transfer is to be made from/to a process's address 116space. 117.El 118.Sh EXAMPLES 119The idea is that the driver maintains a private buffer for its data, 120and processes the request in chunks of maximal the size of this 121buffer. 122Note that the buffer handling below is very simplified and 123won't work (the buffer pointer is not being advanced in case of a 124partial read), it's just here to demonstrate the 125.Nm 126handling. 127.Bd -literal 128/* MIN() can be found there: */ 129#include <sys/param.h> 130 131#define BUFSIZE 512 132static char buffer[BUFSIZE]; 133 134static int data_available; /* amount of data that can be read */ 135 136static int 137fooread(dev_t dev, struct uio *uio, int flag) 138{ 139 int rv, amnt; 140 141 while (uio->uio_resid > 0) { 142 if (data_available > 0) { 143 amnt = MIN(uio->uio_resid, data_available); 144 if ((rv = uiomove((caddr_t)buffer, amnt, uio)) 145 != 0) 146 goto error; 147 data_available -= amnt; 148 } else { 149 tsleep(...); /* wait for a better time */ 150 } 151 } 152 return 0; 153error: 154 /* do error cleanup here */ 155 return rv; 156} 157.Ed 158.Sh RETURN VALUES 159.Fn uiomove 160can return 161.Er EFAULT 162from the invoked 163.Xr copyin 9 164or 165.Xr copyout 9 166in case the transfer was to/from a process's address space. 167.Sh SEE ALSO 168.Xr read 2 , 169.Xr readv 2 , 170.Xr write 2 , 171.Xr writev 2 , 172.Xr copyin 9 , 173.Xr copyout 9 , 174.Xr sleep 9 175.Sh HISTORY 176The 177.Nm 178mechanism appeared in some early version of 179.Ux . 180.Sh AUTHORS 181This man page was written by 182.An J\(:org Wunsch . 183