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 1.3 2004/07/27 13:11:22 hmp 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_USERSPACE" 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_NOCOPY 100Don't copy, already in object. 101.El 102.It Va uio_rw 103The direction of the desired transfer, either 104.Dv UIO_READ , 105or 106.Dv UIO_WRITE . 107.It Va uio_td 108The pointer to a 109.Vt "struct thread" 110for the associated thread; used if 111.Va uio_segflg 112indicates that the transfer is to be made from/to a process's address 113space. 114.El 115.Sh EXAMPLES 116The idea is that the driver maintains a private buffer for its data, 117and processes the request in chunks of maximal the size of this 118buffer. 119Note that the buffer handling below is very simplified and 120won't work (the buffer pointer is not being advanced in case of a 121partial read), it's just here to demonstrate the 122.Nm 123handling. 124.Bd -literal 125/* MIN() can be found there: */ 126#include <sys/param.h> 127 128#define BUFSIZE 512 129static char buffer[BUFSIZE]; 130 131static int data_available; /* amount of data that can be read */ 132 133static int 134fooread(dev_t dev, struct uio *uio, int flag) 135{ 136 int rv, amnt; 137 138 while (uio->uio_resid > 0) { 139 if (data_available > 0) { 140 amnt = MIN(uio->uio_resid, data_available); 141 if ((rv = uiomove((caddr_t)buffer, amnt, uio)) 142 != 0) 143 goto error; 144 data_available -= amnt; 145 } else { 146 tsleep(...); /* wait for a better time */ 147 } 148 } 149 return 0; 150error: 151 /* do error cleanup here */ 152 return rv; 153} 154.Ed 155.Sh RETURN VALUES 156.Fn uiomove 157can return 158.Er EFAULT 159from the invoked 160.Xr copyin 9 161or 162.Xr copyout 9 163in case the transfer was to/from a process's address space. 164.Sh SEE ALSO 165.Xr read 2 , 166.Xr readv 2 , 167.Xr write 2 , 168.Xr writev 2 , 169.Xr copyin 9 , 170.Xr copyout 9 , 171.Xr sleep 9 172.Sh HISTORY 173The 174.Nm 175mechanism appeared in some early version of 176.Ux . 177.Sh AUTHORS 178This man page was written by 179.An J\(:org Wunsch . 180