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.\" $Id$ 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 IO routines 35.Sh SYNOPSIS 36.Fd #include <sys/types.h> 37.Fd #include <sys/cdefs.h> 38.Fd #include <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 IO 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.Em read 68or 69.Em write 70entry will be called with a pointer to a 71.Fa "struct uio" 72being passed. The 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 uio structure are: 78.Bl -tag -width "uio_iovcntXXXX" -compact 79.It Dv uio_iov 80The array of IO vectors to be processed. In the case of scatter/gather 81IO, this will be more than one vector. 82.It Dv uio_iovcnt 83The number of IO vectors present. 84.It Dv uio_offset 85The offset into the device. 86.It Dv uio_resid 87The number of bytes to process. 88.It Dv uio_segflg 89One of the following flags: 90.Bl -tag -width "UIO_USERISPACEX" -compact 91.It Dv UIO_USERSPACE 92The IO vector points into a process's address space. 93.It Dv UIO_SYSSPACE 94The IO vector points into the kernel address space. 95.It Dv UIO_USERISPACE 96The IO vector points into the instruction area of a process's address 97space. 98.It Dv UIO_NOCOPY 99Don't copy, already in object. 100.El 101.It Dv uio_rw uio_rw 102The direction of the desired transfer, either 103.Dv UIO_READ , 104or 105.Dv UIO_WRITE . 106.It Dv uio_procp 107The pointer to a 108.Li struct proc 109for the associated process; used if 110.Dv uio_segflg 111indicates that the transfer is to be made from/to a process's address 112space. 113.El 114.Sh EXAMPLES 115The idea is that the driver maintains a private buffer for its data, 116and processes the request in chunks of maximal the size of this 117buffer. Note that the buffer handling below is very simplified and 118won't work (the buffer pointer is not being advanced in case of a 119partial read), it's just here to demonstrate the uio handling. 120.Bd -literal 121/* MIN() can be found there: */ 122#include <sys/param.h> 123 124#define BUFSIZE 512 125static char buffer[BUFSIZE]; 126 127static int data_available; /* amount of data that can be read */ 128 129static int 130fooread(dev_t dev, struct uio *uio, int flag) 131{ 132 int rv, amnt; 133 134 while (uio->uio_resid > 0) { 135 if (data_available > 0) { 136 amnt = MIN(uio->uio_resid, data_available); 137 if ((rv = uiomove((caddr_t)buffer, amnt, uio)) 138 != 0) 139 goto error; 140 data_available -= amnt; 141 } else { 142 tsleep(...); /* wait for a better time */ 143 } 144 } 145 return 0; 146error: 147 /* do error cleanup here */ 148 return rv; 149} 150 151.Ed 152.Sh RETURN VALUES 153.Fn uiomove 154can return 155.Er EFAULT 156from the invoked 157.Xr copyin 9 158or 159.Xr copyout 9 160in case the transfer was to/from a process's address space. 161.Sh SEE ALSO 162.Xr read 2 , 163.Xr readv 2 , 164.Xr write 2 , 165.Xr writev 2 , 166.Xr copyin 9 , 167.Xr copyout 9 , 168.Xr sleep 9 169.Sh HISTORY 170The uio mechanism appeared in some early version of 171.Ux . 172.Sh AUTHORS 173This man page has been written by 174.ie t J\(:org Wunsch. 175.el Joerg Wunsch. 176