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: uio.9,v 1.3 1997/02/22 13:26:29 peter 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 IO routines 35.Sh SYNOPSIS 36.Fd #include <sys/types.h> 37.Fd #include <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 IO 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.Em read 67or 68.Em write 69entry will be called with a pointer to a 70.Fa "struct uio" 71being passed. The transfer request is encoded in this structure. 72The driver itself should use 73.Fn uiomove 74to get at the data in this structure. 75.Pp 76The fields in the uio structure are: 77.Bl -tag -width "uio_iovcntXXXX" -compact 78.It Dv uio_iov 79The array of IO vectors to be processed. In the case of scatter/gather 80IO, this will be more than one vector. 81.It Dv uio_iovcnt 82The number of IO vectors present. 83.It Dv uio_offset 84The offset into the device. 85.It Dv uio_resid 86The number of bytes to process. 87.It Dv uio_segflg 88One of the following flags: 89.Bl -tag -width "UIO_USERISPACEX" -compact 90.It Dv UIO_USERSPACE 91The IO vector points into a process's address space. 92.It Dv UIO_SYSSPACE 93The IO vector points into the kernel address space. 94.It Dv UIO_USERISPACE 95The IO vector points into the instruction area of a process's address 96space. 97.It Dv UIO_NOCOPY 98Don't copy, already in object. 99.El 100.It Dv uio_rw uio_rw 101The direction of the desired transfer, either 102.Dv UIO_READ , 103or 104.Dv UIO_WRITE . 105.It Dv uio_procp 106The pointer to a 107.Li struct proc 108for the associated process; used if 109.Dv uio_segflg 110indicates that the transfer is to be made from/to a process's address 111space. 112.El 113.Sh EXAMPLES 114The idea is that the driver maintains a private buffer for its data, 115and processes the request in chunks of maximal the size of this 116buffer. Note that the buffer handling below is very simplified and 117won't work (the buffer pointer is not being advanced in case of a 118partial read), it's just here to demonstrate the uio handling. 119.Bd -literal 120/* MIN() can be found there: */ 121#include <sys/param.h> 122 123#define BUFSIZE 512 124static char buffer[BUFSIZE]; 125 126static int data_available; /* amount of data that can be read */ 127 128static int 129fooread(dev_t dev, struct uio *uio, int flag) 130{ 131 int rv, amnt; 132 133 while (uio->uio_resid > 0) { 134 if (data_available > 0) { 135 amnt = MIN(uio->uio_resid, data_available); 136 if ((rv = uiomove((caddr_t)buffer, amnt, uio)) 137 != 0) 138 goto error; 139 data_available -= amnt; 140 } else { 141 tsleep(...); /* wait for a better time */ 142 } 143 } 144 return 0; 145error: 146 /* do error cleanup here */ 147 return rv; 148} 149 150.Ed 151.Sh RETURN VALUES 152.Fn uiomove 153can return 154.Er EFAULT 155from the invoked 156.Xr copyin 9 157or 158.Xr copyout 9 159in case the transfer was to/from a process's address space. 160.Sh SEE ALSO 161.Xr read 2 , 162.Xr readv 2 , 163.Xr write 2 , 164.Xr writev 2 , 165.Xr copyin 9 , 166.Xr copyout 9 , 167.Xr sleep 9 168.Sh HISTORY 169The uio mechanism appeared in some early version of 170.Ux . 171.Sh AUTHORS 172This man page has been written by 173.ie t J\(:org Wunsch. 174.el Joerg Wunsch. 175