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.\" $FreeBSD$ 27.\" 28.Dd March 21, 2010 29.Dt UIO 9 30.Os 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; /* scatter/gather list */ 42 int uio_iovcnt; /* length of scatter/gather list */ 43 off_t uio_offset; /* offset in target object */ 44 ssize_t uio_resid; /* remaining bytes to copy */ 45 enum uio_seg uio_segflg; /* address space */ 46 enum uio_rw uio_rw; /* operation */ 47 struct thread *uio_td; /* owner */ 48}; 49.Ed 50.Ft int 51.Fn uiomove "void *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 remaining number of bytes to process, updated after transfer. 91.It Va uio_segflg 92One of the following flags: 93.Bl -tag -width ".Dv UIO_USERSPACE" 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_NOCOPY 99Do not copy, already in object. 100.El 101.It Va uio_rw 102The direction of the desired transfer, either 103.Dv UIO_READ , 104or 105.Dv UIO_WRITE . 106.It Va uio_td 107The pointer to a 108.Vt "struct thread" 109for the associated thread; used if 110.Va uio_segflg 111indicates that the transfer is to be made from/to a process's address 112space. 113.El 114.Sh RETURN VALUES 115On success 116.Fn uiomove 117will return 0, on error it will return an appropriate errno. 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 123will not work (the buffer pointer is not being advanced in case of a 124partial read), it is 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 rv = 0; 142 while (uio->uio_resid > 0) { 143 if (data_available > 0) { 144 amnt = MIN(uio->uio_resid, data_available); 145 rv = uiomove(buffer, amnt, uio); 146 if (rv != 0) 147 break; 148 data_available -= amnt; 149 } else 150 tsleep(...); /* wait for a better time */ 151 } 152 if (rv != 0) { 153 /* do error cleanup here */ 154 } 155 return (rv); 156} 157.Ed 158.Sh ERRORS 159.Fn uiomove 160will fail and return the following error code if: 161.Bl -tag -width Er 162.It Bq Er EFAULT 163The invoked 164.Xr copyin 9 165or 166.Xr copyout 9 167returned 168.Er EFAULT 169.El 170.Sh SEE ALSO 171.Xr read 2 , 172.Xr readv 2 , 173.Xr write 2 , 174.Xr writev 2 , 175.Xr copyin 9 , 176.Xr copyout 9 , 177.Xr sleep 9 178.Sh HISTORY 179The 180.Nm 181mechanism appeared in some early version of 182.Ux . 183.Sh AUTHORS 184This manual page was written by 185.An J\(:org Wunsch . 186