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.Bd -literal 39struct uio { 40 struct iovec *uio_iov; /* scatter/gather list */ 41 int uio_iovcnt; /* length of scatter/gather list */ 42 off_t uio_offset; /* offset in target object */ 43 ssize_t uio_resid; /* remaining bytes to copy */ 44 enum uio_seg uio_segflg; /* address space */ 45 enum uio_rw uio_rw; /* operation */ 46 struct thread *uio_td; /* owner */ 47}; 48.Ed 49.Ft int 50.Fn uiomove "void *buf" "int howmuch" "struct uio *uiop" 51.Sh DESCRIPTION 52The function 53.Fn uiomove 54is used to handle transfer of data between buffers and I/O vectors 55that might possibly also cross the user/kernel space boundary. 56.Pp 57As a result of any 58.Xr read 2 , 59.Xr write 2 , 60.Xr readv 2 , 61or 62.Xr writev 2 63system call that is being passed to a character-device driver, the 64appropriate driver 65.Va d_read 66or 67.Va d_write 68entry will be called with a pointer to a 69.Vt "struct uio" 70being passed. 71The 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 77.Vt uio 78structure are: 79.Bl -tag -width ".Va uio_iovcnt" 80.It Va uio_iov 81The array of I/O vectors to be processed. 82In the case of scatter/gather 83I/O, this will be more than one vector. 84.It Va uio_iovcnt 85The number of I/O vectors present. 86.It Va uio_offset 87The offset into the device. 88.It Va uio_resid 89The remaining number of bytes to process, updated after transfer. 90.It Va uio_segflg 91One of the following flags: 92.Bl -tag -width ".Dv UIO_USERSPACE" 93.It Dv UIO_USERSPACE 94The I/O vector points into a process's address space. 95.It Dv UIO_SYSSPACE 96The I/O vector points into the kernel address space. 97.It Dv UIO_NOCOPY 98Do not copy, already in object. 99.El 100.It Va uio_rw 101The direction of the desired transfer, either 102.Dv UIO_READ , 103or 104.Dv UIO_WRITE . 105.It Va uio_td 106The pointer to a 107.Vt "struct thread" 108for the associated thread; used if 109.Va uio_segflg 110indicates that the transfer is to be made from/to a process's address 111space. 112.El 113.Sh RETURN VALUES 114On success 115.Fn uiomove 116will return 0, on error it will return an appropriate errno. 117.Sh EXAMPLES 118The idea is that the driver maintains a private buffer for its data, 119and processes the request in chunks of maximal the size of this 120buffer. 121Note that the buffer handling below is very simplified and 122will not work (the buffer pointer is not being advanced in case of a 123partial read), it is just here to demonstrate the 124.Nm 125handling. 126.Bd -literal 127/* MIN() can be found there: */ 128#include <sys/param.h> 129 130#define BUFSIZE 512 131static char buffer[BUFSIZE]; 132 133static int data_available; /* amount of data that can be read */ 134 135static int 136fooread(dev_t dev, struct uio *uio, int flag) 137{ 138 int rv, amnt; 139 140 rv = 0; 141 while (uio->uio_resid > 0) { 142 if (data_available > 0) { 143 amnt = MIN(uio->uio_resid, data_available); 144 rv = uiomove(buffer, amnt, uio); 145 if (rv != 0) 146 break; 147 data_available -= amnt; 148 } else 149 tsleep(...); /* wait for a better time */ 150 } 151 if (rv != 0) { 152 /* do error cleanup here */ 153 } 154 return (rv); 155} 156.Ed 157.Sh ERRORS 158.Fn uiomove 159will fail and return the following error code if: 160.Bl -tag -width Er 161.It Bq Er EFAULT 162The invoked 163.Xr copyin 9 164or 165.Xr copyout 9 166returned 167.Er EFAULT 168.El 169.Sh SEE ALSO 170.Xr read 2 , 171.Xr readv 2 , 172.Xr write 2 , 173.Xr writev 2 , 174.Xr copyin 9 , 175.Xr copyout 9 , 176.Xr sleep 9 177.Sh HISTORY 178The 179.Nm 180mechanism appeared in some early version of 181.Ux . 182.Sh AUTHORS 183This manual page was written by 184.An J\(:org Wunsch . 185