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 1.5 2008/05/02 02:05:06 swildner 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.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 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 number of bytes to process. 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 99Don't 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 115.Fn uiomove 116can return 117.Er EFAULT 118from the invoked 119.Xr copyin 9 120or 121.Xr copyout 9 122in case the transfer was to/from a process's address space. 123.Sh EXAMPLES 124The idea is that the driver maintains a private buffer for its data, 125and processes the request in chunks of maximal the size of this 126buffer. 127Note that the buffer handling below is very simplified and 128won't work (the buffer pointer is not being advanced in case of a 129partial read), it's just here to demonstrate the 130.Nm 131handling. 132.Bd -literal 133/* MIN() can be found there: */ 134#include <sys/param.h> 135 136#define BUFSIZE 512 137static char buffer[BUFSIZE]; 138 139static int data_available; /* amount of data that can be read */ 140 141static int 142fooread(dev_t dev, struct uio *uio, int flag) 143{ 144 int rv, amnt; 145 146 while (uio->uio_resid > 0) { 147 if (data_available > 0) { 148 amnt = MIN(uio->uio_resid, data_available); 149 if ((rv = uiomove((caddr_t)buffer, amnt, uio)) 150 != 0) 151 goto error; 152 data_available -= amnt; 153 } else { 154 tsleep(...); /* wait for a better time */ 155 } 156 } 157 return 0; 158error: 159 /* do error cleanup here */ 160 return rv; 161} 162.Ed 163.Sh SEE ALSO 164.Xr read 2 , 165.Xr readv 2 , 166.Xr write 2 , 167.Xr writev 2 , 168.Xr copyin 9 , 169.Xr copyout 9 , 170.Xr sleep 9 171.Sh HISTORY 172The 173.Nm 174mechanism appeared in some early version of 175.Ux . 176.Sh AUTHORS 177This man page was written by 178.An J\(:org Wunsch . 179