1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
|
.\"
.\" Copyright (c) 1997 Joerg Wunsch
.\"
.\" All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\" notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\" notice, this list of conditions and the following disclaimer in the
.\" documentation and/or other materials provided with the distribution.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE DEVELOPERS ``AS IS'' AND ANY EXPRESS OR
.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
.\" IN NO EVENT SHALL THE DEVELOPERS BE LIABLE FOR ANY DIRECT, INDIRECT,
.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
.\"
.\" $FreeBSD$
.\"
.Dd February 2, 1997
.Os
.Dt UIO 9
.Sh NAME
.Nm uio ,
.Nm uiomove
.Nd device driver I/O routines
.Sh SYNOPSIS
.In sys/types.h
.In sys/uio.h
.Pp
.Bd -literal
struct uio {
struct iovec *uio_iov;
int uio_iovcnt;
off_t uio_offset;
int uio_resid;
enum uio_seg uio_segflg;
enum uio_rw uio_rw;
struct thread *uio_td;
};
.Ed
.Ft int
.Fn uiomove "void *buf" "int howmuch" "struct uio *uiop"
.Sh DESCRIPTION
The function
.Fn uiomove
is used to handle transfer of data between buffers and I/O vectors
that might possibly also cross the user/kernel space boundary.
.Pp
As a result of any
.Xr read 2 ,
.Xr write 2 ,
.Xr readv 2 ,
or
.Xr writev 2
system call that is being passed to a character-device driver, the
appropriate driver
.Va d_read
or
.Va d_write
entry will be called with a pointer to a
.Vt "struct uio"
being passed.
The transfer request is encoded in this structure.
The driver itself should use
.Fn uiomove
to get at the data in this structure.
.Pp
The fields in the
.Vt uio
structure are:
.Bl -tag -width ".Va uio_iovcnt"
.It Va uio_iov
The array of I/O vectors to be processed.
In the case of scatter/gather
I/O, this will be more than one vector.
.It Va uio_iovcnt
The number of I/O vectors present.
.It Va uio_offset
The offset into the device.
.It Va uio_resid
The number of bytes to process.
.It Va uio_segflg
One of the following flags:
.Bl -tag -width ".Dv UIO_USERSPACE"
.It Dv UIO_USERSPACE
The I/O vector points into a process's address space.
.It Dv UIO_SYSSPACE
The I/O vector points into the kernel address space.
.It Dv UIO_NOCOPY
Don't copy, already in object.
.El
.It Va uio_rw
The direction of the desired transfer, either
.Dv UIO_READ ,
or
.Dv UIO_WRITE .
.It Va uio_td
The pointer to a
.Vt "struct thread"
for the associated thread; used if
.Va uio_segflg
indicates that the transfer is to be made from/to a process's address
space.
.El
.Sh EXAMPLES
The idea is that the driver maintains a private buffer for its data,
and processes the request in chunks of maximal the size of this
buffer.
Note that the buffer handling below is very simplified and
won't work (the buffer pointer is not being advanced in case of a
partial read), it's just here to demonstrate the
.Nm
handling.
.Bd -literal
/* MIN() can be found there: */
#include <sys/param.h>
#define BUFSIZE 512
static char buffer[BUFSIZE];
static int data_available; /* amount of data that can be read */
static int
fooread(dev_t dev, struct uio *uio, int flag)
{
int rv, amnt;
while (uio->uio_resid > 0) {
if (data_available > 0) {
amnt = MIN(uio->uio_resid, data_available);
if ((rv = uiomove(buffer, amnt, uio))
!= 0)
goto error;
data_available -= amnt;
} else {
tsleep(...); /* wait for a better time */
}
}
return 0;
error:
/* do error cleanup here */
return rv;
}
.Ed
.Sh RETURN VALUES
.Fn uiomove
can return
.Er EFAULT
from the invoked
.Xr copyin 9
or
.Xr copyout 9
in case the transfer was to/from a process's address space.
.Sh SEE ALSO
.Xr read 2 ,
.Xr readv 2 ,
.Xr write 2 ,
.Xr writev 2 ,
.Xr copyin 9 ,
.Xr copyout 9 ,
.Xr sleep 9
.Sh HISTORY
The
.Nm
mechanism appeared in some early version of
.Ux .
.Sh AUTHORS
This man page was written by
.An J\(:org Wunsch .
|
