2 .\" Copyright (c) 1997 Joerg Wunsch
4 .\" All rights reserved.
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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 1.4 2006/02/17 19:37:10 swildner Exp $
35 .Nd device driver I/O routines
42 struct iovec *uio_iov;
46 enum uio_seg uio_segflg;
48 struct proc *uio_procp;
52 .Fn uiomove "caddr_t buf" "int howmuch" "struct uio *uiop"
56 is used to handle transfer of data between buffers and I/O vectors
57 that might possibly also cross the user/kernel space boundary.
65 system call that is being passed to a character-device driver, the
70 entry will be called with a pointer to a
73 The transfer request is encoded in this structure.
74 The driver itself should use
76 to get at the data in this structure.
81 .Bl -tag -width ".Va uio_iovcnt"
83 The array of I/O vectors to be processed.
84 In the case of scatter/gather
85 I/O, this will be more than one vector.
87 The number of I/O vectors present.
89 The offset into the device.
91 The number of bytes to process.
93 One of the following flags:
94 .Bl -tag -width ".Dv UIO_USERSPACE"
96 The I/O vector points into a process's address space.
98 The I/O vector points into the kernel address space.
100 Don't copy, already in object.
103 The direction of the desired transfer, either
110 for the associated thread; used if
112 indicates that the transfer is to be made from/to a process's address
123 in case the transfer was to/from a process's address space.
125 The idea is that the driver maintains a private buffer for its data,
126 and processes the request in chunks of maximal the size of this
128 Note that the buffer handling below is very simplified and
129 won't work (the buffer pointer is not being advanced in case of a
130 partial read), it's just here to demonstrate the
134 /* MIN() can be found there: */
135 #include <sys/param.h>
138 static char buffer[BUFSIZE];
140 static int data_available; /* amount of data that can be read */
143 fooread(dev_t dev, struct uio *uio, int flag)
147 while (uio->uio_resid > 0) {
148 if (data_available > 0) {
149 amnt = MIN(uio->uio_resid, data_available);
150 if ((rv = uiomove((caddr_t)buffer, amnt, uio))
153 data_available -= amnt;
155 tsleep(...); /* wait for a better time */
160 /* do error cleanup here */
175 mechanism appeared in some early version of
178 This man page was written by