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 1.2 2003/06/17 04:37:01 dillon 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_USERISPACE"
96 The I/O vector points into a process's address space.
98 The I/O vector points into the kernel address space.
100 The I/O vector points into the instruction area of a process's address
103 Don't copy, already in object.
106 The direction of the desired transfer, either
113 for the associated thread; used if
115 indicates that the transfer is to be made from/to a process's address
119 The idea is that the driver maintains a private buffer for its data,
120 and processes the request in chunks of maximal the size of this
122 Note that the buffer handling below is very simplified and
123 won't work (the buffer pointer is not being advanced in case of a
124 partial read), it's just here to demonstrate the
128 /* MIN() can be found there: */
129 #include <sys/param.h>
132 static char buffer[BUFSIZE];
134 static int data_available; /* amount of data that can be read */
137 fooread(dev_t dev, struct uio *uio, int flag)
141 while (uio->uio_resid > 0) {
142 if (data_available > 0) {
143 amnt = MIN(uio->uio_resid, data_available);
144 if ((rv = uiomove((caddr_t)buffer, amnt, uio))
147 data_available -= amnt;
149 tsleep(...); /* wait for a better time */
154 /* do error cleanup here */
166 in case the transfer was to/from a process's address space.
178 mechanism appeared in some early version of
181 This man page was written by