2 .\" Copyright (c) 1997 Joerg Wunsch
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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 $
34 .Nd device driver I/O routines
41 struct iovec *uio_iov;
45 enum uio_seg uio_segflg;
47 struct proc *uio_procp;
51 .Fn uiomove "caddr_t buf" "int howmuch" "struct uio *uiop"
55 is used to handle transfer of data between buffers and I/O vectors
56 that might possibly also cross the user/kernel space boundary.
64 system call that is being passed to a character-device driver, the
69 entry will be called with a pointer to a
72 The transfer request is encoded in this structure.
73 The driver itself should use
75 to get at the data in this structure.
80 .Bl -tag -width ".Va uio_iovcnt"
82 The array of I/O vectors to be processed.
83 In the case of scatter/gather
84 I/O, this will be more than one vector.
86 The number of I/O vectors present.
88 The offset into the device.
90 The number of bytes to process.
92 One of the following flags:
93 .Bl -tag -width ".Dv UIO_USERISPACE"
95 The I/O vector points into a process's address space.
97 The I/O vector points into the kernel address space.
99 The I/O vector points into the instruction area of a process's address
102 Don't copy, already in object.
105 The direction of the desired transfer, either
112 for the associated thread; used if
114 indicates that the transfer is to be made from/to a process's address
118 The idea is that the driver maintains a private buffer for its data,
119 and processes the request in chunks of maximal the size of this
121 Note that the buffer handling below is very simplified and
122 won't work (the buffer pointer is not being advanced in case of a
123 partial read), it's just here to demonstrate the
127 /* MIN() can be found there: */
128 #include <sys/param.h>
131 static char buffer[BUFSIZE];
133 static int data_available; /* amount of data that can be read */
136 fooread(dev_t dev, struct uio *uio, int flag)
140 while (uio->uio_resid > 0) {
141 if (data_available > 0) {
142 amnt = MIN(uio->uio_resid, data_available);
143 if ((rv = uiomove((caddr_t)buffer, amnt, uio))
146 data_available -= amnt;
148 tsleep(...); /* wait for a better time */
153 /* do error cleanup here */
165 in case the transfer was to/from a process's address space.
177 mechanism appeared in some early version of
180 This man page was written by