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 1.6 2008/11/10 22:59:00 swildner Exp $
35 .Nd device driver I/O routines
41 struct iovec *uio_iov;
45 enum uio_seg uio_segflg;
47 struct thread *uio_td;
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
70 .Vt "struct dev_read_args"
72 .Vt "struct dev_write_args"
74 a member of which is a pointer to a
76 The transfer request is encoded in this structure.
77 The driver itself should use
79 to get at the data in this structure.
84 .Bl -tag -width ".Va uio_iovcnt"
86 The array of I/O vectors to be processed.
87 In the case of scatter/gather
88 I/O, this will be more than one vector.
90 The number of I/O vectors present.
92 The offset into the device.
94 The number of bytes to process.
96 One of the following flags:
97 .Bl -tag -width ".Dv UIO_USERSPACE"
99 The I/O vector points into a process's address space.
101 The I/O vector points into the kernel address space.
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
126 in case the transfer was to/from a process's address space.
128 The idea is that the driver maintains a private buffer for its data,
129 and processes the request in chunks of maximal the size of this
131 Note that the buffer handling below is very simplified and
132 won't work (the buffer pointer is not being advanced in case of a
133 partial read), it's just here to demonstrate the
137 /* MIN() can be found there: */
138 #include <sys/param.h>
141 static char buffer[BUFSIZE];
143 static int data_available; /* amount of data that can be read */
146 fooread(struct dev_read_args *ap)
148 cdev_t dev = ap->a_head.a_dev;
151 while (ap->a_uio->uio_resid > 0) {
152 if (data_available > 0) {
153 amnt = MIN(ap->a_uio->uio_resid, data_available);
154 if ((rv = uiomove((caddr_t)buffer, amnt, ap->a_uio))
157 data_available -= amnt;
159 tsleep(...); /* wait for a better time */
164 /* do error cleanup here */
180 mechanism appeared in some early version of
183 This man page was written by