2 .\" Copyright (c) 1997 Joerg Wunsch
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34 .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 "void *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_USERSPACE"
95 The I/O vector points into a process's address space.
97 The I/O vector points into the kernel address space.
99 Don't copy, already in object.
102 The direction of the desired transfer, either
109 for the associated thread; used if
111 indicates that the transfer is to be made from/to a process's address
122 in case the transfer was to/from a process's address space.
124 The idea is that the driver maintains a private buffer for its data,
125 and processes the request in chunks of maximal the size of this
127 Note that the buffer handling below is very simplified and
128 won't work (the buffer pointer is not being advanced in case of a
129 partial read), it's just here to demonstrate the
133 /* MIN() can be found there: */
134 #include <sys/param.h>
137 static char buffer[BUFSIZE];
139 static int data_available; /* amount of data that can be read */
142 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 rv = uiomove(buffer, amnt, uio);
153 data_available -= amnt;
155 tsleep(...); /* wait for a better time */
158 /* do error cleanup here */
174 mechanism appeared in some early version of
177 This man page was written by