2 .\" Copyright (c) 1997 Joerg Wunsch
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35 .Nd device driver I/O routines
41 struct iovec *uio_iov; /* scatter/gather list */
42 int uio_iovcnt; /* length of scatter/gather list */
43 off_t uio_offset; /* offset in target object */
44 ssize_t uio_resid; /* remaining bytes to copy */
45 enum uio_seg uio_segflg; /* address space */
46 enum uio_rw uio_rw; /* operation */
47 struct thread *uio_td; /* owner */
51 .Fn uiomove "void *buf" "int howmuch" "struct uio *uiop"
53 .Fn uiomove_nofault "void *buf" "int howmuch" "struct uio *uiop"
59 are used to transfer data between buffers and I/O vectors that might
60 possibly cross the user/kernel space boundary.
68 system call that is being passed to a character-device driver, the
73 entry will be called with a pointer to a
76 The transfer request is encoded in this structure.
77 The driver itself should use
81 to get at the data in this structure.
86 .Bl -tag -width ".Va uio_iovcnt"
88 The array of I/O vectors to be processed.
89 In the case of scatter/gather
90 I/O, this will be more than one vector.
92 The number of I/O vectors present.
94 The offset into the device.
96 The remaining number of bytes to process, updated after transfer.
98 One of the following flags:
99 .Bl -tag -width ".Dv UIO_USERSPACE"
101 The I/O vector points into a process's address space.
103 The I/O vector points into the kernel address space.
105 Do not copy, already in object.
108 The direction of the desired transfer, either
115 for the associated thread; used if
117 indicates that the transfer is to be made from/to a process's address
123 requires that the buffer and I/O vectors be accessible without
124 incurring a page fault.
125 The source and destination addresses must be physically mapped for
126 read and write access, respectively, and neither the source nor
127 destination addresses may be pageable.
130 can be called from contexts where acquiring virtual memory system
131 locks or sleeping are prohibited.
137 will return 0; on error they will return an appropriate error code.
139 The idea is that the driver maintains a private buffer for its data,
140 and processes the request in chunks of maximal the size of this
142 Note that the buffer handling below is very simplified and
143 will not work (the buffer pointer is not being advanced in case of a
144 partial read), it is just here to demonstrate the
148 /* MIN() can be found there: */
149 #include <sys/param.h>
152 static char buffer[BUFSIZE];
154 static int data_available; /* amount of data that can be read */
157 fooread(struct cdev *dev, struct uio *uio, int flag)
162 while (uio->uio_resid > 0) {
163 if (data_available > 0) {
164 amnt = MIN(uio->uio_resid, data_available);
165 rv = uiomove(buffer, amnt, uio);
168 data_available -= amnt;
170 tsleep(...); /* wait for a better time */
173 /* do error cleanup here */
182 will fail and return the following error code if:
195 will fail and return the following error code if:
211 mechanism appeared in some early version of
214 This manual page was written by