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1 /*
2 * Copyright (c) 2000, 2001, 2002, 2003, 2004, 2005, 2008, 2009
3 * The President and Fellows of Harvard College.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
7 * are met:
8 * 1. Redistributions of source code must retain the above copyright
9 * notice, this list of conditions and the following disclaimer.
10 * 2. Redistributions in binary form must reproduce the above copyright
11 * notice, this list of conditions and the following disclaimer in the
12 * documentation and/or other materials provided with the distribution.
13 * 3. Neither the name of the University nor the names of its contributors
14 * may be used to endorse or promote products derived from this software
15 * without specific prior written permission.
16 *
17 * THIS SOFTWARE IS PROVIDED BY THE UNIVERSITY AND CONTRIBUTORS ``AS IS'' AND
18 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
19 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
20 * ARE DISCLAIMED. IN NO EVENT SHALL THE UNIVERSITY OR CONTRIBUTORS BE LIABLE
21 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
22 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
23 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
24 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
25 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
26 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
27 * SUCH DAMAGE.
28 */
29
30 #ifndef _KERN_IOVEC_H_
31 #define _KERN_IOVEC_H_
32
33 /*
34 * iovec structure, used in the readv/writev scatter/gather I/O calls,
35 * and within the kernel for keeping track of blocks of data for I/O.
36 */
37
38 struct iovec {
39 /*
40 * For maximum type safety, when in the kernel, distinguish
41 * user pointers from kernel pointers.
42 *
43 * (A pointer is a user pointer if it *came* from userspace,
44 * not necessarily if it *points* to userspace. If a system
45 * call passes 0xdeadbeef, it points to the kernel, but it's
46 * still a user pointer.)
47 *
48 * In userspace, there are only user pointers; also, the name
49 * iov_base is defined by POSIX.
50 *
51 * Note that to work properly (without extra unwanted fiddling
52 * around) this scheme requires that void* and userptr_t have
53 * the same machine representation. This is theoretically
54 * possible under the C standard, but such machines do not
55 * exist in practice.
56 */
57 #ifdef _KERNEL
58 union {
59 userptr_t iov_ubase; /* user-supplied pointer */
60 void *iov_kbase; /* kernel-supplied pointer */
61 };
62 #else
63 void *iov_base; /* user-supplied pointer */
64 #endif
65 size_t iov_len; /* Length of data */
66 };
67
68 #endif /* _KERN_IOVEC_H_ */