69 lines
2.8 KiB
C
69 lines
2.8 KiB
C
/*
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* Copyright (c) 2000, 2001, 2002, 2003, 2004, 2005, 2008, 2009
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* The President and Fellows of Harvard College.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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* 3. Neither the name of the University nor the names of its contributors
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* may be used to endorse or promote products derived from this software
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* without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE UNIVERSITY AND CONTRIBUTORS ``AS IS'' AND
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* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE UNIVERSITY OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*/
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#ifndef _KERN_IOVEC_H_
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#define _KERN_IOVEC_H_
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/*
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* iovec structure, used in the readv/writev scatter/gather I/O calls,
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* and within the kernel for keeping track of blocks of data for I/O.
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*/
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struct iovec {
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/*
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* For maximum type safety, when in the kernel, distinguish
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* user pointers from kernel pointers.
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*
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* (A pointer is a user pointer if it *came* from userspace,
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* not necessarily if it *points* to userspace. If a system
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* call passes 0xdeadbeef, it points to the kernel, but it's
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* still a user pointer.)
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*
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* In userspace, there are only user pointers; also, the name
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* iov_base is defined by POSIX.
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*
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* Note that to work properly (without extra unwanted fiddling
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* around) this scheme requires that void* and userptr_t have
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* the same machine representation. Machines where this isn't
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* true are theoretically possible under the C standard, but
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* do not exist in practice.
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*/
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#ifdef _KERNEL
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union {
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userptr_t iov_ubase; /* user-supplied pointer */
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void *iov_kbase; /* kernel-supplied pointer */
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};
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#else
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void *iov_base; /* user-supplied pointer */
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#endif
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size_t iov_len; /* Length of data */
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};
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#endif /* _KERN_IOVEC_H_ */
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