iovec.h

/*
 * Copyright (c) 2000, 2001, 2002, 2003, 2004, 2005, 2008, 2009
 *      The President and Fellows of Harvard College.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE UNIVERSITY AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE UNIVERSITY OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#ifndef _KERN_IOVEC_H_
#define _KERN_IOVEC_H_

/*
 * iovec structure, used in the readv/writev scatter/gather I/O calls,
 * and within the kernel for keeping track of blocks of data for I/O.
 */

struct iovec {
        /*
         * For maximum type safety, when in the kernel, distinguish
         * user pointers from kernel pointers.
         *
         * (A pointer is a user pointer if it *came* from userspace,
         * not necessarily if it *points* to userspace. If a system
         * call passes 0xdeadbeef, it points to the kernel, but it's
         * still a user pointer.)
         *
         * In userspace, there are only user pointers; also, the name
         * iov_base is defined by POSIX.
         *
         * Note that to work properly (without extra unwanted fiddling
         * around) this scheme requires that void* and userptr_t have
         * the same machine representation. This is theoretically
         * possible under the C standard, but such machines do not
         * exist in practice.
         */
#ifdef _KERNEL
        union {
                userptr_t  iov_ubase;   /* user-supplied pointer */
                void      *iov_kbase;   /* kernel-supplied pointer */
        };
#else
        void *iov_base;                 /* user-supplied pointer */
#endif
        size_t iov_len;                 /* Length of data */
};

#endif /* _KERN_IOVEC_H_ */