125 lines
3.1 KiB
C
125 lines
3.1 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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/*
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* Implementation of the null device, "null:", which generates an
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* immediate EOF on read and throws away anything written to it.
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*/
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#include <types.h>
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#include <kern/errno.h>
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#include <lib.h>
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#include <uio.h>
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#include <vfs.h>
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#include <device.h>
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/* For open() */
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static
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int
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nullopen(struct device *dev, int openflags)
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{
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(void)dev;
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(void)openflags;
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return 0;
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}
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/* For d_io() */
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static
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int
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nullio(struct device *dev, struct uio *uio)
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{
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/*
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* On write, discard everything without looking at it.
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* (Notice that you can write to the null device from invalid
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* buffer pointers and it will still succeed. This behavior is
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* traditional.)
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*
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* On read, do nothing, generating an immediate EOF.
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*/
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(void)dev; // unused
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if (uio->uio_rw == UIO_WRITE) {
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uio->uio_resid = 0;
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}
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return 0;
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}
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/* For ioctl() */
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static
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int
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nullioctl(struct device *dev, int op, userptr_t data)
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{
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/*
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* No ioctls.
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*/
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(void)dev;
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(void)op;
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(void)data;
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return EINVAL;
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}
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static const struct device_ops null_devops = {
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.devop_eachopen = nullopen,
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.devop_io = nullio,
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.devop_ioctl = nullioctl,
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};
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/*
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* Function to create and attach null:
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*/
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void
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devnull_create(void)
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{
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int result;
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struct device *dev;
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dev = kmalloc(sizeof(*dev));
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if (dev==NULL) {
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panic("Could not add null device: out of memory\n");
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}
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dev->d_ops = &null_devops;
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dev->d_blocks = 0;
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dev->d_blocksize = 1;
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dev->d_devnumber = 0; /* assigned by vfs_adddev */
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dev->d_data = NULL;
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result = vfs_adddev("null", dev, 0);
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if (result) {
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panic("Could not add null device: %s\n", strerror(result));
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}
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}
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