xnu-792.22.5.tar.gz

[apple/xnu.git] / bsd / dev / memdev.c

/*
 * Copyright (c) 2004 Apple Computer, Inc. All rights reserved.
 *
 * @APPLE_OSREFERENCE_LICENSE_HEADER_START@
 * 
 * This file contains Original Code and/or Modifications of Original Code
 * as defined in and that are subject to the Apple Public Source License
 * Version 2.0 (the 'License'). You may not use this file except in
 * compliance with the License. The rights granted to you under the License
 * may not be used to create, or enable the creation or redistribution of,
 * unlawful or unlicensed copies of an Apple operating system, or to
 * circumvent, violate, or enable the circumvention or violation of, any
 * terms of an Apple operating system software license agreement.
 * 
 * Please obtain a copy of the License at
 * http://www.opensource.apple.com/apsl/ and read it before using this file.
 * 
 * The Original Code and all software distributed under the License are
 * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
 * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
 * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
 * Please see the License for the specific language governing rights and
 * limitations under the License.
 * 
 * @APPLE_OSREFERENCE_LICENSE_HEADER_END@
 */
/*
 * Copyright (c) 1988 University of Utah.
 * Copyright (c) 1990, 1993
 *	The Regents of the University of California.  All rights reserved.
 *
 * This code is derived from software contributed to Berkeley by
 * the Systems Programming Group of the University of Utah Computer
 * Science Department.
 *
 * 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. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *	This product includes software developed by the University of
 *	California, Berkeley and its contributors.
 * 4. 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 REGENTS 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 REGENTS 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
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 * from: Utah Hdr: vn.c 1.13 94/04/02
 *
 *	from: @(#)vn.c	8.6 (Berkeley) 4/1/94
 * $FreeBSD: src/sys/dev/vn/vn.c,v 1.105.2.4 2001/11/18 07:11:00 dillon Exp $
 */

/*
 * RAM disk driver.
 *
 * Block interface to a ramdisk.  
 *
 */

#include <sys/param.h>
#include <sys/kernel.h>
#include <sys/mount.h>
#include <sys/namei.h>
#include <sys/proc.h>
#include <sys/buf.h>
#include <sys/malloc.h>
#include <sys/mount.h>
#include <sys/fcntl.h>
#include <sys/conf.h>
#include <sys/disk.h>
#include <sys/stat.h>
#include <sys/vm.h>
#include <sys/uio_internal.h>
#include <libkern/libkern.h>

#include <vm/pmap.h>
#include <vm/vm_pager.h>
#include <mach/memory_object_types.h>

#include <miscfs/devfs/devfs.h>


void 		mdevinit(int the_cnt);

static open_close_fcn_t	mdevopen;
static open_close_fcn_t	mdevclose;
static psize_fcn_t		mdevsize;
static strategy_fcn_t	mdevstrategy;
static int				mdevbioctl(dev_t dev, u_long cmd, caddr_t data, int flag, struct proc *p);
static int				mdevcioctl(dev_t dev, u_long cmd, caddr_t data, int flag, struct proc *p);
static int 				mdevrw(dev_t dev, struct uio *uio, int ioflag);
static char *			nonspace(char *pos, char *end);
static char *			getspace(char *pos, char *end);
static char *			cvtnum(char *pos, char *end, unsigned int *num);

extern void		bcopy_phys(addr64_t from, addr64_t to, vm_size_t bytes);
extern void		mapping_set_mod(ppnum_t pn);
extern ppnum_t 	pmap_find_phys(pmap_t pmap, addr64_t va);


/*
 * cdevsw
 *	D_DISK		we want to look like a disk
 *	D_CANFREE	We support B_FREEBUF
 */

static struct bdevsw mdevbdevsw = {
	/* open */	mdevopen,
	/* close */	mdevclose,
	/* strategy */	mdevstrategy,
	/* ioctl */	mdevbioctl,
	/* dump */	eno_dump,
	/* psize */	mdevsize,
	/* flags */	D_DISK,
};

static struct cdevsw mdevcdevsw = {
	/* open */	mdevopen,
	/* close */	mdevclose,
	/* read */	mdevrw,
	/* write */	mdevrw,
	/* ioctl */	mdevcioctl,
	/* stop */	eno_stop,
	/* reset */	eno_reset,
	/* ttys */	0,
	/* select */	eno_select,
	/* mmap */	eno_mmap,
	/* strategy */	eno_strat,
	/* getc */	eno_getc,
	/* putc */	eno_putc,
	/* flags */	D_DISK,
};

struct mdev {
	vm_offset_t	mdBase;		/* file size in bytes */
	uint32_t	mdSize;		/* file size in bytes */
	int			mdFlags;	/* flags */
	int			mdSecsize;	/* sector size */
	int			mdBDev;		/* Block device number */
	int			mdCDev;		/* Character device number */
	void *		mdbdevb;
	void *		mdcdevb;
} mdev[16];

/* mdFlags */
#define mdInited	0x01	/* This device defined */
#define	mdRO		0x02	/* This device is read-only */
#define	mdPhys		0x04	/* This device is in physical memory */

int mdevBMajor = -1;
int mdevCMajor = -1;

static int mdevioctl(dev_t dev, u_long cmd, caddr_t data, int flag, struct proc *p, int is_char);
dev_t mdevadd(int devid, ppnum_t base, unsigned int size, int phys);
dev_t mdevlookup(int devid);

static	int mdevclose(__unused dev_t dev, __unused int flags, 
					  __unused int devtype, __unused struct proc *p) {

	return (0);
}

static	int mdevopen(dev_t dev, int flags, __unused int devtype, __unused struct proc *p) {
	
	int devid;

	devid = minor(dev);									/* Get minor device number */

	if (devid > 16) return (ENXIO);						/* Not valid */

	if ((flags & FWRITE) && (mdev[devid].mdFlags & mdRO)) return (EACCES);	/* Currently mounted RO */

	return(0);
}

static int mdevrw(dev_t dev, struct uio *uio, __unused int ioflag) {
	int 			status;
	addr64_t		mdata;
	int 			devid;
	enum uio_seg 	saveflag;

	devid = minor(dev);									/* Get minor device number */

	if (devid > 16) return (ENXIO);						/* Not valid */
	if (!(mdev[devid].mdFlags & mdInited))  return (ENXIO);	/* Have we actually been defined yet? */

	mdata = ((addr64_t)mdev[devid].mdBase << 12) + uio->uio_offset;	/* Point to the area in "file" */
	
	saveflag = uio->uio_segflg;							/* Remember what the request is */
#if LP64_DEBUG
	if (IS_VALID_UIO_SEGFLG(uio->uio_segflg) == 0) {
	  panic("mdevrw - invalid uio_segflg\n"); 
	}
#endif /* LP64_DEBUG */
	/* Make sure we are moving from physical ram if physical device */
	if (mdev[devid].mdFlags & mdPhys) {
		if (uio->uio_segflg == UIO_USERSPACE64) 
			uio->uio_segflg = UIO_PHYS_USERSPACE64;	
		else if (uio->uio_segflg == UIO_USERSPACE32)
			uio->uio_segflg = UIO_PHYS_USERSPACE32;	
		else
			uio->uio_segflg = UIO_PHYS_USERSPACE;	
	}
	status = uiomove64(mdata, uio_resid(uio), uio);		/* Move the data */
	uio->uio_segflg = saveflag;							/* Restore the flag */

	return (status);
}

static void mdevstrategy(struct buf *bp) {
	unsigned int left, lop, csize;
	vm_offset_t vaddr, blkoff;
	int devid;
	addr64_t paddr, fvaddr;
	ppnum_t pp;

	devid = minor(buf_device(bp));							/* Get minor device number */

	if ((mdev[devid].mdFlags & mdInited) == 0) {		/* Have we actually been defined yet? */
	        buf_seterror(bp, ENXIO);
		buf_biodone(bp);
		return;
	}

	buf_setresid(bp, buf_count(bp));						/* Set byte count */
	
	blkoff = buf_blkno(bp) * mdev[devid].mdSecsize;		/* Get offset into file */

/*
 *	Note that reading past end is an error, but reading at end is an EOF.  For these
 *	we just return with resid == count.
 */

	if (blkoff >= (mdev[devid].mdSize << 12)) {			/* Are they trying to read/write at/after end? */
		if(blkoff != (mdev[devid].mdSize << 12)) {		/* Are we trying to read after EOF? */
		        buf_seterror(bp, EINVAL);						/* Yeah, this is an error */
		}
		buf_biodone(bp);								/* Return */
		return;
	}

	if ((blkoff + buf_count(bp)) > (mdev[devid].mdSize << 12)) {		/* Will this read go past end? */
		buf_setcount(bp, ((mdev[devid].mdSize << 12) - blkoff));	/* Yes, trim to max */
	}
	/*
	 * make sure the buffer's data area is
	 * accessible
	 */
	if (buf_map(bp, (caddr_t *)&vaddr))
	        panic("ramstrategy: buf_map failed\n");

	fvaddr = (mdev[devid].mdBase << 12) + blkoff;		/* Point to offset into ram disk */
	
	if (buf_flags(bp) & B_READ) {					/* Is this a read? */
		if(!(mdev[devid].mdFlags & mdPhys)) {			/* Physical mapped disk? */
			bcopy((void *)((uintptr_t)fvaddr),
				(void *)vaddr, (size_t)buf_count(bp));	/* This is virtual, just get the data */
		}
		else {
			left = buf_count(bp);						/* Init the amount left to copy */
			while(left) {								/* Go until it is all copied */
				
				lop = min((4096 - (vaddr & 4095)), (4096 - (fvaddr & 4095)));	/* Get smallest amount left on sink and source */
				csize = min(lop, left);					/* Don't move more than we need to */
				
				pp = pmap_find_phys(kernel_pmap, (addr64_t)((unsigned int)vaddr));	/* Get the sink physical address */
				if(!pp) {								/* Not found, what gives? */
					panic("mdevstrategy: sink address %016llX not mapped\n", (addr64_t)((unsigned int)vaddr));
				}
				paddr = (addr64_t)(((addr64_t)pp << 12) | (addr64_t)(vaddr & 4095));	/* Get actual address */
				bcopy_phys(fvaddr, paddr, csize);		/* Copy this on in */
				mapping_set_mod(paddr >> 12);			/* Make sure we know that it is modified */
				
				left = left - csize;					/* Calculate what is left */
				vaddr = vaddr + csize;					/* Move to next sink address */
				fvaddr = fvaddr + csize;				/* Bump to next physical address */
			}
		}
	}
	else {												/* This is a write */
		if(!(mdev[devid].mdFlags & mdPhys)) {			/* Physical mapped disk? */
			bcopy((void *)vaddr, (void *)((uintptr_t)fvaddr),
				(size_t)buf_count(bp));		/* This is virtual, just put the data */
		}
		else {
			left = buf_count(bp);						/* Init the amount left to copy */
			while(left) {								/* Go until it is all copied */
				
				lop = min((4096 - (vaddr & 4095)), (4096 - (fvaddr & 4095)));	/* Get smallest amount left on sink and source */
				csize = min(lop, left);					/* Don't move more than we need to */
				
				pp = pmap_find_phys(kernel_pmap, (addr64_t)((unsigned int)vaddr));	/* Get the source physical address */
				if(!pp) {								/* Not found, what gives? */
					panic("mdevstrategy: source address %016llX not mapped\n", (addr64_t)((unsigned int)vaddr));
				}
				paddr = (addr64_t)(((addr64_t)pp << 12) | (addr64_t)(vaddr & 4095));	/* Get actual address */
			
				bcopy_phys(paddr, fvaddr, csize);		/* Move this on out */
				
				left = left - csize;					/* Calculate what is left */
				vaddr = vaddr + csize;					/* Move to next sink address */
				fvaddr = fvaddr + csize;				/* Bump to next physical address */
			}
		}
	}
	/*
	 * buf_unmap takes care of all the cases
	 * it will unmap the buffer from kernel
	 * virtual space if that was the state
	 * when we mapped it.
	 */
	buf_unmap(bp);

	buf_setresid(bp, 0);									/* Nothing more to do */	
	buf_biodone(bp);									/* Say we've finished */
}

static int mdevbioctl(dev_t dev, u_long cmd, caddr_t data, int flag, struct proc *p) {
	return (mdevioctl(dev, cmd, data, flag, p, 0));
}

static int mdevcioctl(dev_t dev, u_long cmd, caddr_t data, int flag, struct proc *p) {
	return (mdevioctl(dev, cmd, data, flag, p, 1));
}

static int mdevioctl(dev_t dev, u_long cmd, caddr_t data, __unused int flag, 
					 struct proc *p, int is_char) {
	int error;
	u_long *f;
	u_int64_t *o;
	int devid;

	devid = minor(dev);									/* Get minor device number */

	if (devid > 16) return (ENXIO);						/* Not valid */

	error = proc_suser(p);			/* Are we superman? */
	if (error) return (error);							/* Nope... */

	f = (u_long*)data;
	o = (u_int64_t *)data;

	switch (cmd) {

		case DKIOCGETMAXBLOCKCOUNTREAD:
			*o = 32;
			break;
		
		case DKIOCGETMAXBLOCKCOUNTWRITE:
			*o = 32;
			break;
		
		case DKIOCGETMAXSEGMENTCOUNTREAD:
			*o = 32;
			break;
		
		case DKIOCGETMAXSEGMENTCOUNTWRITE:
			*o = 32;
			break;
		
		case DKIOCGETBLOCKSIZE:
			*f = mdev[devid].mdSecsize;
			break;
		
		case DKIOCSETBLOCKSIZE:
			if (is_char) return (ENODEV);				/* We can only do this for a block */

			if (*f < DEV_BSIZE) return (EINVAL);		/* Too short? */

			mdev[devid].mdSecsize = *f;					/* set the new block size */
			break;
			
		case DKIOCISWRITABLE:
			*f = 1;
			break;
			
		case DKIOCGETBLOCKCOUNT32:
			if(!(mdev[devid].mdFlags & mdInited)) return (ENXIO);
			*f = ((mdev[devid].mdSize << 12) + mdev[devid].mdSecsize - 1) / mdev[devid].mdSecsize;
			break;
			
		case DKIOCGETBLOCKCOUNT:
			if(!(mdev[devid].mdFlags & mdInited)) return (ENXIO);
			*o = ((mdev[devid].mdSize << 12) + mdev[devid].mdSecsize - 1) / mdev[devid].mdSecsize;
			break;
			
		default:
			error = ENOTTY;
			break;
	}
	return(error);
}


static	int mdevsize(dev_t dev) {

	int devid;

	devid = minor(dev);									/* Get minor device number */
	if (devid > 16) return (ENXIO);						/* Not valid */

	if ((mdev[devid].mdFlags & mdInited) == 0) return(-1);		/* Not inited yet */

	return(mdev[devid].mdSecsize);
}

#include <pexpert/pexpert.h>

void mdevinit(__unused int the_cnt) {

	int devid, phys;
	ppnum_t base;
	unsigned int size;
	char *ba, *lp;
	dev_t dev;
	
	
	ba = PE_boot_args();								/* Get the boot arguments */
	lp = ba + 256;										/* Point to the end */
		
	while(1) {											/* Step through, looking for our keywords */
		phys = 0;										/* Assume virtual memory device */
		ba = nonspace(ba, lp);							/* Find non-space */
		if(ba >= lp) return;							/* We are done if no more... */
		if(((ba[0] != 'v') && (ba[0] != 'p'))  
		  || (ba[1] != 'm') || (ba[2] != 'd') || (ba[4] != '=')
		  || (ba[3] < '0') || (ba[3] > 'f') 
		  || ((ba[3] > '9') && (ba[3] < 'a'))) {		/* Is this of form "vmdx=" or "pmdx=" where x is hex digit? */
			
			ba = getspace(ba, lp);						/* Find next white space or end */
			continue;									/* Start looking for the next one */
		}
		
		if(ba[0] == 'p') phys = 1;						/* Set physical memory disk */
		
		devid = ba[3] & 0xF;							/* Assume digit */
		if(ba[3] > '9') devid += 9;						/* Adjust for hex digits */
	
		ba = &ba[5];									/* Step past keyword */
		ba = cvtnum(ba, lp, &base);						/* Convert base of memory disk */
		if(ba >= lp) return;							/* Malformed one at the end, leave */
		if(ba[0] != '.') continue;						/* If not length separater, try next... */
		if(base & 0xFFF) continue;						/* Only allow page aligned stuff */
	
		ba++;											/* Step past '.' */
		ba = cvtnum(ba, lp, &size);						/* Try to convert it */
		if(!size || (size & 0xFFF)) continue;			/* Allow only non-zer page size multiples */
		if(ba < lp) {									/* If we are not at end, check end character */
			if((ba[0] != ' ') && (ba[0] != 0)) continue;	/* End must be null or space */
		}
		
		dev = mdevadd(devid, base >> 12, size >> 12, phys);	/* Go add the device */ 
	}

	return;

}

char *nonspace(char *pos, char *end) {					/* Find next non-space in string */

	if(pos >= end) return end;							/* Don't go past end */
	if(pos[0] == 0) return end;							/* If at null, make end */
	
	while(1) {											/* Keep going */
		if(pos[0] != ' ') return pos;					/* Leave if we found one */
		pos++;											/* Stop */
		if(pos >= end) return end;						/* Quit if we run off end */
	}
}

char *getspace(char *pos, char *end) {					/* Find next non-space in string */

	while(1) {											/* Keep going */
		if(pos >= end) return end;						/* Don't go past end */
		if(pos[0] == 0) return end;						/* Leave if we hit null */
		if(pos[0] == ' ') return pos;					/* Leave if we found one */
		pos++;											/* Stop */
	}
}

char *cvtnum(char *pos, char *end, unsigned int *num) {		/* Convert to a number */

	int rad, dig;
	
	*num = 0;											/* Set answer to 0 to start */	
	rad = 10;

	if(pos >= end) return end;							/* Don't go past end */
	if(pos[0] == 0) return end;							/* If at null, make end */
	
	if(pos[0] == '0' && ((pos[1] == 'x') || (pos[1] == 'x'))) {	/* A hex constant? */
		rad = 16;
		pos += 2;										/* Point to the number */
	}
	
	while(1) {											/* Convert it */
		
		if(pos >= end) return end;						/* Don't go past end */
		if(pos[0] == 0) return end;						/* If at null, make end */
		if(pos[0] < '0') return pos;					/* Leave if non-digit */
		dig = pos[0] & 0xF;								/* Extract digit */
		if(pos[0] > '9') {								/* Is it bigger than 9? */
			if(rad == 10) return pos;					/* Leave if not base 10 */
			if(!(((pos[0] >= 'A') && (pos[0] <= 'F')) 
			  || ((pos[0] >= 'a') && (pos[0] <= 'f')))) return pos;	/* Leave if bogus char */
			 dig = dig + 9;								/* Adjust for character */
		}
		*num = (*num * rad) + dig;						/* Accumulate the number */
		pos++;											/* Step on */
	}
}

dev_t mdevadd(int devid, ppnum_t base, unsigned int size, int phys) {
	
	int i;
	
	if(devid < 0) {

		devid = -1;
		for(i = 0; i < 16; i++) {						/* Search all known memory devices */
			if(!(mdev[i].mdFlags & mdInited)) {			/* Is this a free one? */
				if(devid < 0)devid = i;					/* Remember first free one */
				continue;								/* Skip check */
			}
			if(!(((base + size -1 ) < mdev[i].mdBase) || ((mdev[i].mdBase + mdev[i].mdSize - 1) < base))) {	/* Is there any overlap? */
				panic("mdevadd: attempt to add overlapping memory device at %08X-%08X\n", mdev[i].mdBase, mdev[i].mdBase + mdev[i].mdSize - 1);
			}
		}
		if(devid < 0) {									/* Do we have free slots? */
			panic("mdevadd: attempt to add more than 16 memory devices\n");
		}
	}
	else {
		if(devid >= 16) {								/* Giving us something bogus? */
			panic("mdevadd: attempt to explicitly add a bogus memory device: &08X\n", devid);
		}
		if(mdev[devid].mdFlags &mdInited) {				/* Already there? */
			panic("mdevadd: attempt to explicitly add a previously defined memory device: &08X\n", devid);
		}
	}
	
	if(mdevBMajor < 0) {								/* Have we gotten a major number yet? */
		mdevBMajor = bdevsw_add(-1, &mdevbdevsw);		/* Add to the table and figure out a major number */
		if (mdevBMajor < 0) {
			printf("mdevadd: error - bdevsw_add() returned %d\n", mdevBMajor);
			return -1;
		}
	}
	
	if(mdevCMajor < 0) {								/* Have we gotten a major number yet? */
		mdevCMajor = cdevsw_add_with_bdev(-1, &mdevcdevsw, mdevBMajor);		/* Add to the table and figure out a major number */
		if (mdevCMajor < 0) {
			printf("ramdevice_init: error - cdevsw_add() returned %d\n", mdevCMajor);
			return -1;
		}
	}

	mdev[devid].mdBDev = makedev(mdevBMajor, devid);	/* Get the device number */
	mdev[devid].mdbdevb = devfs_make_node(mdev[devid].mdBDev, DEVFS_BLOCK,	/* Make the node */
						  UID_ROOT, GID_OPERATOR, 
						  0600, "md%d", devid);
	if (mdev[devid].mdbdevb == NULL) {					/* Did we make one? */
		printf("mdevadd: devfs_make_node for block failed!\n");
		return -1;										/* Nope... */
	}

	mdev[devid].mdCDev = makedev(mdevCMajor, devid);	/* Get the device number */
	mdev[devid].mdcdevb = devfs_make_node(mdev[devid].mdCDev, DEVFS_CHAR,		/* Make the node */
						  UID_ROOT, GID_OPERATOR, 
						  0600, "rmd%d", devid);
	if (mdev[devid].mdcdevb == NULL) {					/* Did we make one? */
		printf("mdevadd: devfs_make_node for character failed!\n");
		return -1;										/* Nope... */
	}
	
	mdev[devid].mdBase = base;							/* Set the base address of ram disk */
	mdev[devid].mdSize = size;							/* Set the length of the ram disk */
	mdev[devid].mdSecsize = DEV_BSIZE;					/* Set starting block size */
	if(phys) mdev[devid].mdFlags |= mdPhys;				/* Show that we are in physical memory */
	mdev[devid].mdFlags |= mdInited;					/* Show we are all set up */
	printf("Added memory device md%x/rmd%x (%08X/%08X) at %08X for %08X\n", 
		devid, devid, mdev[devid].mdBDev, mdev[devid].mdCDev, base << 12, size << 12);
	return mdev[devid].mdBDev;
}


dev_t mdevlookup(int devid) {
	
	if((devid < 0) || (devid > 15)) return -1;			/* Filter any bogus requests */
	if(!(mdev[devid].mdFlags & mdInited)) return -1;	/* This one hasn't been defined */
	return mdev[devid].mdBDev;							/* Return the device number */
}