NetBSD/sys/kern/kern_physio.c

/*	$NetBSD: kern_physio.c,v 1.56 2003/02/25 20:35:38 thorpej Exp $	*/

/*-
 * Copyright (c) 1994 Christopher G. Demetriou
 * Copyright (c) 1982, 1986, 1990, 1993
 *	The Regents of the University of California.  All rights reserved.
 * (c) UNIX System Laboratories, Inc.
 * All or some portions of this file are derived from material licensed
 * to the University of California by American Telephone and Telegraph
 * Co. or Unix System Laboratories, Inc. and are reproduced herein with
 * the permission of UNIX System Laboratories, Inc.
 *
 * 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.
 *
 *	@(#)kern_physio.c	8.1 (Berkeley) 6/10/93
 */

#include <sys/cdefs.h>
__KERNEL_RCSID(0, "$NetBSD: kern_physio.c,v 1.56 2003/02/25 20:35:38 thorpej Exp $");

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/buf.h>
#include <sys/malloc.h>
#include <sys/proc.h>

#include <uvm/uvm_extern.h>

/*
 * The routines implemented in this file are described in:
 *	Leffler, et al.: The Design and Implementation of the 4.3BSD
 *	    UNIX Operating System (Addison Welley, 1989)
 * on pages 231-233.
 *
 * The routines "getphysbuf" and "putphysbuf" steal and return a swap
 * buffer.  Leffler, et al., says that swap buffers are used to do the
 * I/O, so raw I/O requests don't have to be single-threaded.
 */

struct buf *getphysbuf __P((void));
void putphysbuf __P((struct buf *bp));

/*
 * Do "physical I/O" on behalf of a user.  "Physical I/O" is I/O directly
 * from the raw device to user buffers, and bypasses the buffer cache.
 *
 * Comments in brackets are from Leffler, et al.'s pseudo-code implementation.
 */
int
physio(strategy, bp, dev, flags, minphys, uio)
	void (*strategy) __P((struct buf *));
	struct buf *bp;
	dev_t dev;
	int flags;
	void (*minphys) __P((struct buf *));
	struct uio *uio;
{
	struct iovec *iovp;
	struct lwp *l = curlwp;
	struct proc *p = l->l_proc;
	int error, done, i, nobuf, s;
	long todo;

	error = 0;
	flags &= B_READ | B_WRITE;

	/* Make sure we have a buffer, creating one if necessary. */
	if ((nobuf = (bp == NULL)) != 0) {

		bp = getphysbuf();
		/* bp was just malloc'd so can't already be busy */
		bp->b_flags |= B_BUSY; 

	} else {

		/* [raise the processor priority level to splbio;] */
		s = splbio();

		/* [while the buffer is marked busy] */
		while (bp->b_flags & B_BUSY) {
			/* [mark the buffer wanted] */
			bp->b_flags |= B_WANTED;
			/* [wait until the buffer is available] */
			tsleep((caddr_t)bp, PRIBIO+1, "physbuf", 0);
		}

		/* Mark it busy, so nobody else will use it. */
		bp->b_flags |= B_BUSY;

		/* [lower the priority level] */
		splx(s);
	}

	/* [set up the fixed part of the buffer for a transfer] */
	bp->b_dev = dev;
	bp->b_error = 0;
	bp->b_proc = p;
	LIST_INIT(&bp->b_dep);

	/*
	 * [while there are data to transfer and no I/O error]
	 * Note that I/O errors are handled with a 'goto' at the bottom
	 * of the 'while' loop.
	 */
	for (i = 0; i < uio->uio_iovcnt; i++) {
		iovp = &uio->uio_iov[i];
		while (iovp->iov_len > 0) {

			/*
			 * [mark the buffer busy for physical I/O]
			 * (i.e. set B_PHYS (because it's an I/O to user
			 * memory, and B_RAW, because B_RAW is to be
			 * "Set by physio for raw transfers.", in addition
			 * to the "busy" and read/write flag.)
			 */
			bp->b_flags = B_BUSY | B_PHYS | B_RAW | flags;

			/* [set up the buffer for a maximum-sized transfer] */
			bp->b_blkno = btodb(uio->uio_offset);
			bp->b_bcount = iovp->iov_len;
			bp->b_data = iovp->iov_base;

			/*
			 * [call minphys to bound the transfer size]
			 * and remember the amount of data to transfer,
			 * for later comparison.
			 */
			(*minphys)(bp);
			todo = bp->b_bcount;
#ifdef DIAGNOSTIC
			if (todo <= 0)
				panic("todo(%ld) <= 0; minphys broken", todo);
			if (todo > MAXPHYS)
				panic("todo(%ld) > MAXPHYS; minphys broken",
				      todo);
#endif

			/*
			 * [lock the part of the user address space involved
			 *    in the transfer]
			 * Beware vmapbuf(); it clobbers b_data and
			 * saves it in b_saveaddr.  However, vunmapbuf()
			 * restores it.
			 */
			PHOLD(l);
			error = uvm_vslock(p, bp->b_data, todo,
					   (flags & B_READ) ?
					   VM_PROT_WRITE : VM_PROT_READ);
			if (error) {
				bp->b_flags |= B_ERROR;
				bp->b_error = error;
				goto after_vsunlock;
			}
			vmapbuf(bp, todo);

			/* [call strategy to start the transfer] */
			(*strategy)(bp);

			/*
			 * Note that the raise/wait/lower/get error
			 * steps below would be done by biowait(), but
			 * we want to unlock the address space before
			 * we lower the priority.
			 *
			 * [raise the priority level to splbio]
			 */
			s = splbio();

			/* [wait for the transfer to complete] */
			while ((bp->b_flags & B_DONE) == 0)
				tsleep((caddr_t) bp, PRIBIO + 1, "physio", 0);

			/* Mark it busy again, so nobody else will use it. */
			bp->b_flags |= B_BUSY;

			/* [lower the priority level] */
			splx(s);

			/*
			 * [unlock the part of the address space previously
			 *    locked]
			 */
			vunmapbuf(bp, todo);
			uvm_vsunlock(p, bp->b_data, todo);
 after_vsunlock:
			PRELE(l);

			/* remember error value (save a splbio/splx pair) */
			if (bp->b_flags & B_ERROR)
				error = (bp->b_error ? bp->b_error : EIO);

			/*
			 * [deduct the transfer size from the total number
			 *    of data to transfer]
			 */
			done = bp->b_bcount - bp->b_resid;
			KASSERT(done >= 0);
			KASSERT(done <= todo);

			iovp->iov_len -= done;
			iovp->iov_base = (caddr_t)iovp->iov_base + done;
			uio->uio_offset += done;
			uio->uio_resid -= done;

			/*
			 * Now, check for an error.
			 * Also, handle weird end-of-disk semantics.
			 */
			if (error || done < todo)
				goto done;
		}
	}

done:
	/*
	 * [clean up the state of the buffer]
	 * Remember if somebody wants it, so we can wake them up below.
	 * Also, if we had to steal it, give it back.
	 */
	s = splbio();
	bp->b_flags &= ~(B_BUSY | B_PHYS | B_RAW);
	if (nobuf)
		putphysbuf(bp);
	else {
		/*
		 * [if another process is waiting for the raw I/O buffer,
		 *    wake up processes waiting to do physical I/O;
		 */
		if (bp->b_flags & B_WANTED) {
			bp->b_flags &= ~B_WANTED;
			wakeup(bp);
		}
	}
	splx(s);

	return (error);
}

/*
 * allocate a buffer structure for use in physical I/O.
 */
struct buf *
getphysbuf()
{
	struct buf *bp;
	int s;

	s = splbio();
	bp = pool_get(&bufpool, PR_WAITOK);
	splx(s);
	memset(bp, 0, sizeof(*bp));
	BUF_INIT(bp);
	return(bp);
}

/*
 * get rid of a swap buffer structure which has been used in physical I/O.
 */
void
putphysbuf(bp)
        struct buf *bp;
{
	int s;

	if (__predict_false(bp->b_flags & B_WANTED))
		panic("putphysbuf: private buf B_WANTED");
	s = splbio();
	pool_put(&bufpool, bp);
	splx(s);
}

/*
 * Leffler, et al., says on p. 231:
 * "The minphys() routine is called by physio() to adjust the
 * size of each I/O transfer before the latter is passed to
 * the strategy routine..."
 *
 * so, just adjust the buffer's count accounting to MAXPHYS here,
 * and return the new count;
 */
void
minphys(bp)
	struct buf *bp;
{

	if (bp->b_bcount > MAXPHYS)
		bp->b_bcount = MAXPHYS;
}