Source to kern/kern_physio.c


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/*-
 * Copyright (c) 1982, 1986, 1990, 1993
 *	The Regents of the University of California.  All rights reserved.
 *
 * This module is believed to contain source code proprietary to AT&T.
 * Use and redistribution is subject to the Berkeley Software License
 * Agreement and your Software Agreement with AT&T (Western Electric).
 *
 *	@(#)kern_physio.c	8.1 (Berkeley) 6/10/93
 */

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

static void freeswbuf __P((struct buf *));
static struct buf *getswbuf __P((int));

/*
 * This routine does device I/O for a user process.
 *
 * If the user has the proper access privileges, the process is
 * marked 'delayed unlock' and the pages involved in the I/O are
 * faulted and locked. After the completion of the I/O, the pages
 * are unlocked.
 */
physio(strat, bp, dev, rw, mincnt, uio)
	int (*strat)(); 
	register struct buf *bp;
	dev_t dev;
	int rw;
	u_int (*mincnt)();
	struct uio *uio;
{
	register struct iovec *iov;
	register int requested = 0, done = 0;
	register struct proc *p = curproc;
	char *a;
	int s, allocbuf = 0, error = 0;

	if (bp == NULL) {
		allocbuf = 1;
		bp = getswbuf(PRIBIO+1);
	}
	for (; uio->uio_iovcnt; uio->uio_iov++, uio->uio_iovcnt--) {
		iov = uio->uio_iov;
		if (iov->iov_len == 0)
			continue;
		if (!useracc(iov->iov_base, (u_int)iov->iov_len,
		    rw == B_READ ? B_WRITE : B_READ)) {
			error = EFAULT;
			break;
		}
		if (!allocbuf) {	/* only if sharing caller's buffer */
			s = splbio();
			while (bp->b_flags&B_BUSY) {
				bp->b_flags |= B_WANTED;
				sleep((caddr_t)bp, PRIBIO+1);
			}
			splx(s);
		}
		bp->b_error = 0;
		bp->b_proc = p;
#ifdef HPUXCOMPAT
		if (ISHPMMADDR(iov->iov_base))
			bp->b_un.b_addr = (caddr_t)HPMMBASEADDR(iov->iov_base);
		else
#endif
		bp->b_un.b_addr = iov->iov_base;
		while (iov->iov_len > 0) {
			bp->b_flags = B_BUSY | B_PHYS | B_RAW | rw;
			bp->b_dev = dev;
			bp->b_blkno = btodb(uio->uio_offset);
			bp->b_bcount = iov->iov_len;
			(*mincnt)(bp);
			requested = bp->b_bcount;
			p->p_flag |= SPHYSIO;
			vslock(a = bp->b_un.b_addr, requested);
			vmapbuf(bp);
			(*strat)(bp);
			s = splbio();
			while ((bp->b_flags & B_DONE) == 0)
				sleep((caddr_t)bp, PRIBIO);
			vunmapbuf(bp);
			vsunlock(a, requested, rw);
			p->p_flag &= ~SPHYSIO;
			if (bp->b_flags&B_WANTED)	/* rare */
				wakeup((caddr_t)bp);
			splx(s);
			done = bp->b_bcount - bp->b_resid;
			bp->b_un.b_addr += done;
			iov->iov_len -= done;
			uio->uio_resid -= done;
			uio->uio_offset += done;
			/* temp kludge for disk drives */
			if (done < requested || bp->b_flags & B_ERROR)
				break;
		}
		bp->b_flags &= ~(B_BUSY | B_WANTED | B_PHYS | B_RAW);
		error = biowait(bp);
		/* temp kludge for disk drives */
		if (done < requested || bp->b_flags & B_ERROR)
			break;
	}
	if (allocbuf)
		freeswbuf(bp);
	return (error);
}

/*
 * Calculate the maximum size of I/O request that can be requested
 * in a single operation. This limit is necessary to prevent a single
 * process from being able to lock more than a fixed amount of memory
 * in the kernel.
 */
u_int
minphys(bp)
	struct buf *bp;
{
	if (bp->b_bcount > MAXPHYS)
		bp->b_bcount = MAXPHYS;
}

static struct buf *
getswbuf(prio)
	int prio;
{
	int s;
	struct buf *bp;

	s = splbio();
	while (bswlist.b_actf == NULL) {
		bswlist.b_flags |= B_WANTED;
		sleep((caddr_t)&bswlist, prio);
	}
	bp = bswlist.b_actf;
	bswlist.b_actf = bp->b_actf;
	splx(s);
	return (bp);
}

static void
freeswbuf(bp)
	struct buf *bp;
{
	int s;

	s = splbio();
	bp->b_actf = bswlist.b_actf;
	bswlist.b_actf = bp;
	if (bp->b_vp)
		brelvp(bp);
	if (bswlist.b_flags & B_WANTED) {
		bswlist.b_flags &= ~B_WANTED;
		wakeup((caddr_t)&bswlist);
		wakeup((caddr_t)pageproc);
	}
	splx(s);
}

/*
 * Do a read on a device for a user process.
 */
rawread(dev, uio)
	dev_t dev;
	struct uio *uio;
{
	return (physio(cdevsw[major(dev)].d_strategy, (struct buf *)NULL,
	    dev, B_READ, minphys, uio));
}

/*
 * Do a write on a device for a user process.
 */
rawwrite(dev, uio)
	dev_t dev;
	struct uio *uio;
{
	return (physio(cdevsw[major(dev)].d_strategy, (struct buf *)NULL,
	    dev, B_WRITE, minphys, uio));
}