initial import of NetBSD tree

1 files changed, 773 insertions, 0 deletions

diff --git a/sys/kern/vfs_cluster.c b/sys/kern/vfs_cluster.c
new file mode 100644
index 00000000000..049dd716990
--- /dev/null
+++ b/sys/kern/vfs_cluster.c
@@ -0,0 +1,773 @@
+/*	$NetBSD: vfs_cluster.c,v 1.8 1995/07/24 21:19:50 cgd Exp $	*/
+
+/*-
+ * Copyright (c) 1993
+ *	The Regents of the University of California.  All rights reserved.
+ *
+ * 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.
+ *
+ *	@(#)vfs_cluster.c	8.8 (Berkeley) 7/28/94
+ */
+
+#include <sys/param.h>
+#include <sys/proc.h>
+#include <sys/buf.h>
+#include <sys/vnode.h>
+#include <sys/mount.h>
+#include <sys/trace.h>
+#include <sys/malloc.h>
+#include <sys/resourcevar.h>
+#include <lib/libkern/libkern.h>
+
+#ifdef DEBUG
+#include <vm/vm.h>
+#include <sys/sysctl.h>
+int doreallocblks = 0;
+struct ctldebug debug13 = { "doreallocblks", &doreallocblks };
+#else
+/* XXX for cluster_write */
+#define doreallocblks 0
+#endif
+
+/*
+ * Local declarations
+ */
+struct buf *cluster_newbuf __P((struct vnode *, struct buf *, long, daddr_t,
+	    daddr_t, long, int));
+struct buf *cluster_rbuild __P((struct vnode *, u_quad_t, struct buf *,
+	    daddr_t, daddr_t, long, int, long));
+void	    cluster_wbuild __P((struct vnode *, struct buf *, long,
+	    daddr_t, int, daddr_t));
+struct cluster_save *cluster_collectbufs __P((struct vnode *, struct buf *));
+
+#ifdef DIAGNOSTIC
+/*
+ * Set to 1 if reads of block zero should cause readahead to be done.
+ * Set to 0 treats a read of block zero as a non-sequential read.
+ *
+ * Setting to one assumes that most reads of block zero of files are due to
+ * sequential passes over the files (e.g. cat, sum) where additional blocks
+ * will soon be needed.  Setting to zero assumes that the majority are
+ * surgical strikes to get particular info (e.g. size, file) where readahead
+ * blocks will not be used and, in fact, push out other potentially useful
+ * blocks from the cache.  The former seems intuitive, but some quick tests
+ * showed that the latter performed better from a system-wide point of view.
+ */
+int	doclusterraz = 0;
+#define ISSEQREAD(vp, blk) \
+	(((blk) != 0 || doclusterraz) && \
+	 ((blk) == (vp)->v_lastr + 1 || (blk) == (vp)->v_lastr))
+#else
+#define ISSEQREAD(vp, blk) \
+	((blk) != 0 && ((blk) == (vp)->v_lastr + 1 || (blk) == (vp)->v_lastr))
+#endif
+
+/*
+ * This replaces bread.  If this is a bread at the beginning of a file and
+ * lastr is 0, we assume this is the first read and we'll read up to two
+ * blocks if they are sequential.  After that, we'll do regular read ahead
+ * in clustered chunks.
+ *
+ * There are 4 or 5 cases depending on how you count:
+ *	Desired block is in the cache:
+ *	    1 Not sequential access (0 I/Os).
+ *	    2 Access is sequential, do read-ahead (1 ASYNC).
+ *	Desired block is not in cache:
+ *	    3 Not sequential access (1 SYNC).
+ *	    4 Sequential access, next block is contiguous (1 SYNC).
+ *	    5 Sequential access, next block is not contiguous (1 SYNC, 1 ASYNC)
+ *
+ * There are potentially two buffers that require I/O.
+ * 	bp is the block requested.
+ *	rbp is the read-ahead block.
+ *	If either is NULL, then you don't have to do the I/O.
+ */
+cluster_read(vp, filesize, lblkno, size, cred, bpp)
+	struct vnode *vp;
+	u_quad_t filesize;
+	daddr_t lblkno;
+	long size;
+	struct ucred *cred;
+	struct buf **bpp;
+{
+	struct buf *bp, *rbp;
+	daddr_t blkno, ioblkno;
+	long flags;
+	int error, num_ra, alreadyincore;
+
+#ifdef DIAGNOSTIC
+	if (size == 0)
+		panic("cluster_read: size = 0");
+#endif
+
+	error = 0;
+	flags = B_READ;
+	*bpp = bp = getblk(vp, lblkno, size, 0, 0);
+	if (bp->b_flags & B_CACHE) {
+		/*
+		 * Desired block is in cache; do any readahead ASYNC.
+		 * Case 1, 2.
+		 */
+		trace(TR_BREADHIT, pack(vp, size), lblkno);
+		flags |= B_ASYNC;
+		ioblkno = lblkno + (vp->v_ralen ? vp->v_ralen : 1);
+		alreadyincore = incore(vp, ioblkno) != NULL;
+		bp = NULL;
+	} else {
+		/* Block wasn't in cache, case 3, 4, 5. */
+		trace(TR_BREADMISS, pack(vp, size), lblkno);
+		bp->b_flags |= B_READ;
+		ioblkno = lblkno;
+		alreadyincore = 0;
+		curproc->p_stats->p_ru.ru_inblock++;		/* XXX */
+	}
+	/*
+	 * XXX
+	 * Replace 1 with a window size based on some permutation of
+	 * maxcontig and rot_delay.  This will let you figure out how
+	 * many blocks you should read-ahead (case 2, 4, 5).
+	 *
+	 * If the access isn't sequential, reset the window to 1.
+	 * Note that a read to the same block is considered sequential.
+	 * This catches the case where the file is being read sequentially,
+	 * but at smaller than the filesystem block size.
+	 */
+	rbp = NULL;
+	if (!ISSEQREAD(vp, lblkno)) {
+		vp->v_ralen = 0;
+		vp->v_maxra = lblkno;
+	} else if ((ioblkno + 1) * size <= filesize && !alreadyincore &&
+	    !(error = VOP_BMAP(vp, ioblkno, NULL, &blkno, &num_ra)) &&
+	    blkno != -1) {
+		/*
+		 * Reading sequentially, and the next block is not in the
+		 * cache.  We are going to try reading ahead.
+		 */
+		if (num_ra) {
+			/*
+			 * If our desired readahead block had been read
+			 * in a previous readahead but is no longer in
+			 * core, then we may be reading ahead too far
+			 * or are not using our readahead very rapidly.
+			 * In this case we scale back the window.
+			 */
+			if (!alreadyincore && ioblkno <= vp->v_maxra)
+				vp->v_ralen = max(vp->v_ralen >> 1, 1);
+			/*
+			 * There are more sequential blocks than our current
+			 * window allows, scale up.  Ideally we want to get
+			 * in sync with the filesystem maxcontig value.
+			 */
+			else if (num_ra > vp->v_ralen && lblkno != vp->v_lastr)
+				vp->v_ralen = vp->v_ralen ?
+					min(num_ra, vp->v_ralen << 1) : 1;
+
+			if (num_ra > vp->v_ralen)
+				num_ra = vp->v_ralen;
+		}
+
+		if (num_ra)				/* case 2, 4 */
+			rbp = cluster_rbuild(vp, filesize,
+			    bp, ioblkno, blkno, size, num_ra, flags);
+		else if (ioblkno == lblkno) {
+			bp->b_blkno = blkno;
+			/* Case 5: check how many blocks to read ahead */
+			++ioblkno;
+			if ((ioblkno + 1) * size > filesize ||
+			    incore(vp, ioblkno) || (error = VOP_BMAP(vp,
+			     ioblkno, NULL, &blkno, &num_ra)) || blkno == -1)
+				goto skip_readahead;
+			/*
+			 * Adjust readahead as above.
+			 * Don't check alreadyincore, we know it is 0 from
+			 * the previous conditional.
+			 */
+			if (num_ra) {
+				if (ioblkno <= vp->v_maxra)
+					vp->v_ralen = max(vp->v_ralen >> 1, 1);
+				else if (num_ra > vp->v_ralen &&
+					 lblkno != vp->v_lastr)
+					vp->v_ralen = vp->v_ralen ?
+						min(num_ra,vp->v_ralen<<1) : 1;
+				if (num_ra > vp->v_ralen)
+					num_ra = vp->v_ralen;
+			}
+			flags |= B_ASYNC;
+			if (num_ra)
+				rbp = cluster_rbuild(vp, filesize,
+				    NULL, ioblkno, blkno, size, num_ra, flags);
+			else {
+				rbp = getblk(vp, ioblkno, size, 0, 0);
+				rbp->b_flags |= flags;
+				rbp->b_blkno = blkno;
+			}
+		} else {
+			/* case 2; read ahead single block */
+			rbp = getblk(vp, ioblkno, size, 0, 0);
+			rbp->b_flags |= flags;
+			rbp->b_blkno = blkno;
+		}
+
+		if (rbp == bp)			/* case 4 */
+			rbp = NULL;
+		else if (rbp) {			/* case 2, 5 */
+			trace(TR_BREADMISSRA,
+			    pack(vp, (num_ra + 1) * size), ioblkno);
+			curproc->p_stats->p_ru.ru_inblock++;	/* XXX */
+		}
+	}
+
+	/* XXX Kirk, do we need to make sure the bp has creds? */
+skip_readahead:
+	if (bp)
+		if (bp->b_flags & (B_DONE | B_DELWRI))
+			panic("cluster_read: DONE bp");
+		else 
+			error = VOP_STRATEGY(bp);
+
+	if (rbp)
+		if (error || rbp->b_flags & (B_DONE | B_DELWRI)) {
+			rbp->b_flags &= ~(B_ASYNC | B_READ);
+			brelse(rbp);
+		} else
+			(void) VOP_STRATEGY(rbp);
+
+	/*
+	 * Recalculate our maximum readahead
+	 */
+	if (rbp == NULL)
+		rbp = bp;
+	if (rbp)
+		vp->v_maxra = rbp->b_lblkno + (rbp->b_bufsize / size) - 1;
+
+	if (bp)
+		return(biowait(bp));
+	return(error);
+}
+
+/*
+ * If blocks are contiguous on disk, use this to provide clustered
+ * read ahead.  We will read as many blocks as possible sequentially
+ * and then parcel them up into logical blocks in the buffer hash table.
+ */
+struct buf *
+cluster_rbuild(vp, filesize, bp, lbn, blkno, size, run, flags)
+	struct vnode *vp;
+	u_quad_t filesize;
+	struct buf *bp;
+	daddr_t lbn;
+	daddr_t blkno;
+	long size;
+	int run;
+	long flags;
+{
+	struct cluster_save *b_save;
+	struct buf *tbp;
+	daddr_t bn;
+	int i, inc;
+
+#ifdef DIAGNOSTIC
+	if (size != vp->v_mount->mnt_stat.f_iosize)
+		panic("cluster_rbuild: size %d != filesize %d\n",
+			size, vp->v_mount->mnt_stat.f_iosize);
+#endif
+	if (size * (lbn + run + 1) > filesize)
+		--run;
+	if (run == 0) {
+		if (!bp) {
+			bp = getblk(vp, lbn, size, 0, 0);
+			bp->b_blkno = blkno;
+			bp->b_flags |= flags;
+		}
+		return(bp);
+	}
+
+	bp = cluster_newbuf(vp, bp, flags, blkno, lbn, size, run + 1);
+	if (bp->b_flags & (B_DONE | B_DELWRI))
+		return (bp);
+
+	b_save = malloc(sizeof(struct buf *) * run + sizeof(struct cluster_save),
+	    M_SEGMENT, M_WAITOK);
+	b_save->bs_bufsize = b_save->bs_bcount = size;
+	b_save->bs_nchildren = 0;
+	b_save->bs_children = (struct buf **)(b_save + 1);
+	b_save->bs_saveaddr = bp->b_saveaddr;
+	bp->b_saveaddr = (caddr_t) b_save;
+
+	inc = btodb(size);
+	for (bn = blkno + inc, i = 1; i <= run; ++i, bn += inc) {
+		/*
+		 * A component of the cluster is already in core,
+		 * terminate the cluster early.
+		 */
+		if (incore(vp, lbn + i))
+			break;
+		tbp = getblk(vp, lbn + i, 0, 0, 0);
+		/*
+		 * getblk may return some memory in the buffer if there were
+		 * no empty buffers to shed it to.  If there is currently
+		 * memory in the buffer, we move it down size bytes to make
+		 * room for the valid pages that cluster_callback will insert.
+		 * We do this now so we don't have to do it at interrupt time
+		 * in the callback routine.
+		 */
+		if (tbp->b_bufsize != 0) {
+			caddr_t bdata = (char *)tbp->b_data;
+
+			/*
+			 * No room in the buffer to add another page,
+			 * terminate the cluster early.
+			 */
+			if (tbp->b_bufsize + size > MAXBSIZE) {
+#ifdef DIAGNOSTIC
+				if (tbp->b_bufsize != MAXBSIZE)
+					panic("cluster_rbuild: too much memory");
+#endif
+				brelse(tbp);
+				break;
+			}
+			if (tbp->b_bufsize > size) {
+				/*
+				 * XXX if the source and destination regions
+				 * overlap we have to copy backward to avoid
+				 * clobbering any valid pages (i.e. pagemove
+				 * implementations typically can't handle
+				 * overlap).
+				 */
+				bdata += tbp->b_bufsize;
+				while (bdata > (char *)tbp->b_data) {
+					bdata -= CLBYTES;
+					pagemove(bdata, bdata + size, CLBYTES);
+				}
+			} else 
+				pagemove(bdata, bdata + size, tbp->b_bufsize);
+		}
+		tbp->b_blkno = bn;
+		tbp->b_flags |= flags | B_READ | B_ASYNC;
+		++b_save->bs_nchildren;
+		b_save->bs_children[i - 1] = tbp;
+	}
+	/*
+	 * The cluster may have been terminated early, adjust the cluster
+	 * buffer size accordingly.  If no cluster could be formed,
+	 * deallocate the cluster save info.
+	 */
+	if (i <= run) {
+		if (i == 1) {
+			bp->b_saveaddr = b_save->bs_saveaddr;
+			bp->b_flags &= ~B_CALL;
+			bp->b_iodone = NULL;
+			free(b_save, M_SEGMENT);
+		}
+		allocbuf(bp, size * i);
+	}
+	return(bp);
+}
+
+/*
+ * Either get a new buffer or grow the existing one.
+ */
+struct buf *
+cluster_newbuf(vp, bp, flags, blkno, lblkno, size, run)
+	struct vnode *vp;
+	struct buf *bp;
+	long flags;
+	daddr_t blkno;
+	daddr_t lblkno;
+	long size;
+	int run;
+{
+	if (!bp) {
+		bp = getblk(vp, lblkno, size, 0, 0);
+		if (bp->b_flags & (B_DONE | B_DELWRI)) {
+			bp->b_blkno = blkno;
+			return(bp);
+		}
+	}
+	allocbuf(bp, run * size);
+	bp->b_blkno = blkno;
+	bp->b_iodone = cluster_callback;
+	bp->b_flags |= flags | B_CALL;
+	return(bp);
+}
+
+/*
+ * Cleanup after a clustered read or write.
+ * This is complicated by the fact that any of the buffers might have
+ * extra memory (if there were no empty buffer headers at allocbuf time)
+ * that we will need to shift around.
+ */
+void
+cluster_callback(bp)
+	struct buf *bp;
+{
+	struct cluster_save *b_save;
+	struct buf **bpp, *tbp;
+	long bsize;
+	caddr_t cp;
+	int error = 0;
+
+	/*
+	 * Must propogate errors to all the components.
+	 */
+	if (bp->b_flags & B_ERROR)
+		error = bp->b_error;
+
+	b_save = (struct cluster_save *)(bp->b_saveaddr);
+	bp->b_saveaddr = b_save->bs_saveaddr;
+
+	bsize = b_save->bs_bufsize;
+	cp = (char *)bp->b_data + bsize;
+	/*
+	 * Move memory from the large cluster buffer into the component
+	 * buffers and mark IO as done on these.
+	 */
+	for (bpp = b_save->bs_children; b_save->bs_nchildren--; ++bpp) {
+		tbp = *bpp;
+		pagemove(cp, tbp->b_data, bsize);
+		tbp->b_bufsize += bsize;
+		tbp->b_bcount = bsize;
+		if (error) {
+			tbp->b_flags |= B_ERROR;
+			tbp->b_error = error;
+		}
+		biodone(tbp);
+		bp->b_bufsize -= bsize;
+		cp += bsize;
+	}
+	/*
+	 * If there was excess memory in the cluster buffer,
+	 * slide it up adjacent to the remaining valid data.
+	 */
+	if (bp->b_bufsize != bsize) {
+		if (bp->b_bufsize < bsize)
+			panic("cluster_callback: too little memory");
+		pagemove(cp, (char *)bp->b_data + bsize, bp->b_bufsize - bsize);
+	}
+	bp->b_bcount = bsize;
+	bp->b_iodone = NULL;
+	free(b_save, M_SEGMENT);
+	if (bp->b_flags & B_ASYNC)
+		brelse(bp);
+	else {
+		bp->b_flags &= ~B_WANTED;
+		wakeup((caddr_t)bp);
+	}
+}
+
+/*
+ * Do clustered write for FFS.
+ *
+ * Three cases:
+ *	1. Write is not sequential (write asynchronously)
+ *	Write is sequential:
+ *	2.	beginning of cluster - begin cluster
+ *	3.	middle of a cluster - add to cluster
+ *	4.	end of a cluster - asynchronously write cluster
+ */
+void
+cluster_write(bp, filesize)
+        struct buf *bp;
+	u_quad_t filesize;
+{
+        struct vnode *vp;
+        daddr_t lbn;
+        int maxclen, cursize;
+
+        vp = bp->b_vp;
+        lbn = bp->b_lblkno;
+
+	/* Initialize vnode to beginning of file. */
+	if (lbn == 0)
+		vp->v_lasta = vp->v_clen = vp->v_cstart = vp->v_lastw = 0;
+
+        if (vp->v_clen == 0 || lbn != vp->v_lastw + 1 ||
+	    (bp->b_blkno != vp->v_lasta + btodb(bp->b_bcount))) {
+		maxclen = MAXBSIZE / vp->v_mount->mnt_stat.f_iosize - 1;
+		if (vp->v_clen != 0) {
+			/*
+			 * Next block is not sequential.
+			 *
+			 * If we are not writing at end of file, the process
+			 * seeked to another point in the file since its
+			 * last write, or we have reached our maximum
+			 * cluster size, then push the previous cluster.
+			 * Otherwise try reallocating to make it sequential.
+			 */
+			cursize = vp->v_lastw - vp->v_cstart + 1;
+			if (!doreallocblks ||
+			    (lbn + 1) * bp->b_bcount != filesize ||
+			    lbn != vp->v_lastw + 1 || vp->v_clen <= cursize) {
+				cluster_wbuild(vp, NULL, bp->b_bcount,
+				    vp->v_cstart, cursize, lbn);
+			} else {
+				struct buf **bpp, **endbp;
+				struct cluster_save *buflist;
+
+				buflist = cluster_collectbufs(vp, bp);
+				endbp = &buflist->bs_children
+				    [buflist->bs_nchildren - 1];
+				if (VOP_REALLOCBLKS(vp, buflist)) {
+					/*
+					 * Failed, push the previous cluster.
+					 */
+					for (bpp = buflist->bs_children;
+					     bpp < endbp; bpp++)
+						brelse(*bpp);
+					free(buflist, M_SEGMENT);
+					cluster_wbuild(vp, NULL, bp->b_bcount,
+					    vp->v_cstart, cursize, lbn);
+				} else {
+					/*
+					 * Succeeded, keep building cluster.
+					 */
+					for (bpp = buflist->bs_children;
+					     bpp <= endbp; bpp++)
+						bdwrite(*bpp);
+					free(buflist, M_SEGMENT);
+					vp->v_lastw = lbn;
+					vp->v_lasta = bp->b_blkno;
+					return;
+				}
+			}
+		}
+		/*
+		 * Consider beginning a cluster.
+		 * If at end of file, make cluster as large as possible,
+		 * otherwise find size of existing cluster.
+		 */
+		if ((lbn + 1) * bp->b_bcount != filesize &&
+		    (VOP_BMAP(vp, lbn, NULL, &bp->b_blkno, &maxclen) ||
+		     bp->b_blkno == -1)) {
+			bawrite(bp);
+			vp->v_clen = 0;
+			vp->v_lasta = bp->b_blkno;
+			vp->v_cstart = lbn + 1;
+			vp->v_lastw = lbn;
+			return;
+		}
+                vp->v_clen = maxclen;
+                if (maxclen == 0) {		/* I/O not contiguous */
+			vp->v_cstart = lbn + 1;
+                        bawrite(bp);
+                } else {			/* Wait for rest of cluster */
+			vp->v_cstart = lbn;
+                        bdwrite(bp);
+		}
+	} else if (lbn == vp->v_cstart + vp->v_clen) {
+		/*
+		 * At end of cluster, write it out.
+		 */
+		cluster_wbuild(vp, bp, bp->b_bcount, vp->v_cstart,
+		    vp->v_clen + 1, lbn);
+		vp->v_clen = 0;
+		vp->v_cstart = lbn + 1;
+	} else
+		/*
+		 * In the middle of a cluster, so just delay the
+		 * I/O for now.
+		 */
+		bdwrite(bp);
+	vp->v_lastw = lbn;
+	vp->v_lasta = bp->b_blkno;
+}
+
+
+/*
+ * This is an awful lot like cluster_rbuild...wish they could be combined.
+ * The last lbn argument is the current block on which I/O is being
+ * performed.  Check to see that it doesn't fall in the middle of
+ * the current block (if last_bp == NULL).
+ */
+void
+cluster_wbuild(vp, last_bp, size, start_lbn, len, lbn)
+	struct vnode *vp;
+	struct buf *last_bp;
+	long size;
+	daddr_t start_lbn;
+	int len;
+	daddr_t	lbn;
+{
+	struct cluster_save *b_save;
+	struct buf *bp, *tbp;
+	caddr_t	cp;
+	int i, s;
+
+#ifdef DIAGNOSTIC
+	if (size != vp->v_mount->mnt_stat.f_iosize)
+		panic("cluster_wbuild: size %d != filesize %d\n",
+			size, vp->v_mount->mnt_stat.f_iosize);
+#endif
+redo:
+	while ((!incore(vp, start_lbn) || start_lbn == lbn) && len) {
+		++start_lbn;
+		--len;
+	}
+
+	/* Get more memory for current buffer */
+	if (len <= 1) {
+		if (last_bp) {
+			bawrite(last_bp);
+		} else if (len) {
+			bp = getblk(vp, start_lbn, size, 0, 0);
+			bawrite(bp);
+		}
+		return;
+	}
+
+	bp = getblk(vp, start_lbn, size, 0, 0);
+	if (!(bp->b_flags & B_DELWRI)) {
+		++start_lbn;
+		--len;
+		brelse(bp);
+		goto redo;
+	}
+
+	/*
+	 * Extra memory in the buffer, punt on this buffer.
+	 * XXX we could handle this in most cases, but we would have to
+	 * push the extra memory down to after our max possible cluster
+	 * size and then potentially pull it back up if the cluster was
+	 * terminated prematurely--too much hassle.
+	 */
+	if (bp->b_bcount != bp->b_bufsize) {
+		++start_lbn;
+		--len;
+		bawrite(bp);
+		goto redo;
+	}
+
+	--len;
+	b_save = malloc(sizeof(struct buf *) * len + sizeof(struct cluster_save),
+	    M_SEGMENT, M_WAITOK);
+	b_save->bs_bcount = bp->b_bcount;
+	b_save->bs_bufsize = bp->b_bufsize;
+	b_save->bs_nchildren = 0;
+	b_save->bs_children = (struct buf **)(b_save + 1);
+	b_save->bs_saveaddr = bp->b_saveaddr;
+	bp->b_saveaddr = (caddr_t) b_save;
+
+	bp->b_flags |= B_CALL;
+	bp->b_iodone = cluster_callback;
+	cp = (char *)bp->b_data + size;
+	for (++start_lbn, i = 0; i < len; ++i, ++start_lbn) {
+		/*
+		 * Block is not in core or the non-sequential block
+		 * ending our cluster was part of the cluster (in which
+		 * case we don't want to write it twice).
+		 */
+		if (!incore(vp, start_lbn) ||
+		    last_bp == NULL && start_lbn == lbn)
+			break;
+
+		/*
+		 * Get the desired block buffer (unless it is the final
+		 * sequential block whose buffer was passed in explictly
+		 * as last_bp).
+		 */
+		if (last_bp == NULL || start_lbn != lbn) {
+			tbp = getblk(vp, start_lbn, size, 0, 0);
+			if (!(tbp->b_flags & B_DELWRI)) {
+				brelse(tbp);
+				break;
+			}
+		} else
+			tbp = last_bp;
+
+		++b_save->bs_nchildren;
+
+		/* Move memory from children to parent */
+		if (tbp->b_blkno != (bp->b_blkno + btodb(bp->b_bufsize))) {
+			printf("Clustered Block: %d addr %x bufsize: %d\n",
+			    bp->b_lblkno, bp->b_blkno, bp->b_bufsize);
+			printf("Child Block: %d addr: %x\n", tbp->b_lblkno,
+			    tbp->b_blkno);
+			panic("Clustered write to wrong blocks");
+		}
+
+		pagemove(tbp->b_data, cp, size);
+		bp->b_bcount += size;
+		bp->b_bufsize += size;
+
+		tbp->b_bufsize -= size;
+		tbp->b_flags &= ~(B_READ | B_DONE | B_ERROR | B_DELWRI);
+		/*
+		 * We might as well AGE the buffer here; it's either empty, or
+		 * contains data that we couldn't get rid of (but wanted to).
+		 */
+		tbp->b_flags |= (B_ASYNC | B_AGE);
+		s = splbio();
+		reassignbuf(tbp, tbp->b_vp);		/* put on clean list */
+		++tbp->b_vp->v_numoutput;
+		splx(s);
+		b_save->bs_children[i] = tbp;
+
+		cp += size;
+	}
+
+	if (i == 0) {
+		/* None to cluster */
+		bp->b_saveaddr = b_save->bs_saveaddr;
+		bp->b_flags &= ~B_CALL;
+		bp->b_iodone = NULL;
+		free(b_save, M_SEGMENT);
+	}
+	bawrite(bp);
+	if (i < len) {
+		len -= i + 1;
+		start_lbn += 1;
+		goto redo;
+	}
+}
+
+/*
+ * Collect together all the buffers in a cluster.
+ * Plus add one additional buffer.
+ */
+struct cluster_save *
+cluster_collectbufs(vp, last_bp)
+	struct vnode *vp;
+	struct buf *last_bp;
+{
+	struct cluster_save *buflist;
+	daddr_t	lbn;
+	int i, len;
+
+	len = vp->v_lastw - vp->v_cstart + 1;
+	buflist = malloc(sizeof(struct buf *) * (len + 1) + sizeof(*buflist),
+	    M_SEGMENT, M_WAITOK);
+	buflist->bs_nchildren = 0;
+	buflist->bs_children = (struct buf **)(buflist + 1);
+	for (lbn = vp->v_cstart, i = 0; i < len; lbn++, i++)
+		    (void)bread(vp, lbn, last_bp->b_bcount, NOCRED,
+			&buflist->bs_children[i]);
+	buflist->bs_children[i] = last_bp;
+	buflist->bs_nchildren = i + 1;
+	return (buflist);
+}