Added msdosfs.

Obtained from: NetBSD

1 files changed, 984 insertions, 0 deletions

diff --git a/sys/fs/msdosfs/msdosfs_fat.c b/sys/fs/msdosfs/msdosfs_fat.c
new file mode 100644
index 0000000..9a2f117
--- /dev/null
+++ b/sys/fs/msdosfs/msdosfs_fat.c
@@ -0,0 +1,984 @@
+/*	$Id$ */
+/*	$NetBSD: msdosfs_fat.c,v 1.12 1994/08/21 18:44:04 ws Exp $	*/
+
+/*-
+ * Copyright (C) 1994 Wolfgang Solfrank.
+ * Copyright (C) 1994 TooLs GmbH.
+ * All rights reserved.
+ * Original code by Paul Popelka (paulp@uts.amdahl.com) (see below).
+ *
+ * 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 TooLs GmbH.
+ * 4. The name of TooLs GmbH may not be used to endorse or promote products
+ *    derived from this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY TOOLS GMBH ``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 TOOLS GMBH 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.
+ */
+/*
+ * Written by Paul Popelka (paulp@uts.amdahl.com)
+ * 
+ * You can do anything you want with this software, just don't say you wrote
+ * it, and don't remove this notice.
+ * 
+ * This software is provided "as is".
+ * 
+ * The author supplies this software to be publicly redistributed on the
+ * understanding that the author is not responsible for the correct
+ * functioning of this software in any circumstances and is not liable for
+ * any damages caused by this software.
+ * 
+ * October 1992
+ */
+
+/*
+ * kernel include files.
+ */
+#include <sys/param.h>
+#include <sys/systm.h>
+#include <sys/buf.h>
+#include <sys/file.h>
+#include <sys/namei.h>
+#include <sys/mount.h>		/* to define statfs structure */
+#include <sys/vnode.h>		/* to define vattr structure */
+#include <sys/errno.h>
+
+/*
+ * msdosfs include files.
+ */
+#include <msdosfs/bpb.h>
+#include <msdosfs/msdosfsmount.h>
+#include <msdosfs/direntry.h>
+#include <msdosfs/denode.h>
+#include <msdosfs/fat.h>
+
+/*
+ * Fat cache stats.
+ */
+int fc_fileextends;		/* # of file extends			 */
+int fc_lfcempty;		/* # of time last file cluster cache entry
+				 * was empty */
+int fc_bmapcalls;		/* # of times pcbmap was called		 */
+
+#define	LMMAX	20
+int fc_lmdistance[LMMAX];	/* counters for how far off the last
+				 * cluster mapped entry was. */
+int fc_largedistance;		/* off by more than LMMAX		 */
+
+/* Byte offset in FAT on filesystem pmp, cluster cn */
+#define	FATOFS(pmp, cn)	(FAT12(pmp) ? (cn) * 3 / 2 : (cn) * 2)
+
+void fc_lookup(struct denode *dep, u_long findcn,
+		      u_long *frcnp, u_long *fsrcnp);
+void fc_purge(struct denode *dep, u_int frcn);
+
+static void
+fatblock(pmp, ofs, bnp, sizep, bop)
+	struct msdosfsmount *pmp;
+	u_long ofs;
+	u_long *bnp;
+	u_long *sizep;
+	u_long *bop;
+{
+	u_long bn, size;
+
+	bn = ofs / pmp->pm_fatblocksize * pmp->pm_fatblocksec;
+	size = min(pmp->pm_fatblocksec, pmp->pm_FATsecs - bn)
+	    * pmp->pm_BytesPerSec;
+	bn += pmp->pm_fatblk;
+	if (bnp)
+		*bnp = bn;
+	if (sizep)
+		*sizep = size;
+	if (bop)
+		*bop = ofs % pmp->pm_fatblocksize;
+}
+
+/*
+ * Map the logical cluster number of a file into a physical disk sector
+ * that is filesystem relative.
+ *
+ * dep	  - address of denode representing the file of interest
+ * findcn - file relative cluster whose filesystem relative cluster number
+ *	    and/or block number are/is to be found
+ * bnp	  - address of where to place the file system relative block number.
+ *	    If this pointer is null then don't return this quantity.
+ * cnp	  - address of where to place the file system relative cluster number.
+ *	    If this pointer is null then don't return this quantity.
+ *
+ * NOTE: Either bnp or cnp must be non-null.
+ * This function has one side effect.  If the requested file relative cluster
+ * is beyond the end of file, then the actual number of clusters in the file
+ * is returned in *cnp.  This is useful for determining how long a directory is.
+ *  If cnp is null, nothing is returned.
+ */
+int
+pcbmap(dep, findcn, bnp, cnp)
+	struct denode *dep;
+	u_long findcn;		/* file relative cluster to get		 */
+	daddr_t *bnp;		/* returned filesys relative blk number	 */
+	u_long *cnp;		/* returned cluster number		 */
+{
+	int error;
+	u_long i;
+	u_long cn;
+	u_long prevcn;
+	u_long byteoffset;
+	u_long bn;
+	u_long bo;
+	struct buf *bp = NULL;
+	u_long bp_bn = -1;
+	struct msdosfsmount *pmp = dep->de_pmp;
+	u_long bsize;
+	int fat12 = FAT12(pmp);	/* 12 bit fat	 */
+
+	fc_bmapcalls++;
+
+	/*
+	 * If they don't give us someplace to return a value then don't
+	 * bother doing anything.
+	 */
+	if (bnp == NULL && cnp == NULL)
+		return 0;
+
+	cn = dep->de_StartCluster;
+	/*
+	 * The "file" that makes up the root directory is contiguous,
+	 * permanently allocated, of fixed size, and is not made up of
+	 * clusters.  If the cluster number is beyond the end of the root
+	 * directory, then return the number of clusters in the file.
+	 */
+	if (cn == MSDOSFSROOT) {
+		if (dep->de_Attributes & ATTR_DIRECTORY) {
+			if (findcn * pmp->pm_SectPerClust > pmp->pm_rootdirsize) {
+				if (cnp)
+					*cnp = pmp->pm_rootdirsize / pmp->pm_SectPerClust;
+				return E2BIG;
+			}
+			if (bnp)
+				*bnp = pmp->pm_rootdirblk + (findcn * pmp->pm_SectPerClust);
+			if (cnp)
+				*cnp = MSDOSFSROOT;
+			return 0;
+		} else {		/* just an empty file */
+			if (cnp)
+				*cnp = 0;
+			return E2BIG;
+		}
+	}
+
+	/*
+	 * Rummage around in the fat cache, maybe we can avoid tromping
+	 * thru every fat entry for the file. And, keep track of how far
+	 * off the cache was from where we wanted to be.
+	 */
+	i = 0;
+	fc_lookup(dep, findcn, &i, &cn);
+	if ((bn = findcn - i) >= LMMAX)
+		fc_largedistance++;
+	else
+		fc_lmdistance[bn]++;
+
+	/*
+	 * Handle all other files or directories the normal way.
+	 */
+	prevcn = 0;
+	for (; i < findcn; i++) {
+		if (MSDOSFSEOF(cn))
+			goto hiteof;
+		byteoffset = FATOFS(pmp, cn);
+		fatblock(pmp, byteoffset, &bn, &bsize, &bo);
+		if (bn != bp_bn) {
+			if (bp)
+				brelse(bp);
+			error = bread(pmp->pm_devvp, bn, bsize, NOCRED, &bp);
+			if (error)
+				return error;
+			bp_bn = bn;
+		}
+		prevcn = cn;
+		cn = getushort(&bp->b_data[bo]);
+		if (fat12) {
+			if (prevcn & 1)
+				cn >>= 4;
+			cn &= 0x0fff;
+			/*
+			 * Force the special cluster numbers in the range
+			 * 0x0ff0-0x0fff to be the same as for 16 bit
+			 * cluster numbers to let the rest of msdosfs think
+			 * it is always dealing with 16 bit fats.
+			 */
+			if ((cn & 0x0ff0) == 0x0ff0)
+				cn |= 0xf000;
+		}
+	}
+
+	if (!MSDOSFSEOF(cn)) {
+		if (bp)
+			brelse(bp);
+		if (bnp)
+			*bnp = cntobn(pmp, cn);
+		if (cnp)
+			*cnp = cn;
+		fc_setcache(dep, FC_LASTMAP, i, cn);
+		return 0;
+	}
+
+hiteof:;
+	if (cnp)
+		*cnp = i;
+	if (bp)
+		brelse(bp);
+	/* update last file cluster entry in the fat cache */
+	fc_setcache(dep, FC_LASTFC, i - 1, prevcn);
+	return E2BIG;
+}
+
+/*
+ * Find the closest entry in the fat cache to the cluster we are looking
+ * for.
+ */
+void fc_lookup(dep, findcn, frcnp, fsrcnp)
+	struct denode *dep;
+	u_long findcn;
+	u_long *frcnp;
+	u_long *fsrcnp;
+{
+	int i;
+	u_long cn;
+	struct fatcache *closest = 0;
+
+	for (i = 0; i < FC_SIZE; i++) {
+		cn = dep->de_fc[i].fc_frcn;
+		if (cn != FCE_EMPTY && cn <= findcn) {
+			if (closest == 0 || cn > closest->fc_frcn)
+				closest = &dep->de_fc[i];
+		}
+	}
+	if (closest) {
+		*frcnp = closest->fc_frcn;
+		*fsrcnp = closest->fc_fsrcn;
+	}
+}
+
+/*
+ * Purge the fat cache in denode dep of all entries relating to file
+ * relative cluster frcn and beyond.
+ */
+void fc_purge(dep, frcn)
+	struct denode *dep;
+	u_int frcn;
+{
+	int i;
+	struct fatcache *fcp;
+
+	fcp = dep->de_fc;
+	for (i = 0; i < FC_SIZE; i++, fcp++) {
+		if (fcp->fc_frcn >= frcn)
+			fcp->fc_frcn = FCE_EMPTY;
+	}
+}
+
+/*
+ * Update all copies of the fat. The first copy is updated last.
+ *
+ * pmp	 - msdosfsmount structure for filesystem to update
+ * bp	 - addr of modified fat block
+ * fatbn - block number relative to begin of filesystem of the modified fat block.
+ */
+void
+updatefats(pmp, bp, fatbn)
+	struct msdosfsmount *pmp;
+	struct buf *bp;
+	u_long fatbn;
+{
+	int i;
+	struct buf *bpn;
+
+#ifdef MSDOSFS_DEBUG
+	printf("updatefats(pmp %08x, bp %08x, fatbn %d)\n",
+	       pmp, bp, fatbn);
+#endif
+
+	/*
+	 * Now copy the block(s) of the modified fat to the other copies of
+	 * the fat and write them out.  This is faster than reading in the
+	 * other fats and then writing them back out.  This could tie up
+	 * the fat for quite a while. Preventing others from accessing it.
+	 * To prevent us from going after the fat quite so much we use
+	 * delayed writes, unless they specfied "synchronous" when the
+	 * filesystem was mounted.  If synch is asked for then use
+	 * bwrite()'s and really slow things down.
+	 */
+	for (i = 1; i < pmp->pm_FATs; i++) {
+		fatbn += pmp->pm_FATsecs;
+		/* getblk() never fails */
+		bpn = getblk(pmp->pm_devvp, fatbn, bp->b_bcount, 0, 0);
+		bcopy(bp->b_data, bpn->b_data, bp->b_bcount);
+		if (pmp->pm_waitonfat)
+			bwrite(bpn);
+		else
+			bdwrite(bpn);
+	}
+	/*
+	 * Write out the first fat last.
+	 */
+	if (pmp->pm_waitonfat)
+		bwrite(bp);
+	else
+		bdwrite(bp);
+}
+
+/*
+ * Updating entries in 12 bit fats is a pain in the butt.
+ * 
+ * The following picture shows where nibbles go when moving from a 12 bit
+ * cluster number into the appropriate bytes in the FAT.
+ * 
+ *	byte m        byte m+1      byte m+2
+ *	+----+----+   +----+----+   +----+----+
+ *	|  0    1 |   |  2    3 |   |  4    5 |   FAT bytes
+ *	+----+----+   +----+----+   +----+----+
+ * 
+ *	+----+----+----+   +----+----+----+
+ *	|  3    0    1 |   |  4    5    2 |
+ *	+----+----+----+   +----+----+----+
+ *	cluster n  	   cluster n+1
+ * 
+ * Where n is even. m = n + (n >> 2)
+ * 
+ */
+extern __inline void
+usemap_alloc(pmp, cn)
+	struct msdosfsmount *pmp;
+	u_long cn;
+{
+	pmp->pm_inusemap[cn / N_INUSEBITS]
+			 |= 1 << (cn % N_INUSEBITS);
+	pmp->pm_freeclustercount--;
+}
+
+extern __inline void
+usemap_free(pmp, cn)
+	struct msdosfsmount *pmp;
+	u_long cn;
+{
+	pmp->pm_freeclustercount++;
+	pmp->pm_inusemap[cn / N_INUSEBITS] &= ~(1 << (cn % N_INUSEBITS));
+}
+
+int
+clusterfree(pmp, cluster, oldcnp)
+	struct msdosfsmount *pmp;
+	u_long cluster;
+	u_long *oldcnp;
+{
+	int error;
+	u_long oldcn;
+
+	error = fatentry(FAT_GET_AND_SET, pmp, cluster, &oldcn, MSDOSFSFREE);
+	if (error == 0) {
+		/*
+		 * If the cluster was successfully marked free, then update
+		 * the count of free clusters, and turn off the "allocated"
+		 * bit in the "in use" cluster bit map.
+		 */
+		usemap_free(pmp, cluster);
+		if (oldcnp)
+			*oldcnp = oldcn;
+	}
+	return error;
+}
+
+/*
+ * Get or Set or 'Get and Set' the cluster'th entry in the fat.
+ *
+ * function	- whether to get or set a fat entry
+ * pmp		- address of the msdosfsmount structure for the filesystem
+ *		  whose fat is to be manipulated.
+ * cn		- which cluster is of interest
+ * oldcontents	- address of a word that is to receive the contents of the
+ *		  cluster'th entry if this is a get function
+ * newcontents	- the new value to be written into the cluster'th element of
+ *		  the fat if this is a set function.
+ * 
+ * This function can also be used to free a cluster by setting the fat entry
+ * for a cluster to 0.
+ * 
+ * All copies of the fat are updated if this is a set function. NOTE: If
+ * fatentry() marks a cluster as free it does not update the inusemap in
+ * the msdosfsmount structure. This is left to the caller.
+ */
+int
+fatentry(function, pmp, cn, oldcontents, newcontents)
+	int function;
+	struct msdosfsmount *pmp;
+	u_long cn;
+	u_long *oldcontents;
+	u_long newcontents;
+{
+	int error;
+	u_long readcn;
+	u_long bn, bo, bsize, byteoffset;
+	struct buf *bp;
+
+	/*
+	 * printf("fatentry(func %d, pmp %08x, clust %d, oldcon %08x, newcon %d)\n",
+	 *	  function, pmp, cluster, oldcontents, newcontents);
+	 */
+
+#ifdef DIAGNOSTIC
+	/*
+	 * Be sure they asked us to do something.
+	 */
+	if ((function & (FAT_SET | FAT_GET)) == 0) {
+		printf("fatentry(): function code doesn't specify get or set\n");
+		return EINVAL;
+	}
+
+	/*
+	 * If they asked us to return a cluster number but didn't tell us
+	 * where to put it, give them an error.
+	 */
+	if ((function & FAT_GET) && oldcontents == NULL) {
+		printf("fatentry(): get function with no place to put result\n");
+		return EINVAL;
+	}
+#endif
+
+	/*
+	 * Be sure the requested cluster is in the filesystem.
+	 */
+	if (cn < CLUST_FIRST || cn > pmp->pm_maxcluster)
+		return EINVAL;
+
+	byteoffset = FATOFS(pmp, cn);
+	fatblock(pmp, byteoffset, &bn, &bsize, &bo);
+	if (error = bread(pmp->pm_devvp, bn, bsize, NOCRED, &bp))
+		return error;
+	
+	if (function & FAT_GET) {
+		readcn = getushort(&bp->b_data[bo]);
+		if (FAT12(pmp)) {
+			if (cn & 1)
+				readcn >>= 4;
+			readcn &= 0x0fff;
+			/* map certain 12 bit fat entries to 16 bit */
+			if ((readcn & 0x0ff0) == 0x0ff0)
+				readcn |= 0xf000;
+		}
+		*oldcontents = readcn;
+	}
+	if (function & FAT_SET) {
+		if (FAT12(pmp)) {
+			readcn = getushort(&bp->b_data[bo]);
+			if (cn & 1) {
+				readcn &= 0x000f;
+				readcn |= newcontents << 4;
+			} else {
+				readcn &= 0xf000;
+				readcn |= newcontents & 0xfff;
+			}
+			putushort(&bp->b_data[bo], readcn);
+		} else
+			putushort(&bp->b_data[bo], newcontents);
+		updatefats(pmp, bp, bn);
+		bp = NULL;
+		pmp->pm_fmod = 1;
+	}
+	if (bp)
+		brelse(bp);
+	return 0;
+}
+
+/*
+ * Update a contiguous cluster chain
+ *
+ * pmp	    - mount point
+ * start    - first cluster of chain
+ * count    - number of clusters in chain
+ * fillwith - what to write into fat entry of last cluster
+ */
+static int
+fatchain(pmp, start, count, fillwith)
+	struct msdosfsmount *pmp;
+	u_long start;
+	u_long count;
+	u_long fillwith;
+{
+	int error;
+	u_long bn, bo, bsize, byteoffset, readcn, newc;
+	struct buf *bp;
+	
+#ifdef MSDOSFS_DEBUG
+	printf("fatchain(pmp %08x, start %d, count %d, fillwith %d)\n",
+	       pmp, start, count, fillwith);
+#endif
+	/*
+	 * Be sure the clusters are in the filesystem.
+	 */
+	if (start < CLUST_FIRST || start + count - 1 > pmp->pm_maxcluster)
+		return EINVAL;
+	
+	while (count > 0) {
+		byteoffset = FATOFS(pmp, start);
+		fatblock(pmp, byteoffset, &bn, &bsize, &bo);
+		if (error = bread(pmp->pm_devvp, bn, bsize, NOCRED, &bp))
+			return error;
+		while (count > 0) {
+			start++;
+			newc = --count > 0 ? start : fillwith;
+			if (FAT12(pmp)) {
+				readcn = getushort(&bp->b_data[bo]);
+				if (start & 1) {
+					readcn &= 0xf000;
+					readcn |= newc & 0xfff;
+				} else {
+					readcn &= 0x000f;
+					readcn |= newc << 4;
+				}
+				putushort(&bp->b_data[bo], readcn);
+				bo++;
+				if (!(start & 1))
+					bo++;
+			} else {
+				putushort(&bp->b_data[bo], newc);
+				bo += 2;
+			}
+			if (bo >= bsize)
+				break;
+		}
+		updatefats(pmp, bp, bn);
+	}
+	pmp->pm_fmod = 1;
+	return 0;
+}
+
+/*
+ * Check the length of a free cluster chain starting at start.
+ *
+ * pmp	 - mount point
+ * start - start of chain
+ * count - maximum interesting length
+ */
+int
+chainlength(pmp, start, count)
+	struct msdosfsmount *pmp;
+	u_long start;
+	u_long count;
+{
+	u_long idx, max_idx;
+	u_int map;
+	u_long len;
+	
+	max_idx = pmp->pm_maxcluster / N_INUSEBITS;
+	idx = start / N_INUSEBITS;
+	start %= N_INUSEBITS;
+	map = pmp->pm_inusemap[idx];
+	map &= ~((1 << start) - 1);
+	if (map) {
+		len = ffs(map) - 1 - start;
+		return len > count ? count : len;
+	}
+	len = N_INUSEBITS - start;
+	if (len >= count)
+		return count;
+	while (++idx <= max_idx) {
+		if (len >= count)
+			break;
+		if (map = pmp->pm_inusemap[idx]) {
+			len +=  ffs(map) - 1;
+			break;
+		}
+		len += N_INUSEBITS;
+	}
+	return len > count ? count : len;
+}
+
+/*
+ * Allocate contigous free clusters.
+ *
+ * pmp	      - mount point.
+ * start      - start of cluster chain.
+ * count      - number of clusters to allocate.
+ * fillwith   - put this value into the fat entry for the
+ *		last allocated cluster.
+ * retcluster - put the first allocated cluster's number here.
+ * got	      - how many clusters were actually allocated.
+ */
+int
+chainalloc(pmp, start, count, fillwith, retcluster, got)
+	struct msdosfsmount *pmp;
+	u_long start;
+	u_long count;
+	u_long fillwith;
+	u_long *retcluster;
+	u_long *got;
+{
+	int error;
+	
+	error = fatchain(pmp, start, count, fillwith);
+	if (error == 0) {
+#ifdef MSDOSFS_DEBUG
+		printf("clusteralloc(): allocated cluster chain at %d (%d clusters)\n",
+		       start, count);
+#endif
+		if (retcluster)
+			*retcluster = start;
+		if (got)
+			*got = count;
+		while (count-- > 0)
+			usemap_alloc(pmp, start++);
+	}
+	return error;
+}
+
+/*
+ * Allocate contiguous free clusters.
+ *
+ * pmp	      - mount point.
+ * start      - preferred start of cluster chain.
+ * count      - number of clusters requested.
+ * fillwith   - put this value into the fat entry for the
+ *		last allocated cluster.
+ * retcluster - put the first allocated cluster's number here.
+ * got	      - how many clusters were actually allocated.
+ */
+int
+clusteralloc(pmp, start, count, fillwith, retcluster, got)
+	struct msdosfsmount *pmp;
+	u_long start;
+	u_long count;
+	u_long fillwith;
+	u_long *retcluster;
+	u_long *got;
+{
+	int error;
+	u_long idx;
+	u_long len, newst, foundcn, foundl, cn, l;
+	u_int map;
+	
+#ifdef MSDOSFS_DEBUG
+	printf("clusteralloc(): find %d clusters\n",count);
+#endif
+	if (start) {
+		if ((len = chainlength(pmp, start, count)) >= count)
+			return chainalloc(pmp, start, count, fillwith, retcluster, got);
+	} else {
+		/*
+		 * This is a new file, initialize start
+		 */
+		struct timeval tv;
+		
+		microtime(&tv);
+		start = (tv.tv_usec >> 10)|tv.tv_usec;
+		len = 0;
+	}
+	
+	/*
+	 * Start at a (pseudo) random place to maximize cluster runs
+	 * under multiple writers.
+	 */
+	foundcn = newst = (start * 1103515245 + 12345) % (pmp->pm_maxcluster + 1);
+	foundl = 0;
+	
+	for (cn = newst; cn <= pmp->pm_maxcluster;) {
+		idx = cn / N_INUSEBITS;
+		map = pmp->pm_inusemap[idx];
+		map |= (1 << (cn % N_INUSEBITS)) - 1;
+		if (map != (u_int)-1) {
+			cn = idx * N_INUSEBITS + ffs(map^(u_int)-1) - 1;
+			if ((l = chainlength(pmp, cn, count)) >= count)
+				return chainalloc(pmp, cn, count, fillwith, retcluster, got);
+			if (l > foundl) {
+				foundcn = cn;
+				foundl = l;
+			}
+			cn += l + 1;
+			continue;
+		}
+		cn += N_INUSEBITS - cn % N_INUSEBITS;
+	}
+	for (cn = 0; cn < newst;) {
+		idx = cn / N_INUSEBITS;
+		map = pmp->pm_inusemap[idx];
+		map |= (1 << (cn % N_INUSEBITS)) - 1;
+		if (map != (u_int)-1) {
+			cn = idx * N_INUSEBITS + ffs(map^(u_int)-1) - 1;
+			if ((l = chainlength(pmp, cn, count)) >= count)
+				return chainalloc(pmp, cn, count, fillwith, retcluster, got);
+			if (l > foundl) {
+				foundcn = cn;
+				foundl = l;
+			}
+			cn += l + 1;
+			continue;
+		}
+		cn += N_INUSEBITS - cn % N_INUSEBITS;
+	}
+
+	if (!foundl)
+		return ENOSPC;
+
+	if (len)
+		return chainalloc(pmp, start, len, fillwith, retcluster, got);
+	else
+		return chainalloc(pmp, foundcn, foundl, fillwith, retcluster, got);
+}
+
+
+/*
+ * Free a chain of clusters.
+ *
+ * pmp		- address of the msdosfs mount structure for the filesystem
+ *		  containing the cluster chain to be freed.
+ * startcluster - number of the 1st cluster in the chain of clusters to be
+ *		  freed.
+ */
+int
+freeclusterchain(pmp, cluster)
+	struct msdosfsmount *pmp;
+	u_long cluster;
+{
+	int error = 0;
+	struct buf *bp = NULL;
+	u_long bn, bo, bsize, byteoffset;
+	u_long readcn, lbn = -1;
+	
+	while (cluster >= CLUST_FIRST && cluster <= pmp->pm_maxcluster) {
+		byteoffset = FATOFS(pmp, cluster);
+		fatblock(pmp, byteoffset, &bn, &bsize, &bo);
+		if (lbn != bn) {
+			if (bp)
+				updatefats(pmp, bp, bn);
+			if (error = bread(pmp->pm_devvp, bn, bsize, NOCRED, &bp))
+				return error;
+			lbn = bn;
+		}
+		usemap_free(pmp, cluster);
+		readcn = getushort(&bp->b_data[bo]);
+		if (FAT12(pmp)) {
+			if (cluster & 1) {
+				cluster = readcn >> 4;
+				readcn &= 0x000f;
+				readcn |= MSDOSFSFREE << 4;
+			} else {
+				cluster = readcn;
+				readcn &= 0xf000;
+				readcn |= MSDOSFSFREE & 0xfff;
+			}
+			putushort(&bp->b_data[bo], readcn);
+			cluster &= 0x0fff;
+			if ((cluster&0x0ff0) == 0x0ff0)
+				cluster |= 0xf000;
+		} else {
+			cluster = readcn;
+			putushort(&bp->b_data[bo], MSDOSFSFREE);
+		}
+	}
+	if (bp)
+		updatefats(pmp, bp, bn);
+	return error;
+}
+
+/*
+ * Read in fat blocks looking for free clusters. For every free cluster
+ * found turn off its corresponding bit in the pm_inusemap.
+ */
+int
+fillinusemap(pmp)
+	struct msdosfsmount *pmp;
+{
+	struct buf *bp = NULL;
+	u_long cn, readcn;
+	int error;
+	int fat12 = FAT12(pmp);
+	u_long bn, bo, bsize, byteoffset;
+
+	/*
+	 * Mark all clusters in use, we mark the free ones in the fat scan
+	 * loop further down.
+	 */
+	for (cn = 0; cn < (pmp->pm_maxcluster + N_INUSEBITS) / N_INUSEBITS; cn++)
+		pmp->pm_inusemap[cn] = (u_int)-1;
+
+	/*
+	 * Figure how many free clusters are in the filesystem by ripping
+	 * through the fat counting the number of entries whose content is
+	 * zero.  These represent free clusters.
+	 */
+	pmp->pm_freeclustercount = 0;
+	for (cn = CLUST_FIRST; cn <= pmp->pm_maxcluster; cn++) {
+		byteoffset = FATOFS(pmp, cn);
+		bo = byteoffset % pmp->pm_fatblocksize;
+		if (!bo || !bp) {
+			/* Read new FAT block */
+			if (bp)
+				brelse(bp);
+			fatblock(pmp, byteoffset, &bn, &bsize, NULL);
+			error = bread(pmp->pm_devvp, bn, bsize, NOCRED, &bp);
+			if (error)
+				return error;
+		}
+		readcn = getushort(&bp->b_data[bo]);
+		if (fat12) {
+			if (cn & 1)
+				readcn >>= 4;
+			readcn &= 0x0fff;
+		}
+
+		if (readcn == 0)
+			usemap_free(pmp, cn);
+	}
+	brelse(bp);
+	return 0;
+}
+
+/*
+ * Allocate a new cluster and chain it onto the end of the file.
+ *
+ * dep	 - the file to extend
+ * count - number of clusters to allocate
+ * bpp	 - where to return the address of the buf header for the first new
+ *	   file block
+ * ncp	 - where to put cluster number of the first newly allocated cluster
+ *	   If this pointer is 0, do not return the cluster number.
+ * flags - see fat.h
+ *
+ * NOTE: This function is not responsible for turning on the DE_UPDATE bit of
+ * the de_flag field of the denode and it does not change the de_FileSize
+ * field.  This is left for the caller to do.
+ */
+int
+extendfile(dep, count, bpp, ncp, flags)
+	struct denode *dep;
+	u_long count;
+	struct buf **bpp;
+	u_long *ncp;
+	int flags;
+{
+	int error = 0;
+	u_long frcn;
+	u_long cn, got;
+	struct msdosfsmount *pmp = dep->de_pmp;
+	struct buf *bp;
+	
+	/*
+	 * Don't try to extend the root directory
+	 */
+	if (DETOV(dep)->v_flag & VROOT) {
+		printf("extendfile(): attempt to extend root directory\n");
+		return ENOSPC;
+	}
+
+	/*
+	 * If the "file's last cluster" cache entry is empty, and the file
+	 * is not empty, then fill the cache entry by calling pcbmap().
+	 */
+	fc_fileextends++;
+	if (dep->de_fc[FC_LASTFC].fc_frcn == FCE_EMPTY &&
+	    dep->de_StartCluster != 0) {
+		fc_lfcempty++;
+		error = pcbmap(dep, 0xffff, 0, &cn);
+		/* we expect it to return E2BIG */
+		if (error != E2BIG)
+			return error;
+		error = 0;
+	}
+	
+	while (count > 0) {
+		/*
+		 * Allocate a new cluster chain and cat onto the end of the file.
+		 * If the file is empty we make de_StartCluster point to the new
+		 * block.  Note that de_StartCluster being 0 is sufficient to be
+		 * sure the file is empty since we exclude attempts to extend the
+		 * root directory above, and the root dir is the only file with a
+		 * startcluster of 0 that has blocks allocated (sort of).
+		 */
+		if (dep->de_StartCluster == 0)
+			cn = 0;
+		else
+			cn = dep->de_fc[FC_LASTFC].fc_fsrcn + 1;
+		if (error = clusteralloc(pmp, cn, count, CLUST_EOFE, &cn, &got))
+			return error;
+		
+		count -= got;
+		
+		/*
+		 * Give them the filesystem relative cluster number if they want
+		 * it.
+		 */
+		if (ncp) {
+			*ncp = cn;
+			ncp = NULL;
+		}
+		
+		if (dep->de_StartCluster == 0) {
+			dep->de_StartCluster = cn;
+			frcn = 0;
+		} else {
+			error = fatentry(FAT_SET, pmp, dep->de_fc[FC_LASTFC].fc_fsrcn,
+					 0, cn);
+			if (error) {
+				clusterfree(pmp, cn, NULL);
+				return error;
+			}
+			
+			frcn = dep->de_fc[FC_LASTFC].fc_frcn + 1;
+		}
+		
+		/*
+		 * Update the "last cluster of the file" entry in the denode's fat
+		 * cache.
+		 */
+		fc_setcache(dep, FC_LASTFC, frcn + got - 1, cn + got - 1);
+		
+		if (flags & DE_CLEAR) {
+			while (got-- > 0) {
+				/*
+				 * Get the buf header for the new block of the file.
+				 */
+				if (dep->de_Attributes & ATTR_DIRECTORY)
+					bp = getblk(pmp->pm_devvp, cntobn(pmp, cn++),
+						    pmp->pm_bpcluster, 0, 0);
+				else {
+					bp = getblk(DETOV(dep), frcn++, pmp->pm_bpcluster, 0, 0);
+					/*
+					 * Do the bmap now, as in msdosfs_write
+					 */
+					if (pcbmap(dep, bp->b_lblkno, &bp->b_blkno, 0))
+						bp->b_blkno = -1;
+					if (bp->b_blkno == -1)
+						panic("extendfile: pcbmap");
+				}
+				clrbuf(bp);
+				if (bpp) {
+					*bpp = bp;
+					bpp = NULL;
+				} else {
+					bp->b_flags |= B_AGE;
+					bawrite(bp);
+				}
+			}
+		}
+	}
+	
+	return 0;
+}