Index: head/usr.sbin/makefs/ffs.c
===================================================================
--- head/usr.sbin/makefs/ffs.c
+++ head/usr.sbin/makefs/ffs.c
@@ -476,13 +476,15 @@
 	char	*buf;
 	int	i, bufsize;
 	off_t	bufrem;
+	int	oflags = O_RDWR | O_CREAT;
 	time_t	tstamp;
-	int	oflags = O_RDWR | O_CREAT | O_TRUNC;
 
 	assert (image != NULL);
 	assert (fsopts != NULL);
 
 		/* create image */
+	if (fsopts->offset == 0)
+		oflags |= O_TRUNC;
 	if ((fsopts->fd = open(image, oflags, 0666)) == -1) {
 		warn("Can't open `%s' for writing", image);
 		return (-1);
@@ -517,6 +519,13 @@
 			    bufsize);
 		buf = ecalloc(1, bufsize);
 	}
+
+	if (fsopts->offset != 0)
+		if (lseek(fsopts->fd, fsopts->offset, SEEK_SET) == -1) {
+			warn("can't seek");
+			return -1;
+		}
+
 	while (bufrem > 0) {
 		i = write(fsopts->fd, buf, MIN(bufsize, bufrem));
 		if (i == -1) {
Index: head/usr.sbin/makefs/ffs/buf.c
===================================================================
--- head/usr.sbin/makefs/ffs/buf.c
+++ head/usr.sbin/makefs/ffs/buf.c
@@ -68,7 +68,7 @@
 		printf("%s: blkno %lld size %d\n", __func__, (long long)blkno,
 		    size);
 	*bpp = getblk(vp, blkno, size, 0, 0, 0);
-	offset = (*bpp)->b_blkno * fsinfo->sectorsize;
+	offset = (*bpp)->b_blkno * fsinfo->sectorsize + fsinfo->offset;
 	if (debug & DEBUG_BUF_BREAD)
 		printf("%s: blkno %lld offset %lld bcount %ld\n", __func__,
 		    (long long)(*bpp)->b_blkno, (long long) offset,
@@ -128,7 +128,7 @@
 	fsinfo_t *fs = bp->b_fs;
 
 	assert (bp != NULL);
-	offset = bp->b_blkno * fs->sectorsize;
+	offset = bp->b_blkno * fs->sectorsize + fs->offset;
 	if (debug & DEBUG_BUF_BWRITE)
 		printf("bwrite: blkno %lld offset %lld bcount %ld\n",
 		    (long long)bp->b_blkno, (long long) offset,
Index: head/usr.sbin/makefs/ffs/mkfs.c
===================================================================
--- head/usr.sbin/makefs/ffs/mkfs.c
+++ head/usr.sbin/makefs/ffs/mkfs.c
@@ -774,8 +774,7 @@
 	int n;
 	off_t offset;
 
-	offset = bno;
-	offset *= fsopts->sectorsize;
+	offset = bno * fsopts->sectorsize + fsopts->offset;
 	if (lseek(fsopts->fd, offset, SEEK_SET) < 0)
 		err(1, "%s: seek error for sector %lld", __func__,
 		    (long long)bno);
@@ -799,11 +798,10 @@
 	int n;
 	off_t offset;
 
-	offset = bno;
-	offset *= fsopts->sectorsize;
+	offset = bno * fsopts->sectorsize + fsopts->offset;
 	if (lseek(fsopts->fd, offset, SEEK_SET) < 0)
 		err(1, "%s: seek error for sector %lld", __func__,
-		    (long long)bno );
+		    (long long)bno);
 	n = write(fsopts->fd, bf, size);
 	if (n == -1)
 		err(1, "%s: write error for sector %lld", __func__,
Index: head/usr.sbin/makefs/makefs.h
===================================================================
--- head/usr.sbin/makefs/makefs.h
+++ head/usr.sbin/makefs/makefs.h
@@ -151,6 +151,7 @@
 	off_t	maxsize;	/* maximum size image can be */
 	off_t	freefiles;	/* free file entries to leave */
 	off_t	freeblocks;	/* free blocks to leave */
+	off_t	offset;		/* offset from start of file */
 	off_t	roundup;	/* round image size up to this value */
 	int	freefilepc;	/* free file % */
 	int	freeblockpc;	/* free block % */
Index: head/usr.sbin/makefs/makefs.8
===================================================================
--- head/usr.sbin/makefs/makefs.8
+++ head/usr.sbin/makefs/makefs.8
@@ -35,7 +35,7 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd May 17, 2017
+.Dd May 26, 2017
 .Dt MAKEFS 8
 .Os
 .Sh NAME
@@ -52,6 +52,7 @@
 .Op Fl M Ar minimum-size
 .Op Fl m Ar maximum-size
 .Op Fl N Ar userdb-dir
+.Op Fl O Ar offset
 .Op Fl o Ar fs-options
 .Op Fl R Ar roundup-size
 .Op Fl S Ar sector-size
@@ -193,6 +194,11 @@
 and
 .Xr getgrnam 3
 (and related) library calls.
+.It Fl O Ar offset
+Instead of creating the filesystem at the beginning of the file, start
+at offset.
+Valid only for
+.Sy ffs .
 .It Fl o Ar fs-options
 Set file system specific options.
 .Ar fs-options
Index: head/usr.sbin/makefs/makefs.c
===================================================================
--- head/usr.sbin/makefs/makefs.c
+++ head/usr.sbin/makefs/makefs.c
@@ -124,7 +124,7 @@
 		err(1, "Unable to get system time");
 
 
-	while ((ch = getopt(argc, argv, "B:b:Dd:f:F:M:m:N:o:pR:s:S:t:T:xZ")) != -1) {
+	while ((ch = getopt(argc, argv, "B:b:Dd:f:F:M:m:N:O:o:pR:s:S:t:T:xZ")) != -1) {
 		switch (ch) {
 
 		case 'B':
@@ -202,7 +202,12 @@
 			fsoptions.maxsize =
 			    strsuftoll("maximum size", optarg, 1LL, LLONG_MAX);
 			break;
-			
+
+		case 'O':
+			fsoptions.offset =
+			    strsuftoll("offset", optarg, 0LL, LLONG_MAX);
+			break;
+
 		case 'o':
 		{
 			char *p;
@@ -479,8 +484,8 @@
 	fprintf(stderr,
 "Usage: %s [-xZ] [-B endian] [-b free-blocks] [-d debug-mask]\n"
 "\t[-F mtree-specfile] [-f free-files] [-M minimum-size] [-m maximum-size]\n"
-"\t[-N userdb-dir] [-o fs-options] [-R roundup-size] [-S sector-size]\n"
-"\t[-s image-size] [-T <timestamp/file>] [-t fs-type]\n"
+"\t[-N userdb-dir] [-O offset] [-o fs-options] [-R roundup-size]\n"
+"\t[-S sector-size] [-s image-size] [-T <timestamp/file>] [-t fs-type]\n"
 "\timage-file directory | manifest [extra-directory ...]\n",
 	    prog);