Index: usr.sbin/bhyve/bhyve.8
===================================================================
--- usr.sbin/bhyve/bhyve.8	(revision 282558)
+++ usr.sbin/bhyve/bhyve.8	(working copy)
@@ -193,8 +193,13 @@
 .Pp
 Block storage devices:
 .Bl -tag -width 10n
-.It Pa /filename Ns Oo , Ns Li nocache Oc Ns Oo , Ns Li direct Oc Ns Oo , Ns Li ro Oc
-.It Pa /dev/xxx Ns Oo , Ns Ar nocache Oc Ns Oo , Ns Ar direct Oc Ns Oo , Ns Ar ro Oc
+.It Pa /filename Ns Oo , Ns Ar block-device-options Oc
+.It Pa /dev/xxx Ns Oo , Ns Ar block-device-options Oc
+.El
+.Pp
+The
+.Ar block-device-options
+are:
 .Bl -tag -width 8n
 .It Li nocache
 Open the file with
@@ -204,16 +209,12 @@
 .Dv O_SYNC .
 .It Li ro
 Force the file to be opened read-only.
+.It Li sectorsize= Ns Ar logical Ns Oo / Ns Ar physical Oc
+Specify the logical and physical sector sizes of the emulated disk.
+The physical sector size is optional and is equal to the logical sector size
+if not explicitly specified.
 .El
 .Pp
-The
-.Li nocache ,
-.Li direct ,
-and
-.Li ro
-options are not available for virtio block devices.
-.El
-.Pp
 TTY devices:
 .Bl -tag -width 10n
 .It Li stdio
Index: usr.sbin/bhyve/block_if.c
===================================================================
--- usr.sbin/bhyve/block_if.c	(revision 282558)
+++ usr.sbin/bhyve/block_if.c	(working copy)
@@ -392,16 +392,18 @@
 {
 	char tname[MAXCOMLEN + 1];
 	char name[MAXPATHLEN];
-	char *nopt, *xopts;
+	char *nopt, *xopts, *cp;
 	struct blockif_ctxt *bc;
 	struct stat sbuf;
 	struct diocgattr_arg arg;
 	off_t size, psectsz, psectoff;
 	int extra, fd, i, sectsz;
-	int nocache, sync, ro, candelete, geom;
+	int nocache, sync, ro, candelete, geom, ssopt, pssopt;
 
 	pthread_once(&blockif_once, blockif_init);
 
+	fd = -1;
+	ssopt = 0;
 	nocache = 0;
 	sync = 0;
 	ro = 0;
@@ -410,16 +412,25 @@
 	 * The first element in the optstring is always a pathname.
 	 * Optional elements follow
 	 */
-	nopt = strdup(optstr);
-	for (xopts = strtok(nopt, ",");
-	     xopts != NULL;
-	     xopts = strtok(NULL, ",")) {
-		if (!strcmp(xopts, "nocache"))
+	nopt = xopts = strdup(optstr);
+	while (xopts != NULL) {
+		cp = strsep(&xopts, ",");
+		if (cp == nopt)		/* file or device pathname */
+			continue;
+		else if (!strcmp(cp, "nocache"))
 			nocache = 1;
-		else if (!strcmp(xopts, "sync"))
+		else if (!strcmp(cp, "sync"))
 			sync = 1;
-		else if (!strcmp(xopts, "ro"))
+		else if (!strcmp(cp, "ro"))
 			ro = 1;
+		else if (sscanf(cp, "sectorsize=%d/%d", &ssopt, &pssopt) == 2)
+			;
+		else if (sscanf(cp, "sectorsize=%d", &ssopt) == 1)
+			pssopt = ssopt;
+		else {
+			fprintf(stderr, "Invalid device option \"%s\"\n", cp);
+			goto err;
+		}
 	}
 
 	extra = 0;
@@ -437,13 +448,12 @@
 
 	if (fd < 0) {
 		perror("Could not open backing file");
-		return (NULL);
+		goto err;
 	}
 
         if (fstat(fd, &sbuf) < 0) {
                 perror("Could not stat backing file");
-                close(fd);
-                return (NULL);
+		goto err;
         }
 
         /*
@@ -457,8 +467,7 @@
 		if (ioctl(fd, DIOCGMEDIASIZE, &size) < 0 ||
 		    ioctl(fd, DIOCGSECTORSIZE, &sectsz)) {
 			perror("Could not fetch dev blk/sector size");
-			close(fd);
-			return (NULL);
+			goto err;
 		}
 		assert(size != 0);
 		assert(sectsz != 0);
@@ -473,10 +482,39 @@
 	} else
 		psectsz = sbuf.st_blksize;
 
+	if (ssopt != 0) {
+		if (!powerof2(ssopt) || !powerof2(pssopt) || ssopt < 512 ||
+		    ssopt > pssopt) {
+			fprintf(stderr, "Invalid sector size %d/%d\n",
+			    ssopt, pssopt);
+			goto err;
+		}
+
+		/*
+		 * Some backend drivers (e.g. cd0, ada0) require that the I/O
+		 * size be a multiple of the device's sector size.
+		 *
+		 * Validate that the emulated sector size complies with this
+		 * requirement.
+		 */
+		if (S_ISCHR(sbuf.st_mode)) {
+			if (ssopt < sectsz || (ssopt % sectsz) != 0) {
+				fprintf(stderr, "Sector size %d incompatible "
+				    "with underlying device sector size %d\n",
+				    ssopt, sectsz);
+				goto err;
+			}
+		}
+
+		sectsz = ssopt;
+		psectsz = pssopt;
+		psectoff = 0;
+	}
+
 	bc = calloc(1, sizeof(struct blockif_ctxt));
 	if (bc == NULL) {
-		close(fd);
-		return (NULL);
+		perror("calloc");
+		goto err;
 	}
 
 	bc->bc_magic = BLOCKIF_SIG;
@@ -506,6 +544,10 @@
 	}
 
 	return (bc);
+err:
+	if (fd >= 0)
+		close(fd);
+	return (NULL);
 }
 
 static int