Index: head/sys/boot/common/bcache.c
===================================================================
--- head/sys/boot/common/bcache.c
+++ head/sys/boot/common/bcache.c
@@ -272,20 +272,43 @@
     for (i = 0; i < p_size; i++) {
 	bcache_invalidate(bc, p_blk + i);
     }
+
     r_size = 0;
+    /*
+     * with read-ahead, it may happen we are attempting to read past
+     * disk end, as bcache has no information about disk size.
+     * in such case we should get partial read if some blocks can be
+     * read or error, if no blocks can be read.
+     * in either case we should return the data in bcache and only
+     * return error if there is no data.
+     */
     result = dd->dv_strategy(dd->dv_devdata, rw, p_blk, 0,
 	p_size * bcache_blksize, p_buf, &r_size);
 
-    if (result)
-	goto done;
-
     r_size /= bcache_blksize;
     for (i = 0; i < r_size; i++)
 	bcache_insert(bc, p_blk + i);
 
-    bcache_rablks += ra;
-    bcopy(bc->bcache_data + (bcache_blksize * BHASH(bc, blk)) + offset, buf,
-	size);
+    /* update ra statistics */
+    if (r_size != 0) {
+	if (r_size < p_size)
+	    bcache_rablks += (p_size - r_size);
+	else
+	    bcache_rablks += ra;
+    }
+
+    /* check how much data can we copy */
+    for (i = 0; i < nblk; i++) {
+	if (BCACHE_LOOKUP(bc, (daddr_t)(blk + i)))
+	    break;
+    }
+
+    size = i * bcache_blksize;
+    if (size != 0) {
+	bcopy(bc->bcache_data + (bcache_blksize * BHASH(bc, blk)) + offset,
+	    buf, size);
+	result = 0;
+    }
 
  done:
     if ((result == 0) && (rsize != NULL))
@@ -349,8 +372,16 @@
 
 	    ret = read_strategy(devdata, rw, blk, offset,
 		csize, buf+total, &isize);
-	    if (ret != 0)
-		return (ret);
+
+	    /*
+	     * we may have error from read ahead, if we have read some data
+	     * return partial read.
+	     */
+	    if (ret != 0 || isize == 0) {
+		if (total != 0)
+		    ret = 0;
+		break;
+	    }
 	    blk += (offset+isize) / bcache_blksize;
 	    offset = 0;
 	    total += isize;
Index: head/sys/boot/efi/libefi/efipart.c
===================================================================
--- head/sys/boot/efi/libefi/efipart.c
+++ head/sys/boot/efi/libefi/efipart.c
@@ -321,6 +321,15 @@
 	if (size == 0 || (size % 512) != 0)
 		return (EIO);
 
+	off = blk * 512;
+	/* make sure we don't read past disk end */
+	if ((off + size) / blkio->Media->BlockSize - 1 >
+	    blkio->Media->LastBlock) {
+		size = blkio->Media->LastBlock + 1 -
+		    off / blkio->Media->BlockSize;
+		size = size * blkio->Media->BlockSize;
+	}
+
 	if (rsize != NULL)
 		*rsize = size;
 
@@ -335,7 +344,6 @@
 		return (ENOMEM);
 
 	error = 0;
-	off = blk * 512;
 	blk = off / blkio->Media->BlockSize;
 	blkoff = off % blkio->Media->BlockSize;
 	blksz = blkio->Media->BlockSize - blkoff;
Index: head/sys/boot/i386/libi386/bioscd.c
===================================================================
--- head/sys/boot/i386/libi386/bioscd.c
+++ head/sys/boot/i386/libi386/bioscd.c
@@ -271,14 +271,25 @@
 
 	if (rsize)
 		*rsize = 0;
-	if (blks && bc_read(unit, dblk, blks, buf)) {
+	if ((blks = bc_read(unit, dblk, blks, buf)) < 0) {
 		DEBUG("read error");
 		return (EIO);
+	} else {
+		if (size / BIOSCD_SECSIZE > blks) {
+			if (rsize)
+				*rsize = blks * BIOSCD_SECSIZE;
+			return (0);
+		}
 	}
 #ifdef BD_SUPPORT_FRAGS
 	DEBUG("frag read %d from %lld+%d to %p", 
 	    fragsize, dblk, blks, buf + (blks * BIOSCD_SECSIZE));
-	if (fragsize && bc_read(unit, dblk + blks, 1, fragbuf)) {
+	if (fragsize && bc_read(unit, dblk + blks, 1, fragbuf) != 1) {
+		if (blks) {
+			if (rsize)
+				*rsize = blks * BIOSCD_SECSIZE;
+			return (0);
+		}
 		DEBUG("frag read error");
 		return(EIO);
 	}
@@ -292,6 +303,7 @@
 /* Max number of sectors to bounce-buffer at a time. */
 #define	CD_BOUNCEBUF	8
 
+/* return negative value for an error, otherwise blocks read */
 static int
 bc_read(int unit, daddr_t dblk, int blks, caddr_t dest)
 {
@@ -368,6 +380,8 @@
 			result = V86_CY(v86.efl);
 			if (result == 0)
 				break;
+			/* fall back to 1 sector read */
+			x = 1;
 		}
 	
 #ifdef DISK_DEBUG
@@ -376,6 +390,11 @@
 		DEBUG("%d sectors from %lld to %p (0x%x) %s", x, dblk, p,
 		    VTOP(p), result ? "failed" : "ok");
 		DEBUG("unit %d  status 0x%x", unit, error);
+
+		/* still an error? break off */
+		if (result != 0)
+			break;
+
 		if (bbuf != NULL)
 			bcopy(bbuf, p, x * BIOSCD_SECSIZE);
 		p += (x * BIOSCD_SECSIZE);
@@ -384,7 +403,11 @@
 	}
 	
 /*	hexdump(dest, (blks * BIOSCD_SECSIZE)); */
-	return(0);
+
+	if (blks - resid == 0)
+		return (-1);		/* read failed */
+
+	return (blks - resid);
 }
 
 /*
Index: head/sys/boot/i386/libi386/biosdisk.c
===================================================================
--- head/sys/boot/i386/libi386/biosdisk.c
+++ head/sys/boot/i386/libi386/biosdisk.c
@@ -508,6 +508,18 @@
     if (rsize)
 	*rsize = 0;
 
+    if (dblk >= BD(dev).bd_sectors) {
+	DEBUG("IO past disk end %llu", (unsigned long long)dblk);
+	return (EIO);
+    }
+
+    if (dblk + blks > BD(dev).bd_sectors) {
+	/* perform partial read */
+	blks = BD(dev).bd_sectors - dblk;
+	size = blks * BD(dev).bd_sectorsize;
+	DEBUG("short read %d", blks);
+    }
+
     switch(rw){
     case F_READ:
 	DEBUG("read %d from %lld to %p", blks, dblk, buf);