Before VirtualBox is fixed, mark with #ifdef what has to be done to make

it possible to boot from ZFS RAIDZ for example from within VirtualBox.
The problem with VirtualBox is that its BIOS reports only one disk present.
If we choose to ignore this report, we can find all the disks available.
We can't have this work-around to be turned on by default, because some broken
BIOSes report true when it comes to number of disks, but present the same disk
multiple times.

sys/boot/i386/libi386/biosdisk.c

@@ -214,10 +214,12 @@ bd_init(void)
     /* sequence 0, 0x80 */
     for (base = 0; base <= 0x80; base += 0x80) {
 	for (unit = base; (nbdinfo < MAXBDDEV); unit++) {
+#ifndef VIRTUALBOX
 	    /* check the BIOS equipment list for number of fixed disks */
 	    if((base == 0x80) &&
 	       (nfd >= *(unsigned char *)PTOV(BIOS_NUMDRIVES)))
-	        break;
+		break;
+#endif
 
 	    bdinfo[nbdinfo].bd_unit = unit;
 	    bdinfo[nbdinfo].bd_flags = (unit < 0x80) ? BD_FLOPPY : 0;

sys/boot/i386/zfsboot/zfsboot.c

@@ -94,7 +94,7 @@ __FBSDID("$FreeBSD$");
 #define V86_CY(x)	((x) & 1)
 #define V86_ZR(x)	((x) & 0x40)
 
-#define BIOS_NUMDRIVES		0x475
+#define BIOS_NUMDRIVES	0x475
 #define DRV_HARD	0x80
 #define DRV_MASK	0x7f
 
@@ -667,7 +667,12 @@ main(void)
      * will find any other available pools and it may fill in missing
      * vdevs for the boot pool.
      */
-    for (i = 0; i < *(unsigned char *)PTOV(BIOS_NUMDRIVES); i++) {
+#ifndef VIRTUALBOX
+    for (i = 0; i < *(unsigned char *)PTOV(BIOS_NUMDRIVES); i++)
+#else
+    for (i = 0; i < MAXBDDEV; i++)
+#endif
+    {
 	if ((i | DRV_HARD) == *(uint8_t *)PTOV(ARGS))
 	    continue;