[PATCH] fix disk geometry calculation for large disks

[Tom Coughlan <coughlan@xxxxxxxxxx>]

Testing with multi-terabyte disks shows that HDIO_GETGEO sometimes
returns heads=0. This causes parted to die with a Floating Point
Exception, among other possible effects. 

The problem occurs because several routines in scsicam_bios_param cast
sector_t capacity to unsigned long. 

The attached patch avoids this, by checking first to see if the capacity
exceeds the maximum allowed values for cylinder/sector/head
(65535*63*255). If so, just return those values right away. 

Tom

--- linux-2.6.12-rc3/drivers/scsi/scsicam.c.orig
+++ linux-2.6.12-rc3/drivers/scsi/scsicam.c
@@ -59,6 +59,15 @@ int scsicam_bios_param(struct block_devi
 	unsigned char *p;
 	int ret;
 
+	/* Are we above the max. allowed for cylinder/sector/head? */
+	if (capacity > 65535*63*255) {
+		ip[0] = 255;
+		ip[1] = 63;
+		ip[2] = 65535;
+
+		return 0;
+	}
+
 	p = scsi_bios_ptable(bdev);
 	if (!p)
 		return -1;
@@ -86,11 +95,7 @@ int scsicam_bios_param(struct block_devi
 			ip[0] = 64;
 			ip[1] = 32;
 		}
-
-		if (capacity > 65535*63*255)
-			ip[2] = 65535;
-		else
-			ip[2] = (unsigned long)capacity / (ip[0] * ip[1]);
+		ip[2] = (unsigned long)capacity / (ip[0] * ip[1]);
 	}
 
 	return 0;