[SCSI] sd: tell the user when a disk's capacity is adjusted

This patch (as1188) combines the tests for decrementing a drive's
reported capacity and expands the comment.  It also adds an
informational message to the system log, informing the user when the
reported value has been changed.
Signed-off-by: NAlan Stern <stern@rowland.harvard.edu>
Signed-off-by: NJames Bottomley <James.Bottomley@HansenPartnership.com>

drivers/scsi/sd.c

@@ -1383,18 +1383,22 @@ sd_read_capacity(struct scsi_disk *sdkp, unsigned char *buffer)
 		sd_read_protection_type(sdkp, buffer);
 	}	
 
-	/* Some devices return the total number of sectors, not the
-	 * highest sector number.  Make the necessary adjustment. */
-	if (sdp->fix_capacity) {
+	/* Some devices are known to return the total number of blocks,
+	 * not the highest block number.  Some devices have versions
+	 * which do this and others which do not.  Some devices we might
+	 * suspect of doing this but we don't know for certain.
+	 *
+	 * If we know the reported capacity is wrong, decrement it.  If
+	 * we can only guess, then assume the number of blocks is even
+	 * (usually true but not always) and err on the side of lowering
+	 * the capacity.
+	 */
+	if (sdp->fix_capacity ||
+	    (sdp->guess_capacity && (sdkp->capacity & 0x01))) {
+		sd_printk(KERN_INFO, sdkp, "Adjusting the sector count "
+				"from its reported value: %llu\n",
+				(unsigned long long) sdkp->capacity);
 		--sdkp->capacity;
-
-	/* Some devices have version which report the correct sizes
-	 * and others which do not. We guess size according to a heuristic
-	 * and err on the side of lowering the capacity. */
-	} else {
-		if (sdp->guess_capacity)
-			if (sdkp->capacity & 0x01) /* odd sizes are odd */
-				--sdkp->capacity;
 	}
 
 got_data: