Make log->disk_header 1 sector in size rather than the actual size of
the struct, since we can't read less than a sector.
--- diff/drivers/md/dm-log.c	2004-01-07 14:40:45.000000000 +0000
+++ source/drivers/md/dm-log.c	2004-01-14 14:42:18.000000000 +0000
@@ -389,7 +389,12 @@
 	lc->header_location.bdev = lc->log_dev->bdev;
 	lc->header_location.sector = 0;
 	lc->header_location.count = 1;
-	lc->disk_header = vmalloc(sizeof(struct log_header));
+
+	/*
+	 * We can't read less than this amount, even though we'll
+	 * not be using most of this space.
+	 */
+	lc->disk_header = vmalloc(1 << SECTOR_SHIFT);
 	if (!lc->disk_header)
 		goto bad;