Tighten the DVA validity check, as requested by @amotin

Every non-embedded, non-hole BP should have at least one valid DVA, and
it must be the first one.

Signed-off-by:	Alan Somers <[email protected]>

Author: asomers

module/zfs/zio.c

@@ -1212,9 +1212,10 @@ zfs_blkptr_verify(spa_t *spa, const blkptr_t *bp,
 			    bp, (longlong_t)BPE_GET_PSIZE(bp));
 		}
 		return (errors == 0);
-	}
-	if (unlikely(!BP_IS_EMBEDDED(bp) && !BP_IS_HOLE(bp) &&
-	    BP_GET_NDVAS(bp) <= 0)) {
+	} else if (BP_IS_HOLE(bp)) {
+		/* Holes are allowed (expected, even) to have no DVAs */
+	} else if (unlikely(!DVA_IS_VALID(&bp->blk_dva[0]))) {
+		/* Non-hole, non-embedded BPs _must_ have at least one DVA */
 		errors += zfs_blkptr_verify_log(spa, bp, blk_verify,
 		    "blkptr at %px has no valid DVAs", bp);
 	}