Look at the superblock magic number before attempting to read the address

of the first alternate out of it.  If the magic number doesn't match one
of our known numbers, the primary is invalid and we have no way of locating
an alternate.  Bail out in that case.

Makes fsck_lfs work for LFS64, at least in the minimal sense of being able
to report that a newly created LFS64 has no errors.

Author: perseant

sbin/fsck_lfs/lfs.c

@@ -1,4 +1,4 @@
-/* $NetBSD: lfs.c,v 1.75 2020/04/03 19:36:33 joerg Exp $ */
+/* $NetBSD: lfs.c,v 1.76 2025/10/12 01:44:26 perseant Exp $ */
 /*-
  * Copyright (c) 2003 The NetBSD Foundation, Inc.
  * All rights reserved.
@@ -449,8 +449,12 @@ check_sb(struct lfs *fs)
 		break;
 	    default:
 		printf("Superblock magic number (0x%lx) does not match "
-		       "expected 0x%lx\n", (unsigned long) magic,
-		       (unsigned long) LFS_MAGIC);
+		       "any of the expected 0x%lx, 0x%lx, 0x%lx or 0x%lx\n",
+		       (unsigned long)magic,
+		       (unsigned long)LFS_MAGIC,
+		       (unsigned long)LFS_MAGIC_SWAPPED,
+		       (unsigned long)LFS64_MAGIC,
+		       (unsigned long)LFS64_MAGIC_SWAPPED);
 		return 1;
 	}
 
@@ -508,14 +512,35 @@ lfs_init(int devfd, daddr_t sblkno, daddr_t idaddr, int dummy_read, int debug)
 		bp->b_flags |= B_INVAL;
 		brelse(bp, 0);
 
+		/*
+		 * Look at the magic number before validating the rest
+		 * of the superblock.  If the magic number is bad, too,
+		 * we don't know where to look for an alternate superblock
+		 * either; so bail out now.
+		 */
+		switch (fs->lfs_dlfs_u.u_32.dlfs_magic) {
+		case LFS_MAGIC:
+		case LFS_MAGIC_SWAPPED:
+			break;
+			
+		case LFS64_MAGIC:
+		case LFS64_MAGIC_SWAPPED:
+			fs->lfs_is64 = true;
+			break;
+			
+		default:
+			return NULL;
+		}
+		
+
 		dev_bsize = lfs_sb_getfsize(fs) >> lfs_sb_getfsbtodb(fs);
 
 		if (tryalt) {
 			(void)bread(devvp, LFS_FSBTODB(fs, lfs_sb_getsboff(fs, 1)),
 		    	LFS_SBPAD, 0, &bp);
 			altfs = ecalloc(1, sizeof(*altfs));
 			memcpy(&altfs->lfs_dlfs_u, bp->b_data,
-			       sizeof(struct dlfs));
+			       sizeof(altfs->lfs_dlfs_u));
 			altfs->lfs_devvp = devvp;
 			bp->b_flags |= B_INVAL;
 			brelse(bp, 0);
@@ -667,7 +692,7 @@ try_verify(struct lfs *osb, struct uvnode *devvp, daddr_t goal, int debug)
 			break;
 		}
 		if (debug)
-			pwarn("summary good: 0x%x/%d\n", (uintmax_t)daddr,
+			pwarn("summary good: 0x%jx/%d\n", (uintmax_t)daddr,
 			      (int)lfs_ss_getserial(osb, sp));
 		assert (bc > 0);
 		odaddr = daddr;