Yesterday I had to fix a badly broken disk, and found that fsck kept dying:

  DIR I=64512 CONNECTED. PARENT WAS I=4032
  fsck: cannot find inode 995904

fsdb found the inodes with no problem:

  fsdb (inum: 64512)> inode 995904
  current inode: directory
  I=995904 MODE=40777 SIZE=512
        MTIME=Feb 14 15:27:07 2000 [0 nsec]
        CTIME=Feb 14 15:27:07 2000 [0 nsec]
        ATIME=Feb 24 10:31:58 2000 [0 nsec]
  OWNER=nobody GRP=nobody LINKCNT=4 FLAGS=0 BLKCNT=2 GEN=38a41386
  Direct blocks: 8094568 0 0 0 0 0 0 0 0 0 0 0
  Indirect blocks:  0 0 0

The problem turns out to be a program logic error in fsck.  It stores
directory inodes internally in hash lists, using the number of
directories to form the hash key:

        inpp = &inphead[inumber % numdirs];

Elsewhere, however, it increments numdirs when it finds unattached
directories.  I've made the following fix, which solved the problem in
the case in hand.

Submitted by:	Greg Lehey <grog@lemis.com>
Reviewed by:	Matthew Dillon <dillon@apollo.backplane.com>
Approved by:	Kirk McKusick <mckusick@mckusick.com>

3 files changed, 4 insertions, 3 deletions

diff --git a/sbin/fsck_ifs/fsck.h b/sbin/fsck_ifs/fsck.h
index f7ac12c..9d59c8f 100644
--- a/sbin/fsck_ifs/fsck.h
+++ b/sbin/fsck_ifs/fsck.h
@@ -182,7 +182,7 @@ struct inoinfo {
 	u_int	i_numblks;		/* size of block array in bytes */
 	ufs_daddr_t i_blks[1];		/* actually longer */
 } **inphead, **inpsort;
-long numdirs, listmax, inplast;
+long numdirs, dirhash, listmax, inplast;
 long countdirs;			/* number of directories we actually found */
 
 char	*cdevname;		/* name of device being checked */
diff --git a/sbin/fsck_ifs/inode.c b/sbin/fsck_ifs/inode.c
index 98295be..dbf86f7 100644
--- a/sbin/fsck_ifs/inode.c
+++ b/sbin/fsck_ifs/inode.c
@@ -396,7 +396,7 @@ cacheino(dp, inumber)
 		malloc(sizeof(*inp) + (blks - 1) * sizeof(ufs_daddr_t));
 	if (inp == NULL)
 		errx(EEXIT, "cannot increase directory list");
-	inpp = &inphead[inumber % numdirs];
+	inpp = &inphead[inumber % dirhash];
 	inp->i_nexthash = *inpp;
 	*inpp = inp;
 	inp->i_parent = inumber == ROOTINO ? ROOTINO : (ino_t)0;
@@ -424,7 +424,7 @@ getinoinfo(inumber)
 {
 	register struct inoinfo *inp;
 
-	for (inp = inphead[inumber % numdirs]; inp; inp = inp->i_nexthash) {
+	for (inp = inphead[inumber % dirhash]; inp; inp = inp->i_nexthash) {
 		if (inp->i_number != inumber)
 			continue;
 		return (inp);
diff --git a/sbin/fsck_ifs/setup.c b/sbin/fsck_ifs/setup.c
index 0df8e98..49bbc8d 100644
--- a/sbin/fsck_ifs/setup.c
+++ b/sbin/fsck_ifs/setup.c
@@ -286,6 +286,7 @@ setup(dev)
 		goto badsb;
 	}
 	numdirs = sblock.fs_cstotal.cs_ndir;
+	dirhash = numdirs;
 	if (numdirs == 0) {
 		printf("numdirs is zero, try using an alternate superblock\n");
 		goto badsb;