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Date: Fri, 14 Dec 2007 11:41:41 -0600
From: Eric Sandeen <sandeen@redhat.com>
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To: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
CC: ext4 development <linux-ext4@vger.kernel.org>,
       Mingming Cao <cmm@us.ibm.com>, Theodore Tso <tytso@mit.edu>
Subject: [PATCH] ext4: issue warning when bad inode found via ext4_lookup
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I have a hand-crafted bad filesystem image which has corruption:

[root@inode ~]# ls mnt/dir
file1  file2  file3  file4  file5
[root@inode ~]# ls mnt/dir/file4 
ls: cannot access mnt/dir/file4: No such file or directory
[root@inode ~]# ls -l mnt/dir
ls: cannot access mnt/dir/file4: No such file or directory
total 8
drwxr-xr-x 2 root root 1024 2007-09-04 13:36 file1
drwxr-xr-x 2 root root 1024 2007-09-04 13:36 file2
drwxr-xr-x 2 root root 1024 2007-09-04 13:36 file3
d????????? ? ?    ?       ?                ? file4
drwxr-xr-x 2 root root 1024 2007-09-04 13:36 file5

e2fsck also knows it's corrupted:
Pass 2: Checking directory structure
Entry 'file4' in /dir (2049) has deleted/unused inode 13.  Clear? no

Entry 'file4' in /dir (2049) has an incorrect filetype (was 2, should be 1).
Fix? no

Pass 3: Checking directory connectivity
Unconnected directory inode 2053 (/dir/???)

BUT there are no kernel messages logged anywhere because ext4_read_inode
silently makes a bad_inode in this case, so that stale NFS filehandles
aren't noisy.  However, when we encounter such a problem after a by-name
lookup, I think a warning is appropriate, as it indicates filesystem
corruption.

Signed-off-by: Eric Sandeen <sandeen@redhat.com
---

Index: linux-2.6.24-rc3/fs/ext4/namei.c
===================================================================
--- linux-2.6.24-rc3.orig/fs/ext4/namei.c
+++ linux-2.6.24-rc3/fs/ext4/namei.c
@@ -1050,6 +1050,9 @@ static struct dentry *ext4_lookup(struct
 			return ERR_PTR(-EACCES);
 
 		if (is_bad_inode(inode)) {
+			ext4_warning(inode->i_sb, __FUNCTION__,
+				     "bad inode %lu in dir #%lu",
+				     inode->i_ino, dir->i_ino);
 			iput(inode);
 			return ERR_PTR(-ENOENT);
 		}