[Bug 12534] New: ext4 extent structure backwards

[Bug 12534] New: ext4 extent structure backwards

[bugme-daemon]

http://bugzilla.kernel.org/show_bug.cgi?id=12534

           Summary: ext4 extent structure backwards
           Product: File System
           Version: 2.5
     KernelVersion: 2.6.28
          Platform: All
        OS/Version: Linux
              Tree: Mainline
            Status: NEW
          Severity: normal
          Priority: P1
         Component: ext4
        AssignedTo: fs_ext4@kernel-bugs.osdl.org
        ReportedBy: markus@cs.wisc.edu


Latest working kernel version: 2.6.28
Earliest failing kernel version: 2.6.28
Distribution: Gentoo
Hardware Environment: i686

I was figuring out ext4 with hexedit (don't ask), and I noticed that the extent
structure is backwards.  It's defined in ext4_extents.h with this order:

block(32-bit), len(16), start_hi(16), start_lo(32)

Here's what I see (including 12 byte header):

0A F3 01 00  04 00 00 00  00 00 00 00
00 00 00 00  01 00 00 00  3E 17 13 00
(another 36 bytes of zeros)

You can see that the block is 0x13173e, len is 1, and start is 0.  (The
header's just fine, and only says that there is 1 extent and there can be no
more than 4 extents.)


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[Bug 12534] ext4 extent structure backwards

[bugme-daemon]

http://bugzilla.kernel.org/show_bug.cgi?id=12534


sandeen@redhat.com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         AssignedTo|fs_ext4@kernel-bugs.osdl.org|sandeen@redhat.com
             Status|NEW                         |ASSIGNED




------- Comment #1 from sandeen@redhat.com  2009-01-24 08:07 -------
It'd be a good trick to have the on-disk format not match the header ;)

For this file:

debugfs:  stat testfile
Inode: 12   Type: regular    Mode:  0644   Flags: 0x80000
Generation: 1797761550    Version: 0x00000000:00000001
User:     0   Group:     0   Size: 98304
File ACL: 0    Directory ACL: 0
Links: 1   Blockcount: 128
Fragment:  Address: 0    Number: 0    Size: 0
 ctime: 0x497b8705:5cc91558 -- Sat Jan 24 15:24:21 2009
 atime: 0x497b86f8:c29715dc -- Sat Jan 24 15:24:08 2009
 mtime: 0x497b8705:5cc91558 -- Sat Jan 24 15:24:21 2009
crtime: 0x497b86f8:c29715dc -- Sat Jan 24 15:24:08 2009
Size of extra inode fields: 28
Extended attributes stored in inode body: 
  selinux = "unconfined_u:object_r:file_t:s0\000" (32)
BLOCKS:
(8-23):9256-9271
TOTAL: 16

(logical start 0x8, len 0x10, physical start 0x2428)

the inode looks like this:

00421b00  a4 81 00 00 00 80 01 00  f8 86 7b 49 4b 87 7b 49  |..........{IK.{I|
00421b10  05 87 7b 49 00 00 00 00  00 00 01 00 80 00 00 00  |..{I............|
00421b20  00 00 08 00 01 00 00 00  0a f3 01 00 04 00 00 00  |................|
00421b30  00 00 00 00 08 00 00 00  10 00 00 00 28 24 00 00  |............($..|
00421b40  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
*
00421b60  00 00 00 00 0e aa 27 6b  00 00 00 00 00 00 00 00  |......'k........|
00421b70  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00421b80  1c 00 00 00 6c 19 d5 e2  58 15 c9 5c dc 15 97 c2  |....l...X..\....|
00421b90  f8 86 7b 49 dc 15 97 c2  00 00 00 00 00 00 02 ea  |..{I............|
00421ba0  07 06 40 00 00 00 00 00  20 00 00 00 00 00 00 00  |..@..... .......|
00421bb0  73 65 6c 69 6e 75 78 00  04 01 38 00 00 00 00 00  |selinux...8.....|
00421bc0  05 00 00 00 00 00 00 00  61 74 74 72 00 00 00 00  |........attr....|
00421bd0  00 00 00 00 00 00 00 00  76 34 6c 75 65 00 00 00  |........v4lue...|
00421be0  75 6e 63 6f 6e 66 69 6e  65 64 5f 75 3a 6f 62 6a  |unconfined_u:obj|
00421bf0  65 63 74 5f 72 3a 66 69  6c 65 5f 74 3a 73 30 00  |ect_r:file_t:s0.|

An extent looks like this:
struct ext4_extent {
        __le32  ee_block;       /* first logical block extent covers */
        __le16  ee_len;         /* number of blocks covered by extent */
        __le16  ee_start_hi;    /* high 16 bits of physical block */
        __le32  ee_start_lo;    /* low 32 bits of physical block */
};

The extents portion is here:
                                   0a f3 01 00 04 00 00 00  |................|
00421b30  00 00 00 00 08 00 00 00  10 00 00 00 28 24 00 00  |............($..|
                    ^logical 0x8^  ^len^ ^ hi^  ^start lo^
                                    0x16   0      0x2428

There is nothing wrong with this; you are just looking at it wrong.


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