Reverse lookup of inode/file from offset in raw device on linux and ext3/4?

I just had to do a similar thing, so I thought I'd share my solution.

You can see which partition a drive byte offset belongs to by checking the 'offset' and 'size' elements of the udisks --show-info output; e.g.

user@host:~$ sudo udisks --show-info /dev/sda1 | grep -i 'offset'
    offset:                    1048576
    alignment offset:          0

Subtract this offset from the disk offset to get the byte offset into the partition. So disk offset (10000000) in /dev/sda is partition offset (10000000 - 1048576) = 8951424 in /dev/sda1

You can find out how large blocks are in a partition using the following command:

user@host:~$ sudo tune2fs -l /dev/sda1  | grep -i 'block size'
Block size:               4096

Divide the partition byte offset by the block size to determine the block offset, in this case 8951424 / 4096 = 2185

Run the following command to find out what inode occupies that block:

user@host:~$ sudo debugfs -R "icheck 2185" /dev/sda1
debugfs 1.41.11 (14-Mar-2010)
Block   Inode number
2185    123456 

then the following command to find out what the filename is for that inode:

user@host:~$ sudo debugfs -R "ncheck 123456" /dev/sda1
debugfs 1.41.11 (14-Mar-2010)
Inode   Pathname
123456  /tmp/some-filename.txt

There's a longer description of how this at http://www.randomnoun.com/wp/2013/09/12/determining-the-file-at-a-specific-vmdk-offset