On Sun, 14 Mar 2010 17:18:45 +0100 Miroslav Lachman <000....@quip.cz> wrote:

Well, it's pretty hairy.

Looking at findblk() it does this to go from disk block to file system block (this is greatly simplified)

file_system_blockno = disk_blockno >> fs_fsbtodb;

So conversely, you'd do disk_blockno = file_system_blockno << fs_fsbtodb.

You can get this information using "ffsinfo -l 0x001 -o some_file /dev/ataXY" (using ahci) and grep'ing for fsbtodb in some_file. The 0x001 means to only dump the first super block.

I looked at a file system which has default 16kB file system blocks and fsbtodb is 2 ==> *multiply file_system_block by 4 not 32*. This is probably because it's a multiple of a 4kB block, which is the smallest usable file system block size AFAIK.

BTW looking at the code leads me to conclude that fsdb will not print out anything if the disk block you're trying to find has bever been allocated to an inode ==> unused disk block, safe to overwrite. This assumes that you calculated the disk block correctly.