Type of filesystem block

Type of filesystem block

[Subranshu Patel]

Query related to finding the block usage information of metadata
blocks in ext4 filesystem.

Using debugfs testb command I can check whether a particular
filesystem block is used or not.
# debugfs -R "testb 171428" /dev/sdd4
debugfs 1.41.12 (17-May-2010)
Block 171428 marked in use

Also its icheck command prints the inode associated, if any, with a
filesystem block.
# debugfs -R "icheck 171428" /dev/sdd4
debugfs 1.41.12 (17-May-2010)
Block     Inode number
171428    65152
But I don’t find any  debugfs command which can show similar block
usage information about metadata blocks, whether it is a superblock,
or inode bitmap block or block group descriptor, etc.
Is there any way to extract the usage information of metadata blocks
in ext4 filesystem ?
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Re: Type of filesystem block

[Theodore Ts'o]

On Sun, Mar 24, 2013 at 10:05:12PM +0530, Subranshu Patel wrote:
> But I don’t find any  debugfs command which can show similar block
> usage information about metadata blocks, whether it is a superblock,
> or inode bitmap block or block group descriptor, etc.
> Is there any way to extract the usage information of metadata blocks
> in ext4 filesystem ?

There isn't one today.  Normally I'll just look it up using the output
of dumpe2fs.

What's the use case where you need to get that information?  We could
add that as a new feature into debugfs, but it might be helpful to
understand the circumstances where you're needing that feature to
understand how best to add it into debugfs (or maybe some other
e2fsprogs command, such as e2fsck --- although in many cases e2fsck
has some of this already).

						- Ted
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