Block allocation in EXT4

Block allocation in EXT4

[Subranshu Patel]

 In EXT4 it seems that both direct/indirect and extent tree based
block allocation is used. I used debugfs and it seems that the root
inode uses the direct/indirect block allocation. The other files and
direcyories used extent based allocation.

Do all the EXT4 reserved inode (0 -11) use the direct/indirect
allocation scheme?

Re: Block allocation in EXT4

[Felipe Monteiro de Carvalho]

Hello,

I'm no expert, but I think that you should read i_node.i_flags and
check it for the flag EXT4_EXTENTS_FL to determine which inodes use
the old or the new (extents) method of allocation.

I'm not sure what your objective is, so hopefully this helps something =)

-- 
Felipe Monteiro de Carvalho

Re: Block allocation in EXT4

[Eric Sandeen]

On 8/26/13 10:55 AM, Subranshu Patel wrote:
>  In EXT4 it seems that both direct/indirect and extent tree based
> block allocation is used. I used debugfs and it seems that the root
> inode uses the direct/indirect block allocation. The other files and
> direcyories used extent based allocation.
> 
> Do all the EXT4 reserved inode (0 -11) use the direct/indirect
> allocation scheme?

Nope; looks like a leftover oddity from old mkfs.

mkfs-time created dirs weren't created w/ the extents flag until:

commit 1afb468b9a80031b39eab37272709f45727fb221
Author: Theodore Ts'o <tytso@mit.edu>
Date:   Fri Jun 10 13:58:18 2011 -0400

    libext2fs: create extent-based directories if the extents feature is enabled
    
    This allows mke2fs to create the root and lost+found directories using
    extents.
    
    Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

so newly mkfs'd filesystems w/ newer e2fsprogs shouldn't exhibit
what you see.

-Eric