Btrfs devel - Jul 2012 - Question about btrfs metadata structure

Hi!

I''m writing my bsc thesis about btrfs and I''m analyzing 
the
btrfs metadata structure at the moment.

I''m using fedora 17 with kernel 3.4 and btrfs-prog from 
your
git-repository. For an overview I use "btrfs-debug-tree" 
and
here are my questions:

The root tree contains some inode_items, but I don''t 
understand
the meaning of them:
item 4 key (ROOT_TREE_DIR INODE_ITEM 0) itemoff 3101 
itemsize 160
inode generation 3 size 0 block group 0 mode 40555 links 1

item 5 key (ROOT_TREE_DIR INODE_REF 6) itemoff 3089 
itemsize 12
inode ref index 0 namelen 2 name: ..

The key for an inode_item is objectid=ROOT_TREE_DIR. 
ROOT-TREE-DIR is the inode-Nr.?
What does offset=6 regarding INODE_REF mean? --> item 5

Also placed in the root tree, I''ve found entries of
(FREE_SPACE UNTYPED ....)
What does UNTYPED mean in this context and the offset is
the logical address of a block group (I guess...)? This
item has a pointer to an inode_item, is that right?

And last question about this entries:
item 2 key (FS_TREE INODE_REF 6) itemoff 3500 itemsize 17
  inode ref index 0 namelen 7 name: default
...
item 6 key (ROOT_TREE_DIR DIR_ITEM 2378154706) itemoff 
3052 itemsize 37
  location key (FS_TREE ROOT_ITEM 18446744073709551615) 
type 2
  namelen 7 datalen 0 name: default

There is an INODE_REF (again, offset 6...?) pointing to
which inode? I cannot find some...
What''s about that offset in location key (FS_TREE....)

Thx in advance for your patience and answers!

Regards
Guenther
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Hi,

closed by my debug output from btrfs-debug-tree regarding
my question above...

Günther
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Oops, here is the attachement...

On 07/25/2012 06:41 PM, Guenther Rasch wrote:
> Hi!
> 
> I''m writing my bsc thesis about btrfs and I''m analyzing
the
> btrfs metadata structure at the moment.
> 
> I''m using fedora 17 with kernel 3.4 and btrfs-prog from your
> git-repository. For an overview I use "btrfs-debug-tree" and
> here are my questions:
> 
> The root tree contains some inode_items, but I don''t understand
> the meaning of them:
> item 4 key (ROOT_TREE_DIR INODE_ITEM 0) itemoff 3101 itemsize 160
> inode generation 3 size 0 block group 0 mode 40555 links 1
> 
> item 5 key (ROOT_TREE_DIR INODE_REF 6) itemoff 3089 itemsize 12
> inode ref index 0 namelen 2 name: ..
> 
> The key for an inode_item is objectid=ROOT_TREE_DIR. ROOT-TREE-DIR is
> the inode-Nr.?
> What does offset=6 regarding INODE_REF mean? --> item 5
> 

I think you can find the answer by doing grep ROOT_TREE_DIR in btrfs-progs
source code. ;)
> Also placed in the root tree, I''ve found entries of
> (FREE_SPACE UNTYPED ....)
> What does UNTYPED mean in this context and the offset is
> the logical address of a block group (I guess...)? This
> item has a pointer to an inode_item, is that right?
> 

It''s free space cache, which refers to free-space-cache.c in
upstream''s code.
> And last question about this entries:
> item 2 key (FS_TREE INODE_REF 6) itemoff 3500 itemsize 17
>  inode ref index 0 namelen 7 name: default
> ...
> item 6 key (ROOT_TREE_DIR DIR_ITEM 2378154706) itemoff 3052 itemsize 37
>  location key (FS_TREE ROOT_ITEM 18446744073709551615) type 2
>  namelen 7 datalen 0 name: default
> 
> There is an INODE_REF (again, offset 6...?) pointing to
> which inode? I cannot find some...
> What''s about that offset in location key (FS_TREE....)
> 
> Thx in advance for your patience and answers!
> 
> Regards
> Guenther
> -- 
> To unsubscribe from this list: send the line "unsubscribe
linux-btrfs" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> 

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