linux-ext4 - Re: [PATCH 08/11] ext4: introduce subtree logic

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Message-id: <494905CF-659F-4F8E-ACB3-D0030CE69B6C@sun.com>
Date:	Mon, 08 Feb 2010 17:49:51 -0700
From:	Andreas Dilger <adilger@....com>
To:	Dmitry Monakhov <dmonakhov@...nvz.org>
Cc:	linux-ext4@...r.kernel.org, Jan Kara <jack@...e.cz>
Subject: Re: [PATCH 08/11] ext4: introduce subtree logic

On 2010-02-08, at 06:28, Dmitry Monakhov wrote:
>  A subtree of a directory tree T is a tree consisting of a directory
>  (the subtree root) in T and all of its descendants in T.
>
>  Subtree feature allows to create an isolated (from user point of  
> view)
>  trees.
>
>  Subtree assumptions:
>  (1) Each inode has subtree id. This id is persistently stored inside
>      inode (xattr, usually inside ibody)
>  (2) Subtree id is inherent from parent directory
>  (3) Inode can not belongs to different subtree
>      Otherwise changes in one subtree result in changes in other  
> subtree
>      which contradict to isolation criteria.
>
>  This feature is similar to project-id in XFS. One may assign some  
> id to
>  a subtree. Each entry from the subtree may be accounted in directory
>  subtree quota. Will appear in later patches.
>
> * Disk layout
>  Subtree id is stored on disk inside xattr usually inside ibody.
>  Xattr is used only as a data storage, It has not user visiable xattr
>  interface.


Presumably this would need e2fsck support, in order to ensure that  
inodes in a given directory have the same subtree ID as the parent  
directory.

Also, how are the subtree IDs generated, to ensure that they are  
unique between subtrees?

Cheers, Andreas
--
Andreas Dilger
Sr. Staff Engineer, Lustre Group
Sun Microsystems of Canada, Inc.

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