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Re: [PATCH] xfs: reserve fields in inode for parent ptr and alloc policy

To: Eric Sandeen <sandeen@xxxxxxxxxxx>
Subject: Re: [PATCH] xfs: reserve fields in inode for parent ptr and alloc policy
From: Rich Johnston <rjohnston@xxxxxxx>
Date: Wed, 10 Apr 2013 14:39:32 -0500
Cc: Mark Tinguely <tinguely@xxxxxxx>, <xfs@xxxxxxxxxxx>
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <5165B5CB.2070203@xxxxxxxxxxx>
References: <20130410182438.268267840@xxxxxxx> <5165B5CB.2070203@xxxxxxxxxxx>
User-agent: Mozilla/5.0 (X11; Linux i686; rv:13.0) Gecko/20120615 Thunderbird/13.0.1
On 04/10/2013 01:56 PM, Eric Sandeen wrote:
On 4/10/13 1:24 PM, Mark Tinguely wrote:
Reserve fields in new inode layout for parent pointer and
allocation policy.
The inode will hold the parent information for the first
link to a file. Information for the other links will be
held in extended attribute entries.

The "di_parino" is the inode of the parent directory. The
directory information for this entry is located the parent
directory with "di_paroff" offset.

The di_parino/di_paroff concept code is running.
The "di_allocpolicy" will be used to remember the allocation
policy associated with this inode.

can you say more about this allocation policy?


No its super secret information. ;)

Its on my plate Eric, because Mark was making a change for parent ptrs, I asked him to request space for allocation policies also.

I don't have all the details yet but here is a very high level concept.

Identify allocation groups by names (or numbers -- preferably using names
in user-visible areas), allowing many different areas. Placing the allocation
policy outside of user programs is necessary for this to be successful.

 Current thoughts on proposed a layered allocation policies:

    Policy for the entire filesystem
Policy attached to a directory (whose policy would be inherited by subdirectories when subdirectories are created)
    Policy for a single file

The policy would define:

   where to place file data
   where to place metadata for the files.
   a prefered allocation group for placing file data (for directories).


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