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

[Rich Johnston <rjohnston@sgi.com>]

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?
>
> -Eric

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).

--Rich

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