Re: tail policy question

[Hans Reiser <reiser@namesys.com>]

Alex Zarochentsev wrote:

>On Thu, Nov 13, 2003 at 01:34:07PM -0500, Zhihui Zhang wrote:
>  
>
>>Thanks for your and Alex's reply.  I poke around a little bit more and
>>find out that the mkfs.c does use ITEM_TAIL40_ID, which happens to have
>>the same value as TAIL_ID (0x6) in the kernel file. 
>>    
>>
>
>they are from different name spaces.
>  
>

>  
>
>>However, I am confused
>>when I see the following in plugin.h:
>>
>>PLUGIN_BY_ID(item_plugin, REISER4_ITEM_PLUGIN_TYPE, item);
>>PLUGIN_BY_ID(tail_plugin, REISER4_TAIL_PLUGIN_TYPE, tail);
>>    
>>
>
>IFAIK above defines service functions for plugins of different types, 
>it does not define concrete plugins. tail_plugin_type should be named
>as tail_policy_plugin for better understanding.
>
>  
>
>>The item plugin has TAIL_ID if the item is of tail type. So what is the
>>use of a separate tail_plugin?  Plus, the tail_plugin has three IDs
>>defined: NEVER, ALWAYS, and DEFAULT, none of which has a value of 0x6. My
>>guess is that the item plugin for tails are used to manage tails (merge,
>>split, read, write?), 
>>    
>>
>
>yes
>
>  
>
>>while the tail_plugin is used to decide if a
>>conversion between tail format and extent format is needed.  If so, the
>>reiser4.h file should have:
>>
>>#define REISER4_TAIL_PLUGIN       (DEFAULT_TAIL_ID)
>>
>>instead of
>>
>>#define REISER4_TAIL_PLUGIN       (ALWAYS_TAIL_ID)
>>
>>Does this make sense? Please clarify this for me.  Thanks.
>>    
>>
>
>what i would like to see:
>rename *_TAIL_ID to *_TAIL_POLICY_ID
>DEFAULT_TAIL_POLICY__ID renamed to SMART_TAIL_POLICY_ID
>  
>
16K_TAIL_POLICY is more informative....

>#define REISER4_TAIL_POLICY_PLUGIN (one of SMART_TAIL_POLICY_ID ALWAYS_TAIL_POLICY_ID,
> NEVER_TAIL_POLICY_ID)
>
>Does it make things more clear?
>
>Thanks.
>  
>


-- 
Hans