#10850 NORM 12.1.0: zhashfs: use FIEMAP for detecting unused disk blocks

[Zarro Boogs per Child]

#10850: zhashfs: use FIEMAP for detecting unused disk blocks
------------------------------------+---------------------------------------
           Reporter:  dsd           |       Owner:  dsd          
               Type:  enhancement   |      Status:  closed       
           Priority:  normal        |   Milestone:  12.1.0       
          Component:  build-system  |     Version:  not specified
         Resolution:  fixed         |    Keywords:               
        Next_action:  code          |    Verified:  0            
Deployment_affected:                |   Blockedby:               
           Blocking:                |  
------------------------------------+---------------------------------------
Changes (by dsd):

  * status:  new => closed
  * resolution:  => fixed
  * milestone:  Future Release => 12.1.0


Comment:

 On new F17 builds, the resultant disk image includes holes - something
 (mke2fs?) is actively punching holes in the disk image, losing the marker
 that was put in place. So I've implemented the FIEMAP based approach which
 avoids this issue.

 I also tested that it performs the same as the existing format, by
 backporting it to olpc-os-builder 4.0.0 and rebuilding 11.3.0 four times,
 twice with the previous fill-based system and twice with FIEMAP.


 Values are: filesize of .zd image, line count of .zsp file (i.e. number of
 blocks)

 {{{
 Test 1 with existing fill-pattern code:
 2gb: 761274739, 12885
 4gb: 762773004, 13377
 8gb: 764029458, 14365

 Test 2 with existing fill-pattern code:
 2gb: 761222412, 12887
 4gb: 762941008, 13379
 8gb: 763959516, 14366

 Test 1 with FIEMAP:
 2gb: 760980361, 12881
 4gb: 762623007, 13371
 8gb: 763506946, 14360

 Test 2 with FIEMAP:
 2gb: 761056419, 12880
 4gb: 762560031, 13370
 8gb: 763454544, 14361
 }}}

 Overall the FIEMAP approach does not regress over the fill-pattern method;
 it could even be argued that FIEMAP is ever so slightly better.

-- 
Ticket URL: <http://dev.laptop.org/ticket/10850#comment:2>
One Laptop Per Child <http://laptop.org/>
OLPC bug tracking system