[Ocfs2-tools-devel] Re: [Ocfs2-devel] [patch 1/1] offline de-fragmentation tool

[wengang wang]

tao.ma wrote:
>
>
> wengang wang wrote:
>>
>>
>> tao.ma wrote:
>>>
>>>
>>> wengang wang wrote:
>>>> added/revised some lines.
>>>> and what's important, I don't know how to write ordering -- make 
>>>> use of jbd?
>>> No, you just need to be very careful of your writing order so that 
>>> any corruption after any operation will be either harmless or can be 
>>> recovered by fsck.ocfs2. So this may means that you need to revise 
>>> fsck.ocfs2 also to fix the corruption your tool do to the volume.
>>> Good luck and enjoy it. ;)
>> while, for example, power down when committing a group to disk, and 
>> the bitmap was written to disk partially.
>> for fsck.ocfs2, how to determine whether the bitmap is good?
> Do you mean you change the group's bitmap and want to commit?
> A group descriptor including its bitmap is contained in a block, not a 
> cluster. so it is the block driver that guarantee this block is 
> written as a whole not us.
>
I meant the above.
block driver can not guarantee this.
block concept in ocfs2 is not the same as it in block device.
a block in ocfs2 can include 1,2,4... blocks of a block device.
while, block device hardware can only guarantee one block (normally 512 
bytes) to be written with consistency, not several blocks.

> If you mean change the group descriptor and chain information of the 
> inode, then you can do like this:
> 1. update the inode. so if panic after this, fsck will recover the 
> inode according to the group descriptor.
> 2. update the group descriptor.