[Ocfs2-tools-devel] Re: New patch for backup superblock against r1273 of ocfs2-tools

[Sunil Mushran]

tao.ma wrote:
> I am sure about this. Since the block is calculated from backup byte 
> offset and the least byte offset is 1G, with all the cluster size(from 
> 4K to 1M), they are all cluster-aligned. So these blocks num should be 
> the cluster start. Your option about fs_clustersize is right. I will 
> change it.
That may be so but for clarity sake use ocfs2_blocks_to_clusters().
 
> Yes, it is necessary. There is no place for releasing it. ocfs2_close 
> doesn't do the work for us.
Ok
 
> I am not quite sure of your modification of tunefs. Why you want to 
> take resize as a specific activity? I think it is a condition like the 
> change of volume and slot add. Just want to make the whole mechanism 
> clear?  It seems that the new backup offset is written twice in 
> update_backup_sb and refresh_backup_sb. And actually these two 
> functions almost do the same thing except that your function of 
> update_backup_sb will update the backup sb according to the 
> "newblocks" while refresh_backup_sb doesn't take it into 
> consideration. I have to admitted my old mechanism is a little 
> complex. So I will revise it and I think only one update_backup_sb is 
> needed here.

Let me try to explain this. In the scheme I am imagining, --backup-super 
will only be allowed alone.
As in, one will not be able to issue a resize or change label etc with 
--backup-super.

update_backup_sb's task is two fold. One is to add backup super 
retroactively to volumes not
having it (--backup-super). The other is to add new backup supers that 
are required when the
user is performing a resize. As in, user grows device from 3G to 5G on a 
volume having backup sb
compat set.

The refresh_backup_super is for operations like change label or uuid. If 
the backup super compat
is set, tune should refresh the existing backup supers too.

Lastly, it may be clearer if we call this feature backup super rather 
than backup sb. super is clearer
than sb.