development APIs for used/free blocks information

[Benjamin Wirth]

Hi David,

I proceeded to parse the on-disk free blocks BTree for finding the free blocks information. Is there a way I could force a flush of BTree information to disk, so that in an online filesystem that is being changed I can also handle the changes in the BTree?

I was looking at XFS_FSOP_GOING_FLAGS_LOGFLUSH flag but it might do more then I need to do and actually shutdown the filesystem. Any other options? I don't mind about performance degradation so interested in any option.

Thanks,
Ben

-----Original Message-----
From: Dave Chinner [mailto:david at fromorbit.com] 
Sent: Wednesday, April 27, 2016 7:41 PM
To: Benjamin Wirth
Cc: xfs at oss.sgi.com
Subject: Re: development APIs for used/free blocks information

On Wed, Apr 27, 2016 at 12:54:24PM +0000, Benjamin Wirth wrote:
> Hello Dave,
> 
> Thanks for your response.
> 
> And I apologize, reading back my email I wasn't clear about what I was 
> looking for.
> 
> I want to be able to query which blocks are free or used, not just the 
> counts. In EXT I was able to use ext2fs_test_block_bitmap() for that. 
> XFS has a BTree with the free extents ordered by block number which I 
> was hoping to be able to access from user-space, but couldn't find any 
> APIs for it (or the headers containing the structure definitions) in 
> the xfsprogs-devel package. Am I trying to do something impossible 
> here?

There are prototypes that need a bit of polishing to complete:

http://oss.sgi.com/archives/xfs/2016-04/msg00633.html

Cheers,

Dave.
--
Dave Chinner
david at fromorbit.com