Re: [RFC PATCH] Btrfs: export btrfs space shared info to userspace

[Liu Bo <bo.li.liu@oracle.com>]

On Wed, Aug 28, 2013 at 07:29:38PM +0200, David Sterba wrote:
> On Fri, Aug 16, 2013 at 04:27:28PM +0800, Liu Bo wrote:
> > Similar to ocfs2, btrfs also supports that extents can be shared by
> > different inodes, and there are some userspace tools requesting
> > for this kind of 'space shared infomation'.[1]
> > 
> > ocfs2 uses flag FIEMAP_EXTENT_SHARED, so does btrfs.
> 
> Looks ok to me.
> 
> > +			int ref_cnt = 0;
> 
> I think using long is cleaner here, it always fits into (void*), int
> does not.

Good point.

> 
> > +			/*
> > +			 * As btrfs supports shared space, this information
> > +			 * can be exported to userspace tools via
> > +			 * flag FIEMAP_EXTENT_SHARED.
> > +			 */
> > +			ret = iterate_inodes_from_logical(
> > +					em->block_start,
> > +					BTRFS_I(inode)->root->fs_info,
> > +					path, count_ext_ref, &ref_cnt);
> > +			if (ret < 0)
> > +				goto out_free;
> > +
> > +			if (ref_cnt > 1)
> > +				flags |= FIEMAP_EXTENT_SHARED;
> 
> AFAICS, e2fsprogs filefrag does not yet know about FIEMAP_EXTENT_SHARED.

With checking filefrag's code, it's easy to make filefrag aware of this
flag.

I'll make a patch for filefrag unless someone has already done it, thanks.

-liubo