[Ocfs2-devel] ocfs2's bmap output

[Shaya Potter]

On Thu, 2005-10-13 at 23:12 -0700, Mark Fasheh wrote:
> Hi,
> 
> On Fri, Oct 14, 2005 at 01:33:35AM -0400, Shaya Potter wrote:
> > I'm guessing this is because of its use of extents, and probably means
> > I've screwed myself in trying to use bmap in this way.  Is that a
> > correct assumption?  Is there any other interface into OCFS2 to tell if
> > a block is a "blank" sparse area?
> Unfortunately, no. Since OCFS2 doesn't currently support sparse files, the
> "holes" created are actually allocated and filled with zeros. Once
> allocated, they'll look no different from other file data.
> 
> I suppose you could read back those clusters in a file to see if they have
> zero's, though that might not be particularly performant. Also, it would be
> impossible to differentiate between a block that was zero'd as part of
> a process file write versus a block which was zero'd as a hole.

or, I could make a bitmap file (on page boundary as that's what readpage
cares about), but my experience is that this is performant either.

thanks for the quick response.