[Cluster-devel] [PATCH][try6] VFS: new want_holesize and got_holesize buffer_head flags for fiemap

[Bob Peterson <rpeterso@redhat.com>]

----- Original Message -----
> On Wed, Oct 22, 2014 at 08:28:53AM -0400, Bob Peterson wrote:
> > Yes, I thought about that.
> > One of my early prototypes had a separate function used by fiemap.
> > Function __generic_block_fiemap would call get_block() which
> > returned an indication of a hole as it does today. When it saw
> > the hole, fiemap called a new function get_hole_size() that was
> > passed in like get_block. The problem is: it's grossly inefficient,
> > since the new function get_hole_size() has to redo most of the work
> > that get_block just did (at least in the case of GFS2). (Which in the
> > case of a 1PB sparse file is non-trivial, since it involves several
> > levels of metadata indirection). Combining it with get_block made it
> > much more efficient.
> > 
> > Making a separate get_block_map_fiemap() function just seems like an
> > exercise in redundancy.
> 
> I was thinking of replacing get_blocks entirely.  We're not actually
> using a buffer_head in fiemap, so the interface seems somewhat awkward.
> If it used something like the iomap interface proposed by Dave long
> time ago we'd have a much saner interface that for example XFS could use
> as well.

Hi Christoph. Can you send a link to the thread regarding Dave's iomap?
proposal? I don't recall it offhand, so I don't know what it was or
why it was never implemented. I assume you mean Dave Chinner. Maybe it's
time to revisit the concept as a long-term solution.

In the meantime, do you otherwise object to this patch as a short-term
solution?

Regards,

Bob Peterson
Red Hat File Systems