rbd: temp layering support

Pretend we support layering...

Signed-off-by: Alex Elder <elder@inktank.com>
rbd: probe the parent of an image if present

Call the probe function for the parent device.

Signed-off-by: Alex Elder <elder@inktank.com>
rbd: define rbd object request flags field

We're going to need some more Boolean values for object requests,
so create a flags bit field and use it to record whether the request
is done.

Signed-off-by: Alex Elder <elder@inktank.com>
rbd: add object request flag for image data objects

Add a flag to distinguish between object requests being done on
standalone objects and requests being sent for objects representing
rbd image data (i.e., object requests that are the result of image
request).

Signed-off-by: Alex Elder <elder@inktank.com>
rbd: implement layered reads

First try.  It works, but it needs a LOT of testing.

Signed-off-by: Alex Elder <elder@inktank.com>
rbd: add an object exists flag

Used for pre-checking for a layered write.

Signed-off-by: Alex Elder <elder@inktank.com>
rbd: try layered write stuff

Not done.

Signed-off-by: Alex Elder <elder@inktank.com>
rbd: more layered write crapola

That is all.

Signed-off-by: Alex Elder <elder@inktank.com>
rbd: implement a synchronous stat function

This is for testing the stat operation.

Signed-off-by: Alex Elder <elder@inktank.com>