on architecture of dumping

[Andriy Gapon]

I think that the following is quite obvious, but it needs to be said anyway.

I think that we should switch from current approach of hierarchically configuring
dumper to having a hierarchy of dumpers.

Right now only disks provide dumping routines and the layers above disks can only
set offset and size of dump area. This results in the following limitations:
1. dump can be made only to contiguous area of a disk
2. dump can be made only to a single disk

Having a hierarchy of dumpers is a need that arises from having a GEOM hierarchy.
I think that each compliant GEOM provider could expose a dump method for writing
out a blob of data to certain offset within the provider. Such a dump routine
would dispatch data to dump methods of underlying provider(s) according to
provider's logic. Disk providers would have almost the same dump routines as they
do now (they are actually in disk drivers).

This would allow, for example, mirrored dumping to gmirror devices.
And this would pave a way for porting dumping to a zvol from OpenSolaris.

Please comment.
Thank you.

-- 
Andriy Gapon