GEOM architecture and the (lack of) need for foot-shooting

[Andrey Chernov]

On Thu, Apr 07, 2005 at 11:18:17PM -0700, Marcel Moolenaar wrote:
> >It bring some problems like illegal on-disk modification synced to
> >in-core.
> 
> Q: what would you consider illegal on-disk modifications?

F.e. one can temporary remove whole BSD partition for other OS better 
install, then re-create it again inside other OS.

> > Since on-disk editing is not controlled (and should not be), it
> >may overlap or be incorrect in some other way.
> 
> Q: why is on-disk editing not controlled and why shouldn't it be?

There was a cases when filesystem is damaged, sectors goes off partition 
limits, etc. There must be temporary way to fix - to write bigger 
(overlap) partition, grab needed files, then restore correct one.

It can be controlled minimally with warnings, but not with disalowing.

> > But, if you edit in-core
> >partition instead, as I suggest, you can do all sorts of checking and
> >safety, easily excluding overlaps, etc.
> 
> I can't say I buy into that. I don't see how in-core editing can be 
> better
> checked than on-disk editing. Can you explain?

In-core editing always suppose currently running correct partition table. 
It must not allow to add, say, overlaping partition entry. On-disk editing 
should allow to write incorrect partition table for temporary disk surgery 
purposes.

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