[dm-devel] [RFC] Message ioctl direct to device

[Alasdair G Kergon]

On Fri, Jul 09, 2004 at 04:16:32PM -0400, Daniel Phillips wrote:
> Let's work though this nice and slowly please.  You're saying that LVM2 
> can go change the table, e.g., by inserting a mirror for pvmove, at any 
> time.  

Yes.  Applications like LVM2 should be free to insert new layers & split
targets up whenever they want.

> But if that happens, we can end sending the message to the wrong 
> target (e.g., a temporary mirror instead of the snapshot target) 

This is one of the complexities still to be worked out: how we 
see that the message (ie the ioctl "payload") gets passed on down 
to the right layer.

If it's done by index and there are multiple layers - no chance.  
If it's done by sector, I think it's possible.
And it probably requires that the "payload" strings conform to a 
standard too, so that the right target knows to intercept them.

[There are alternative approaches; intend to explore each of them
before making decisions.]

Alasdair
-- 
agk at redhat.com