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

Daniel Phillips phillips at redhat.com
Fri Jul 9 20:16:32 UTC 2004

On Friday 09 July 2004 13:51, Alasdair G Kergon wrote:
> On Fri, Jul 09, 2004 at 11:52:00AM -0500, Kevin Corry wrote:
> > On Thursday 08 July 2004 9:34 pm, Daniel Phillips wrote:
> > >   - What is the advantage of passing the sector address instead
> > >     a direct index into the target table?
> I believe it's easier in general for applications to work with the
> offset than it would be to work with the index (which will often
> be completely arbitrary).  The offset can be trusted to remain
> constant across a range of operations that change the index.
> [e.g. pvmove, remapping bad blocks etc.]

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.  But if that happens, we can end sending the message to the wrong 
target (e.g., a temporary mirror instead of the snapshot target) 
regardless of whether it's indexed by logical sector or ordinary index.  
Is that correct?



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