[dm-devel] Re: LVM on dmraid breakage

[Phillip Susi]

Luca Berra wrote:
> On Fri, Aug 03, 2007 at 02:10:02PM -0400, Phillip Susi wrote:
>> I agree with moving the partition detection code to user space, but 
>> trying to undo it after the fact doesn't help because udev is already 
>> processing the add events.  Also you do not need to remove the 
>> partitions so long as pvscan understands that it shouldn't be using them.
> which is the modification i proposed to lvm tools, isn't it?

You suggested deleting the partition table after it has already been 
detected.  I am saying that while I agree in principal that partition 
detection should be moved out of the kernel, for now, it is in there and 
deleting them after they have already been detected doesn't help matters 
because pvscan may already be running on them.

>> Udev is supposed to be the new model for enumerating devices and 
> i know that, and i will withdraw from this discussion, since it might
> get to an useless flame war.
> 
> Is there any technical reason for not having lvm tools filter out 
> devices that
> are used by device mapper?
> 
> besides dmraid, think of multipath.

None that I can see at the moment, but that doesn't mean there isn't 
one, or won't be one in the future.  The other problem is that there are 
likely other factors besides being used already as a dm target that 
might give reason for lvm to not scan the volume.  These kind of policy 
decisions seem like they should be made by udev rather than hard coded 
into lvm.  If the admin wants a policy where lvm should look at volumes, 
or indeed, maybe only certain volumes, that already happen to be dm 
targets, he should be able to do that.  Likewise, there may be some 
other reason to not look at a disk for lvm pvs.  Editing a conf file to 
specify a filter list of devices by name is all well and good for a 
static system, but it does not play well in the modern udev managed plug 
and play world.