On Tue, 2009-07-07 at 13:51 -0400, Peter Jones wrote: > On 07/07/2009 01:12 PM, James Bottomley wrote: > > On Fri, 2009-06-26 at 09:56 -0400, Peter Jones wrote: > >> James, I think Chandra and I have responded to most if not all of your points, > >> and would appreciate your thoughts on what we've said. > > > > Well, you didn't respond to the important one: > > > > You're seeking to change the binding of these helpers from manual to > > automatic. This would mean that the modules are loaded in the single > > controller case, for which they may not be wanted and also when some > > multi path tool other than dm-mp is managing the device, in which case > > they may actively interfere with operations. Your basic contention is > > that you "don't see any concern here". > > I think Chandra addressed this in his reply to your previous email: I don't think so: > [From him] > > This is by design (of SCSI DH). We do want the device to be attached to > > its handler _irrespective_ of whether multipath comes along or not. > > > > BTW, there is _no_ infrastructure in multipath for handlers. They were > > removed from multipath when scsi dh came along. So, no worries about > > proprietary multipath handlers. Also, multipath _can_ attach a device to > > a different (SCSI) device handler if it finds that the one that is > > already attached is not the right one. I want to know what happens when some multipath system other than dm-mp tries to use a system with a device handler attached ... I don't see how that addresses the issue at all. The device handlers, when they're attached can alter sense and return code processing .. this has the potential to interfere with how the other multipath code is expecting things to happen If we have to get really concrete: what happens with something like powerpath and scsi_dh_emc attached? > [From you again] > > When I ask what testing you've done for either of these, the studied > > silence eloquently illustrates "none". A policy change like this > > can't be made without being incredibly sure we're not going to screw > > up existing installations. > > I'll let Chandra address this, as it is my understanding that he has > hardware and has tested this code with it. > > > The second point I made speaks to the technical ugliness of this: what > > you're basically doing is open coding multiple binding for a device > > handler specific case. If you can persuade me the policy above is > > correct, then technically all this should be done correctly via multiple > > binding in the generic device core ... before this interface nastiness > > you're constructing propagates outwards and becomes part of the user > > ABI. > > I'm willing to re-implement the functionality with a different mechanism > if it has your blessing, if you can be specific about what it is you think > would be better. Obviously I'll hold off on that until we've come to some > agreement about the other aspects. Well, the two things aren't so dependent: this dh_state attribute that hannes just NAK'd is precisely a binding attribute for your hand rolled multiple driver attachment, so actually getting generic device multiple binding sorted out would help out regardless of what the final attachment policy decision is. James -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
