linux-kernel - Re: [PATCH v2 0/2] Simplify mtty driver and mdev core

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Date:   Wed, 14 Aug 2019 10:01:35 +0200
From:   Cornelia Huck <cohuck@...hat.com>
To:     Parav Pandit <parav@...lanox.com>
Cc:     Alex Williamson <alex.williamson@...hat.com>,
        Kirti Wankhede <kwankhede@...dia.com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "cjia@...dia.com" <cjia@...dia.com>
Subject: Re: [PATCH v2 0/2] Simplify mtty driver and mdev core

On Wed, 14 Aug 2019 05:54:36 +0000
Parav Pandit <parav@...lanox.com> wrote:

> > > I get that part. I prefer to remove the UUID itself from the structure
> > > and therefore removing this API makes lot more sense?  
> > 
> > Mdev and support tools around mdev are based on UUIDs because it's defined
> > in the documentation.    
> When we introduce newer device naming scheme, it will update the documentation also.
> May be that is the time to move to .rst format too.

You are aware that there are existing tools that expect a uuid naming
scheme, right?

> 
> > I don't think it's as simple as saying "voila, UUID
> > dependencies are removed, users are free to use arbitrary strings".  We'd need
> > to create some kind of naming policy, what characters are allows so that we
> > can potentially expand the creation parameters as has been proposed a couple
> > times, how do we deal with collisions and races, and why should we make such
> > a change when a UUID is a perfectly reasonable devices name.  Thanks,
> >  
> Sure, we should define a policy on device naming to be more relaxed.
> We have enough examples in-kernel.
> Few that I am aware of are netdev (vxlan, macvlan, ipvlan, lot more), rdma etc which has arbitrary device names and ID based device names.
>  
> Collisions and race is already taken care today in the mdev core. Same unique device names continue.

I'm still completely missing a rationale _why_ uuids are supposedly
bad/restricting/etc. We want to uniquely identify a device, across
different types of vendor drivers. An uuid is a unique identifier and
even a well-defined one. Tools (e.g. mdevctl) are relying on it for
mdev devices today.

What is the problem you're trying to solve?