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

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Date:   Tue, 20 Aug 2019 19:55:19 +0200
From:   Cornelia Huck <cohuck@...hat.com>
To:     Alex Williamson <alex.williamson@...hat.com>
Cc:     Parav Pandit <parav@...lanox.com>, Jiri Pirko <jiri@...lanox.com>,
        "David S . Miller" <davem@...emloft.net>,
        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>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH v2 0/2] Simplify mtty driver and mdev core

On Tue, 20 Aug 2019 11:19:04 -0600
Alex Williamson <alex.williamson@...hat.com> wrote:

> What about an alias based on the uuid?  For example, we use 160-bit
> sha1s daily with git (uuids are only 128-bit), but we generally don't
> reference git commits with the full 20 character string.  Generally 12
> characters is recommended to avoid ambiguity.  Could mdev automatically
> create an abbreviated sha1 alias for the device?  If so, how many
> characters should we use and what do we do on collision?  The colliding
> device could add enough alias characters to disambiguate (we likely
> couldn't re-alias the existing device to disambiguate, but I'm not sure
> it matters, userspace has sysfs to associate aliases).  Ex.
> 
> UUID=$(uuidgen)
> ALIAS=$(echo $UUID | sha1sum | colrm 13)
> 
> Since there seems to be some prefix overhead, as I ask about above in
> how many characters we actually have to work with in IFNAMESZ, maybe we
> start with 8 characters (matching your "index" namespace) and expand as
> necessary for disambiguation.  If we can eliminate overhead in
> IFNAMESZ, let's start with 12.  Thanks,
> 
> Alex

I really like that idea, and it seems the best option proposed yet, as
we don't need to create a secondary identifier.