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

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Message-ID: <AM0PR05MB48660532A1A063FF1BD5E4AED1AA0@AM0PR05MB4866.eurprd05.prod.outlook.com>
Date:   Wed, 21 Aug 2019 03:57:19 +0000
From:   Parav Pandit <parav@...lanox.com>
To:     Cornelia Huck <cohuck@...hat.com>,
        Alex Williamson <alex.williamson@...hat.com>
CC:     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 <cjia@...dia.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: RE: [PATCH v2 0/2] Simplify mtty driver and mdev core



> -----Original Message-----
> From: Cornelia Huck <cohuck@...hat.com>
> Sent: Tuesday, August 20, 2019 11:25 PM
> 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; linux-
> kernel@...r.kernel.org; cjia <cjia@...dia.com>; 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.
User setting this alias at mdev creation time and exposed via sysfs as read only attribute works.
Exposing that as
const char *mdev_alias(struct mdev_device *dev) to vendor drivers..