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

[Parav Pandit]

> -----Original Message-----
> From: Cornelia Huck <cohuck@xxxxxxxxxx>
> Sent: Tuesday, August 20, 2019 11:25 PM
> To: Alex Williamson <alex.williamson@xxxxxxxxxx>
> Cc: Parav Pandit <parav@xxxxxxxxxxxx>; Jiri Pirko <jiri@xxxxxxxxxxxx>;
> David S . Miller <davem@xxxxxxxxxxxxx>; Kirti Wankhede
> <kwankhede@xxxxxxxxxx>; kvm@xxxxxxxxxxxxxxx; linux-
> kernel@xxxxxxxxxxxxxxx; cjia <cjia@xxxxxxxxxx>; netdev@xxxxxxxxxxxxxxx
> 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@xxxxxxxxxx> 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..