netdev - RE: [PATCH 1/4] mdev: Introduce sha1 based mdev alias

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Date:   Tue, 27 Aug 2019 11:57:07 +0000
From:   Parav Pandit <parav@...lanox.com>
To:     Cornelia Huck <cohuck@...hat.com>
CC:     "alex.williamson@...hat.com" <alex.williamson@...hat.com>,
        Jiri Pirko <jiri@...lanox.com>,
        "kwankhede@...dia.com" <kwankhede@...dia.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: RE: [PATCH 1/4] mdev: Introduce sha1 based mdev alias



> -----Original Message-----
> From: Cornelia Huck <cohuck@...hat.com>
> Sent: Tuesday, August 27, 2019 5:11 PM
> To: Parav Pandit <parav@...lanox.com>
> Cc: alex.williamson@...hat.com; Jiri Pirko <jiri@...lanox.com>;
> kwankhede@...dia.com; davem@...emloft.net; kvm@...r.kernel.org; linux-
> kernel@...r.kernel.org; netdev@...r.kernel.org
> Subject: Re: [PATCH 1/4] mdev: Introduce sha1 based mdev alias
> 
> On Tue, 27 Aug 2019 11:33:54 +0000
> Parav Pandit <parav@...lanox.com> wrote:
> 
> > > -----Original Message-----
> > > From: Cornelia Huck <cohuck@...hat.com>
> > > Sent: Tuesday, August 27, 2019 4:54 PM
> > > To: Parav Pandit <parav@...lanox.com>
> > > Cc: alex.williamson@...hat.com; Jiri Pirko <jiri@...lanox.com>;
> > > kwankhede@...dia.com; davem@...emloft.net; kvm@...r.kernel.org;
> > > linux- kernel@...r.kernel.org; netdev@...r.kernel.org
> > > Subject: Re: [PATCH 1/4] mdev: Introduce sha1 based mdev alias
> > >
> > > On Tue, 27 Aug 2019 11:12:23 +0000
> > > Parav Pandit <parav@...lanox.com> wrote:
> > >
> > > > > -----Original Message-----
> > > > > From: Cornelia Huck <cohuck@...hat.com>
> > > > > Sent: Tuesday, August 27, 2019 3:54 PM
> > > > > To: Parav Pandit <parav@...lanox.com>
> > > > > Cc: alex.williamson@...hat.com; Jiri Pirko <jiri@...lanox.com>;
> > > > > kwankhede@...dia.com; davem@...emloft.net; kvm@...r.kernel.org;
> > > > > linux- kernel@...r.kernel.org; netdev@...r.kernel.org
> > > > > Subject: Re: [PATCH 1/4] mdev: Introduce sha1 based mdev alias
> > > > >
> 
> > > > > What about:
> > > > >
> > > > > * @get_alias_length: optional callback to specify length of the
> > > > > alias to
> > > create
> > > > > *                    Returns unsigned integer: length of the alias to be created,
> > > > > *                                              0 to not create an alias
> > > > >
> > > > Ack.
> > > >
> > > > > I also think it might be beneficial to add a device parameter
> > > > > here now (rather than later); that seems to be something that makes
> sense.
> > > > >
> > > > Without showing the use, it shouldn't be added.
> > >
> > > It just feels like an omission: Why should the vendor driver only be
> > > able to return one value here, without knowing which device it is for?
> > > If a driver supports different devices, it may have different
> > > requirements for them.
> > >
> > Sure. Lets first have this requirement to add it.
> > I am against adding this length field itself without an actual vendor use case,
> which is adding some complexity in code today.
> > But it was ok to have length field instead of bool.
> >
> > Lets not further add "no-requirement futuristic knobs" which hasn't shown its
> need yet.
> > When a vendor driver needs it, there is nothing prevents such addition.
> 
> Frankly, I do not see how it adds complexity; the other callbacks have device
> arguments already,
Other ioctls such as create, remove, mmap, likely need to access the parent.
Hence it make sense to have parent pointer in there.

I am not against complexity, I am just saying, at present there is no use-case. Let have use case and we add it.

> and the vendor driver is free to ignore it if it does not have
> a use for it. I'd rather add the argument before a possible future user tries
> weird hacks to allow multiple values, but I'll leave the decision to the
> maintainers.
Why would a possible future user tries a weird hack?
If user needs to access parent device, that driver maintainer should ask for it.