netdev - Re: [PATCH] Make virtio_net support carrier detection

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Date:	Thu, 12 Mar 2009 12:23:39 +0200
From:	Pantelis Koukousoulas <pktoss@...il.com>
To:	Rusty Russell <rusty@...tcorp.com.au>
Cc:	netdev@...r.kernel.org
Subject: Re: [PATCH] Make virtio_net support carrier detection

> No, that's absolutely sane behavior, the previous was buggy.  If a network
> doesn't support carrier, you shouldn't look for it.
>
> Since they've fixed this in Network Manager, I'm not tempted to lie about it
> in the driver (though the distributions might choose to).
>
> Rusty.
>

Ok, if "lying" is reporting that the driver supports carrier
detection, this looks
like an innocent lie :). Because the carrier *is* on, this is the truth and you
could just as well claim that the virtual hardware supports detection
as that it doesn't :)

(Plus there is no technical reason why virtio_net cannot report carrier status,
the only argument against it is saving 2 lines of code)

IMHO, if someone has such an ancient card whose hardware cannot report
carrier status (even my ne2k isa can do this iirc) they would be trained
to set the network up manually.

NetworkManager 's purpose is to automatically select the 'best' network
to connect to. By default it prefers wired networks from wireless.

If a wired eth card that does not report carrier status has no cable connected,
then (with the 'default ON' hack) NM will prefer that (useless) card even if
there is a possibility for a successful wireless connection.

That would upset me as a user and that is why I think this hack is wrong.
If the hardware cannot report carrier, then only the user can know whether
this card should be preferred or not, it has to be explicit.

Anyway, that is as much arguing as I can afford for  a 2-liner :)
If you still don't like it, that 's fine with me, I doubt I 'll have
too much trouble
carrying it forward myself :)

Thanks a lot for taking the time to review :)

Pantelis

P.s., as an added bonus, ethtool eth0 shows a nice "Link detected: yes"
with this patch, instead of the scary "Operation not supported".
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