Date:	Thu, 13 Dec 2012 17:17:50 +0100
From:	Jiri Pirko <jiri@...nulli.us>
To:	Stephen Hemminger <shemminger@...tta.com>
Cc:	netdev@...r.kernel.org, davem@...emloft.net, edumazet@...gle.com,
	bhutchings@...arflare.com, mirqus@...il.com,
	greearb@...delatech.com, fbl@...hat.com
Subject: Re: [patch net-next 0/4] net: allow to change carrier from userspace

Wed, Dec 12, 2012 at 08:34:33PM CET, shemminger@...tta.com wrote:
>On Wed, 12 Dec 2012 20:06:13 +0100
>Jiri Pirko <jiri@...nulli.us> wrote:
>
>> Wed, Dec 12, 2012 at 07:54:48PM CET, shemminger@...tta.com wrote:
>> >On Wed, 12 Dec 2012 19:49:26 +0100
>> >Jiri Pirko <jiri@...nulli.us> wrote:
>> >
>> >> Wed, Dec 12, 2012 at 07:36:32PM CET, shemminger@...tta.com wrote:
>> >> >On Wed, 12 Dec 2012 19:25:56 +0100
>> >> >Jiri Pirko <jiri@...nulli.us> wrote:
>> >> >
>> >> >> Wed, Dec 12, 2012 at 07:12:08PM CET, shemminger@...tta.com wrote:
>> >> >> >On Wed, 12 Dec 2012 19:10:17 +0100
>> >> >> >Jiri Pirko <jiri@...nulli.us> wrote:
>> >> >> >
>> >> >> >> ># ip li show dev dummy0
>> >> >> >> >12: dummy0: <NO-CARRIER,BROADCAST,NOARP,UP,LOWER_UP> mtu 1500 qdisc noqueue state DORMANT mode DORMANT   
>> >> >> >> 
>> >> >> >> if you mean this "NO-CARRIER"
>> >> >> >> it has no direct relation with netif_carrier_ok().
>> >> >> >
>> >> >> >It is the same value (IFF_RUNNING) that is visible from user space.
>> >> >> 
>> >> >> static inline bool netif_carrier_ok(const struct net_device *dev)
>> >> >> {
>> >> >> 	        return !test_bit(__LINK_STATE_NOCARRIER, &dev->state);
>> >> >> }
>> >> >> 
>> >> >> So netif_carrier[ok/on/off] are working with on __LINK_STATE_NOCARRIER
>> >> >> bit. Not with IFF_RUNNING flag.
>> >> >
>> >> >What is the code path that you are worried about netif_carrier_ok being set or clear?
>> >> >The interaction here is complex, and right now LINK_STATE_NOCARRIER is purely
>> >> >controlled by the driver, your patch changes that, but before acking I want
>> >> >to make sure why it is required.
>> >> 
>> >> This patchset would provide a possibility to set or clear the carrier
>> >> from userspace. For dummy device it would serve for direct emulation
>> >> of link fail.
>> >> 
>> >> Also for team deriver, that would serve for teamd (userspace part) to
>> >> set the carrier actually on or off (in case of LACP runner for example
>> >> this is required).
>> >> 
>> >
>> >You want to able to control the dummy device, so that you can test carrier
>> >management in the team device. Another alternative is to use carrier control
>> >on a virtual device. Vmware can do it, there were patches to do this with KVM/QEMU
>> >not sure if they ever got incorporated.
>> >
>> >Since this is a specific feature of the dummy device which is specialized for
>> >testing, maybe it should just be done by adding device specific ioctl rather
>> >than letting it creep in as a general facility.
>> 
>> Ugh, specific ioctl stinks...
>> But this is not only for dummy. As I said, we need this for team driver.
>> Maybe I did not explain that correctly. Given the fact that the whole
>> Team logic is in userspace, teamd (userspace daemon) needs to set the
>> carrier state as if it was done in kernel. Yes, we would be able to do
>> this by specific Team option in team driver, but I thought this would be
>> nicer to do that more generally.
>
>That is what the operstate mechanism was for. Why did we build that mechanism
>if it doesn't work from userspace.
>
>Maybe the fix is to make setting linkstate also set carrier bits.

Hmm. You mean to call netif_carrier_on/off as a reaction to operstate
change? How exactly would you like to do that?

Thanks

Jiri

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