Re: [patch net-next 0/4] net: allow to change carrier from userspace

On Wed, 12 Dec 2012 19:49:26 +0100
Jiri Pirko [off-list ref] wrote:

Wed, Dec 12, 2012 at 07:36:32PM CET, shemminger@vyatta.com wrote:

quoted

On Wed, 12 Dec 2012 19:25:56 +0100
Jiri Pirko [off-list ref] wrote:

quoted

Wed, Dec 12, 2012 at 07:12:08PM CET, shemminger@vyatta.com wrote:

quoted

On Wed, 12 Dec 2012 19:10:17 +0100
Jiri Pirko [off-list ref] wrote:

quoted

quoted

# 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.