netdev - Re: [PATCH] 6lowpan: Sync default hardware address of lowpan links to their wpan

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Date:	Sun, 6 Oct 2013 03:29:08 +0200
From:	Alexander Aring <alex.aring@...il.com>
To:	Alan Ott <alan@...nal11.us>
Cc:	Alexander Smirnov <alex.bluesman.smirnov@...il.com>,
	Dmitry Eremin-Solenikov <dbaryshkov@...il.com>,
	"David S. Miller" <davem@...emloft.net>,
	linux-zigbee-devel@...ts.sourceforge.net, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] 6lowpan: Sync default hardware address of lowpan links
 to their wpan

On Sat, Oct 05, 2013 at 09:01:52PM -0400, Alan Ott wrote:
> On 10/05/2013 08:24 PM, Alexander Aring wrote:
> >Hi Alan,
> >
> >On Sat, Oct 05, 2013 at 05:38:00PM -0400, Alan Ott wrote:
> >>When a lowpan link to a wpan device is created, set the hardware address
> >>of the lowpan link to that of the wpan device.
> >>
> >>Signed-off-by: Alan Ott<alan@...nal11.us>
> >>---
> >>  net/ieee802154/6lowpan.c | 3 +++
> >>  1 file changed, 3 insertions(+)
> >>
> >>diff --git a/net/ieee802154/6lowpan.c b/net/ieee802154/6lowpan.c
> >>index c85e71e..fb89133 100644
> >>--- a/net/ieee802154/6lowpan.c
> >>+++ b/net/ieee802154/6lowpan.c
> >>@@ -1386,6 +1386,9 @@ static int lowpan_newlink(struct net *src_net, struct net_device *dev,
> >>  	entry->ldev = dev;
> >>+	BUG_ON(IEEE802154_ADDR_LEN != dev->addr_len);
> >So if somebody make a:
> >"ip link add link $NOT_8BYTE_HWADDR_DEV name $NAME type lowpan"
> >
> >the kernel creates a BUG_ON? Okay it seems that case is very unusual but
> >better is to return a errno so "maybe(I don't know it)" the userspace
> >software will generate a error and the whole kernel doesn't crash.
> 
> That line checks the length of the address of the lowpan device, not
> the real device the lowpan device is attached to (and on second
> look, I don't like the Yoda code; didn't notice that before).
> 
> Further, running:
>     ip link add link eth0 name lowpan0 type lowpan
> 
> like you suggest, crashes the kernel hard, with or without my patch.
> More stuff to fix....
>

Okay isn't the dev->addr_len some static value?

Maybe we should check than for:

if (real_dev->type != ARPHRD_IEEE802154)
	return -EINVAL;

after we set real_dev. It's all ARPHRD_IEEE802154 specific code.

> 
> >>+	memcpy(dev->dev_addr, real_dev->dev_addr, IEEE802154_ADDR_LEN);
> >Is there one case where we read the dev->dev_addr? I saw a case when we
> >set this [1], but I don't know why we need this. Did you detect some
> >problems because this isn't the "real" hw addr?
> >
> >Other case is I am feeling uneasy when we have two netdev devices with
> >the same hw addr.
> >[1]https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/net/ieee802154/6lowpan.c?id=refs/tags/v3.12-rc3#n1102
> 
> In my testing, lowpan devices need a hardware address which is the
> same as the wpan, or else stuff like ping doesn't work at all. In
> all the examples I've ever seen, the lowpan's hardware address has
> been set manually.
> 
Ah ok.

> What does your test setup look like that you don't have a hardware
> address for your lowpan device? Are you able to ping other Linux
> hosts?
> 

I have a little script for setting up a lowpan device.
I set the hardware address with:

ip link set $LOWPAN_DEV address $EUI64_ADDR

after I add the lowpan link. I am able to ping linux and contiki(without
fragmentation).

- Alex
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