netdev - Re: [PATCH net] bonding: fix vlan

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Date:	Tue, 6 May 2014 15:03:15 +0200
From:	Michal Kubecek <mkubecek@...e.cz>
To:	Jay Vosburgh <jay.vosburgh@...onical.com>
Cc:	David Miller <davem@...emloft.net>, netdev@...r.kernel.org,
	vfalico@...il.com, andy@...yhouse.net, mirq-linux@...e.qmqm.pl
Subject: Re: [PATCH net] bonding: fix vlan_features computing

On Tue, May 06, 2014 at 12:53:27AM -0700, Jay Vosburgh wrote:
> 
> 	The VLAN device doesn't get _HW_CSUM (aka _GEN_CSUM)?  In
> ethtool, this is tx-checksum-ip-generic, I believe.
> 
> 	I have only one machine with a _IP_CSUM only device (a tg3) set
> up at the moment, it's running a Fedora 20 3.13 kernel, and a vlan ->
> bond0 -> eth0 stack shows "generic" offload for the vlan and bond0, and
> "ipv4" offload for the eth0 itself.

I checked now and at least since 3.12 bond has NETIF_F_HW_CSUM in its
features even if its slaves have only NETIF_F_IP(V6)_CSUM. Therefore
NETIF_F_HW_CSUM in vlan_features does no harm and vlan on top of the
bond gets NETIF_F_HW_CSUM.

Unfortunately it means that while I still think the change I proposed
is correct, it would break things unless computing features of the bond
is fixed in similar way or vlan_dev_fix_features is modified to handle
checksumming features more carefully.

                                                        Michal Kubecek

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