From: Daniel Lezcano <daniel.lezcano@free•fr>
To: Stephen Hemminger <shemminger@vyatta•com>
Cc: David Miller <davem@davemloft•net>,
eric.dumazet@gmail•com, kaber@trash•net, nightnord@gmail•com,
netdev@vger•kernel.org
Subject: Re: [PATCH][v3] dev : fix mtu check when TSO is enabled
Date: Wed, 16 Mar 2011 14:56:09 +0100 [thread overview]
Message-ID: <4D80C179.8000900@free.fr> (raw)
In-Reply-To: <20110315111756.64b5f4b1@nehalam>
On 03/15/2011 07:17 PM, Stephen Hemminger wrote:
> On Tue, 15 Mar 2011 14:57:40 +0100
> Daniel Lezcano<daniel.lezcano@free•fr> wrote:
>
>> On 03/15/2011 12:59 AM, David Miller wrote:
>>> From: Daniel Lezcano<daniel.lezcano@free•fr>
>>> Date: Mon, 14 Mar 2011 21:39:50 +0100
>>>
>>>> + len = dev->mtu + dev->hard_header_len + VLAN_HLEN;
>>>> + if (skb->len< len)
>>>> + return true;
>>> This is not a correct translation of the original test:
>>>
>>>> - (skb->len> (dev->mtu + dev->hard_header_len + VLAN_HLEN)))) {
>>> You need to use "<=" in your version, which currently rejects all
>>> full sized frames. :-)
>> Right, thanks.
>>
>>>> +
>>>> + /* if TSO is enabled, we don't care about the length as the packet
>>>> + * could be forwarded without being segmented before
>>>> + */
>>>> + if (skb->dev&& skb->dev->features& NETIF_F_TSO)
>>>> + return true;
>>> I am trying to understand why you aren't simply checking also if this
>>> is a segmented frame? Perhaps skb_is_gso()&& device has NETIF_F_TSO
>>> set?
>> Maybe I am misunderstanding but the packet was forwarded by another device.
>> In our case from macvlan:
>>
>> macvlan_start_xmit
>> macvlan_queue_xmit
>> dest->forward
>> dev_skb_forward
>>
>> When we reached dev_skb_forward, that means we passed through
>> dev_hard_start_xmit where the packet was already segmented so we should
>> exit at the first test (skb->len< len). I don't see the point of adding
>> the skb_is_gso.
>> But maybe I am missing something, can you explain ?
> The macvlan device only has one downstream device (slave).
> If kernel is working properly, macvlan device should have a subset
> of the features of the underlying device
Right, dev->features = lowerdev->features & MACVLAN_FEATURES
> and macvlan device should
> have same MTU as underlying device.
Right,
...
if (!tb[IFLA_MTU])
dev->mtu = lowerdev->mtu;
...
> If the feature/MTU flags
> were correct, then the path calling macvlan should be respecting
> the MTU.
But if the TSO is enabled on the macvlan (inherited from eg e1000), the
packet won't be fragmented to the mtu size no ?
next prev parent reply other threads:[~2011-03-16 13:56 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-03-14 20:39 [PATCH][v3] dev : fix mtu check when TSO is enabled Daniel Lezcano
2011-03-14 23:59 ` David Miller
2011-03-15 13:57 ` Daniel Lezcano
2011-03-15 18:17 ` Stephen Hemminger
2011-03-16 13:56 ` Daniel Lezcano [this message]
2011-03-16 15:35 ` Stephen Hemminger
2011-03-16 16:19 ` Daniel Lezcano
2011-03-16 16:45 ` Stephen Hemminger
2011-03-21 22:58 ` Eric W. Biederman
2011-03-22 2:31 ` Jesse Gross
2011-03-22 3:02 ` Eric W. Biederman
2011-03-22 0:05 ` Michał Mirosław
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