r8169: fix driver drop incoming packets >= 1515 if MTU is set between 1515 and 1536

r8169: fix driver drop incoming packets >= 1515 if MTU is set between 1515 and 1536

[Raimonds Cicans]

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Driver drop incoming packets >= 1515(1) if MTU is set between 1515(1) and 1536.

1) exact number depends on some factors:
- VLAN tagged or not
- patch "r8169: Fix card drop incoming VLAN tagged MTU byte large jumbo frames"
  applied or not

Bonus: got rid of magic number 8

Signed-off-by: Raimonds Cicans <ray@apollo.lv>

---

--- linux-2.6.31/drivers/net/r8169.c.orig	2009-11-06 21:52:12.722326601 +0200
+++ linux-2.6.31/drivers/net/r8169.c	2009-11-06 22:09:17.242224014 +0200
@@ -2229,9 +2229,9 @@ static void __devexit rtl8169_remove_one
 static void rtl8169_set_rxbufsize(struct rtl8169_private *tp,
 				  struct net_device *dev)
 {
-	unsigned int mtu = dev->mtu;
+	unsigned int max_frame = dev->mtu + VLAN_ETH_HLEN + ETH_FCS_LEN;
 
-	tp->rx_buf_sz = (mtu > RX_BUF_SIZE) ? mtu + ETH_HLEN + 8 : RX_BUF_SIZE;
+	tp->rx_buf_sz = (max_frame > RX_BUF_SIZE) ? max_frame : RX_BUF_SIZE;
 }
 
 static int rtl8169_open(struct net_device *dev)

Re: r8169: fix driver drop incoming packets >= 1515 if MTU is set between 1515 and 1536

[Ben Hutchings]

On Wed, 2009-11-11 at 20:20 +0200, Raimonds Cicans wrote:
> Driver drop incoming packets >= 1515(1) if MTU is set between 1515(1) and 1536.
> 
> 1) exact number depends on some factors:
> - VLAN tagged or not
> - patch "r8169: Fix card drop incoming VLAN tagged MTU byte large jumbo frames"
>   applied or not
[...]

MTU is a limit on transmission; it is not required to limit received
frames.

Ben.

-- 
Ben Hutchings, Senior Software Engineer, Solarflare Communications
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.

Re: r8169: fix driver drop incoming packets >= 1515 if MTU is set between 1515 and 1536

[Raimonds Cicans]

Ben Hutchings:
> On Wed, 2009-11-11 at 20:20 +0200, Raimonds Cicans wrote:
>> Driver drop incoming packets >= 1515(1) if MTU is set between 1515(1) and 1536.
>>
>> 1) exact number depends on some factors:
>> - VLAN tagged or not
>> - patch "r8169: Fix card drop incoming VLAN tagged MTU byte large jumbo frames"
>>   applied or not
> [...]
> 
> MTU is a limit on transmission; it is not required to limit received
> frames.

???

In r8169 driver MTU is used to calculate receive buffer size.
Receive buffer size is used to configure hardware incoming packet filter.

For jumbo frames:
Receive buffer size = Max frame size = MTU + 14 (ethernet header) + 4
(vlan header) + 4 (ethernet checksum) = MTU + 22

Bug:
driver for all MTU up to 1536 use receive buffer size 1536

As you can see from formula, this mean all IP packets > 1536 - 22
(for vlan tagged, 1536 - 18 for not tagged) are dropped by hardware
filter.

Example:

host_good>  ifconfig eth0 mtu 1536
host_r8169> ifconfig eth0 mtu 1536
host_good>  ping host_r8169
Ok
host_good>  ping -s 1500 host_r8169
Fail
host_good>  ifconfig eth0 mtu 7000
host_r8169> ifconfig eth0 mtu 7000
host_good>  ping -s 1500 host_r8169
Ok

Raimonds Cicans

Re: r8169: fix driver drop incoming packets >= 1515 if MTU is set between 1515 and 1536

[Ben Hutchings]

On Wed, 2009-11-11 at 22:05 +0200, Raimonds Cicans wrote:
> Ben Hutchings:
> > On Wed, 2009-11-11 at 20:20 +0200, Raimonds Cicans wrote:
> >> Driver drop incoming packets >= 1515(1) if MTU is set between 1515(1) and 1536.
> >>
> >> 1) exact number depends on some factors:
> >> - VLAN tagged or not
> >> - patch "r8169: Fix card drop incoming VLAN tagged MTU byte large jumbo frames"
> >>   applied or not
> > [...]
> > 
> > MTU is a limit on transmission; it is not required to limit received
> > frames.
> 
> ???
> 
> In r8169 driver MTU is used to calculate receive buffer size.
> Receive buffer size is used to configure hardware incoming packet filter.
> 
> For jumbo frames:
> Receive buffer size = Max frame size = MTU + 14 (ethernet header) + 4
> (vlan header) + 4 (ethernet checksum) = MTU + 22
> 
> Bug:
> driver for all MTU up to 1536 use receive buffer size 1536
[...]

OK, now I understand.  The subject line you used is not grammatical and
I originally thought you considered it a bug that the driver might
accept packets with payload greater than MTU.

To make it clear, perhaps you could change the subject to:
'r8169: Fix receive buffer length when MTU is between 1515 and 1536'
and then explain the current behaviour below that.

Ben.

-- 
Ben Hutchings, Senior Software Engineer, Solarflare Communications
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.

Re: r8169: fix driver drop incoming packets >= 1515 if MTU is set between 1515 and 1536

[Raimonds Cicans]

Ben Hutchings:
> On Wed, 2009-11-11 at 22:05 +0200, Raimonds Cicans wrote:
>> Ben Hutchings:
>>> On Wed, 2009-11-11 at 20:20 +0200, Raimonds Cicans wrote:
>>>> Driver drop incoming packets >= 1515(1) if MTU is set between 1515(1) and 1536.
>>>>
>>>> 1) exact number depends on some factors:
>>>> - VLAN tagged or not
>>>> - patch "r8169: Fix card drop incoming VLAN tagged MTU byte large jumbo frames"
>>>>   applied or not
>>> [...]
>>>
>>> MTU is a limit on transmission; it is not required to limit received
>>> frames.
>> ???
>>
>> In r8169 driver MTU is used to calculate receive buffer size.
>> Receive buffer size is used to configure hardware incoming packet filter.
>>
>> For jumbo frames:
>> Receive buffer size = Max frame size = MTU + 14 (ethernet header) + 4
>> (vlan header) + 4 (ethernet checksum) = MTU + 22
>>
>> Bug:
>> driver for all MTU up to 1536 use receive buffer size 1536
> [...]
> 
> OK, now I understand.  The subject line you used is not grammatical and
> I originally thought you considered it a bug that the driver might
> accept packets with payload greater than MTU.

Sorry for my poor English.

> To make it clear, perhaps you could change the subject to:
> 'r8169: Fix receive buffer length when MTU is between 1515 and 1536'
> and then explain the current behaviour below that.

Ok. I will try to make new version tomorrow.

Raimonds Cicans