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From: Greg KH on 30 Mar 2010 19:10
2.6.27-stable review patch. If anyone has any objections, please let us know.

------------------

From: Raimonds Cicans <ray(a)apollo.lv>

commit 8812304cf1110ae16b0778680f6022216cf4716a upstream.

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

Bonus: got rid of magic number 8

Signed-off-by: Raimonds Cicans <ray(a)apollo.lv>
Signed-off-by: David S. Miller <davem(a)davemloft.net>
Cc: Jean Delvare <khali(a)linux-fr.org>
Signed-off-by: Greg Kroah-Hartman <gregkh(a)suse.de>

---
drivers/net/r8169.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

--- a/drivers/net/r8169.c
+++ b/drivers/net/r8169.c
@@ -1842,9 +1842,9 @@ 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)


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Prev: [06/45] resource: add helpers for fetching rlimits
Next: [13/45] sit: fix off-by-one in ipip6_tunnel_get_prl