netdev - acenic swallowing 802.1q tag when kernel compiled with VLAN support

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Date:	Fri, 16 Feb 2007 12:30:53 +0100
From:	Florian Lohoff <flo@...822.org>
To:	netdev@...r.kernel.org
Subject: acenic swallowing 802.1q tag when kernel compiled with VLAN support


Hi,
i discovered that once the kernel is compiled 802.1Q VLAN Support the acenic driver
swallows the 802.1q header in promiscous mode. I am tracing an gigabit ethernet
with 802.1q in 802.1q so i would usually see 2 802.1q VLAN header. When compiling
with VLAN aka 802.1q support the first or outer vlan header disappears from the traces
even though the vlan support kernel module is not loaded nor vlans activated on the link.

Card i am using:

	0000:06:02.0 Ethernet controller: 3Com Corporation 3c985 1000BaseSX (SX/TX) (rev 01)
		Subsystem: Unknown device 9850:0001
		Control: I/O- Mem+ BusMaster+ SpecCycle- MemWINV- VGASnoop- ParErr+ Stepping- SERR+ FastB2B-
		Status: Cap- 66MHz+ UDF- FastB2B+ ParErr- DEVSEL=medium >TAbort- <TAbort- <MAbort- >SERR- <PERR-
		Latency: 64 (16000ns min), Cache Line Size: 0x10 (64 bytes)
		Interrupt: pin A routed to IRQ 225
		Region 0: Memory at fdff0000 (32-bit, non-prefetchable) [size=16K]

dmesg output:

	acenic.c: v0.92 08/05/2002  Jes Sorensen, linux-acenic@...SITE.dk
				    http://home.cern.ch/~jes/gige/acenic.html
	ACPI: PCI Interrupt 0000:06:02.0[A] -> GSI 78 (level, low) -> IRQ 225
	0000:06:02.0: 3Com 3C985 Gigabit Ethernet at 0xfdff0000, irq 225
	  Tigon II (Rev. 6), Firmware: 12.4.11, MAC: 00:60:08:f6:f5:4e
	  PCI cache line size set incorrectly (64 bytes) by BIOS/FW, expecting 32
	  PCI bus width: 64 bits, speed: 66MHz, latency: 64 clks
	  Disabling PCI memory write and invalidate
	0000:06:02.0: Firmware up and running

Kernel:
	lnxp-1115:~# uname -a
	Linux lnxp-1115 2.6.18-3-686 #1 SMP Mon Dec 4 16:41:14 UTC 2006 i686 GNU/Linux

	lnxp-1115:~# egrep "CONFIG_ACENIC|CONFIG_VLAN" /boot/config-2.6.18-3-686
	CONFIG_VLAN_8021Q=m
	CONFIG_ACENIC=m
	# CONFIG_ACENIC_OMIT_TIGON_I is not set

Thats the default Debian Etch kernel. I have seen this behaviour in a couple kernel
releases since i started tracing stuff so its not a new bug.

Flo
-- 
Florian Lohoff                  flo@...822.org             +49-171-2280134
	Those who would give up a little freedom to get a little 
          security shall soon have neither - Benjamin Franklin

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