tcpdump mailing list archives
Re: [PATCH net 1/2] net: dev_queue_xmit_nit: fix skb->vlan_tci field value
From: Ani Sinha <ani () aristanetworks com>
Date: Wed, 9 Jan 2013 11:27:10 -0800
Thats irrelevant. This only shows that user land was depending on a prior undocumented behavior.
Why do you say that? The following patch from Pirko ensured that on both RX and TX regardless whether the driver/hw supported vlan acceleration, the outermost vlan tags will always be extracted out of the packet and put in skb aux data : commit bcc6d47903612c3861201cc3a866fb604f26b8b2 Author: Jiri Pirko <jpirko () redhat com> Date: Thu Apr 7 19:48:33 2011 +0000 net: vlan: make non-hw-accel rx path similar to hw-accel Now this meant that the filter code should always look into the aux data for vlan tagging, not in the packet, regardless of hw acceleration availability. Your patch b40863c667c16b7a73d4f034a8eab67029b5b15a broke this symmetric semantics - now on TX on the network tap, we do not have the vlan tags in the skb aux data. In my opinion, for a given kernel, the filter code should either look into the packet offset or in the packet aux data for vlan tags but not both. Otherwise the filter code becomes incredibly complex since an inline vlan tag in the packet changes offsets of all headers coming afterwords and I don't even know if filter code can be correctly generated in this case. tcpdump-workers folks are CC's here and they clearly have more experience with libpcap filter code that I do. Hence I leave it up to them to provide inputs here.
What's wrong instructing libpcap to extend the filter to be able to get the correct result, vlan id being in skb->vlan_id (vlan accel on), or in the packet itself (vlan accel off) This way, you could chose if you want to get only accelerated vlan, or non accelerated vlan, or both. And you need no kernel hacking.
This is wrong. Accelerated or not, the kernel code was organized to have the tags in the packet aux data. So I think this is how user land should be coded as well. ani _______________________________________________ tcpdump-workers mailing list tcpdump-workers () lists tcpdump org https://lists.sandelman.ca/mailman/listinfo/tcpdump-workers
Current thread:
- Re: [PATCH net 1/2] net: dev_queue_xmit_nit: fix skb->vlan_tci field value Ani Sinha (Jan 08)
- Re: [PATCH net 1/2] net: dev_queue_xmit_nit: fix skb->vlan_tci field value Ani Sinha (Jan 09)
- Re: [PATCH net 1/2] net: dev_queue_xmit_nit: fix skb->vlan_tci field value Eric Dumazet (Jan 09)
- Re: [PATCH net 1/2] net: dev_queue_xmit_nit: fix skb->vlan_tci field value Ani Sinha (Jan 09)
- Re: [PATCH net 1/2] net: dev_queue_xmit_nit: fix skb->vlan_tci field value Ani Sinha (Jan 09)
- Message not available
- Re: [PATCH net 1/2] net: dev_queue_xmit_nit: fix skb->vlan_tci field value Paul Pearce (Jan 10)
- Re: [PATCH net 1/2] net: dev_queue_xmit_nit: fix skb->vlan_tci field value Daniel Borkmann (Jan 11)
- Re: [PATCH net 1/2] net: dev_queue_xmit_nit: fix skb->vlan_tci field value Eric W. Biederman (Feb 15)
- Re: [PATCH net 1/2] net: dev_queue_xmit_nit: fix skb->vlan_tci field value Eric Dumazet (Jan 09)
- Re: [PATCH net 1/2] net: dev_queue_xmit_nit: fix skb->vlan_tci field value Ani Sinha (Jan 09)