On 06/07/2023 16.46, Larysa Zaremba wrote:
On Tue, Jul 04, 2023 at 04:18:04PM +0200, Jesper Dangaard Brouer wrote:
On 04/07/2023 13.02, Larysa Zaremba wrote:
On Tue, Jul 04, 2023 at 12:23:45PM +0200, Jesper Dangaard Brouer wrote:
On 04/07/2023 10.23, Larysa Zaremba wrote:
On Mon, Jul 03, 2023 at 01:15:34PM -0700, John Fastabend wrote:
Larysa Zaremba wrote:
Implement functionality that enables drivers to expose VLAN tag
to XDP code.
Signed-off-by: Larysa Zaremba <larysa.zaremba@xxxxxxxxx>
---
Documentation/networking/xdp-rx-metadata.rst | 8 +++++++-
include/linux/netdevice.h | 2 ++
include/net/xdp.h | 2 ++
kernel/bpf/offload.c | 2 ++
net/core/xdp.c | 20 ++++++++++++++++++++
5 files changed, 33 insertions(+), 1 deletion(-)
diff --git a/Documentation/networking/xdp-rx-metadata.rst b/Documentation/networking/xdp-rx-metadata.rst
index 25ce72af81c2..ea6dd79a21d3 100644
--- a/Documentation/networking/xdp-rx-metadata.rst
+++ b/Documentation/networking/xdp-rx-metadata.rst
@@ -18,7 +18,13 @@ Currently, the following kfuncs are supported. In the future, as more
metadata is supported, this set will grow:
.. kernel-doc:: net/core/xdp.c
- :identifiers: bpf_xdp_metadata_rx_timestamp bpf_xdp_metadata_rx_hash
+ :identifiers: bpf_xdp_metadata_rx_timestamp
+
+.. kernel-doc:: net/core/xdp.c
+ :identifiers: bpf_xdp_metadata_rx_hash
+
+.. kernel-doc:: net/core/xdp.c
+ :identifiers: bpf_xdp_metadata_rx_vlan_tag
An XDP program can use these kfuncs to read the metadata into stack
variables for its own consumption. Or, to pass the metadata on to other
[...]
diff --git a/net/core/xdp.c b/net/core/xdp.c
index 41e5ca8643ec..f6262c90e45f 100644
--- a/net/core/xdp.c
+++ b/net/core/xdp.c
@@ -738,6 +738,26 @@ __bpf_kfunc int bpf_xdp_metadata_rx_hash(const struct xdp_md *ctx, u32 *hash,
return -EOPNOTSUPP;
}
+/**
+ * bpf_xdp_metadata_rx_vlan_tag - Get XDP packet outermost VLAN tag with protocol
+ * @ctx: XDP context pointer.
+ * @vlan_tag: Destination pointer for VLAN tag
+ * @vlan_proto: Destination pointer for VLAN protocol identifier in network byte order.
+ *
+ * In case of success, vlan_tag contains VLAN tag, including 12 least significant bytes
+ * containing VLAN ID, vlan_proto contains protocol identifier.
Above is a bit confusing to me at least.
The vlan tag would be both the 16bit TPID and 16bit TCI. What fields
are to be included here? The VlanID or the full 16bit TCI meaning the
PCP+DEI+VID?
It contains PCP+DEI+VID, in patch 16 ("selftests/bpf: Add flags and new hints to
xdp_hw_metadata") this is more clear, because the tag is parsed.
Do we really care about the "EtherType" proto (in VLAN speak TPID = Tag
Protocol IDentifier)?
I mean, it can basically only have two values[1], and we just wanted to
know if it is a VLAN (that hardware offloaded/removed for us):
If we assume everyone follows the standard, this would be correct.
But apparently, some applications use some ambiguous value as a TPID [0].
So it is not hard to imagine, some NICs could alllow you to configure your
custom TPID. I am not sure if any in-tree drivers actually do this, but I think
it's nice to provide some flexibility on XDP level, especially considering
network stack stores full vlan_proto.
I'm buying your argument, and agree it makes sense to provide TPID in
the call signature. Given weird hardware exists that allow people to
configure custom TPID.
Looking through kernel defines (in uapi/linux/if_ether.h) I see evidence
that funky QinQ EtherTypes have been used in the past:
#define ETH_P_QINQ1 0x9100 /* deprecated QinQ VLAN [ NOT AN OFFICIALLY
REGISTERED ID ] */
#define ETH_P_QINQ2 0x9200 /* deprecated QinQ VLAN [ NOT AN OFFICIALLY
REGISTERED ID ] */
#define ETH_P_QINQ3 0x9300 /* deprecated QinQ VLAN [ NOT AN OFFICIALLY
REGISTERED ID ] */
[0]
https://techhub.hpe.com/eginfolib/networking/docs/switches/7500/5200-1938a_l2-lan_cg/content/495503472.htm
static __always_inline int proto_is_vlan(__u16 h_proto)
{
return !!(h_proto == bpf_htons(ETH_P_8021Q) ||
h_proto == bpf_htons(ETH_P_8021AD));
}
[1] https://github.com/xdp-project/bpf-examples/blob/master/include/xdp/parsing_helpers.h#L75-L79
Cc. Andrew Lunn, as I notice DSA have a fake VLAN define ETH_P_DSA_8021Q
(in file include/uapi/linux/if_ether.h)
Is this actually in use?
Maybe some hardware can "VLAN" offload this?
What about rephrasing it this way:
In case of success, vlan_proto contains VLAN protocol identifier (TPID),
vlan_tag contains the remaining 16 bits of a 802.1Q tag (PCP+DEI+VID).
Hmm, I think we can improve this further. This text becomes part of the
documentation for end-users (target audience). Thus, I think it is
worth being more verbose and even mention the existing defines that we
are expecting end-users to take advantage of.
What about:
In case of success. The VLAN EtherType is stored in vlan_proto (usually
either ETH_P_8021Q or ETH_P_8021AD) also known as TPID (Tag Protocol
IDentifier). The VLAN tag is stored in vlan_tag, which is a 16-bit field
containing sub-fields (PCP+DEI+VID). The VLAN ID (VID) is 12-bits
commonly extracted using mask VLAN_VID_MASK (0x0fff). For the meaning
of the sub-fields Priority Code Point (PCP) and Drop Eligible Indicator
(DEI) (formerly CFI) please reference other documentation. Remember
these 16-bit fields are stored in network-byte. Thus, transformation
with byte-order helper functions like bpf_ntohs() are needed.
AFAIK, vlan_tag is stored in host byte order, this is how it is in skb.
I'm not sure we should follow SKB storage scheme for XDP.
I think following SKB convention is a good idea in this particular case. As I
have mentioned below, in ice VLAN TCI in descriptor already comes in LE, so no
point in converting it into BE, so somebody would use bpf_ntohs() later anyway.
We are not the only manufacturer that does this.
As long as other NIC hardware does the same this seems okay.
In ice, we receive VLAN tag in descriptor already in LE.
Only protocol is BE (network byte order). So I would replace the last 2
sentences with the following:
vlan_tag is stored in host byte order, so no byte order conversion is needed.
Yikes, that was unexpected. This needs to be heavily documented in docs.
You mean the motivation, why it is so and not the other way around?
No, I don't mean the motivation.
I simply mean write it in *bold*.
Look at the description for bpf_xdp_metadata_rx_hash, how it gets
rendered [1] and how the code comments look [2].
[1]
https://kernel.org/doc/html/latest/networking/xdp-rx-metadata.html#general-design
[2] https://elixir.bootlin.com/linux/v6.4/source/net/core/xdp.c#L724
To save you some time compiling htmldocs target:
make SPHINXDIRS="networking" V=1 htmldocs
When parsing packets, it is in network-byte-order, else my code is wrong
here[1]:
[1] https://github.com/xdp-project/bpf-examples/blob/master/include/xdp/parsing_helpers.h#L122
I'm accessing the skb->vlan_tci here [2], and I notice I don't do any
byte-order conversions, so fortunately I didn't make a code mistake.
[2] https://github.com/xdp-project/bpf-examples/blob/master/traffic-pacing-edt/edt_pacer_vlan.c#L215
In raw packet, VLAN TCI is in network byte order, but skb requires NIC/driver
to convert it into host byte order before putting it into skb.
I'm interested in if *most* NIC hardware will deliver this in LE
(Little-Endian) which is host-byte order on x86 ?
vlan_proto is stored in network byte order, the suggested way to use this value:
vlan_proto == bpf_htons(ETH_P_8021Q)
--Jesper
