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):
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.
I think by "including 12 least significant bytes" you
mean bits,
Yes, my bad.
but also not clear about those 4 other bits.
I can likely figure it out in next patches from implementation but
would be nice to clean up docs.
+ *
+ * Return:
+ * * Returns 0 on success or ``-errno`` on error.
+ * * ``-EOPNOTSUPP`` : device driver doesn't implement kfunc
+ * * ``-ENODATA`` : VLAN tag was not stripped or is not available
+ */
+__bpf_kfunc int bpf_xdp_metadata_rx_vlan_tag(const struct xdp_md *ctx, u16 *vlan_tag,
+ __be16 *vlan_proto)
+{
+ return -EOPNOTSUPP;
+}
+
