netdev - [RFC bpf-next v2 19/24] net: make vlan_get_tag() return -ENODATA instead of -EINVAL

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Date: Wed, 27 Sep 2023 09:51:19 +0200
From: Larysa Zaremba <larysa.zaremba@...el.com>
To: bpf@...r.kernel.org
Cc: Larysa Zaremba <larysa.zaremba@...el.com>,
	ast@...nel.org,
	daniel@...earbox.net,
	andrii@...nel.org,
	martin.lau@...ux.dev,
	song@...nel.org,
	yhs@...com,
	john.fastabend@...il.com,
	kpsingh@...nel.org,
	sdf@...gle.com,
	haoluo@...gle.com,
	jolsa@...nel.org,
	David Ahern <dsahern@...il.com>,
	Jakub Kicinski <kuba@...nel.org>,
	Willem de Bruijn <willemb@...gle.com>,
	Jesper Dangaard Brouer <brouer@...hat.com>,
	Anatoly Burakov <anatoly.burakov@...el.com>,
	Alexander Lobakin <alexandr.lobakin@...el.com>,
	Magnus Karlsson <magnus.karlsson@...il.com>,
	Maryam Tahhan <mtahhan@...hat.com>,
	xdp-hints@...-project.net,
	netdev@...r.kernel.org,
	Willem de Bruijn <willemdebruijn.kernel@...il.com>,
	Alexei Starovoitov <alexei.starovoitov@...il.com>,
	Simon Horman <simon.horman@...igine.com>,
	Tariq Toukan <tariqt@...lanox.com>,
	Saeed Mahameed <saeedm@...lanox.com>,
	Maciej Fijalkowski <maciej.fijalkowski@...el.com>,
	Jesper Dangaard Brouer <jbrouer@...hat.com>
Subject: [RFC bpf-next v2 19/24] net: make vlan_get_tag() return -ENODATA instead of -EINVAL

__vlan_hwaccel_get_tag() is used in veth XDP hints implementation,
its return value (-EINVAL if skb is not VLAN tagged) is passed to bpf code,
but XDP hints specification requires drivers to return -ENODATA, if a hint
cannot be provided for a particular packet.

Solve this inconsistency by changing error return value of
__vlan_hwaccel_get_tag() from -EINVAL to -ENODATA, do the same thing to
__vlan_get_tag(), because this function is supposed to follow the same
convention. This, in turn, makes -ENODATA the only non-zero value
vlan_get_tag() can return. We can do this with no side effects, because
none of the users of the 3 above-mentioned functions rely on the exact
value.

Suggested-by: Jesper Dangaard Brouer <jbrouer@...hat.com>
Acked-by: Stanislav Fomichev <sdf@...gle.com>
Signed-off-by: Larysa Zaremba <larysa.zaremba@...el.com>
---
 include/linux/if_vlan.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/include/linux/if_vlan.h b/include/linux/if_vlan.h
index 3028af87716e..c1645c86eed9 100644
--- a/include/linux/if_vlan.h
+++ b/include/linux/if_vlan.h
@@ -540,7 +540,7 @@ static inline int __vlan_get_tag(const struct sk_buff *skb, u16 *vlan_tci)
 	struct vlan_ethhdr *veth = skb_vlan_eth_hdr(skb);
 
 	if (!eth_type_vlan(veth->h_vlan_proto))
-		return -EINVAL;
+		return -ENODATA;
 
 	*vlan_tci = ntohs(veth->h_vlan_TCI);
 	return 0;
@@ -561,7 +561,7 @@ static inline int __vlan_hwaccel_get_tag(const struct sk_buff *skb,
 		return 0;
 	} else {
 		*vlan_tci = 0;
-		return -EINVAL;
+		return -ENODATA;
 	}
 }
 
-- 
2.41.0