xdp: bpf_xdp_metadata use EOPNOTSUPP for no driver support

When driver doesn't implement a bpf_xdp_metadata kfunc the fallback
implementation returns EOPNOTSUPP, which indicate device driver doesn't
implement this kfunc.

Currently many drivers also return EOPNOTSUPP when the hint isn't
available, which is ambiguous from an API point of view. Instead
change drivers to return ENODATA in these cases.

There can be natural cases why a driver doesn't provide any hardware
info for a specific hint, even on a frame to frame basis (e.g. PTP).
Lets keep these cases as separate return codes.

When describing the return values, adjust the function kernel-doc layout
to get proper rendering for the return values.

Fixes: ab46182d ("net/mlx4_en: Support RX XDP metadata")
Fixes: bc8d405b ("net/mlx5e: Support RX XDP metadata")
Fixes: 306531f0 ("veth: Support RX XDP metadata")
Fixes: 3d76a4d3 ("bpf: XDP metadata RX kfuncs")
Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Acked-by: Stanislav Fomichev <sdf@google.com>
Acked-by: Toke Høiland-Jørgensen <toke@redhat.com>
Acked-by: Tariq Toukan <tariqt@nvidia.com>
Link: https://lore.kernel.org/r/167940675120.2718408.8176058626864184420.stgit@firesoulSigned-off-by: Alexei Starovoitov <ast@kernel.org>

Documentation/networking/xdp-rx-metadata.rst

@@ -23,10 +23,13 @@ metadata is supported, this set will grow:
 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
 consumers, an XDP program can store it into the metadata area carried
-ahead of the packet.
+ahead of the packet. Not all packets will necessary have the requested
+metadata available in which case the driver returns ``-ENODATA``.
 
 Not all kfuncs have to be implemented by the device driver; when not
-implemented, the default ones that return ``-EOPNOTSUPP`` will be used.
+implemented, the default ones that return ``-EOPNOTSUPP`` will be used
+to indicate the device driver have not implemented this kfunc.
+
 
 Within an XDP frame, the metadata layout (accessed via ``xdp_buff``) is
 as follows::

drivers/net/ethernet/mellanox/mlx4/en_rx.c

@@ -674,7 +674,7 @@ int mlx4_en_xdp_rx_timestamp(const struct xdp_md *ctx, u64 *timestamp)
 	struct mlx4_en_xdp_buff *_ctx = (void *)ctx;
 
 	if (unlikely(_ctx->ring->hwtstamp_rx_filter != HWTSTAMP_FILTER_ALL))
-		return -EOPNOTSUPP;
+		return -ENODATA;
 
 	*timestamp = mlx4_en_get_hwtstamp(_ctx->mdev,
 					  mlx4_en_get_cqe_ts(_ctx->cqe));
@@ -686,7 +686,7 @@ int mlx4_en_xdp_rx_hash(const struct xdp_md *ctx, u32 *hash)
 	struct mlx4_en_xdp_buff *_ctx = (void *)ctx;
 
 	if (unlikely(!(_ctx->dev->features & NETIF_F_RXHASH)))
-		return -EOPNOTSUPP;
+		return -ENODATA;
 
 	*hash = be32_to_cpu(_ctx->cqe->immed_rss_invalid);
 	return 0;

drivers/net/ethernet/mellanox/mlx5/core/en/xdp.c

@@ -162,7 +162,7 @@ static int mlx5e_xdp_rx_timestamp(const struct xdp_md *ctx, u64 *timestamp)
 	const struct mlx5e_xdp_buff *_ctx = (void *)ctx;
 
 	if (unlikely(!mlx5e_rx_hw_stamp(_ctx->rq->tstamp)))
-		return -EOPNOTSUPP;
+		return -ENODATA;
 
 	*timestamp =  mlx5e_cqe_ts_to_ns(_ctx->rq->ptp_cyc2time,
 					 _ctx->rq->clock, get_cqe_ts(_ctx->cqe));
@@ -174,7 +174,7 @@ static int mlx5e_xdp_rx_hash(const struct xdp_md *ctx, u32 *hash)
 	const struct mlx5e_xdp_buff *_ctx = (void *)ctx;
 
 	if (unlikely(!(_ctx->xdp.rxq->dev->features & NETIF_F_RXHASH)))
-		return -EOPNOTSUPP;
+		return -ENODATA;
 
 	*hash = be32_to_cpu(_ctx->cqe->rss_hash_result);
 	return 0;

drivers/net/veth.c

@@ -1610,7 +1610,7 @@ static int veth_xdp_rx_timestamp(const struct xdp_md *ctx, u64 *timestamp)
 	struct veth_xdp_buff *_ctx = (void *)ctx;
 
 	if (!_ctx->skb)
-		return -EOPNOTSUPP;
+		return -ENODATA;
 
 	*timestamp = skb_hwtstamps(_ctx->skb)->hwtstamp;
 	return 0;
@@ -1621,7 +1621,7 @@ static int veth_xdp_rx_hash(const struct xdp_md *ctx, u32 *hash)
 	struct veth_xdp_buff *_ctx = (void *)ctx;
 
 	if (!_ctx->skb)
-		return -EOPNOTSUPP;
+		return -ENODATA;
 
 	*hash = skb_get_hash(_ctx->skb);
 	return 0;

net/core/xdp.c

@@ -720,7 +720,10 @@ __diag_ignore_all("-Wmissing-prototypes",
  * @ctx: XDP context pointer.
  * @timestamp: Return value pointer.
  *
- * Returns 0 on success or ``-errno`` on error.
+ * Return:
+ * * Returns 0 on success or ``-errno`` on error.
+ * * ``-EOPNOTSUPP`` : means device driver does not implement kfunc
+ * * ``-ENODATA``    : means no RX-timestamp available for this frame
  */
 __bpf_kfunc int bpf_xdp_metadata_rx_timestamp(const struct xdp_md *ctx, u64 *timestamp)
 {
@@ -732,7 +735,10 @@ __bpf_kfunc int bpf_xdp_metadata_rx_timestamp(const struct xdp_md *ctx, u64 *tim
  * @ctx: XDP context pointer.
  * @hash: Return value pointer.
  *
- * Returns 0 on success or ``-errno`` on error.
+ * Return:
+ * * Returns 0 on success or ``-errno`` on error.
+ * * ``-EOPNOTSUPP`` : means device driver doesn't implement kfunc
+ * * ``-ENODATA``    : means no RX-hash available for this frame
  */
 __bpf_kfunc int bpf_xdp_metadata_rx_hash(const struct xdp_md *ctx, u32 *hash)
 {