ethtool: rss: support setting hfunc via Netlink

Support setting RSS hash function / algo via ethtool Netlink.
Like IOCTL we don't validate that the function is within the
range known to the kernel. The drivers do a pretty good job
validating the inputs, and the IDs are technically "dynamically
queried" rather than part of uAPI.

Only change should be that in Netlink we don't support user
explicitly passing ETH_RSS_HASH_NO_CHANGE (0), if no change
is requested the attribute should be absent.

The ETH_RSS_HASH_NO_CHANGE is retained in driver-facing
API for consistency (not that I see a strong reason for it).

Reviewed-by: Gal Pressman <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Jakub Kicinski <[email protected]>

Author: kuba-moo

Documentation/netlink/specs/ethtool.yaml

@@ -2654,6 +2654,7 @@ operations:
           attributes:
             - header
             - context
+            - hfunc
             - indir
     -
       name: rss-ntf

Documentation/networking/ethtool-netlink.rst

@@ -1999,6 +1999,7 @@ Request contents:
 =====================================  ======  ==============================
   ``ETHTOOL_A_RSS_HEADER``             nested  request header
   ``ETHTOOL_A_RSS_CONTEXT``            u32     context number
+  ``ETHTOOL_A_RSS_HFUNC``              u32     RSS hash func
   ``ETHTOOL_A_RSS_INDIR``              binary  Indir table bytes
 =====================================  ======  ==============================
 

net/ethtool/rss.c

@@ -475,6 +475,7 @@ void ethtool_rss_notify(struct net_device *dev, u32 rss_context)
 const struct nla_policy ethnl_rss_set_policy[ETHTOOL_A_RSS_START_CONTEXT + 1] = {
 	[ETHTOOL_A_RSS_HEADER] = NLA_POLICY_NESTED(ethnl_header_policy),
 	[ETHTOOL_A_RSS_CONTEXT] = { .type = NLA_U32, },
+	[ETHTOOL_A_RSS_HFUNC] = NLA_POLICY_MIN(NLA_U32, 1),
 	[ETHTOOL_A_RSS_INDIR] = { .type = NLA_BINARY, },
 };
 
@@ -489,6 +490,9 @@ ethnl_rss_set_validate(struct ethnl_req_info *req_info, struct genl_info *info)
 	if (request->rss_context && !ops->create_rxfh_context)
 		bad_attr = bad_attr ?: tb[ETHTOOL_A_RSS_CONTEXT];
 
+	if (request->rss_context && !ops->rxfh_per_ctx_key)
+		bad_attr = bad_attr ?: tb[ETHTOOL_A_RSS_HFUNC];
+
 	if (bad_attr) {
 		NL_SET_BAD_ATTR(info->extack, bad_attr);
 		return -EOPNOTSUPP;
@@ -588,6 +592,8 @@ rss_set_ctx_update(struct ethtool_rxfh_context *ctx, struct nlattr **tb,
 			ethtool_rxfh_context_indir(ctx)[i] = rxfh->indir[i];
 		ctx->indir_configured = !!nla_len(tb[ETHTOOL_A_RSS_INDIR]);
 	}
+	if (rxfh->hfunc != ETH_RSS_HASH_NO_CHANGE)
+		ctx->hfunc = rxfh->hfunc;
 }
 
 static int
@@ -618,7 +624,11 @@ ethnl_rss_set(struct ethnl_req_info *req_info, struct genl_info *info)
 		goto exit_clean_data;
 	indir_mod = !!tb[ETHTOOL_A_RSS_INDIR];
 
-	rxfh.hfunc = ETH_RSS_HASH_NO_CHANGE;
+	rxfh.hfunc = data.hfunc;
+	ethnl_update_u8(&rxfh.hfunc, tb[ETHTOOL_A_RSS_HFUNC], &mod);
+	if (rxfh.hfunc == data.hfunc)
+		rxfh.hfunc = ETH_RSS_HASH_NO_CHANGE;
+
 	rxfh.input_xfrm = RXH_XFRM_NO_CHANGE;
 
 	mutex_lock(&dev->ethtool->rss_lock);