On Mon, 18 Feb 2019 19:22:14 +0100 (CET), Michal Kubecek wrote:

Requests a contents of one or more string sets, i.e. indexed arrays of
strings; this information is provided by ETHTOOL_GSSET_INFO and
ETHTOOL_GSTRINGS commands of ioctl interface. There are three types of
requests:

  - no NLM_F_DUMP, no device: get "global" stringsets
  - no NLM_F_DUMP, with device: get string sets related to the device
  - NLM_F_DUMP, no device: get device related string sets for all devices

It's possible to request all string sets of given type or only specific
sets. With ETHA_STRSET_COUNTS flag, only set sizes (number of strings) are
returned.

+GET_STRSET
+----------
+
+Requests contents of a string set as provided by ioctl commands
+ETHTOOL_GSSET_INFO and ETHTOOL_GSTRINGS. String sets are not user writeable so
+that the corresponding SET_STRSET message is only used in kernel replies.
+There are two types of string sets: global (independent of a device, e.g.
+device feature names) and device specific (e.g. device private flags).
+
+Request contents:
+
+    ETHA_STRSET_DEV		(nested)	device identification
+    ETHA_STRSET_COUNTS		(flag)		request only string counts
+    ETHA_STRSET_STRINGSET	(nested)	string set to request
+        ETHA_STRINGSET_ID		(u32)		set id
+
+Kernel response contents:
+
+    ETHA_STRSET_DEV		(nested)	device identification
+    ETHA_STRSET_STRINGSET	(nested)	string set to request

Is it common to put the device information outside of the main
attribute nest?

+        ETHA_STRINGSET_ID		(u32)		set id
+        ETHA_STRINGSET_COUNT		(u32)		number of strings
+        ETHA_STRINGSET_STRINGS		(nested)	array of strings
+            ETHA_STRING_INDEX			(u32)		string index
+            ETHA_STRING_VALUE			(string)	string value
+
+ETHA_STRSET_DEV, if present, identifies the device to request device specific
+string sets for. Depending on its presence a and NLM_F_DUMP flag, there are
+three type of GET_STRSET requests:
+
+ - no NLM_F_DUMP, no device: get "global" stringsets
+ - no NLM_F_DUMP, with device: get string sets related to the device
+ - NLM_F_DUMP, no device: get device related string sets for all devices
+
+If there is no ETHA_STRSET_STRINGSET attribute, all string sets of requested
+type are returned, otherwise only those specified in the request. Flag
+ETHA_STRSET_COUNTS tells kernel to only return string counts of the sets, not
+the actual strings.
+
+

+static int get_strset_id(const struct nlattr *nest, u32 *val,
+			 struct genl_info *info)
+{
+	struct nlattr *tb[ETHA_STRINGSET_MAX + 1];
+	int ret;
+
+	ret = nla_parse_nested(tb, ETHA_STRINGSET_MAX, nest, stringset_policy,
+			       info ? info->extack : NULL);

Would it make sense to use strict parsing everywhere from the start?
You seem to add REJECTS, but won't attributes > max get ignored?

+	if (ret < 0)
+		return ret;
+	if (!tb[ETHA_STRINGSET_ID])
+		return -EINVAL;
+
+	*val = nla_get_u32(tb[ETHA_STRINGSET_ID]);
+	return 0;
+}
+
+static int parse_strset(struct common_req_info *req_info, struct sk_buff *skb,
+			struct genl_info *info, const struct nlmsghdr *nlhdr)
+{
+	struct strset_data *data =
+		container_of(req_info, struct strset_data, reqinfo_base);
+	struct nlattr *attr;
+	int rem, ret;
+
+	ret = nlmsg_validate(nlhdr, GENL_HDRLEN, ETHA_STRSET_MAX,
+			     get_strset_policy, info ? info->extack : NULL);
+	if (ret < 0)
+		return ret;