[iproute2-next v3 2/3] mnlg: add function to get CTRL_ATTR_MAXATTR value

[Jacob Keller <jacob.e.keller@xxxxxxxxx>]

Add a new function to extract the CTRL_ATTR_MAXATTR attribute of the
CTRL_CMD_GETFAMILY request. This will be used to allow reading the
maximum supported devlink attribute of the running kernel in an upcoming
change.

Signed-off-by: Jacob Keller <jacob.e.keller@xxxxxxxxx>
---
 devlink/mnlg.c | 56 ++++++++++++++++++++++++++++++++++++++++++++++++++
 devlink/mnlg.h |  1 +
 2 files changed, 57 insertions(+)

diff --git a/devlink/mnlg.c b/devlink/mnlg.c
index e6d92742c150..348c3ff5c959 100644
--- a/devlink/mnlg.c
+++ b/devlink/mnlg.c
@@ -41,6 +41,10 @@ struct group_info {
 	const char *name;
 };
 
+struct family_info {
+	uint32_t max_attr;
+};
+
 static int parse_mc_grps_cb(const struct nlattr *attr, void *data)
 {
 	const struct nlattr **tb = data;
@@ -149,6 +153,58 @@ int mnlg_socket_group_add(struct mnlu_gen_socket *nlg, const char *group_name)
 	return 0;
 }
 
+static int get_family_attr_cb(const struct nlattr *attr, void *data)
+{
+	const struct nlattr **tb = data;
+	int type = mnl_attr_get_type(attr);
+
+	if (mnl_attr_type_valid(attr, CTRL_ATTR_MAX) < 0)
+		return MNL_CB_ERROR;
+
+	tb[type] = attr;
+	return MNL_CB_OK;
+}
+
+static int get_family_cb(const struct nlmsghdr *nlh, void *data)
+{
+	struct family_info *family = data;
+	struct nlattr *tb[CTRL_ATTR_MAX + 1] = {};
+	struct genlmsghdr *genl = mnl_nlmsg_get_payload(nlh);
+
+	mnl_attr_parse(nlh, sizeof(*genl), get_family_attr_cb, tb);
+	if (!tb[CTRL_ATTR_MAXATTR])
+		return MNL_CB_ERROR;
+
+	family->max_attr = mnl_attr_get_u32(tb[CTRL_ATTR_MAXATTR]);
+
+	return MNL_CB_OK;
+}
+
+int mnlg_socket_get_max_attr(struct mnlu_gen_socket *nlg, uint32_t *max_attr)
+{
+	struct nlmsghdr *nlh;
+	struct family_info family;
+	int err;
+
+	nlh = _mnlu_gen_socket_cmd_prepare(nlg, CTRL_CMD_GETFAMILY,
+					   NLM_F_REQUEST | NLM_F_ACK,
+					   GENL_ID_CTRL, 1);
+
+	mnl_attr_put_u16(nlh, CTRL_ATTR_FAMILY_ID, nlg->family);
+
+	err = mnlg_socket_send(nlg, nlh);
+	if (err < 0)
+		return err;
+
+	err = mnlu_gen_socket_recv_run(nlg, get_family_cb, &family);
+	if (err < 0)
+		return err;
+
+	*max_attr = family.max_attr;
+
+	return 0;
+}
+
 int mnlg_socket_get_fd(struct mnlu_gen_socket *nlg)
 {
 	return mnl_socket_get_fd(nlg->nl);
diff --git a/devlink/mnlg.h b/devlink/mnlg.h
index 24aa17566a9b..6348ad45ed26 100644
--- a/devlink/mnlg.h
+++ b/devlink/mnlg.h
@@ -18,6 +18,7 @@ struct mnlu_gen_socket;
 
 int mnlg_socket_send(struct mnlu_gen_socket *nlg, const struct nlmsghdr *nlh);
 int mnlg_socket_group_add(struct mnlu_gen_socket *nlg, const char *group_name);
+int mnlg_socket_get_max_attr(struct mnlu_gen_socket *nlg, uint32_t *max_attr);
 int mnlg_socket_get_fd(struct mnlu_gen_socket *nlg);
 
 #endif /* _MNLG_H_ */
-- 
2.35.1.456.ga9c7032d4631