netdev - [RFC iproute2 2/6] utils: extract CTRL_ATTR

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Date:   Fri,  5 Aug 2022 16:41:51 -0700
From:   Jacob Keller <jacob.e.keller@...el.com>
To:     netdev@...r.kernel.org
Cc:     Jacob Keller <jacob.e.keller@...el.com>,
        Jonathan Corbet <corbet@....net>, Jiri Pirko <jiri@...dia.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        David Ahern <dsahern@...nel.org>,
        Stephen Hemminger <stephen@...workplumber.org>
Subject: [RFC iproute2 2/6] utils: extract CTRL_ATTR_MAXATTR and save it

mnlu_gen_socket_open opens a socket and configures it for use with a
generic netlink family. As part of this process it sends a
CTRL_CMD_GETFAMILY to get the ID for the family name requested.

In addition to the family id, this command reports a few other useful
values including the maximum attribute. The maximum attribute is useful in
order to know whether a given attribute is supported and for knowing the
necessary size to allocate for other operations such as policy dumping.

Since we already have to issue a CTRL_CMD_GETFAMILY to get the id, we can
also store the maximum attribute as well. Modify the callback functions to
parse the maximum attribute NLA and store it in the mnlu_gen_socket
structure.

Signed-off-by: Jacob Keller <jacob.e.keller@...el.com>
---
 include/mnl_utils.h |  1 +
 lib/mnl_utils.c     | 18 ++++++++++++------
 2 files changed, 13 insertions(+), 6 deletions(-)

diff --git a/include/mnl_utils.h b/include/mnl_utils.h
index aa5f0a9b17c7..2193934849e1 100644
--- a/include/mnl_utils.h
+++ b/include/mnl_utils.h
@@ -6,6 +6,7 @@ struct mnlu_gen_socket {
 	struct mnl_socket *nl;
 	char *buf;
 	uint32_t family;
+	uint32_t maxattr;
 	unsigned int seq;
 	uint8_t version;
 };
diff --git a/lib/mnl_utils.c b/lib/mnl_utils.c
index d5abff58d816..79bac5cfd4de 100644
--- a/lib/mnl_utils.c
+++ b/lib/mnl_utils.c
@@ -110,7 +110,7 @@ int mnlu_socket_recv_run(struct mnl_socket *nl, unsigned int seq, void *buf, siz
 	return err;
 }
 
-static int get_family_id_attr_cb(const struct nlattr *attr, void *data)
+static int get_family_attrs_cb(const struct nlattr *attr, void *data)
 {
 	int type = mnl_attr_get_type(attr);
 	const struct nlattr **tb = data;
@@ -121,20 +121,26 @@ static int get_family_id_attr_cb(const struct nlattr *attr, void *data)
 	if (type == CTRL_ATTR_FAMILY_ID &&
 	    mnl_attr_validate(attr, MNL_TYPE_U16) < 0)
 		return MNL_CB_ERROR;
+	if (type == CTRL_ATTR_MAXATTR &&
+	    mnl_attr_validate(attr, MNL_TYPE_U32) < 0)
+		return MNL_CB_ERROR;
 	tb[type] = attr;
 	return MNL_CB_OK;
 }
 
-static int get_family_id_cb(const struct nlmsghdr *nlh, void *data)
+static int get_family_cb(const struct nlmsghdr *nlh, void *data)
 {
 	struct genlmsghdr *genl = mnl_nlmsg_get_payload(nlh);
 	struct nlattr *tb[CTRL_ATTR_MAX + 1] = {};
-	uint32_t *p_id = data;
+	struct mnlu_gen_socket *nlg = data;
 
-	mnl_attr_parse(nlh, sizeof(*genl), get_family_id_attr_cb, tb);
+	mnl_attr_parse(nlh, sizeof(*genl), get_family_attrs_cb, tb);
 	if (!tb[CTRL_ATTR_FAMILY_ID])
 		return MNL_CB_ERROR;
-	*p_id = mnl_attr_get_u16(tb[CTRL_ATTR_FAMILY_ID]);
+	if (!tb[CTRL_ATTR_MAXATTR])
+		return MNL_CB_ERROR;
+	nlg->family = mnl_attr_get_u16(tb[CTRL_ATTR_FAMILY_ID]);
+	nlg->maxattr = mnl_attr_get_u32(tb[CTRL_ATTR_MAXATTR]);
 	return MNL_CB_OK;
 }
 
@@ -159,7 +165,7 @@ static int family_get(struct mnlu_gen_socket *nlg, const char *family_name)
 
 	err = mnlu_socket_recv_run(nlg->nl, nlh->nlmsg_seq, nlg->buf,
 				   MNL_SOCKET_BUFFER_SIZE,
-				   get_family_id_cb, &nlg->family);
+				   get_family_cb, nlg);
 	return err;
 }
 
-- 
2.37.1.208.ge72d93e88cb2