genl: Support registration of families without depending on caches

Introduces the functions genl_register_family() and
genl_unregister_family() to register a Generic Netlink family
which does not implement a cachable type.

API users can direct received messages into genl_handle_msg() which
will validate the messages and call the callback functions defined
in the commands definition.

See test/test-genl.c for an example on how to use it.

1 files changed, 83 insertions, 4 deletions

diff --git a/tests/test-genl.c b/tests/test-genl.c
index 2706a92..63862b3 100644
--- a/tests/test-genl.c
+++ b/tests/test-genl.c
@@ -1,4 +1,72 @@
 #include <netlink/cli/utils.h>
+#include <linux/taskstats.h>
+
+static struct nla_policy attr_policy[TASKSTATS_TYPE_MAX+1] = {
+	[TASKSTATS_TYPE_PID]	= { .type = NLA_U32 },
+	[TASKSTATS_TYPE_TGID]	= { .type = NLA_U32 },
+	[TASKSTATS_TYPE_STATS]	= { .minlen = sizeof(struct taskstats) },
+	[TASKSTATS_TYPE_AGGR_PID] = { .type = NLA_NESTED },
+	[TASKSTATS_TYPE_AGGR_TGID] = { .type = NLA_NESTED },
+};
+
+
+static int parse_cmd_new(struct nl_cache_ops *unused, struct genl_cmd *cmd,
+			 struct genl_info *info, void *arg)
+{
+	struct nlattr *attrs[TASKSTATS_TYPE_MAX+1];
+	struct nlattr *nested;
+	int err;
+
+	if (info->attrs[TASKSTATS_TYPE_AGGR_PID])
+		nested = info->attrs[TASKSTATS_TYPE_AGGR_PID];
+	else if (info->attrs[TASKSTATS_TYPE_AGGR_TGID])
+		nested = info->attrs[TASKSTATS_TYPE_AGGR_TGID];
+	else {
+		fprintf(stderr, "Invalid taskstats message: Unable to find "
+				"nested attribute/\n");
+		return NL_SKIP;
+	}
+
+	err = nla_parse_nested(attrs, TASKSTATS_TYPE_MAX, nested, attr_policy);
+	if (err < 0) {
+		nl_perror(err, "Error while parsing generic netlink message");
+		return err;
+	}
+
+
+	if (attrs[TASKSTATS_TYPE_STATS]) {
+		struct taskstats *stats = nla_data(attrs[TASKSTATS_TYPE_STATS]);
+
+		printf("%s pid %u uid %u gid %u parent %u\n",
+		       stats->ac_comm, stats->ac_pid, stats->ac_uid,
+		       stats->ac_gid, stats->ac_ppid);
+	}
+
+	return 0;
+}
+
+static int parse_cb(struct nl_msg *msg, void *arg)
+{
+	return genl_handle_msg(msg, NULL);
+}
+
+static struct genl_cmd cmds[] = {
+	{
+		.c_id		= TASKSTATS_CMD_NEW,
+		.c_name		= "taskstats_new()",
+		.c_maxattr	= TASKSTATS_TYPE_MAX,
+		.c_attr_policy	= attr_policy,
+		.c_msg_parser	= &parse_cmd_new,
+	},
+};
+
+#define ARRAY_SIZE(X) (sizeof(X) / sizeof((X)[0]))
+
+static struct genl_ops ops = {
+	.o_name = TASKSTATS_GENL_NAME,
+	.o_cmds = cmds,
+	.o_ncmds = ARRAY_SIZE(cmds),
+};
 
 int main(int argc, char *argv[])
 {
@@ -10,25 +78,36 @@ int main(int argc, char *argv[])
 	sock = nl_cli_alloc_socket();
 	nl_cli_connect(sock, NETLINK_GENERIC);
 
+	if ((err = genl_register_family(&ops)) < 0)
+		nl_cli_fatal(err, "Unable to register Generic Netlink family");
+
+	if ((err = genl_ops_resolve(sock, &ops)) < 0)
+		nl_cli_fatal(err, "Unable to resolve family name");
+
 	msg = nlmsg_alloc();
 	if (msg == NULL)
 		nl_cli_fatal(NLE_NOMEM, "Unable to allocate netlink message");
 
-	hdr = genlmsg_put(msg, NL_AUTO_PID, NL_AUTO_SEQ, GENL_ID_CTRL,
-			  0, 0, CTRL_CMD_GETFAMILY, 1);
+	hdr = genlmsg_put(msg, NL_AUTO_PORT, NL_AUTO_SEQ, ops.o_id,
+			  0, 0, TASKSTATS_CMD_GET, TASKSTATS_GENL_VERSION);
 	if (hdr == NULL)
 		nl_cli_fatal(ENOMEM, "Unable to write genl header");
 
-	if ((err = nla_put_u32(msg, CTRL_ATTR_FAMILY_ID, GENL_ID_CTRL)) < 0)
+	if ((err = nla_put_u32(msg, TASKSTATS_CMD_ATTR_PID, 1)) < 0)
 		nl_cli_fatal(err, "Unable to add attribute: %s", nl_geterror(err));
 
 	if ((err = nl_send_auto_complete(sock, msg)) < 0)
 		nl_cli_fatal(err, "Unable to send message: %s", nl_geterror(err));
 
+	nlmsg_free(msg);
+
+	if ((err = nl_socket_modify_cb(sock, NL_CB_VALID, NL_CB_CUSTOM,
+			parse_cb, NULL)) < 0)
+		nl_cli_fatal(err, "Unable to modify valid message callback");
+
 	if ((err = nl_recvmsgs_default(sock)) < 0)
 		nl_cli_fatal(err, "Unable to receive message: %s", nl_geterror(err));
 
-	nlmsg_free(msg);
 	nl_close(sock);
 	nl_socket_free(sock);