devlink: allow user to narrow per-instance dumps by passing handle attrs

For SFs, one devlink instance per SF is created. There might be
thousands of these on a single host. When a user needs to know port
handle for specific SF, he needs to dump all devlink ports on the host
which does not scale good.

Allow user to pass devlink handle attributes alongside the dump command
and dump only objects which are under selected devlink instance.

Example:
$ devlink port show
auxiliary/mlx5_core.eth.0/65535: type eth netdev eth2 flavour physical port 0 splittable false
auxiliary/mlx5_core.eth.1/131071: type eth netdev eth3 flavour physical port 1 splittable false

$ devlink port show auxiliary/mlx5_core.eth.0
auxiliary/mlx5_core.eth.0/65535: type eth netdev eth2 flavour physical port 0 splittable false

$ devlink port show auxiliary/mlx5_core.eth.1
auxiliary/mlx5_core.eth.1/131071: type eth netdev eth3 flavour physical port 1 splittable false
Signed-off-by: Jiri Pirko <jiri@nvidia.com>
Acked-by: Jakub Kicinski <kuba@kernel.org>
Link: https://lore.kernel.org/r/20230811155714.1736405-11-jiri@resnulli.usSigned-off-by: Jakub Kicinski <kuba@kernel.org>

net/devlink/netlink.c

@@ -170,8 +170,30 @@ void devlink_nl_post_doit(const struct genl_split_ops *ops,
 	devlink_put(devlink);
 }
 
-int devlink_nl_dumpit(struct sk_buff *msg, struct netlink_callback *cb,
-		      devlink_nl_dump_one_func_t *dump_one)
+static int devlink_nl_inst_single_dumpit(struct sk_buff *msg,
+					 struct netlink_callback *cb, int flags,
+					 devlink_nl_dump_one_func_t *dump_one,
+					 struct nlattr **attrs)
+{
+	struct devlink *devlink;
+	int err;
+
+	devlink = devlink_get_from_attrs_lock(sock_net(msg->sk), attrs);
+	if (IS_ERR(devlink))
+		return PTR_ERR(devlink);
+	err = dump_one(msg, devlink, cb, flags | NLM_F_DUMP_FILTERED);
+
+	devl_unlock(devlink);
+	devlink_put(devlink);
+
+	if (err != -EMSGSIZE)
+		return err;
+	return msg->len;
+}
+
+static int devlink_nl_inst_iter_dumpit(struct sk_buff *msg,
+				       struct netlink_callback *cb, int flags,
+				       devlink_nl_dump_one_func_t *dump_one)
 {
 	struct devlink_nl_dump_state *state = devlink_dump_state(cb);
 	struct devlink *devlink;
@@ -182,7 +204,7 @@ int devlink_nl_dumpit(struct sk_buff *msg, struct netlink_callback *cb,
 		devl_lock(devlink);
 
 		if (devl_is_registered(devlink))
-			err = dump_one(msg, devlink, cb, NLM_F_MULTI);
+			err = dump_one(msg, devlink, cb, flags);
 		else
 			err = 0;
 
@@ -203,6 +225,21 @@ int devlink_nl_dumpit(struct sk_buff *msg, struct netlink_callback *cb,
 	return msg->len;
 }
 
+int devlink_nl_dumpit(struct sk_buff *msg, struct netlink_callback *cb,
+		      devlink_nl_dump_one_func_t *dump_one)
+{
+	const struct genl_dumpit_info *info = genl_dumpit_info(cb);
+	struct nlattr **attrs = info->attrs;
+	int flags = NLM_F_MULTI;
+
+	if (attrs &&
+	    (attrs[DEVLINK_ATTR_BUS_NAME] || attrs[DEVLINK_ATTR_DEV_NAME]))
+		return devlink_nl_inst_single_dumpit(msg, cb, flags, dump_one,
+						     attrs);
+	else
+		return devlink_nl_inst_iter_dumpit(msg, cb, flags, dump_one);
+}
+
 struct genl_family devlink_nl_family __ro_after_init = {
 	.name		= DEVLINK_GENL_NAME,
 	.version	= DEVLINK_GENL_VERSION,