devlink: use an explicit structure for dump context

Create a dump context structure instead of using cb->args
as an unsigned long array. This is a pure conversion which
is intended to be as much of a noop as possible.
Subsequent changes will use this to simplify the code.

The two non-trivial parts are:
 - devlink_nl_cmd_health_reporter_dump_get_dumpit() checks args[0]
   to see if devlink_fmsg_dumpit() has already been called (whether
   this is the first msg), but doesn't use the exact value, so we
   can drop the local variable there already
 - devlink_nl_cmd_region_read_dumpit() uses args[0] for address
   but we'll use args[1] now, shouldn't matter
Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
Reviewed-by: Jiri Pirko <jiri@nvidia.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

net/devlink/devl_internal.h

@@ -107,6 +107,21 @@ enum devlink_multicast_groups {
 	DEVLINK_MCGRP_CONFIG,
 };
 
+/* state held across netlink dumps */
+struct devlink_nl_dump_state {
+	int idx;
+	union {
+		/* DEVLINK_CMD_REGION_READ */
+		struct {
+			u64 start_offset;
+		};
+		/* DEVLINK_CMD_HEALTH_REPORTER_DUMP_GET */
+		struct {
+			u64 dump_ts;
+		};
+	};
+};
+
 extern const struct genl_small_ops devlink_nl_ops[56];
 
 struct devlink *devlink_get_from_attrs(struct net *net, struct nlattr **attrs);
@@ -114,6 +129,14 @@ struct devlink *devlink_get_from_attrs(struct net *net, struct nlattr **attrs);
 void devlink_notify_unregister(struct devlink *devlink);
 void devlink_notify_register(struct devlink *devlink);
 
+static inline struct devlink_nl_dump_state *
+devlink_dump_state(struct netlink_callback *cb)
+{
+	NL_ASSET_DUMP_CTX_FITS(struct devlink_nl_dump_state);
+
+	return (struct devlink_nl_dump_state *)cb->ctx;
+}
+
 /* Ports */
 int devlink_port_netdevice_event(struct notifier_block *nb,
 				 unsigned long event, void *ptr);