netdevsim: Add extack error message for devlink reload

devlink reset command can fail if a FIB resource limit is set to a value
lower than the current occupancy. Return a proper message indicating the
reason for the failure.

$ devlink resource sh netdevsim/netdevsim0
netdevsim/netdevsim0:
name IPv4 size unlimited unit entry size_min 0 size_max unlimited size_gran 1 dpipe_tables none
resources:
name fib size unlimited occ 43 unit entry size_min 0 size_max unlimited size_gran 1 dpipe_tables none
name fib-rules size unlimited occ 4 unit entry size_min 0 size_max unlimited size_gran 1 dpipe_tables none
name IPv6 size unlimited unit entry size_min 0 size_max unlimited size_gran 1 dpipe_tables none
resources:
name fib size unlimited occ 54 unit entry size_min 0 size_max unlimited size_gran 1 dpipe_tables none
name fib-rules size unlimited occ 3 unit entry size_min 0 size_max unlimited size_gran 1 dpipe_tables none

$ devlink resource set netdevsim/netdevsim0 path /IPv4/fib size 40

$ devlink dev reload netdevsim/netdevsim0
Error: netdevsim: New size is less than current occupancy.
devlink answers: Invalid argument

Signed-off-by: David Ahern <[e-mail]>
Acked-by: Jakub Kicinski <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

drivers/net/netdevsim/devlink.c

···
 
 		err = devlink_resource_size_get(devlink, res_ids[i], &val);
 		if (!err) {
-			err = nsim_fib_set_max(net, res_ids[i], val);
+			err = nsim_fib_set_max(net, res_ids[i], val, extack);
 			if (err)
 				return err;
 		}
···
 	int i;
 
 	for (i = 0; i < ARRAY_SIZE(res_ids); ++i) {
-		if (nsim_fib_set_max(net, res_ids[i], (u64)-1)) {
+		if (nsim_fib_set_max(net, res_ids[i], (u64)-1, NULL)) {
 			pr_err("Failed to reset limit for resource %u\n",
 			       res_ids[i]);
 		}

drivers/net/netdevsim/fib.c

···
 	return max ? entry->max : entry->num;
 }
 
-int nsim_fib_set_max(struct net *net, enum nsim_resource_id res_id, u64 val)
+int nsim_fib_set_max(struct net *net, enum nsim_resource_id res_id, u64 val,
+		     struct netlink_ext_ack *extack)
 {
 	struct nsim_fib_data *fib_data = net_generic(net, nsim_fib_net_id);
 	struct nsim_fib_entry *entry;
···
 	/* not allowing a new max to be less than curren occupancy
 	 * --> no means of evicting entries
 	 */
-	if (val < entry->num)
+	if (val < entry->num) {
+		NL_SET_ERR_MSG_MOD(extack, "New size is less than current occupancy");
 		err = -EINVAL;
-	else
+	} else {
 		entry->max = val;
+	}
 
 	return err;
 }

drivers/net/netdevsim/netdevsim.h

···
 int nsim_fib_init(void);
 void nsim_fib_exit(void);
 u64 nsim_fib_get_val(struct net *net, enum nsim_resource_id res_id, bool max);
-int nsim_fib_set_max(struct net *net, enum nsim_resource_id res_id, u64 val);
+int nsim_fib_set_max(struct net *net, enum nsim_resource_id res_id, u64 val,
+		     struct netlink_ext_ack *extack);
 #else
 static inline int nsim_devlink_setup(struct netdevsim *ns)
 {