Re: [patch net-next v2 14/15] devlink: move port_del() to devlink_port_ops

[Jiri Pirko <jiri@resnulli.us>]

Tue, May 30, 2023 at 03:41:19AM CEST, kuba@kernel.org wrote:
>On Mon, 29 May 2023 10:31:14 +0200 Jiri Pirko wrote:
>> >One could argue logically removing a port is also an operation of 
>> >the parent (i.e. the devlink instance). The fact that the port gets
>> >destroyed in the process is secondary. Ergo maybe we should skip 
>> >this patch?  
>> 
>> Well, the port_del() could differ for different port flavours. The
>> embedding structure of struct devlink_port is also different.
>> 
>> Makes sense to me to skip the flavour switch and have one port_del() for
>> each port.
>
>The asymmetry bothers me. It's hard to comment on what the best

Yeah, I had the same problem with that, but after a lots of thinking,
it is a best I could think of. Please see below for the reasoning.


>approach is given this series shows no benefit of moving port_del().
>Maybe even a loss, as mlx5 now has an ifdef in two places:
>
>> diff --git a/drivers/net/ethernet/mellanox/mlx5/core/devlink.c b/drivers/net/ethernet/mellanox/mlx5/core/devlink.c
>> index e39fd85ea2f9..63635cc44479 100644
>> --- a/drivers/net/ethernet/mellanox/mlx5/core/devlink.c
>> +++ b/drivers/net/ethernet/mellanox/mlx5/core/devlink.c
>> @@ -320,7 +320,6 @@ static const struct devlink_ops mlx5_devlink_ops = {
>>  #endif
>>  #ifdef CONFIG_MLX5_SF_MANAGER
>>  	.port_new = mlx5_devlink_sf_port_new,
>> -	.port_del = mlx5_devlink_sf_port_del,
>>  #endif
>>  	.flash_update = mlx5_devlink_flash_update,
>>  	.info_get = mlx5_devlink_info_get,
>> diff --git a/drivers/net/ethernet/mellanox/mlx5/core/esw/devlink_port.c b/drivers/net/ethernet/mellanox/mlx5/core/esw/devlink_port.c
>> index 76c5d6e9d47f..f370f67d9e33 100644
>> --- a/drivers/net/ethernet/mellanox/mlx5/core/esw/devlink_port.c
>> +++ b/drivers/net/ethernet/mellanox/mlx5/core/esw/devlink_port.c
>> @@ -145,6 +145,9 @@ struct devlink_port *mlx5_esw_offloads_devlink_port(struct mlx5_eswitch *esw, u1
>>  }
>>  
>>  static const struct devlink_port_ops mlx5_esw_dl_sf_port_ops = {
>> +#ifdef CONFIG_MLX5_SF_MANAGER
>> +	.port_del = mlx5_devlink_sf_port_del,
>> +#endif

Btw, this ifdef is going to go away in a follow-up patchset.


>>  	.port_fn_hw_addr_get = mlx5_devlink_port_fn_hw_addr_get,
>>  	.port_fn_hw_addr_set = mlx5_devlink_port_fn_hw_addr_set,
>>  	.port_fn_roce_get = mlx5_devlink_port_fn_roce_get,
>
>Is it okay if we deferred the port_del() patch until there's some
>clear benefit?

Well actually, there is a clear benefit even in this patchset:

We have 2 flavours of ports each with different ops in mlx5:
VF:
static const struct devlink_port_ops mlx5_esw_dl_port_ops = {
        .port_fn_hw_addr_get = mlx5_devlink_port_fn_hw_addr_get,
        .port_fn_hw_addr_set = mlx5_devlink_port_fn_hw_addr_set,
        .port_fn_roce_get = mlx5_devlink_port_fn_roce_get,
        .port_fn_roce_set = mlx5_devlink_port_fn_roce_set,
        .port_fn_migratable_get = mlx5_devlink_port_fn_migratable_get,
        .port_fn_migratable_set = mlx5_devlink_port_fn_migratable_set,
};

SF:
static const struct devlink_port_ops mlx5_esw_dl_sf_port_ops = {
        .port_del = mlx5_devlink_sf_port_del,
        .port_fn_hw_addr_get = mlx5_devlink_port_fn_hw_addr_get,
        .port_fn_hw_addr_set = mlx5_devlink_port_fn_hw_addr_set,
        .port_fn_roce_get = mlx5_devlink_port_fn_roce_get,
        .port_fn_roce_set = mlx5_devlink_port_fn_roce_set,
        .port_fn_state_get = mlx5_devlink_sf_port_fn_state_get,
        .port_fn_state_set = mlx5_devlink_sf_port_fn_state_set,
};

You can see that the port_del() op is supported only on the SF flavour.
VF does not support it and therefore port_del() is not defined on it.

Without this patch, I would have to have a helper
mlx5_devlink_port_del() that would check if the port is SF and call
mlx5_devlink_sf_port_del() in that case. This patch reduces the
boilerplate.


Btw if you look at the cmd line api, it also aligns:
$ devlink port add pci/0000:08:00.0 flavour pcisf pfnum 0 sfnum 101
pci/0000:08:00.0/32768: type eth netdev eth4 flavour pcisf controller 0 pfnum 0 sfnum 101 splittable false
  function:
    hw_addr 00:00:00:00:00:00 state inactive opstate detached
$ devlink port del pci/0000:08:00.0/32768

You use pci/0000:08:00.0/32768 as a delete handle.

port_del() is basically an object destructor. Would it perhaps help to
rename is to .port_destructor()? That would somehow ease the asymmetry
:) IDK. I would leave the name as it is a and move to port_ops.