linux-kernel - Re: [PATCH net-next 5/5] net: dsa: split dsa

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Date:   Thu, 12 Oct 2017 19:21:54 -0400
From:   Vivien Didelot <vivien.didelot@...oirfairelinux.com>
To:     Florian Fainelli <f.fainelli@...il.com>, netdev@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, kernel@...oirfairelinux.com,
        "David S. Miller" <davem@...emloft.net>,
        Andrew Lunn <andrew@...n.ch>
Subject: Re: [PATCH net-next 5/5] net: dsa: split dsa_port's netdev member

Hi Florian,

Florian Fainelli <f.fainelli@...il.com> writes:

> On 10/12/2017 03:51 PM, Vivien Didelot wrote:
>> The dsa_port structure has a "netdev" member, which can be used for
>> either the master device, or the slave device, depending on its type.
>> 
>> It is true that today, CPU port are not exposed to userspace, thus the
>> port's netdev member can be used to point to its master interface.
>> 
>> But it is still slightly confusing, so split it into more explicit
>> "master" and "slave" members.
>
> I do see some value in doing that, although I also see value in having
> structure members be named after what they are, rather than their use
> (oh well, it's all debatable anyway), see below for a suggestion on how
> to reconcile the two:
>
>>  struct dsa_port {
>> +	/* Master device, physically connected if this is a CPU port */
>> +	struct net_device *master;
>> +
>> +	/* Slave device, if this port is exposed to userspace */
>> +	struct net_device *slave;
>> +
>
> How about using:
>
> 	union {
> 		struct net_device *master;
> 		struct net_device *slave;
> 	} netdev;
>
> Such that this serves both purposes of clearly communicating what the
> structure member is, and it can be either one of the two, but not both
> at the same time?

I love that! It makes clear that master is not available for a non-CPU
port. Using this union is correct for the moment because DSA and CPU
ports don't have a slave device attached to them. If this becomes true
one day (unlikely), we'll remove the union.


Thanks,

        Vivien