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SubjectRe: [PATCH] net: dsa: use NET_NAME_PREDICTABLE for user ports with name given in DT
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On 11/11/2022 18.10, Andrew Lunn wrote:
>> diff --git a/net/dsa/slave.c b/net/dsa/slave.c
>> index a9fde48cffd4..dfefcc4a9ccf 100644
>> --- a/net/dsa/slave.c
>> +++ b/net/dsa/slave.c
>> @@ -2374,16 +2374,25 @@ int dsa_slave_create(struct dsa_port *port)
>> {
>> struct net_device *master = dsa_port_to_master(port);
>> struct dsa_switch *ds = port->ds;
>> - const char *name = port->name;
>> struct net_device *slave_dev;
>> struct dsa_slave_priv *p;
>> + const char *name;
>> + int assign_type;
>> int ret;
>>
>> if (!ds->num_tx_queues)
>> ds->num_tx_queues = 1;
>>
>> + if (port->name) {
>> + name = port->name;
>> + assign_type = NET_NAME_PREDICTABLE;
>> + } else {
>> + name = "eth%d";
>> + assign_type = NET_NAME_UNKNOWN;
>> + }
>
> I know it is a change in behaviour, but it seems like NET_NAME_ENUM
> should be used, not NET_NAME_UNKNOWN. alloc_etherdev_mqs() uses
> NET_NAME_ENUM.

I don't really have any strong opinion on the case where we fall back to
eth%d, as its not relevant to any board I've worked on.

> https://elixir.bootlin.com/linux/latest/source/include/uapi/linux/netdevice.h#L42
> says that NET_NAME_UNKNOWN does not get passed to user space, but i
> assume NET_NAME_ENUM does. So maybe changing it would be an ABI
> change?

Well, the name_assign_type ABI is kind of silly. I mean, userspace knows
that when one gets EINVAL trying to read the value, that really means
that the value is NET_NAME_UNKNOWN. But I won't propose changing that.

However, what I do propose here is obviously already an ABI change; I
_want_ to expose more proper information in the case where the port has
a label, and just kept the NET_NAME_UNKNOWN for the eth%d case to make
the minimal change. But if people want to change that to NET_NAME_ENUM
while we're here, I can certainly do that. I can't think of any real
scenario where NET_NAME_ENUM would be treated differently than
NET_NAME_UNKNOWN - in both cases, userspace don't know that the name can
be trusted to be predictable.

Rasmus

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