Re: [PATCH net-next v5 05/22] ethtool: introduce ethtool netlink interface

[Florian Fainelli]

On 3/28/19 6:23 AM, Jiri Pirko wrote:
> Thu, Mar 28, 2019 at 10:37:46AM CET, mkubecek@xxxxxxx wrote:
>> On Thu, Mar 28, 2019 at 09:10:10AM +0100, Jiri Pirko wrote:
>>> Thu, Mar 28, 2019 at 03:05:14AM CET, f.fainelli@xxxxxxxxx wrote:
>>>>
>>>>
>>>> On 3/27/2019 2:50 AM, Jiri Pirko wrote:
>>>>>
>>>>> Why don't you have ETHTOOL_MSG_SET_FOO for set? I think that for
>>>>> kerne->userspace the ETHTOOL_MSG_FOO if fine. I would change the
>>>>> ordering of words thought, but it is cosmetics:
>>>>> ETHTOOL_MSG_FOO /* kernel->userspace messages - replies, notifications */
>>>>> ETHTOOL_MSG_FOO_GET
>>>>> ETHTOOL_MSG_FOO_SET
>>>>> ETHTOOL_MSG_FOO_ACT
>>>>>
>>>>> What do you think?
>>>>
>>>> We could even name the notification explicitly with: ETHTOOL_MSG_NOTIF
>>>> or ETHTOOL_MSG_NTF just so we spell out exactly what those messages are.
>>>
>>> Sound good. Something like:
>>>
>>> ETHTOOL_MSG_FOO_GET
>>> ETHTOOL_MSG_FOO_GET_RPLY /* kernel->userspace replies to get */
>>> ETHTOOL_MSG_FOO_SET
>>> ETHTOOL_MSG_FOO_ACT
>>> ETHTOOL_MSG_FOO_NTF /* kernel->userspace async messages - notifications */
>>
>> The names sound fine to me and having different message ids would still
>> allow processing messages by the same handler easily.
>>
>> But there is one potential issue I would like to point out: this way we
>> spend 4 message ids for a get/set pair rather than 2. These message ids
>> (genlmsghdr::cmd) are u8, i.e. the resource is not as infinite as one
>> would wish. There are 80 ioctl commands (43 "get" and 29 "set") at the
>> moment.
>>
>> Netlink API should be less greedy in general. I already combined some
>> ioctl commands into one netlink request type and with an easy way to add
>> new attributes to existing commands, we won't need to add new commands
>> as often (certainly not in a way which left us with 9 "get" and 9 "set"
>> ioctl commands for netdev features). So even with 4 ids per get/set
>> pair, we might be safe for reasonably long time. But it's still
>> something to keep in mind.
> 
> There are still 16 bits reserve in genl msg header:
> struct genlmsghdr {
>         __u8    cmd;
>         __u8    version;
>         __u16   reserved;
> };
> 

And you know not all message IDs will be making sense depending on the
direction, so aliasing specific message IDs to an existing value should
be fine?
-- 
Florian