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

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Date:   Thu, 28 Mar 2019 14:23:16 +0100
From:   Jiri Pirko <jiri@...nulli.us>
To:     Michal Kubecek <mkubecek@...e.cz>
Cc:     Florian Fainelli <f.fainelli@...il.com>,
        David Miller <davem@...emloft.net>, netdev@...r.kernel.org,
        Jakub Kicinski <jakub.kicinski@...ronome.com>,
        Andrew Lunn <andrew@...n.ch>,
        John Linville <linville@...driver.com>,
        Stephen Hemminger <stephen@...workplumber.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next v5 05/22] ethtool: introduce ethtool netlink
 interface

Thu, Mar 28, 2019 at 10:37:46AM CET, mkubecek@...e.cz 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@...il.com 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;
};