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Subject: Re: [PATCH net-next v5 05/22] ethtool: introduce ethtool netlink
 interface
To:     Jiri Pirko <jiri@resnulli.us>, Michal Kubecek <mkubecek@suse.cz>
Cc:     David Miller <davem@davemloft.net>, netdev@vger.kernel.org,
        Jakub Kicinski <jakub.kicinski@netronome.com>,
        Andrew Lunn <andrew@lunn.ch>,
        John Linville <linville@tuxdriver.com>,
        Stephen Hemminger <stephen@networkplumber.org>,
        linux-kernel@vger.kernel.org
References: <cover.1553532199.git.mkubecek@suse.cz>
 <8795d07d3315b232b4e7ebc7d109c9aa3185e555.1553532199.git.mkubecek@suse.cz>
 <20190326120909.GF2230@nanopsycho> <20190326132427.GK26076@unicorn.suse.cz>
 <20190326134251.GA5181@nanopsycho.orion>
 <20190327092604.GP26076@unicorn.suse.cz> <20190327095023.GC6979@nanopsycho>
 <7e883a7c-7f1a-b1a0-4735-0ad368998c65@gmail.com>
 <20190328081010.GJ14297@nanopsycho> <20190328093746.GA26076@unicorn.suse.cz>
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From:   Florian Fainelli <f.fainelli@gmail.com>
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Message-ID: <5edb07f0-427f-8a06-97f5-d904b4a50cc1@gmail.com>
Date:   Thu, 28 Mar 2019 10:00:20 -0700
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On 3/28/19 6:23 AM, Jiri Pirko wrote:
> Thu, Mar 28, 2019 at 10:37:46AM CET, mkubecek@suse.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@gmail.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;
> };
> 

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