netdev - Re: [PATCH] vsock: ratelimit unknown ioctl error message

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Date:   Mon, 26 Oct 2020 11:01:12 +0100
From:   Stefano Garzarella <sgarzare@...hat.com>
To:     David Laight <David.Laight@...lab.com>,
        Jakub Kicinski <kuba@...nel.org>
Cc:     Colin King <colin.king@...onical.com>,
        "David S . Miller" <davem@...emloft.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "kernel-janitors@...r.kernel.org" <kernel-janitors@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] vsock: ratelimit unknown ioctl error message

On Mon, Oct 26, 2020 at 09:46:17AM +0000, David Laight wrote:
>From: Stefano Garzarella
>> Sent: 26 October 2020 09:39
>>
>> On Mon, Oct 26, 2020 at 09:13:23AM +0000, David Laight wrote:
>> >From: Stefano Garzarella
>> >> Sent: 26 October 2020 08:43
>> >...
>> >> >Isn't the canonical error for unknown ioctl codes -ENOTTY?
>> >> >
>> >>
>> >> Oh, thanks for pointing that out!
>> >>
>> >> I had not paid attention to the error returned, but looking at it I
>> >> noticed that perhaps the most appropriate would be -ENOIOCTLCMD.
>> >> In the ioctl syscall we return -ENOTTY, if the callback returns
>> >> -ENOIOCTLCMD.
>> >>
>> >> What do you think?
>> >
>> >It is 729 v 443 in favour of ENOTTY (based on grep).
>>
>> Under net/ it is 6 vs 83 in favour of ENOIOCTLCMD.
>>
>> >
>> >No idea where ENOIOCTLCMD comes from, but ENOTTY probably
>> >goes back to the early 1970s.
>>
>> Me too.
>>
>> >
>> >The fact that the ioctl wrapper converts the value is a good
>> >hint that userspace expects ENOTTY.
>>
>> Agree on that, but since we are not interfacing directly with userspace,
>> I think it is better to return the more specific error (ENOIOCTLCMD).
>
>I bet Linux thought it could use a different error code then
>found that 'unknown ioctl' was spelt ENOTTY.

It could be :-)

Anyway, as you pointed out, I think we should change the -EINVAL with 
-ENOTTY or -ENOIOCTLCMD.

@Jakub what do you suggest?

Thanks,
Stefano