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

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Date:   Mon, 26 Oct 2020 19:24:57 +0100
From:   Stefano Garzarella <sgarzare@...hat.com>
To:     Colin King <colin.king@...onical.com>,
        Jakub Kicinski <kuba@...nel.org>
Cc:     David Laight <David.Laight@...lab.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 10:55:48AM -0700, Jakub Kicinski wrote:
>On Mon, 26 Oct 2020 11:01:12 +0100 Stefano Garzarella wrote:
>> 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?
>
>ENOIOCTLCMD is a kernel-internal high return code (515) which should
>be returned by the driver, but it's then caught inside the core and
>translated to ENOTTY which is then returned to user space.
>
>So you're both right, I guess? But the driver should use ENOIOCTLCMD.
>

Thanks for clarify!

@Colin, can you send a v2 removing the error message and updating the 
return value?

Thanks,
Stefano