RE: [PATCH] vsock: ratelimit unknown ioctl error message

From: Stefano Garzarella

Sent: 26 October 2020 09:39

On Mon, Oct 26, 2020 at 09:13:23AM +0000, David Laight wrote:

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From: Stefano Garzarella

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Sent: 26 October 2020 08:43

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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.

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No idea where ENOIOCTLCMD comes from, but ENOTTY probably
goes back to the early 1970s.

Me too.

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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.

Back in the old days error values were probably almost unique.
strerror(EAGIAN) was "No more processes" for a long time!

	David

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