linux-kernel - Re: Kernel version numbers after 4.9.255 and 4.4.255

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Message-ID: <a85b7749-38b2-8ce9-c15a-8acb9a54c5b5@kernel.org>
Date:   Thu, 4 Feb 2021 12:00:31 +0100
From:   Jiri Slaby <jirislaby@...nel.org>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Jari Ruusu <jariruusu@...tonmail.com>,
        Sasha Levin <sashal@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>,
        "torvalds@...ux-foundation.org" <torvalds@...ux-foundation.org>,
        masahiroy@...nel.org
Subject: Re: Kernel version numbers after 4.9.255 and 4.4.255

On 04. 02. 21, 9:51, Greg Kroah-Hartman wrote:
>> It might work somewhere, but there are a lot of (X * 65536 + Y * 256 + Z)
>> assumptions all around the world. So this doesn't look like a good idea.
> 
> Ok, so what happens if we "wrap"?  What will break with that?  At first
> glance, I can't see anything as we keep the padding the same, and our
> build scripts seem to pick the number up from the Makefile and treat it
> like a string.
> 
> It's only the crazy out-of-tree kernel stuff that wants to do minor
> version checks that might go boom.  And frankly, I'm not all that
> concerned if they have problems :)

Agreed. But currently, sublevel won't "wrap", it will "overflow" to 
patchlevel. And that might be a problem. So we might need to update the 
header generation using e.g. "sublevel & 0xff" (wrap around) or 
"sublevel > 255 : 255 : sublevel" (be monotonic and get stuck at 255).

In both LINUX_VERSION_CODE generation and KERNEL_VERSION proper.

thanks,
-- 
js