Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Subject: Re: Kernel version numbers after 4.9.255 and 4.4.255
To:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc:     Jari Ruusu <jariruusu@protonmail.com>,
        Sasha Levin <sashal@kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "stable@vger.kernel.org" <stable@vger.kernel.org>,
        "torvalds@linux-foundation.org" <torvalds@linux-foundation.org>,
        masahiroy@kernel.org
References: <7pR0YCctzN9phpuEChlL7_SS6auHOM80bZBcGBTZPuMkc6XjKw7HUXf9vZUPi-IaV2gTtsRVXgywQbja8xpzjGRDGWJsVYSGQN5sNuX1yaQ=@protonmail.com>
 <YBuSJqIG+AeqDuMl@kroah.com>
 <78ada91b-21ee-563f-9f75-3cbaeffafad4@kernel.org>
 <YBu1d0+nfbWGfMtj@kroah.com>
From:   Jiri Slaby <jirislaby@kernel.org>
Message-ID: <a85b7749-38b2-8ce9-c15a-8acb9a54c5b5@kernel.org>
Date:   Thu, 4 Feb 2021 12:00:31 +0100
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101
 Thunderbird/78.6.0
MIME-Version: 1.0
In-Reply-To: <YBu1d0+nfbWGfMtj@kroah.com>
Content-Type: text/plain; charset=iso-8859-2; format=flowed
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Precedence: bulk

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