linux-kernel - Re: [PATCH RFC 0/4] Introduce uts

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Date: Mon, 5 Feb 2024 08:25:10 +0000
From: John Garry <john.g.garry@...cle.com>
To: Masahiro Yamada <masahiroy@...nel.org>
Cc: mcgrof@...nel.org, russ.weight@...ux.dev, gregkh@...uxfoundation.org,
        rafael@...nel.org, rostedt@...dmis.org, mhiramat@...nel.org,
        mathieu.desnoyers@...icios.com, davem@...emloft.net,
        edumazet@...gle.com, kuba@...nel.org, pabeni@...hat.com,
        keescook@...omium.org, nathan@...nel.org, nicolas@...sle.eu,
        linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
        netdev@...r.kernel.org, linux-kbuild@...r.kernel.org
Subject: Re: [PATCH RFC 0/4] Introduce uts_release

On 02/02/2024 15:01, Masahiro Yamada wrote:
>> --
>> 2.35.3
> 
> As you see, several drivers store UTS_RELEASE in their driver data,
> and even print it in debug print.
> 
> 
> I do not see why it is useful.

I would tend to agree, and mentioned that earlier.

> As you discussed in 3/4, if UTS_RELEASE is unneeded,
> it is better to get rid of it.

Jakub replied about this.

> 
> 
> If such version information is useful for drivers, the intention is
> whether the version of the module, or the version of vmlinux.
> That is a question.
> They differ when CONFIG_MODVERSION.
> 

I think often this information in UTS_RELEASE is shared as informative 
only, so the user can conveniently know the specific kernel git version.

> 
> When module developers intend to printk the git version
> from which the module was compiled from,
> presumably they want to use UTS_RELEASE, which
> was expanded at the compile time of the module.
> 
> If you replace it with uts_release, it is the git version
> of vmlinux.
> 
> 
> Of course, the replacement is safe for always-builtin code.
> 
> 
> 
> Lastly, we can avoid using UTS_RELEASE without relying
> on your patch.
> 
> 
> 
> For example, commit 3a3a11e6e5a2bc0595c7e36ae33c861c9e8c75b1
> replaced  UTS_RELEASE with init_uts_ns.name.release
> 
> 
> So, is your uts_release a shorthand of init_uts_ns.name.release?

Yes - well that both are strings containing UTS_RELEASE. Using a struct 
sub-member is bit ungainly, but I suppose that we should not be making 
life easy for people using this.

However we already have init_utsname in:

static inline struct new_utsname *init_utsname(void)
{
	return &init_uts_ns.name;
}

So could use init_utsname()->release, which is a bit nicer.

> 
> 
> 
> I think what you can contribute are:
> 
>   - Explore the UTS_RELEASE users, and check if you can get rid of it.

Unfortunately I expect resistance for this. I also expect places like FW 
loader it is necessary. And when this is used in sysfs, people will say 
that it is part of the ABI now.

How about I send the patch to update to use init_uts_ns and mention also 
that it would be better to not use at all, if possible? I can cc you.

> 
>   - Where UTS_RELEASE is useful, consider if it is possible
>     to replace it with init_uts_ns.name.release

ok, but, as above, could use init_utsname()->release also

Thanks,
John