linux-kernel - Re: [PATCH 6/8] x86: add MULTIUSER dependency for KVM

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Date:   Wed, 19 Jul 2017 16:18:09 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Radim Krčmář <rkrcmar@...hat.com>
Cc:     "the arch/x86 maintainers" <x86@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Alex Williamson <alex.williamson@...hat.com>,
        kvm@...r.kernel.org
Subject: Re: [PATCH 6/8] x86: add MULTIUSER dependency for KVM

On Wed, Jul 19, 2017 at 4:11 PM, Radim Krčmář <rkrcmar@...hat.com> wrote:
> 2017-07-19 14:53+0200, Arnd Bergmann:
>> KVM tries to select 'TASKSTATS', which had additional dependencies:
>>
>> warning: (KVM) selects TASKSTATS which has unmet direct dependencies (NET && MULTIUSER)
>>
>> Signed-off-by: Arnd Bergmann <arnd@...db.de>
>> ---
>
> Hm, do you know why Kconfig warns instead of propagating the
> dependencies?

Kconfig propagates 'depends on' dependencies, but cannot turn a 'select'
into 'depends on', as those two mean different things.

Another solution to the problem would be to use 'depends on TASKSTATS'.

Generally speaking, using 'select' to turn on a user-visible option is a bad
idea, but blindly turning those 'select' into 'depends on' is also dangerous,
as it can break configurations of existing users that would here end up with
neither TASKSTATS nor KVM after a 'make oldconfig'.

      Arnd