linux-kernel - Re: [PATCH v2 15/15] KVM: Dynamically size memslot array based on number of used slots

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Message-ID: <20191022152223.GB2343@linux.intel.com>
Date:   Tue, 22 Oct 2019 08:22:24 -0700
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     James Hogan <jhogan@...nel.org>,
        Paul Mackerras <paulus@...abs.org>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        Janosch Frank <frankja@...ux.ibm.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Marc Zyngier <maz@...nel.org>,
        David Hildenbrand <david@...hat.com>,
        Cornelia Huck <cohuck@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        James Morse <james.morse@....com>,
        Julien Thierry <julien.thierry.kdev@...il.com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        linux-mips@...r.kernel.org, kvm-ppc@...r.kernel.org,
        kvm@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        kvmarm@...ts.cs.columbia.edu, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 15/15] KVM: Dynamically size memslot array based on
 number of used slots

On Tue, Oct 22, 2019 at 04:04:21PM +0200, Paolo Bonzini wrote:
> On 22/10/19 02:35, Sean Christopherson wrote:
> > +	struct kvm_memory_slot memslots[];
> > +	/*
> > +	 * WARNING: 'memslots' is dynamically-sized.  It *MUST* be at the end.
> > +	 */
> 
> Isn't that obvious from the flexible array member?

Probably.  It's also unnecessary as the compiler (at least as of gcc 5.4)
will throw an error if it's not at the end.  I think I even verified this
during development and still decided to leave the obnoxious warning in for
some reason...

include/linux/kvm_host.h:436:25: error: flexible array member not at end of struct
  struct kvm_memory_slot memslots[];