linux-kernel - Re: [PATCH 3/6] x86: kvm: no need to check return value of debugfs

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Date:   Sat, 26 Jan 2019 14:53:36 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, linux-kernel@...r.kernel.org,
        Radim Krčmář <rkrcmar@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, kvm@...r.kernel.org
Subject: Re: [PATCH 3/6] x86: kvm: no need to check return value of
 debugfs_create functions

On Fri, Jan 25, 2019 at 06:49:47PM +0100, Paolo Bonzini wrote:
> On 22/01/19 15:35, Greg Kroah-Hartman wrote:
> > When calling debugfs functions, there is no need to ever check the
> > return value.  The function can work or not, but the code logic should
> > never do something different based on this.
> > 
> > Cc: Paolo Bonzini <pbonzini@...hat.com>
> > Cc: "Radim Krčmář" <rkrcmar@...hat.com>
> > Cc: Thomas Gleixner <tglx@...utronix.de>
> > Cc: Ingo Molnar <mingo@...hat.com>
> > Cc: Borislav Petkov <bp@...en8.de>
> > Cc: "H. Peter Anvin" <hpa@...or.com>
> > Cc: <x86@...nel.org>
> > Cc: <kvm@...r.kernel.org>
> > Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> > ---
> >  arch/x86/kvm/debugfs.c | 26 ++++++++------------------
> >  1 file changed, 8 insertions(+), 18 deletions(-)
> > 
> > diff --git a/arch/x86/kvm/debugfs.c b/arch/x86/kvm/debugfs.c
> > index c19c7ede9bd6..827cd58400d2 100644
> > --- a/arch/x86/kvm/debugfs.c
> > +++ b/arch/x86/kvm/debugfs.c
> > @@ -43,26 +43,16 @@ DEFINE_SIMPLE_ATTRIBUTE(vcpu_tsc_scaling_frac_fops, vcpu_get_tsc_scaling_frac_bi
> >  
> >  int kvm_arch_create_vcpu_debugfs(struct kvm_vcpu *vcpu)
> >  {
> > -	struct dentry *ret;
> > -
> > -	ret = debugfs_create_file("tsc-offset", 0444,
> > -							vcpu->debugfs_dentry,
> > -							vcpu, &vcpu_tsc_offset_fops);
> > -	if (!ret)
> > -		return -ENOMEM;
> > +	debugfs_create_file("tsc-offset", 0444, vcpu->debugfs_dentry, vcpu,
> > +			    &vcpu_tsc_offset_fops);
> >  
> >  	if (kvm_has_tsc_control) {
> > -		ret = debugfs_create_file("tsc-scaling-ratio", 0444,
> > -							vcpu->debugfs_dentry,
> > -							vcpu, &vcpu_tsc_scaling_fops);
> > -		if (!ret)
> > -			return -ENOMEM;
> > -		ret = debugfs_create_file("tsc-scaling-ratio-frac-bits", 0444,
> > -							vcpu->debugfs_dentry,
> > -							vcpu, &vcpu_tsc_scaling_frac_fops);
> > -		if (!ret)
> > -			return -ENOMEM;
> > -
> > +		debugfs_create_file("tsc-scaling-ratio", 0444,
> > +				    vcpu->debugfs_dentry, vcpu,
> > +				    &vcpu_tsc_scaling_fops);
> > +		debugfs_create_file("tsc-scaling-ratio-frac-bits", 0444,
> > +				    vcpu->debugfs_dentry, vcpu,
> > +				    &vcpu_tsc_scaling_frac_fops);
> >  	}
> >  
> >  	return 0;
> > 
> 
> I'm still not sure about this.  I think it's better if debugfs files are
> created "all or none", i.e. something like
> 
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 5ecea812cb6a..ce70c30b2861 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -2573,9 +2573,7 @@ static int kvm_vm_ioctl_create_vcpu(
>  	if (r)
>  		goto vcpu_destroy;
> 
> -	r = kvm_create_vcpu_debugfs(vcpu);
> -	if (r)
> -		goto vcpu_destroy;
> +	kvm_create_vcpu_debugfs(vcpu);

Ah, yes, sorry, I missed that.  I'll respin the patch with this change
in it in a few days.

thanks for the review.

greg k-h