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

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Date:   Fri, 25 Jan 2019 18:49:47 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org
Cc:     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 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);

 	mutex_lock(&kvm->lock);
 	if (kvm_get_vcpu_by_id(kvm, id)) {


Paolo