linux-kernel - Re: [PATCH] KVM: Replace DEFINE_SIMPLE_ATTRIBUTE with DEFINE_DEBUGFS

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Date:   Mon, 1 Feb 2021 10:01:09 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Jiapeng Chong <jiapeng.chong@...ux.alibaba.com>
Cc:     seanjc@...gle.com, vkuznets@...hat.com, wanpengli@...cent.com,
        jmattson@...gle.com, joro@...tes.org, tglx@...utronix.de,
        mingo@...hat.com, bp@...en8.de, x86@...nel.org, hpa@...or.com,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] KVM: Replace DEFINE_SIMPLE_ATTRIBUTE with
 DEFINE_DEBUGFS_ATTRIBUTE

On 01/02/21 09:38, Jiapeng Chong wrote:
> Fix the following coccicheck warning:
> 
> ./arch/x86/kvm/debugfs.c:44:0-23: WARNING: vcpu_tsc_scaling_frac_fops
> should be defined with DEFINE_DEBUGFS_ATTRIBUTE.
> 
> ./arch/x86/kvm/debugfs.c:36:0-23: WARNING: vcpu_tsc_scaling_fops should
> be defined with DEFINE_DEBUGFS_ATTRIBUTE.
> 
> ./arch/x86/kvm/debugfs.c:27:0-23: WARNING: vcpu_tsc_offset_fops should
> be defined with DEFINE_DEBUGFS_ATTRIBUTE.
> 
> Reported-by: Abaci Robot <abaci@...ux.alibaba.com>
> Signed-off-by: Jiapeng Chong <jiapeng.chong@...ux.alibaba.com>
> ---
>   arch/x86/kvm/debugfs.c | 9 +++++----
>   1 file changed, 5 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/x86/kvm/debugfs.c b/arch/x86/kvm/debugfs.c
> index 7e818d6..9c0e29e 100644
> --- a/arch/x86/kvm/debugfs.c
> +++ b/arch/x86/kvm/debugfs.c
> @@ -15,7 +15,7 @@ static int vcpu_get_timer_advance_ns(void *data, u64 *val)
>   	return 0;
>   }
>   
> -DEFINE_SIMPLE_ATTRIBUTE(vcpu_timer_advance_ns_fops, vcpu_get_timer_advance_ns, NULL, "%llu\n");
> +DEFINE_DEBUGFS_ATTRIBUTE(vcpu_timer_advance_ns_fops, vcpu_get_timer_advance_ns, NULL, "%llu\n");
>   
>   static int vcpu_get_tsc_offset(void *data, u64 *val)
>   {
> @@ -24,7 +24,7 @@ static int vcpu_get_tsc_offset(void *data, u64 *val)
>   	return 0;
>   }
>   
> -DEFINE_SIMPLE_ATTRIBUTE(vcpu_tsc_offset_fops, vcpu_get_tsc_offset, NULL, "%lld\n");
> +DEFINE_DEBUGFS_ATTRIBUTE(vcpu_tsc_offset_fops, vcpu_get_tsc_offset, NULL, "%lld\n");
>   
>   static int vcpu_get_tsc_scaling_ratio(void *data, u64 *val)
>   {
> @@ -33,7 +33,7 @@ static int vcpu_get_tsc_scaling_ratio(void *data, u64 *val)
>   	return 0;
>   }
>   
> -DEFINE_SIMPLE_ATTRIBUTE(vcpu_tsc_scaling_fops, vcpu_get_tsc_scaling_ratio, NULL, "%llu\n");
> +DEFINE_DEBUGFS_ATTRIBUTE(vcpu_tsc_scaling_fops, vcpu_get_tsc_scaling_ratio, NULL, "%llu\n");
>   
>   static int vcpu_get_tsc_scaling_frac_bits(void *data, u64 *val)
>   {
> @@ -41,7 +41,8 @@ static int vcpu_get_tsc_scaling_frac_bits(void *data, u64 *val)
>   	return 0;
>   }
>   
> -DEFINE_SIMPLE_ATTRIBUTE(vcpu_tsc_scaling_frac_fops, vcpu_get_tsc_scaling_frac_bits, NULL, "%llu\n");
> +DEFINE_DEBUGFS_ATTRIBUTE(vcpu_tsc_scaling_frac_fops, vcpu_get_tsc_scaling_frac_bits,
> +			  NULL, "%llu\n");
>   
>   void kvm_arch_create_vcpu_debugfs(struct kvm_vcpu *vcpu, struct dentry *debugfs_dentry)
>   {
> 

If you wanted to do this, you would have to use 
debugfs_create_file_unsafe() as well.

In practice, nobody does that because it's not a performance-sensitive 
path and it's not worth the maintenance cost of using a less safe API.

Paolo