[PATCH] KVM: replace DEFINE_SIMPLE_ATTRIBUTE with DEFINE_DEBUGFS_ATTRIBUTE

[PATCH] KVM: replace DEFINE_SIMPLE_ATTRIBUTE with DEFINE_DEBUGFS_ATTRIBUTE

[Bo Liu]

Fix the following coccicheck warning:
  virt/kvm/kvm_main.c:3847:0-23: WARNING
    vcpu_get_pid_fops should be defined with DEFINE_DEBUGFS_ATTRIBUTE

Signed-off-by: Bo Liu <liubo03@inspur.com>
---
 virt/kvm/kvm_main.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index f1df24c2bc84..3f383f27d3d7 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -3844,7 +3844,7 @@ static int vcpu_get_pid(void *data, u64 *val)
 	return 0;
 }
 
-DEFINE_SIMPLE_ATTRIBUTE(vcpu_get_pid_fops, vcpu_get_pid, NULL, "%llu\n");
+DEFINE_DEBUGFS_ATTRIBUTE(vcpu_get_pid_fops, vcpu_get_pid, NULL, "%llu\n");
 
 static void kvm_create_vcpu_debugfs(struct kvm_vcpu *vcpu)
 {
-- 
2.27.0

Re: [PATCH] KVM: replace DEFINE_SIMPLE_ATTRIBUTE with DEFINE_DEBUGFS_ATTRIBUTE

[Paolo Bonzini]

On 11/1/22 08:25, Bo Liu wrote:
> Fix the following coccicheck warning:
>    virt/kvm/kvm_main.c:3847:0-23: WARNING
>      vcpu_get_pid_fops should be defined with DEFINE_DEBUGFS_ATTRIBUTE
> 
> Signed-off-by: Bo Liu <liubo03@inspur.com>
> ---
>   virt/kvm/kvm_main.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index f1df24c2bc84..3f383f27d3d7 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -3844,7 +3844,7 @@ static int vcpu_get_pid(void *data, u64 *val)
>   	return 0;
>   }
>   
> -DEFINE_SIMPLE_ATTRIBUTE(vcpu_get_pid_fops, vcpu_get_pid, NULL, "%llu\n");
> +DEFINE_DEBUGFS_ATTRIBUTE(vcpu_get_pid_fops, vcpu_get_pid, NULL, "%llu\n");
>   
>   static void kvm_create_vcpu_debugfs(struct kvm_vcpu *vcpu)
>   {

If you really wanted to do this, you would also have to replace 
debugfs_create_file with debugfs_create_file_unsafe.

However, this is not a good idea.  The rationale in the .cocci file is 
that "DEFINE_SIMPLE_ATTRIBUTE + debugfs_create_file() imposes some 
significant overhead", but this should not really be relevant for a 
debugfs file.

Such a patch would only make sense if there was a version of 
debugfs_create_file_unsafe() with a less-terrible name (e.g. 
debugfs_create_simple_attr?), which could _only_ be used with fops 
created by DEFINE_DEBUGFS_ATTRIBUTE.  Without such a type-safe trick, 
the .cocci file is only adding confusion to perfectly fine code.

Paolo

Re: [PATCH] KVM: replace DEFINE_SIMPLE_ATTRIBUTE with DEFINE_DEBUGFS_ATTRIBUTE

[Sean Christopherson]

On Wed, Nov 02, 2022, Paolo Bonzini wrote:
> On 11/1/22 08:25, Bo Liu wrote:
> > Fix the following coccicheck warning:
> >    virt/kvm/kvm_main.c:3847:0-23: WARNING
> >      vcpu_get_pid_fops should be defined with DEFINE_DEBUGFS_ATTRIBUTE
> > 
> > Signed-off-by: Bo Liu <liubo03@inspur.com>
> > ---
> >   virt/kvm/kvm_main.c | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> > index f1df24c2bc84..3f383f27d3d7 100644
> > --- a/virt/kvm/kvm_main.c
> > +++ b/virt/kvm/kvm_main.c
> > @@ -3844,7 +3844,7 @@ static int vcpu_get_pid(void *data, u64 *val)
> >   	return 0;
> >   }
> > -DEFINE_SIMPLE_ATTRIBUTE(vcpu_get_pid_fops, vcpu_get_pid, NULL, "%llu\n");
> > +DEFINE_DEBUGFS_ATTRIBUTE(vcpu_get_pid_fops, vcpu_get_pid, NULL, "%llu\n");
> >   static void kvm_create_vcpu_debugfs(struct kvm_vcpu *vcpu)
> >   {
> 
> If you really wanted to do this, you would also have to replace
> debugfs_create_file with debugfs_create_file_unsafe.
> 
> However, this is not a good idea.  The rationale in the .cocci file is that
> "DEFINE_SIMPLE_ATTRIBUTE + debugfs_create_file() imposes some significant
> overhead", but this should not really be relevant for a debugfs file.
> 
> Such a patch would only make sense if there was a version of
> debugfs_create_file_unsafe() with a less-terrible name (e.g.
> debugfs_create_simple_attr?), which could _only_ be used with fops created
> by DEFINE_DEBUGFS_ATTRIBUTE.  Without such a type-safe trick, the .cocci
> file is only adding confusion to perfectly fine code.

Heh, some serious deja vu here[1].  This is the second case of identical, flawed
patches being sent in response to misguided coccinelle warnings in a rather short
amount of time, the "return min(r, 0)" horror being the other case[2][3].

The min() thing is supposed to be fixed by commit aeb300c1dbfc ("coccinelle: misc:
minmax: suppress patch generation for err returns").  Is that patch broken, or are
folks just running old scripts?

As for the DEFINE_DEBUGFS_ATTRIBUTE check, can that warning be downgraded (is that
even a thing?) or even deleted?  As much as I enjoyed the opportunity to learn more
about debugfs, the unnecessary confusion and wasted time was/is annoying.

[1] https://lore.kernel.org/all/Yxoo1A2fmlAWruyV@google.com
[2] https://lore.kernel.org/all/8881d7b4-0c31-cafd-1158-0d42c1c7f43a@redhat.com
[3] https://lore.kernel.org/all/d8a518c4a4014307b30020b38022d633@AcuMS.aculab.com

[PATCH] KVM: Replace DEFINE_SIMPLE_ATTRIBUTE with DEFINE_DEBUGFS_ATTRIBUTE

[Jiapeng Chong]

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@linux.alibaba.com>
Signed-off-by: Jiapeng Chong <jiapeng.chong@linux.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)
 {
-- 
1.8.3.1

Re: [PATCH] KVM: Replace DEFINE_SIMPLE_ATTRIBUTE with DEFINE_DEBUGFS_ATTRIBUTE

[Paolo Bonzini]

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@linux.alibaba.com>
> Signed-off-by: Jiapeng Chong <jiapeng.chong@linux.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