[PATCH] virtio: Change typecasts in vring_init()

[PATCH] virtio: Change typecasts in vring_init()

[Matej Genci]

Compilers such as g++ 7.3 complain about assigning void* variable to
a non-void* variable (like struct pointers) and pointer arithmetics
on void*.

Signed-off-by: Matej Genci <matej.genci@nutanix.com>
---
 include/uapi/linux/virtio_ring.h | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/include/uapi/linux/virtio_ring.h b/include/uapi/linux/virtio_ring.h
index 4c4e24c291a5..2c339b9e2923 100644
--- a/include/uapi/linux/virtio_ring.h
+++ b/include/uapi/linux/virtio_ring.h
@@ -168,10 +168,11 @@ static inline void vring_init(struct vring *vr, unsigned int num, void *p,
 			      unsigned long align)
 {
 	vr->num = num;
-	vr->desc = p;
-	vr->avail = p + num*sizeof(struct vring_desc);
-	vr->used = (void *)(((uintptr_t)&vr->avail->ring[num] + sizeof(__virtio16)
-		+ align-1) & ~(align - 1));
+	vr->desc = (struct vring_desc *)p;
+	vr->avail = (struct vring_avail *)((uintptr_t)p
+		+ num*sizeof(struct vring_desc));
+	vr->used = (struct vring_used *)(((uintptr_t)&vr->avail->ring[num]
+		+ sizeof(__virtio16) + align-1) & ~(align - 1));
 }
 
 static inline unsigned vring_size(unsigned int num, unsigned long align)
-- 
2.22.0

Re: [PATCH] virtio: Change typecasts in vring_init()

[Jason Wang]

On 2019/8/27 下午11:20, Matej Genci wrote:
> Compilers such as g++ 7.3 complain about assigning void* variable to
> a non-void* variable (like struct pointers) and pointer arithmetics
> on void*.
>
> Signed-off-by: Matej Genci <matej.genci@nutanix.com>
> ---
>  include/uapi/linux/virtio_ring.h | 9 +++++----
>  1 file changed, 5 insertions(+), 4 deletions(-)
>
> diff --git a/include/uapi/linux/virtio_ring.h b/include/uapi/linux/virtio_ring.h
> index 4c4e24c291a5..2c339b9e2923 100644
> --- a/include/uapi/linux/virtio_ring.h
> +++ b/include/uapi/linux/virtio_ring.h
> @@ -168,10 +168,11 @@ static inline void vring_init(struct vring *vr, unsigned int num, void *p,
>  			      unsigned long align)
>  {
>  	vr->num = num;
> -	vr->desc = p;
> -	vr->avail = p + num*sizeof(struct vring_desc);
> -	vr->used = (void *)(((uintptr_t)&vr->avail->ring[num] + sizeof(__virtio16)
> -		+ align-1) & ~(align - 1));
> +	vr->desc = (struct vring_desc *)p;
> +	vr->avail = (struct vring_avail *)((uintptr_t)p
> +		+ num*sizeof(struct vring_desc));


It's better to let the code pass checkpath.pl here.

Other looks good.

Thanks


> +	vr->used = (struct vring_used *)(((uintptr_t)&vr->avail->ring[num]
> +		+ sizeof(__virtio16) + align-1) & ~(align - 1));
>  }
>  
>  static inline unsigned vring_size(unsigned int num, unsigned long align)

Re: [PATCH] virtio: Change typecasts in vring_init()

[Michael S. Tsirkin]

On Tue, Aug 27, 2019 at 03:20:57PM +0000, Matej Genci wrote:
> Compilers such as g++ 7.3 complain about assigning void* variable to
> a non-void* variable (like struct pointers) and pointer arithmetics
> on void*.
> 
> Signed-off-by: Matej Genci <matej.genci@nutanix.com>
> ---
>  include/uapi/linux/virtio_ring.h | 9 +++++----
>  1 file changed, 5 insertions(+), 4 deletions(-)
> 
> diff --git a/include/uapi/linux/virtio_ring.h b/include/uapi/linux/virtio_ring.h
> index 4c4e24c291a5..2c339b9e2923 100644
> --- a/include/uapi/linux/virtio_ring.h
> +++ b/include/uapi/linux/virtio_ring.h
> @@ -168,10 +168,11 @@ static inline void vring_init(struct vring *vr, unsigned int num, void *p,
>  			      unsigned long align)
>  {
>  	vr->num = num;
> -	vr->desc = p;
> -	vr->avail = p + num*sizeof(struct vring_desc);
> -	vr->used = (void *)(((uintptr_t)&vr->avail->ring[num] + sizeof(__virtio16)
> -		+ align-1) & ~(align - 1));
> +	vr->desc = (struct vring_desc *)p;
> +	vr->avail = (struct vring_avail *)((uintptr_t)p
> +		+ num*sizeof(struct vring_desc));
> +	vr->used = (struct vring_used *)(((uintptr_t)&vr->avail->ring[num]
> +		+ sizeof(__virtio16) + align-1) & ~(align - 1));
>  }
>  
>  static inline unsigned vring_size(unsigned int num, unsigned long align)

I'm not really interested in building with g++, sorry.
Centainly not if it makes code less robust by forcing
casts where they weren't previously necessary.

However, vring_init and vring_size are legacy APIs anyway,
so I'd be happy to add ifndefs that will allow userspace
simply hide these functions if it does not need them.


> -- 
> 2.22.0
> 

Re: [PATCH] virtio: Change typecasts in vring_init()

[Matej Genci]

On 8/30/2019 4:48 AM, Jason Wang wrote:
> 
> On 2019/8/27 下午11:20, Matej Genci wrote:
>> Compilers such as g++ 7.3 complain about assigning void* variable to
>> a non-void* variable (like struct pointers) and pointer arithmetics
>> on void*.
>>
>> Signed-off-by: Matej Genci <matej.genci@nutanix.com>
>> ---
>>   include/uapi/linux/virtio_ring.h | 9 +++++----
>>   1 file changed, 5 insertions(+), 4 deletions(-)
>>
>> diff --git a/include/uapi/linux/virtio_ring.h b/include/uapi/linux/virtio_ring.h
>> index 4c4e24c291a5..2c339b9e2923 100644
>> --- a/include/uapi/linux/virtio_ring.h
>> +++ b/include/uapi/linux/virtio_ring.h
>> @@ -168,10 +168,11 @@ static inline void vring_init(struct vring *vr, unsigned int num, void *p,
>>   			      unsigned long align)
>>   {
>>   	vr->num = num;
>> -	vr->desc = p;
>> -	vr->avail = p + num*sizeof(struct vring_desc);
>> -	vr->used = (void *)(((uintptr_t)&vr->avail->ring[num] + sizeof(__virtio16)
>> -		+ align-1) & ~(align - 1));
>> +	vr->desc = (struct vring_desc *)p;
>> +	vr->avail = (struct vring_avail *)((uintptr_t)p
>> +		+ num*sizeof(struct vring_desc));
> 
> 
> It's better to let the code pass checkpath.pl here.
> 
It passes for me

--------8<--------
./scripts/checkpatch.pl 0001-virtio-Change-typecasts-in-vring_init.patch
total: 0 errors, 0 warnings, 15 lines checked

0001-virtio-Change-typecasts-in-vring_init.patch has no obvious style problems and is ready for submission.
--------8<--------

Is there something I'm missing?

> Other looks good.
> 
> Thanks
> 
> 
>> +	vr->used = (struct vring_used *)(((uintptr_t)&vr->avail->ring[num]
>> +		+ sizeof(__virtio16) + align-1) & ~(align - 1));
>>   }
>>   
>>   static inline unsigned vring_size(unsigned int num, unsigned long align)

Re: [PATCH] virtio: Change typecasts in vring_init()

[Matej Genci]

On 8/30/2019 3:02 PM, Michael S. Tsirkin wrote:
> On Tue, Aug 27, 2019 at 03:20:57PM +0000, Matej Genci wrote:
>> Compilers such as g++ 7.3 complain about assigning void* variable to
>> a non-void* variable (like struct pointers) and pointer arithmetics
>> on void*.
>>
>> Signed-off-by: Matej Genci <matej.genci@nutanix.com>
>> ---
>>   include/uapi/linux/virtio_ring.h | 9 +++++----
>>   1 file changed, 5 insertions(+), 4 deletions(-)
>>
>> diff --git a/include/uapi/linux/virtio_ring.h b/include/uapi/linux/virtio_ring.h
>> index 4c4e24c291a5..2c339b9e2923 100644
>> --- a/include/uapi/linux/virtio_ring.h
>> +++ b/include/uapi/linux/virtio_ring.h
>> @@ -168,10 +168,11 @@ static inline void vring_init(struct vring *vr, unsigned int num, void *p,
>>   			      unsigned long align)
>>   {
>>   	vr->num = num;
>> -	vr->desc = p;
>> -	vr->avail = p + num*sizeof(struct vring_desc);
>> -	vr->used = (void *)(((uintptr_t)&vr->avail->ring[num] + sizeof(__virtio16)
>> -		+ align-1) & ~(align - 1));
>> +	vr->desc = (struct vring_desc *)p;
>> +	vr->avail = (struct vring_avail *)((uintptr_t)p
>> +		+ num*sizeof(struct vring_desc));
>> +	vr->used = (struct vring_used *)(((uintptr_t)&vr->avail->ring[num]
>> +		+ sizeof(__virtio16) + align-1) & ~(align - 1));
>>   }
>>   
>>   static inline unsigned vring_size(unsigned int num, unsigned long align)
> 
> I'm not really interested in building with g++, sorry.
> Centainly not if it makes code less robust by forcing
> casts where they weren't previously necessary.

Can you elaborate on how these casts make the code less robust?
They aren't necessary in C but I think being explicit can improve
readability as argued in
https://softwareengineering.stackexchange.com/a/275714

> 
> However, vring_init and vring_size are legacy APIs anyway,
> so I'd be happy to add ifndefs that will allow userspace
> simply hide these functions if it does not need them.
> 

I feel like my patch is a harmless way of allowing this header
to be used in C++ projects, but I'm happy to drop it in lieu of
the guards if you feel strongly about it.

Thanks.
Matej

> 
>> -- 
>> 2.22.0
>>

Re: [PATCH] virtio: Change typecasts in vring_init()

[Michael S. Tsirkin]

On Fri, Aug 30, 2019 at 05:58:23PM +0000, Matej Genci wrote:
> On 8/30/2019 3:02 PM, Michael S. Tsirkin wrote:
> > On Tue, Aug 27, 2019 at 03:20:57PM +0000, Matej Genci wrote:
> >> Compilers such as g++ 7.3 complain about assigning void* variable to
> >> a non-void* variable (like struct pointers) and pointer arithmetics
> >> on void*.
> >>
> >> Signed-off-by: Matej Genci <matej.genci@nutanix.com>
> >> ---
> >>   include/uapi/linux/virtio_ring.h | 9 +++++----
> >>   1 file changed, 5 insertions(+), 4 deletions(-)
> >>
> >> diff --git a/include/uapi/linux/virtio_ring.h b/include/uapi/linux/virtio_ring.h
> >> index 4c4e24c291a5..2c339b9e2923 100644
> >> --- a/include/uapi/linux/virtio_ring.h
> >> +++ b/include/uapi/linux/virtio_ring.h
> >> @@ -168,10 +168,11 @@ static inline void vring_init(struct vring *vr, unsigned int num, void *p,
> >>   			      unsigned long align)
> >>   {
> >>   	vr->num = num;
> >> -	vr->desc = p;
> >> -	vr->avail = p + num*sizeof(struct vring_desc);
> >> -	vr->used = (void *)(((uintptr_t)&vr->avail->ring[num] + sizeof(__virtio16)
> >> -		+ align-1) & ~(align - 1));
> >> +	vr->desc = (struct vring_desc *)p;
> >> +	vr->avail = (struct vring_avail *)((uintptr_t)p
> >> +		+ num*sizeof(struct vring_desc));
> >> +	vr->used = (struct vring_used *)(((uintptr_t)&vr->avail->ring[num]
> >> +		+ sizeof(__virtio16) + align-1) & ~(align - 1));
> >>   }
> >>   
> >>   static inline unsigned vring_size(unsigned int num, unsigned long align)
> > 
> > I'm not really interested in building with g++, sorry.
> > Centainly not if it makes code less robust by forcing
> > casts where they weren't previously necessary.
> 
> Can you elaborate on how these casts make the code less robust?

If we ever change the variable types build will still pass
because of the cast.

> They aren't necessary in C but I think being explicit can improve
> readability as argued in
> https://softwareengineering.stackexchange.com/a/275714
> 
> > 
> > However, vring_init and vring_size are legacy APIs anyway,
> > so I'd be happy to add ifndefs that will allow userspace
> > simply hide these functions if it does not need them.
> > 
> 
> I feel like my patch is a harmless way of allowing this header
> to be used in C++ projects, but I'm happy to drop it in lieu of
> the guards if you feel strongly about it.
> 
> Thanks.
> Matej

Yea let's not even start.

> > 
> >> -- 
> >> 2.22.0
> >>
> 

Re: [PATCH] virtio: Change typecasts in vring_init()

[Matej Genci]

On 8/31/2019 6:43 PM, Michael S. Tsirkin wrote:
> On Fri, Aug 30, 2019 at 05:58:23PM +0000, Matej Genci wrote:
>> On 8/30/2019 3:02 PM, Michael S. Tsirkin wrote:
>>> On Tue, Aug 27, 2019 at 03:20:57PM +0000, Matej Genci wrote:
>>>> Compilers such as g++ 7.3 complain about assigning void* variable to
>>>> a non-void* variable (like struct pointers) and pointer arithmetics
>>>> on void*.
>>>>
>>>> Signed-off-by: Matej Genci <matej.genci@nutanix.com>
>>>> ---
>>>>    include/uapi/linux/virtio_ring.h | 9 +++++----
>>>>    1 file changed, 5 insertions(+), 4 deletions(-)
>>>>
>>>> diff --git a/include/uapi/linux/virtio_ring.h b/include/uapi/linux/virtio_ring.h
>>>> index 4c4e24c291a5..2c339b9e2923 100644
>>>> --- a/include/uapi/linux/virtio_ring.h
>>>> +++ b/include/uapi/linux/virtio_ring.h
>>>> @@ -168,10 +168,11 @@ static inline void vring_init(struct vring *vr, unsigned int num, void *p,
>>>>    			      unsigned long align)
>>>>    {
>>>>    	vr->num = num;
>>>> -	vr->desc = p;
>>>> -	vr->avail = p + num*sizeof(struct vring_desc);
>>>> -	vr->used = (void *)(((uintptr_t)&vr->avail->ring[num] + sizeof(__virtio16)
>>>> -		+ align-1) & ~(align - 1));
>>>> +	vr->desc = (struct vring_desc *)p;
>>>> +	vr->avail = (struct vring_avail *)((uintptr_t)p
>>>> +		+ num*sizeof(struct vring_desc));
>>>> +	vr->used = (struct vring_used *)(((uintptr_t)&vr->avail->ring[num]
>>>> +		+ sizeof(__virtio16) + align-1) & ~(align - 1));
>>>>    }
>>>>    
>>>>    static inline unsigned vring_size(unsigned int num, unsigned long align)
>>>
>>> I'm not really interested in building with g++, sorry.
>>> Centainly not if it makes code less robust by forcing
>>> casts where they weren't previously necessary.
>>
>> Can you elaborate on how these casts make the code less robust?
> 
> If we ever change the variable types build will still pass
> because of the cast.
> 

Wouldn't that be the case in the original as well?
You're assigning void*, which is implicitly cast to everything.

>> They aren't necessary in C but I think being explicit can improve
>> readability as argued in
>> https://urldefense.proofpoint.com/v2/url?u=https-3A__softwareengineering.stackexchange.com_a_275714&d=DwIBAg&c=s883GpUCOChKOHiocYtGcg&r=dbPDDn52JgZndd-WPvGcL5PLZTrms-72TItYJx-If5I&m=sw6xxC2EOF9g3XtUKuI6OvT5xhYF7XcWBqyQvGb-UMw&s=QWoZHF4XlOzPesnnbfsf1_KORrzkXb6yfd6yQGCwepc&e=
>>
>>>
>>> However, vring_init and vring_size are legacy APIs anyway,
>>> so I'd be happy to add ifndefs that will allow userspace
>>> simply hide these functions if it does not need them.
>>>
>>
>> I feel like my patch is a harmless way of allowing this header
>> to be used in C++ projects, but I'm happy to drop it in lieu of
>> the guards if you feel strongly about it.
>>
>> Thanks.
>> Matej
> 
> Yea let's not even start.
> 

Sure. I can re-send the patch with guards. But for my own sake,
can you elaborate on the above?

>>>
>>>> -- 
>>>> 2.22.0
>>>>
>>

Re: [PATCH] virtio: Change typecasts in vring_init()

[Michael S. Tsirkin]

On Mon, Sep 02, 2019 at 09:56:42AM +0000, Matej Genci wrote:
> On 8/31/2019 6:43 PM, Michael S. Tsirkin wrote:
> > On Fri, Aug 30, 2019 at 05:58:23PM +0000, Matej Genci wrote:
> >> On 8/30/2019 3:02 PM, Michael S. Tsirkin wrote:
> >>> On Tue, Aug 27, 2019 at 03:20:57PM +0000, Matej Genci wrote:
> >>>> Compilers such as g++ 7.3 complain about assigning void* variable to
> >>>> a non-void* variable (like struct pointers) and pointer arithmetics
> >>>> on void*.
> >>>>
> >>>> Signed-off-by: Matej Genci <matej.genci@nutanix.com>
> >>>> ---
> >>>>    include/uapi/linux/virtio_ring.h | 9 +++++----
> >>>>    1 file changed, 5 insertions(+), 4 deletions(-)
> >>>>
> >>>> diff --git a/include/uapi/linux/virtio_ring.h b/include/uapi/linux/virtio_ring.h
> >>>> index 4c4e24c291a5..2c339b9e2923 100644
> >>>> --- a/include/uapi/linux/virtio_ring.h
> >>>> +++ b/include/uapi/linux/virtio_ring.h
> >>>> @@ -168,10 +168,11 @@ static inline void vring_init(struct vring *vr, unsigned int num, void *p,
> >>>>    			      unsigned long align)
> >>>>    {
> >>>>    	vr->num = num;
> >>>> -	vr->desc = p;
> >>>> -	vr->avail = p + num*sizeof(struct vring_desc);
> >>>> -	vr->used = (void *)(((uintptr_t)&vr->avail->ring[num] + sizeof(__virtio16)
> >>>> -		+ align-1) & ~(align - 1));
> >>>> +	vr->desc = (struct vring_desc *)p;
> >>>> +	vr->avail = (struct vring_avail *)((uintptr_t)p
> >>>> +		+ num*sizeof(struct vring_desc));
> >>>> +	vr->used = (struct vring_used *)(((uintptr_t)&vr->avail->ring[num]
> >>>> +		+ sizeof(__virtio16) + align-1) & ~(align - 1));
> >>>>    }
> >>>>    
> >>>>    static inline unsigned vring_size(unsigned int num, unsigned long align)
> >>>
> >>> I'm not really interested in building with g++, sorry.
> >>> Centainly not if it makes code less robust by forcing
> >>> casts where they weren't previously necessary.
> >>
> >> Can you elaborate on how these casts make the code less robust?
> > 
> > If we ever change the variable types build will still pass
> > because of the cast.
> > 
> 
> Wouldn't that be the case in the original as well?
> You're assigning void*, which is implicitly cast to everything.


Right. And if we change that void * to something else,
build will fail. Not so with a cast.

> >> They aren't necessary in C but I think being explicit can improve
> >> readability as argued in
> >> https://urldefense.proofpoint.com/v2/url?u=https-3A__softwareengineering.stackexchange.com_a_275714&d=DwIBAg&c=s883GpUCOChKOHiocYtGcg&r=dbPDDn52JgZndd-WPvGcL5PLZTrms-72TItYJx-If5I&m=sw6xxC2EOF9g3XtUKuI6OvT5xhYF7XcWBqyQvGb-UMw&s=QWoZHF4XlOzPesnnbfsf1_KORrzkXb6yfd6yQGCwepc&e=
> >>
> >>>
> >>> However, vring_init and vring_size are legacy APIs anyway,
> >>> so I'd be happy to add ifndefs that will allow userspace
> >>> simply hide these functions if it does not need them.
> >>>
> >>
> >> I feel like my patch is a harmless way of allowing this header
> >> to be used in C++ projects, but I'm happy to drop it in lieu of
> >> the guards if you feel strongly about it.
> >>
> >> Thanks.
> >> Matej
> > 
> > Yea let's not even start.
> > 
> 
> Sure. I can re-send the patch with guards. But for my own sake,
> can you elaborate on the above?
> 
> >>>
> >>>> -- 
> >>>> 2.22.0
> >>>>
> >>
>