netdev - Re: [PATCH] vDPA/ifcvf: allow userspace to suspend a queue

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Message-ID: <097bbe19-82a7-91ed-cdb3-2becdc4051d4@linux.intel.com>
Date:   Thu, 21 Apr 2022 22:27:04 +0800
From:   Zhou Furong <furong.zhou@...ux.intel.com>
To:     "Zhu, Lingshan" <lingshan.zhu@...el.com>, jasowang@...hat.com,
        mst@...hat.com
Cc:     virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org
Subject: Re: [PATCH] vDPA/ifcvf: allow userspace to suspend a queue



On 2022/4/21 19:05, Zhu, Lingshan wrote:
> 
> 
> On 4/12/2022 2:55 PM, Zhou Furong wrote:
>> Hi,
>>
>>> +bool ifcvf_get_vq_ready(struct ifcvf_hw *hw, u16 qid)
>>> +{
>>> +    struct virtio_pci_common_cfg __iomem *cfg = hw->common_cfg;
>>> +    bool queue_enable;
>>> +
>>> +    vp_iowrite16(qid, &cfg->queue_select);
>>> +    queue_enable = vp_ioread16(&cfg->queue_enable);
>>> +
>>> +    return (bool)queue_enable;
>> queue_enable is bool, why cast? looks like remove the variable is better.
>> return vp_ioread16(&cfg->queue_enable);
> Hi, thanks for your comments. This cast tries to make some static 
> checkers happy.
> Please correct me if I misunderstood it:
> vp_ioread16() returns an u16, and bool is not an one bit variable, it is 
> C99 _Bool.
> C99 defines _Bool to be true(expends to int 1) or false(expends to int 0).
> I think this implies a bool is actually capable to store an u16.
> so I am afraid some checkers may complain about "queue_enable = 
> vp_ioread16(&cfg->queue_enable);",
> a cast here can help us silence the checkers.
> 
> see http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1256.pdf section 7.16
> and https://www.kernel.org/doc/Documentation/process/coding-style.rst 
> section 17
> 
> Thanks,
> Zhu Lingshan
>>
bool type contains 1 bit 1/0 only, any number assign to a boolean 
variable will auto cast to 1 or 0.

if you want make static checker happy(if there is)
queue_enable = (bool)vp_ioread16(&cfg->queue_enable);
return queue_enable;

or
return (bool)vp_ioread16(&cfg->queue_enable);




>>>   static bool ifcvf_vdpa_get_vq_ready(struct vdpa_device *vdpa_dev, 
>>> u16 qid)
>>>   {
>>>       struct ifcvf_hw *vf = vdpa_to_vf(vdpa_dev);
>>> +    bool ready;
>>>   -    return vf->vring[qid].ready;
>>> +    ready = ifcvf_get_vq_ready(vf, qid);
>>> +
>>> +    return ready;
>> remove ready looks better
>> return ifcvf_get_vq_ready(vf, qid);
>>
>>
>> Best regards,
>> Furong
>