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Re: [PATCH v2 1/8] driver/pci: Get next capability without passing caps
- To: Jan Beulich <jbeulich@xxxxxxxx>
- From: "Chen, Jiqian" <Jiqian.Chen@xxxxxxx>
- Date: Fri, 11 Apr 2025 02:51:59 +0000
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- Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Anthony PERARD <anthony.perard@xxxxxxxxxx>, "Orzel, Michal" <Michal.Orzel@xxxxxxx>, Julien Grall <julien@xxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>, "Huang, Ray" <Ray.Huang@xxxxxxx>, "Chen, Jiqian" <Jiqian.Chen@xxxxxxx>
- Delivery-date: Fri, 11 Apr 2025 02:52:15 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
- Thread-index: AQHbqRsYW9r+TjshqU+vmdXYCVrO/7Oc16GAgAFv6YA=
- Thread-topic: [PATCH v2 1/8] driver/pci: Get next capability without passing caps
On 2025/4/10 20:34, Jan Beulich wrote:
> On 09.04.2025 08:45, Jiqian Chen wrote:
>> --- a/xen/drivers/pci/pci.c
>> +++ b/xen/drivers/pci/pci.c
>> @@ -40,7 +40,7 @@ unsigned int pci_find_cap_offset(pci_sbdf_t sbdf, unsigned
>> int cap)
>> }
>>
>> unsigned int pci_find_next_cap_ttl(pci_sbdf_t sbdf, unsigned int pos,
>> - const unsigned int caps[], unsigned int
>> n,
>> + const unsigned int *caps, unsigned int n,
>
> I don't follow the need for this change.
This changed is for my next patch "vpci/header: Emulate legacy capability list
for host".
Currently, vpci only emulates capability list for domU, not for dom0.
For domU, vpci exposes a fixed capability array which calls "supported_caps".
My changes want to emulate capability list for dom0.
I think vpci should expose all devices capabilities to dom0.
When I emulate it, I need to iterate over all capabilities without another
fixed array,
so I need this function to return the position of next capability directly when
passing a zero length array to this function.
>
>> @@ -55,6 +55,10 @@ unsigned int pci_find_next_cap_ttl(pci_sbdf_t sbdf,
>> unsigned int pos,
>>
>> if ( id == 0xff )
>> break;
>> +
>> + if ( !caps || n == 0 )
>> + return pos;
>
> Checking n to be zero ought to suffice here? In that case it doesn't matter
> what caps is. Plus if n is non-zero, it clearly is an error if caps was NULL.
Two checking is to prevent null pointer errors.
But as you said, if checking n to be zero is enough, then I don't need to
change the definition of this function.
I will change in next version.
>
> Jan
--
Best regards,
Jiqian Chen.
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