Re: [dpdk-dev] [PATCH] vhost: fix packed ring defines declaration

[Maxime Coquelin <maxime.coquelin@redhat.com>]

On 11/22/18 7:23 PM, Ferruh Yigit wrote:
> On 11/22/2018 5:09 PM, Maxime Coquelin wrote:
>> The packed ring defines were declared only if kernel
>> header does not declare them.
>> The problem is that they are not applied in upstream kernel,
>> and some changes in the names have been required.
>>
>> This patch declares the defines unconditionally, which
>> fixes potential build issues.
> 
> +1 to address possible build issues.
> 
>>
>> Fixes: 297b1e7350f6 ("vhost: add virtio packed virtqueue defines")
>> Cc: stable@dpdk.org
>>
>> Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>
>> ---
>>   lib/librte_vhost/vhost.h | 22 +++++++++++-----------
>>   1 file changed, 11 insertions(+), 11 deletions(-)
>>
>> diff --git a/lib/librte_vhost/vhost.h b/lib/librte_vhost/vhost.h
>> index 760f42192..5218f1b12 100644
>> --- a/lib/librte_vhost/vhost.h
>> +++ b/lib/librte_vhost/vhost.h
>> @@ -219,13 +219,6 @@ struct vhost_msg {
>>   
>>   #define VIRTIO_F_RING_PACKED 34
>>   
>> -#define VRING_DESC_F_NEXT	1
>> -#define VRING_DESC_F_WRITE	2
>> -#define VRING_DESC_F_INDIRECT	4
> 
> Why these are not re-defined below? Not used?

These defines are in kernel headers since the beginning of virtio
support, so there are no reasons to keep them (and they aren't packed-
ring specific).

I can let them if you prefer, it does not hurt but shouldn't be here.

>> -
>> -#define VRING_DESC_F_AVAIL	(1ULL << 7)
>> -#define VRING_DESC_F_USED	(1ULL << 15)
>> -
>>   struct vring_packed_desc {
>>   	uint64_t addr;
>>   	uint32_t len;
>> @@ -233,16 +226,23 @@ struct vring_packed_desc {
>>   	uint16_t flags;
>>   };
>>   
>> -#define VRING_EVENT_F_ENABLE 0x0
>> -#define VRING_EVENT_F_DISABLE 0x1
>> -#define VRING_EVENT_F_DESC 0x2
>> -
>>   struct vring_packed_desc_event {
>>   	uint16_t off_wrap;
>>   	uint16_t flags;
>>   };
>>   #endif
>>   
>> +/*
>> + * Declare below packed ring defines unconditionally
>> + * as Kernel header might use different names.
>> + */
>> +#define VRING_DESC_F_AVAIL	(1ULL << 7)
>> +#define VRING_DESC_F_USED	(1ULL << 15)
>> +
>> +#define VRING_EVENT_F_ENABLE 0x0
>> +#define VRING_EVENT_F_DISABLE 0x1
>> +#define VRING_EVENT_F_DESC 0x2
> 
> What if Linux changes mind and uses old names again, build will fail again. If
> related part in Linux is not released yet, what do you think being on safe side
> and adding these defines with "#ifndef" wrap?

There are the "old" ones.
In any case it will work (I tested it).

In a future release, I plan to get rid of this dependency with Kernel
which only causes problems.

There was a benefit at the beginning when all needed declarations where
in the Kernel headers. But now, every time we add a new virtio feature,
we have to check kernel supports it and if not define it.

Thanks,
Maxime
>> +
>>   /*
>>    * Available and used descs are in same order
>>    */
>>
>