[dpdk-dev] [PATCH 1/7] ethdev: remove unused flag from header

[Vlad Zolotarov]

On 12/01/2017 06:51 PM, Ferruh Yigit wrote:
> On 12/1/2017 2:17 PM, Vlad Zolotarov wrote:
>>
>> On 11/30/2017 09:29 PM, Ferruh Yigit wrote:
>>> remove RTE_ETHDEV_HAS_LRO_SUPPORT flag from header.
>>>
>>> Flag seems added with the patch that adds LRO support, and intention
>>> looks like giving a pointer to application that library supports LRO.
>> Exactly. Removing this flag may make the existing application "think" that LRO
>> is not supported.
>> Why do you want to remove it to begin with?
> I agree that this is a little controversial, and I don't have a strong opinion
> about it, I thought twice before sending or not sending the patch :)
>
> This flag can be useful for the applications that use different versions of the
> DPDK library (with the ones does and doesn't support LRO), so that application
> can be more portable.
> I would understand a dynamic approach, which would be useful for distributed
> applications that you don't know and can't control what version of the DPDK
> library used.
> But here to benefit from this flag you need to compile your application against
> DPDK library, and if you are compiling it you already know if your DPDK supports
> LRO or not. And this is not something keeps changing platform to platform etc,
> after a specific release LRO is always supported.

True but DPDK is usually not a part of your source tree - it (should) 
come as a library and currently there isn't any proper way to query 
feature set.
This flag was also added after a lot of consideration as a rather ugly 
compromise since there wasn't (and there isn't) a proper way to do that 
at that (this) time. See more on that below.

>
> And this is the only capability support flag in the ethdev, there are many new
> features introduced in each release but they are not advertised by a capability
> flag. Only having LRO flag can be confusing.
>
> _Perhaps_ DPDK should have a way to expose the supported features, and a dynamic
> runtime way can be better option than compile time macros, but it should be
> generic nothing specific to LRO support.

IMO it's not "perhaps" it's a "must" _however_ you can't remove this 
flag without giving some other tool to do the same.
Querying a DPDK version would be a wrong direction because some Linux 
distributions (yes, I'm talking about you, Ubuntu) tend to have it's own 
trees with their own backports and these trees may be light years ahead 
in their patch level compared to vanilla trees with the same version.

>
>>> Fixes: 8eecb3295aed ("ixgbe: add LRO support")
>>> Cc: vladz at cloudius-systems.com
>>>
>>> Signed-off-by: Ferruh Yigit <ferruh.yigit at intel.com>
>>> ---
>>>   lib/librte_ether/rte_ethdev.h | 3 ---
>>>   1 file changed, 3 deletions(-)
>>>
>>> diff --git a/lib/librte_ether/rte_ethdev.h b/lib/librte_ether/rte_ethdev.h
>>> index 341c2d624..e620c3706 100644
>>> --- a/lib/librte_ether/rte_ethdev.h
>>> +++ b/lib/librte_ether/rte_ethdev.h
>>> @@ -172,9 +172,6 @@ extern "C" {
>>>   
>>>   #include <stdint.h>
>>>   
>>> -/* Use this macro to check if LRO API is supported */
>>> -#define RTE_ETHDEV_HAS_LRO_SUPPORT
>>> -
>>>   #include <rte_log.h>
>>>   #include <rte_interrupts.h>
>>>   #include <rte_dev.h>