Re: [dpdk-dev] [PATCH v2] vhost: add virtio configuration space messages

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

On 03/28/2018 11:19 AM, Wodkowski, PawelX wrote:
>> -----Original Message-----
>> From: Maxime Coquelin [mailto:maxime.coquelin@redhat.com]
>> Sent: Wednesday, March 28, 2018 11:12 AM
>> To: Kulasek, TomaszX <tomaszx.kulasek@intel.com>; yliu@fridaylinux.org
>> Cc: Verkamp, Daniel <daniel.verkamp@intel.com>; Harris, James R
>> <james.r.harris@intel.com>; Wodkowski, PawelX
>> <pawelx.wodkowski@intel.com>; dev@dpdk.org; Liu, Changpeng
>> <changpeng.liu@intel.com>; Tan, Jianfeng <jianfeng.tan@intel.com>
>> Subject: Re: [dpdk-dev] [PATCH v2] vhost: add virtio configuration space
>> messages
>>
>>
>>
>> On 03/27/2018 05:35 PM, Tomasz Kulasek wrote:
>>> This patch adds new vhost user messages GET_CONFIG and SET_CONFIG used
>>> for get/set virtio device's configuration space.
>>>
>>> Signed-off-by: Changpeng Liu <changpeng.liu@intel.com>
>>> Signed-off-by: Tomasz Kulasek <tomaszx.kulasek@intel.com>
>>> ---
>>> Changes in v2:
>>>    - code cleanup
>>>
>>>    lib/librte_vhost/rte_vhost.h  |  4 ++++
>>>    lib/librte_vhost/vhost_user.c | 22 ++++++++++++++++++++++
>>>    lib/librte_vhost/vhost_user.h | 16 ++++++++++++++++
>>>    3 files changed, 42 insertions(+)
>>>
>>> diff --git a/lib/librte_vhost/rte_vhost.h b/lib/librte_vhost/rte_vhost.h
>>> index d332069..fe30518 100644
>>> --- a/lib/librte_vhost/rte_vhost.h
>>> +++ b/lib/librte_vhost/rte_vhost.h
>>> @@ -84,6 +84,10 @@ struct vhost_device_ops {
>>>    	int (*new_connection)(int vid);
>>>    	void (*destroy_connection)(int vid);
>>>
>>> +	int (*get_config)(int vid, uint8_t *config, uint32_t config_len);
>>> +	int (*set_config)(int vid, uint8_t *config, uint32_t offset,
>>> +			uint32_t len, uint32_t flags);
>>> +
>>>    	void *reserved[2]; /**< Reserved for future extension */
>>
>> You are breaking the ABI, as you grow the size of the ops struct.
>>
>> Also, I'm wondering if we shouldn't have a different ops for external
>> backends. Here these ops are more intended to the application, we could
>> have a specific ops struct for external backends IMHO.
> 
> What do mean by "external backends" ?

Libs like SPDK or Crypto that implements their own ring processing,
comparing to an application like DPDK that doesn't care of rings
details.