Re: [PATCH for-next v3 3/4] RDMA/efa: User/kernel compatibility handshake mechanism

[Gal Pressman <galpress@xxxxxxxxxx>]

On 22/07/2020 15:08, Jason Gunthorpe wrote:
> On Wed, Jul 22, 2020 at 03:04:20PM +0300, Gal Pressman wrote:
>> On 22/07/2020 14:55, Jason Gunthorpe wrote:
>>> On Tue, Jul 21, 2020 at 04:30:48PM +0300, Gal Pressman wrote:
>>>> Introduce a mechanism that performs an handshake between the userspace
>>>> provider and kernel driver which verifies that the user supports all
>>>> required features in order to operate correctly.
>>>>
>>>> The handshake verifies the needed functionality by comparing the
>>>> reported device caps and the provider caps. If the device reports a
>>>> non-zero capability the appropriate comp mask is required from the
>>>> userspace provider in order to allocate the context.
>>>>
>>>> Reviewed-by: Shadi Ammouri <sammouri@xxxxxxxxxx>
>>>> Reviewed-by: Yossi Leybovich <sleybo@xxxxxxxxxx>
>>>> Signed-off-by: Gal Pressman <galpress@xxxxxxxxxx>
>>>>  drivers/infiniband/hw/efa/efa_verbs.c | 49 +++++++++++++++++++++++++++
>>>>  include/uapi/rdma/efa-abi.h           | 10 ++++++
>>>>  2 files changed, 59 insertions(+)
>>>>
>>>> diff --git a/drivers/infiniband/hw/efa/efa_verbs.c b/drivers/infiniband/hw/efa/efa_verbs.c
>>>> index 26102ab333b2..7ca40df81ee5 100644
>>>> +++ b/drivers/infiniband/hw/efa/efa_verbs.c
>>>> @@ -1501,11 +1501,48 @@ static int efa_dealloc_uar(struct efa_dev *dev, u16 uarn)
>>>>  	return efa_com_dealloc_uar(&dev->edev, &params);
>>>>  }
>>>>  
>>>> +#define EFA_CHECK_COMP(_dev, _comp_mask, _attr, _mask)                         \
>>>> +	(!(_dev)->dev_attr._attr || ((_comp_mask) & (_mask)))
>>>> +
>>>> +#define DEFINE_COMP_HANDSHAKE(_dev, _comp_mask, _attr, _mask)                  \
>>>> +	{                                                                      \
>>>> +		.attr = #_attr,                                                \
>>>> +		.check_comp = EFA_CHECK_COMP(_dev, _comp_mask, _attr, _mask)   \
>>>> +	}
>>>> +
>>>> +int efa_user_comp_handshake(const struct ib_ucontext *ibucontext,
>>>> +			    const struct efa_ibv_alloc_ucontext_cmd *cmd)
>>>> +{
>>>> +	struct efa_dev *dev = to_edev(ibucontext->device);
>>>> +	int i;
>>>> +	struct {
>>>> +		char *attr;
>>>> +		bool check_comp;
>>>> +	} user_comp_handshakes[] = {
>>>> +		DEFINE_COMP_HANDSHAKE(dev, cmd->comp_mask, max_tx_batch,
>>>> +				      EFA_ALLOC_UCONTEXT_CMD_COMP_TX_BATCH),
>>>> +		DEFINE_COMP_HANDSHAKE(dev, cmd->comp_mask, min_sq_depth,
>>>> +				      EFA_ALLOC_UCONTEXT_CMD_COMP_MIN_SQ_WR),
>>>> +	};
>>>
>>> This seems like a very expensive construct
>>>
>>> Why have the array at all? Just list the macros and have them jump to
>>> err
>>
>> Do you mean:
>>
>> if (CHECK_COMP(x1)) {
>>     ibdev_dbg(err);
>>     goto err;
>> }
>>
>> if (CHECK_COMP(x2)) {
>>     ibdev_dbg(err);
>>     goto err;
>> }
>>
>> [...]
>>
>> That adds much more boilerplate code for each feature. Or do you have something
>> else in mind?
> 
> #define DO_COMP_HANDSHAKE() \
>     if (...) goto err
> 
> DO_COMP_HANDSHAKE(x1)
> DO_COMP_HANDSHAKE(2)

I'd rather not have gotos inside macros, I find that very confusing.
I can add the ifs I suggested if you want the array removed.