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

[Gal Pressman <galpress@xxxxxxxxxx>]

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?