Re: [PATCH rdma-next v1 1/6] IB/uverbs: Allow CQ moderation with modify CQ

Yishai Hadas
2017-10-31T11:31:28Z

On 10/31/2017 7:08 AM, Leon Romanovsky wrote:
> On Mon, Oct 30, 2017 at 05:07:53PM -0600, Jason Gunthorpe wrote:
>> On Mon, Oct 30, 2017 at 09:09:52PM +0200, Leon Romanovsky wrote:
>>
>>> However, I don't think that kernel to libibverbs API should follow the
>>> same path. The centralized entry points to the kernel provides better
>>> enforcement and minimizes system call bloat.
>>
>> How so? I didn't think selinux intersected with the CQs at all..
>> I've never worried about the # of verbs entries, we have so many
>> already.
>
> Not SELinux enforcement, but various copy_{to|from}_user checks, unified
> return values, easy folding in case of errors, e.t.c.
>
> It is a matter of personal view and less technical thing. You prefer bazillion
> entry points to the kernel and I think that such design good for user-space only,
> and mostly not applicable for kernel<->user interfaces.

Even for the user area having a dedicated 'setter' per field might bring
some redundant overhead and limitation. This will prevent the option
from application to modify few fields in one API and resulted in a
system call per field. Also libibverbs and user drivers may need to
maintain some wrapping over the kernel command which in turn might lead
to some extra/duplication of code. I would vote to follow modify
QP/SRQ/WQ by having one API with an 'attr_mask' field as this series has
introduced in both kernel and user.

The matching user space series was published and can be seen at: