Re: [PATCHv12 1/3] rdmacg: Added rdma cgroup controller

[Leon Romanovsky <leon-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>]

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On Sun, Sep 11, 2016 at 11:52:35AM -0600, Jason Gunthorpe wrote:
> On Sun, Sep 11, 2016 at 07:24:45PM +0200, Christoph Hellwig wrote:
> > > > > I've posted some initial work toward a) a while ago, and once we
> > >
> > > Did it get merged? Do you have a pointer?
> >
> > http://www.spinics.net/lists/linux-rdma/msg31958.html
>
> Right, I remember that. Certainly the right direction
>
> > > However, everything under verbs is not straightforward. The files in
> > > userspace are not copies...
> > >
> > > user:
> > >
> > > struct ibv_query_device {
> > >        __u32 command;
> > >        __u16 in_words;
> > >        __u16 out_words;
> > >        __u64 response;
> > >        __u64 driver_data[0];
> > > };
> > >
> > > kernel:
> > >
> > > struct ib_uverbs_query_device {
> > >         __u64 response;
> > >         __u64 driver_data[0];
> > > };
> >
> > We'll obviously need different strutures for the libibvers API
> > and the kernel interface in this case, and we'll need to figure out
> > how to properly translate them.  I think a cast, plus compile time
> > type checking ala BUILD_BUG_ON is the way to go.
>
> I'm not sure I follow, which would I cast?
>
> BUILD_BUG_ON(sizeof(ibv_query_device) == sizeof(ib_uverbs_cmd_hdr) +
>              sizeof(ib_uverbs_query_device))
>
> ?
>
> > > I'm thinking the best way forward might be to use a script and
> > > transform userspace into:
> > >
> > > struct ibv_query_device {
> > > 	struct ib_uverbs_cmd_hdr hdr;
> > > 	struct ib_uverbs_query_device cmd;
> > > };
> >
> > That would break the users of the interface.
>
> Sorry, I mean doing this inside rdma-plumbing. Since the change is ABI
> identical the modified libibverbs would still be binary compatible
> with all providers but not source compatible. Since all kernel
> supported providers are in rdma-plumbing we can add the '.cmd.' at the
> same time.
>
> The kernel uapi header would stay the same.
>
> > However automatically generating the user ABI from the kernel one
> > might still be a good idea in the long run.
>
> My preference would be to try and use the kernel headers directly.

I thought the same, especially after realizing that they are almost
copy/paste from the vendor *-abi.h files.

>
> Jason

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