On Sun, Sep 11, 2016 at 11:14:09AM -0600, Jason Gunthorpe wrote:

quoted

quoted

We stil always have the common structure first.  And at least for
cgroups supports that's what matters.

Re the actual structures - we'll really need to make sure we

 a) expose proper userspace abi headers in the kernel for all code
    in the RDMA subsystem
 b) actually use that in the userspace components

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

this without it would be very hard, as everything is cross-linked, I
couldnn't unwind libibcm until I fixed a bit of verbs, and rdmacm can't
even include its uapi header until the duplicate definitions in the
verbs copy are delt with .. and I've also learned we are making
changing to the kernel uapi header and since nothing uses them we never even
compile test :( :( eg
https://github.com/torvalds/linux/commit/b493d91d333e867a043f7ff1397bcba6e2d0dda2]

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.

eg the userspace version stuffs the header into the struct and the
kernel version does not. Presumably this is for efficiency so that no
copies are required when marshaling. This impacts everything :(

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.  However automatically
generating the user ABI from the kernel one might still be a good idea
in the long run.