Merge branch 'net-smc-add-support-for-generic-netlink-api'

Merge branch 'net-smc-add-support-for-generic-netlink-api'

Karsten Graul says:

====================
net/smc: Add support for generic netlink API

Up to version 4 this patch series was using the sock_diag netlink
infrastructure. This version is using the generic netlink API. Generic
netlink API offers a better type safety between kernel and userspace
communication.
Using the generic netlink API the smc module can now provide information
about SMC linkgroups, links and devices (both for SMC-R and SMC-D).

v2: Add missing include to uapi header smc_diag.h.

v3: Apply code style recommendations from review comments.
    Instead of using EXPORTs to allow the smc_diag module to access
    data of the smc module, introduce struct smc_diag_ops and let
    smc_diag access the required data using function pointers.

v4: Address checkpatch.pl warnings. Do not use static inline for
    functions.

v5: Use generic netlink API instead of the sock_diag netlink
    infrastructure.

v6: Integrate more review comments from Jakub.

v7: Use nla_nest_start() with the new family. Use .maxattr=1 in the
    genl family and define one entry for attribute 1 in the policy to
    reject this attritbute for all commands. All other possible attributes
    are rejected because NL_VALIDATE_STRICT is set for the policy
    implicitely, which includes NL_VALIDATE_MAXTYPE.
    Setting policy[0].strict_start_type=1 does not work here because there
    is no valid attribute defined for this family, only plain commands. For
    any type > maxtype (which is .maxattr) validate_nla() would return 0 to
    userspace instead of -EINVAL. What helps here is __nla_validate_parse()
    which checks for type > maxtype and returns -EINVAL when NL_VALIDATE_MAXTYPE
    is set. This requires the one entry for type == .maxattr with
    .type = NLA_REJECT in the nla_policy.
    When a future command wants to allow attributes then it can easily specify a
    dedicated .policy for this new command in the genl_ops array. This dedicated
    policy overlays the global policy specified in the genl_family structure.
====================

Link: https://lore.kernel.org/r/20201201192049.53517-1-kgraul@linux.ibm.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>