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>