Re: [PATCH RDMA/netlink] RDMA/netlink: Adhere to returning zero on success

[Leon Romanovsky <leon@kernel.org>]

On Wed, Dec 11, 2019 at 11:34:00AM +0100, Håkon Bugge wrote:
> In rdma_nl_rcv_skb(), the local variable err is assigned the return
> value of the supplied callback function, which could be one of
> ib_nl_handle_resolve_resp(), ib_nl_handle_set_timeout(), or
> ib_nl_handle_ip_res_resp(). These three functions all return skb->len
> on success.
>
> rdma_nl_rcv_skb() is merely a copy of netlink_rcv_skb(). The callback
> functions used by the latter have the convention: "Returns 0 on
> success or a negative error code".
>
> In particular, the statement (equal for both functions):
>
>    if (nlh->nlmsg_flags & NLM_F_ACK || err)
>
> implies that rdma_nl_rcv_skb() always will ack a message, independent
> of the NLM_F_ACK being set in nlmsg_flags or not.

The more accurate description is that rdma_nl_rcv_skb() always generates
NLMSG_ERROR without relation to NLM_F_ACK flag. The NLM_F_ACK flag is
requested to get acknowledges for the success.

>
> The fix could be to change the above statement, but it is better to
> keep the two *_rcv_skb() functions equal in this respect and instead
> change the callback functions in the rdma subsystem to the correct
> convention.

AFAIR, RTNETLINK has the same implementation as RDMA netlink.

Thanks