netlink: add snl writer

[melifaro]

Summary

Add basic netlink writing API.

Usage:

struct snl_state ss = {};
struct snl_writer nw;
int nl_type = 0, nl_flags = 0;

if (!snl_init(&ss, NETLINK_ROUTE))
        return (ENOTSUP);
snl_init_writer(&ss, &nw);

struct nlmsghdr *hdr = snl_create_msg_request(&nw, nl_type);
hdr->nlmsg_flags |= nl_flags;

struct rtmsg *rtm = snl_reserve_msg_object(&nw, struct rtmsg);
rtm->rtm_family = dst->sa_family;
rtm->rtm_protocol = RTPROT_STATIC;
rtm->rtm_type = rtm_type;
rtm->rtm_dst_len = plen;

snl_add_msg_attr_ip(&nw, RTA_DST, dst);
snl_add_msg_attr_u32(&nw, RTA_TABLE, fib);

hdr = snl_finalize_msg(&nw);
if (hdr != NULL) {
        hdr = snl_get_reply(&ss, hdr);
        struct snl_errmsg_data e = {};
        if (!snl_check_return(&ss, hdr, &e))
                return (EINVAL);
        return (e.error);
}

Documentation to follow soon.

[melifaro]

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[melifaro]

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[melifaro]

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[kp]

sys/netlink/netlink_snl.h

616

This makes clang sad:

In file included from netlink_netlink_snl.c:1:
/usr/obj/usr/src/amd64.amd64/tmp/usr/include/netlink/netlink_snl.h:568:13: error: cast from 'char *' to 'struct nlmsghdr *' increases required alignment from 1 to 4 [-Werror,-Wcast-align]
                nw->hdr = (struct nlmsghdr *)((char *)new_base + hdr_off);
                          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

[melifaro]

sys/netlink/netlink_snl.h

616

Ack. Will add (void *) cast to silence this.