Cannot build on FreeBSD 11-CURRENT

[mkushnir]

When building on a not so old 11-CURRENT, I'm getting this:

cc -fPIC -fno-strict-aliasing -D_GNU_SOURCE -fstack-protector-all -U_FORTIFY_SOURCE -D_FORTIFY_SOURCE=2  -Wall -O2 -g -DPCP_DEBUG -DPCP_VERSION=\"3.11.0\" -I../../../src/include -I../../../src/include/pcp   -c -o netif.o netif.c
netif.c:148:35: error: no member named 'if_data' in 'struct ifnet'
                    atom->ul = (__uint32_t)ifp->if_data.ifi_mtu;
                                           ~~~  ^
netif.c:156:24: error: no member named 'if_data' in 'struct ifnet'
                    atom->ull = ifp->if_data.ifi_baudrate;
                                ~~~  ^
netif.c:160:24: error: no member named 'if_data' in 'struct ifnet'
                    atom->ull = ifp->if_data.ifi_ibytes;
                                ~~~  ^
netif.c:164:24: error: no member named 'if_data' in 'struct ifnet'
                    atom->ull = ifp->if_data.ifi_ipackets;
                                ~~~  ^
netif.c:168:24: error: no member named 'if_data' in 'struct ifnet'
                    atom->ull = ifp->if_data.ifi_imcasts;
                                ~~~  ^
netif.c:172:24: error: no member named 'if_data' in 'struct ifnet'
                    atom->ull = ifp->if_data.ifi_ierrors;
                                ~~~  ^
netif.c:176:24: error: no member named 'if_data' in 'struct ifnet'
                    atom->ull = ifp->if_data.ifi_iqdrops;
                                ~~~  ^
netif.c:180:24: error: no member named 'if_data' in 'struct ifnet'
                    atom->ull = ifp->if_data.ifi_obytes;
                                ~~~  ^
netif.c:184:24: error: no member named 'if_data' in 'struct ifnet'
                    atom->ull = ifp->if_data.ifi_opackets;
                                ~~~  ^
netif.c:188:24: error: no member named 'if_data' in 'struct ifnet'
                    atom->ull = ifp->if_data.ifi_omcasts;
                                ~~~  ^
netif.c:192:24: error: no member named 'if_data' in 'struct ifnet'
                    atom->ull = ifp->if_data.ifi_oerrors;
                                ~~~  ^
netif.c:196:24: error: no member named 'if_data' in 'struct ifnet'
                    atom->ull = ifp->if_data.ifi_collisions;
                                ~~~  ^
netif.c:200:24: error: no member named 'if_data' in 'struct ifnet'
                    atom->ull = ifp->if_data.ifi_ibytes + ifp->if_data.ifi_obytes;
                                ~~~  ^
netif.c:200:50: error: no member named 'if_data' in 'struct ifnet'
                    atom->ull = ifp->if_data.ifi_ibytes + ifp->if_data.ifi_obytes;
                                                          ~~~  ^
netif.c:204:24: error: no member named 'if_data' in 'struct ifnet'
                    atom->ull = ifp->if_data.ifi_ipackets + ifp->if_data.ifi_opackets;
                                ~~~  ^
netif.c:204:52: error: no member named 'if_data' in 'struct ifnet'
                    atom->ull = ifp->if_data.ifi_ipackets + ifp->if_data.ifi_opackets;
                                                            ~~~  ^
netif.c:208:24: error: no member named 'if_data' in 'struct ifnet'
                    atom->ull = ifp->if_data.ifi_imcasts + ifp->if_data.ifi_omcasts;
                                ~~~  ^
netif.c:208:51: error: no member named 'if_data' in 'struct ifnet'
                    atom->ull = ifp->if_data.ifi_imcasts + ifp->if_data.ifi_omcasts;
                                                           ~~~  ^
netif.c:212:24: error: no member named 'if_data' in 'struct ifnet'
                    atom->ull = ifp->if_data.ifi_ierrors + ifp->if_data.ifi_oerrors;
                                ~~~  ^
fatal error: too many errors emitted, stopping now [-ferror-limit=]
20 errors generated.
<builtin>: recipe for target 'netif.o' failed
gmake: *** [netif.o] Error 1

After some digging into it, looks like FreeBSD's kvm(3) was used, directly interpreting kernel memory structures. The interface turns out to be quite unstable. I would suggest to re-implement it using getifaddrs(3) API. The attached patch worked for me.
out.txt

[kmcdonell]

You're correct on a couple of fronts.

1. using /dev/kmem was a throwback to Unix versions 20+ years ago ... rather than the plan of choice it is the fallback plan wired into my brain when ignorance hides a more modern API ... and I'm clearly not a FreeBSD guru.
2. FreeBSD 11 is missing from my QA matrix.

Let me fix 2. then apply your patch (which looks OK from a quick scan), test and then I'll commit.

Thanks for taking the time and effort.

[kmcdonell]

Code based mostly on mkushnir's patch has been committed to my tree and will flow upsteam in due course (including to github).
Thanks.