[Nix-dev] NetBIOS/WINS name lookup in NixOS

[Bjørn Forsman]

Hi everyone,

In Ubuntu I can install libnss-winbind + winbind and append "wins" to
the "hosts:" section in /etc/nsswitch.conf to have NetBIOS/WINS name
lookup (Windows machine names). But when I try to do "the same" for
NixOS, it doesn't work:

$ ping windows-pc
ping: unknown host windows-pc

I've already made the samba package install libnss_winbind.so and
libnss_wins.so (in git master), but I don't think they are picked up.
nscd seems to load several libnss*.so libraries, but not
libnss_{winbind,wins}.so:

$ sudo pmap $(pidof nscd) | grep libnss
00007fb5859c7000     12K r-x--
/nix/store/n9yvgrp6i1fh3jzpbw1cyfvdil0n9j1r-systemd-203/lib/libnss_myhostname.so.2
00007fb5859ca000   2044K -----
/nix/store/n9yvgrp6i1fh3jzpbw1cyfvdil0n9j1r-systemd-203/lib/libnss_myhostname.so.2
00007fb585bc9000      4K r----
/nix/store/n9yvgrp6i1fh3jzpbw1cyfvdil0n9j1r-systemd-203/lib/libnss_myhostname.so.2
00007fb585bca000      4K rw---
/nix/store/n9yvgrp6i1fh3jzpbw1cyfvdil0n9j1r-systemd-203/lib/libnss_myhostname.so.2
00007fb585bcb000      8K r-x--
/nix/store/67dm2724h0cl8gj2pklf009nir0p28l4-nss-mdns-0.10/lib/libnss_mdns.so.2
00007fb585bcd000   2048K -----
/nix/store/67dm2724h0cl8gj2pklf009nir0p28l4-nss-mdns-0.10/lib/libnss_mdns.so.2
00007fb585dcd000      4K rw---
/nix/store/67dm2724h0cl8gj2pklf009nir0p28l4-nss-mdns-0.10/lib/libnss_mdns.so.2
00007fb585fe5000     20K r-x--
/nix/store/zm4bhsm8lprkzvrjgqr0klfkvr21als4-glibc-2.17/lib/libnss_dns-2.17.so
00007fb585fea000   2044K -----
/nix/store/zm4bhsm8lprkzvrjgqr0klfkvr21als4-glibc-2.17/lib/libnss_dns-2.17.so
00007fb5861e9000      4K r----
/nix/store/zm4bhsm8lprkzvrjgqr0klfkvr21als4-glibc-2.17/lib/libnss_dns-2.17.so
00007fb5861ea000      4K rw---
/nix/store/zm4bhsm8lprkzvrjgqr0klfkvr21als4-glibc-2.17/lib/libnss_dns-2.17.so
00007fb5861eb000      8K r-x--
/nix/store/67dm2724h0cl8gj2pklf009nir0p28l4-nss-mdns-0.10/lib/libnss_mdns_minimal.so.2
00007fb5861ed000   2048K -----
/nix/store/67dm2724h0cl8gj2pklf009nir0p28l4-nss-mdns-0.10/lib/libnss_mdns_minimal.so.2
00007fb5863ed000      4K rw---
/nix/store/67dm2724h0cl8gj2pklf009nir0p28l4-nss-mdns-0.10/lib/libnss_mdns_minimal.so.2
00007fb5863ee000     48K r-x--
/nix/store/zm4bhsm8lprkzvrjgqr0klfkvr21als4-glibc-2.17/lib/libnss_files-2.17.so
00007fb5863fa000   2044K -----
/nix/store/zm4bhsm8lprkzvrjgqr0klfkvr21als4-glibc-2.17/lib/libnss_files-2.17.so
00007fb5865f9000      4K r----
/nix/store/zm4bhsm8lprkzvrjgqr0klfkvr21als4-glibc-2.17/lib/libnss_files-2.17.so
00007fb5865fa000      4K rw---
/nix/store/zm4bhsm8lprkzvrjgqr0klfkvr21als4-glibc-2.17/lib/libnss_files-2.17.so

I tried increasing the loglevel of nscd but it didn't give me anything
more to work with.

Below is the patch I'm using. You can also see it online:
https://github.com/bjornfor/nixos/commit/6922607a8022432b054bc6e765f9d84ffc31fb19

Is "system.nssModules = optional cfg.nsswins samba;" not being picked up?

diff --git a/modules/config/nsswitch.nix b/modules/config/nsswitch.nix
index 7e989c1..7e29e42 100644
--- a/modules/config/nsswitch.nix
+++ b/modules/config/nsswitch.nix
@@ -28,6 +28,7 @@ let
   };

   inherit (config.services.avahi) nssmdns;
+  inherit (config.services.samba) nsswins;

 in

@@ -43,7 +44,7 @@ in
             passwd:    files ldap
             group:     files ldap
             shadow:    files ldap
-            hosts:     files ${optionalString nssmdns "mdns_minimal
[NOTFOUND=return]"} dns ${optionalString nssmdns "mdns"} myhostname
+            hosts:     files ${optionalString nssmdns "mdns_minimal
[NOTFOUND=return]"} dns ${optionalString nssmdns "mdns"}
${optionalString nsswins "wins"} myhostname
             networks:  files dns
             ethers:    files
             services:  files
diff --git a/modules/services/network-filesystems/samba.nix
b/modules/services/network-filesystems/samba.nix
index 518142b..779f919 100644
--- a/modules/services/network-filesystems/samba.nix
+++ b/modules/services/network-filesystems/samba.nix
@@ -170,6 +170,15 @@ in
         example = "share";
       };

+      nsswins = mkOption {
+        default = true; # FIXME: just for debug
+        description = ''
+          Whether to enable the WINS NSS (Name Service Switch)
plug-in.
+          Enabling it allows applications to resolve NetBIOS names
(a.k.a.
+          Windows machine names) by transparently querying the
winbindd daemon.
+        '';
+      };
+
     };

   };
@@ -196,6 +205,8 @@ in

         users.extraGroups.smbguest.gid = config.ids.uids.smbguest;

+        system.nssModules = optional cfg.nsswins samba;
+
         systemd = {
           targets.samba = {
             description = "Samba server";

Best regards,
Bjørn Forsman