nss: Introduce libvirt-guest module

So far the NSS module looks up only hostnames as provided by
guests themselves. However, there are some cases where this is
not enough: e.g. when there's a fresh new guest being installed
(with some generic hostname) say from a live ISO image; or some
(older) systems don't advertise their hostname in DHCP
transactions at all.
In cases like that it would be helpful if we translate domain
name as seen by libvirt too so that users can:

  # virsh start $dom && ssh $dom

In order to achieve that new libvirt-guest module is introduced,
while older libvirt module maintains its current behaviour (that
is translating guest provided names into IP addresses).
Signed-off-by: NMichal Privoznik <mprivozn@redhat.com>

docs/news.html.in

@@ -21,6 +21,10 @@
           domain <disk> <iotune> subelement "group_name"
           to allow sharing I/O throttling quota between multiple drives
           </li>
+          <li>nss: Introduce <code>libvirt-guest</code><br/>
+          New <code>libvirt-guest</code> nss module that translates libvirt
+          guest names into IP addresses
+          </li>
         </ul>
       </li>
       <li><strong>Improvements</strong>

docs/nss.html.in

@@ -62,6 +62,48 @@ hosts:       files libvirt dns
     lookup given host name.
     </p>
 
+    <h2><a name="Sources">Sources of information</a></h2>
+
+    <p>
+    As of <code>v3.0.0</code> release, libvirt offers two NSS modules
+    implementing two different methods of hostname translation. The first and
+    older method is implemented by <code>libvirt</code> plugin and
+    basically looks up the hostname to IP address translation in DHCP server
+    records. Therefore this is dependent on hostname provided by guests. Thing
+    is, not all the guests out there provide one in DHCP transactions, or not
+    every sysadmin out there believes all the guests. Hence libvirt implements
+    second method in <code>libvirt-guest</code> module which does libvirt guest
+    name to IP address translation (regardless of hostname set in the guest).
+    </p>
+
+    <p>
+    To enable either of the modules put their name into the
+    <code>nsswitch.conf</code> file. For instance, to enable
+    <code>libvirt-guest</code> module:
+    </p>
+
+<pre>
+$ cat /etc/nsswitch.conf
+# /etc/nsswitch.conf:
+hosts:       files libvirt-guest dns
+# ...
+</pre>
+    <p>Or users can enable both at the same time:</p>
+<pre>
+$ cat /etc/nsswitch.conf
+# /etc/nsswitch.conf:
+hosts:       files libvirt libvirt-guest dns
+# ...
+</pre>
+
+    <p>
+    This configuration will mean that if hostname is not found by the
+    <code>libvirt</code> module (e.g. because a guest did not sent hostname
+    during DHCP transaction), the <code>libvirt-guest</code> module is
+    consulted (and if the hostname matches libvirt guest name it will be
+    resolved).
+    </p>
+
     <h2><a name="Internals">How does it work?</a></h2>
 
     <p>
@@ -100,15 +142,18 @@ hosts:       files libvirt dns
     <h2><a name="Limitations">Limitations</a></h2>
 
     <ol>
-      <li>The libvirt NSS module matches only hostnames provided by guest. If
-        the libvirt name and one advertised by guest differs, the latter is
-        matched.</li>
+      <li>The <code>libvirt</code> NSS module matches only hostnames provided by guest.
+        If the libvirt name and one advertised by guest differs, the latter is
+        matched. However, as of <code>v3.0.0</code> there are two libvirt NSS modules
+        translating both hostnames provided by guest and libvirt guest names.</li>
       <li>The module works only in that cases where IP addresses are assigned by
         dnsmasq spawned by libvirt. Libvirt NATed networks are typical
         example.</li>
     </ol>
 
     <p>
+    <i>The following paragraph describes implementation limitation of the
+    <code>libvirt</code> NSS module.</i>
     These limitation are result of libvirt's internal implementation. While
     libvirt can report IP addresses regardless of their origin, a public API
     must be used to obtain those. However, for the API a connection object is
@@ -134,8 +179,11 @@ virsh domifaddr --source lease $domain
 </pre>
 
     <p>
-    If there's no record for either of the aforementioned commands, it's very
-    likely that NSS module won't find anything and vice versa.
+    If there's no record for either of the aforementioned commands, it's
+    very likely that NSS module won't find anything and vice versa.
+    As of <code>v3.0.0</code> libvirt provides <code>libvirt-guest</code> NSS
+    module that doesn't have this limitation. However, the statement is still
+    true for the <code>libvirt</code> NSS module.
     </p>
   </body>
 </html>

src/Makefile.am

@@ -3033,6 +3033,10 @@ libvirt_nss_la_SOURCES =		\
 		util/virerror.h			\
 		util/virfile.c			\
 		util/virfile.h			\
+		util/virhash.c			\
+		util/virhash.h			\
+		util/virhashcode.c		\
+		util/virhashcode.h		\
 		util/virjson.c			\
 		util/virjson.h			\
 		util/virkmod.c			\
@@ -3041,12 +3045,16 @@ libvirt_nss_la_SOURCES =		\
 		util/virlease.h			\
 		util/virlog.c			\
 		util/virlog.h			\
+		util/virmacmap.c		\
+		util/virmacmap.h		\
 		util/virobject.c		\
 		util/virobject.h		\
 		util/virpidfile.c		\
 		util/virpidfile.h		\
 		util/virprocess.c		\
 		util/virprocess.h		\
+		util/virrandom.c		\
+		util/virrandom.h		\
 		util/virsocketaddr.c	\
 		util/virsocketaddr.h	\
 		util/virstring.c		\

tests/Makefile.am

@@ -335,8 +335,8 @@ test_programs += virscsitest
 endif WITH_LINUX
 
 if WITH_NSS
-test_helpers += nsslinktest
-test_programs += nsstest
+test_helpers += nsslinktest nssguestlinktest
+test_programs += nsstest nssguesttest
 endif WITH_NSS
 
 test_programs += storagevolxml2xmltest storagepoolxml2xmltest
@@ -1125,6 +1125,16 @@ nsstest_LDADD = \
 	$(LDADDS)	\
 	../tools/nss/libnss_libvirt_impl.la
 
+nssguesttest_SOURCES = \
+	nsstest.c testutils.h testutils.c
+nssguesttest_CFLAGS = \
+	-DLIBVIRT_NSS_GUEST	\
+	$(AM_CFLAGS)	\
+	-I$(top_srcdir)/tools/nss
+nssguesttest_LDADD = \
+	$(LDADDS)	\
+	../tools/nss/libnss_libvirt_guest_impl.la
+
 nssmock_la_SOURCES = \
 	nssmock.c
 nssmock_la_CFLAGS = $(AM_CFLAGS)
@@ -1140,6 +1150,14 @@ nsslinktest_CFLAGS = 	\
 nsslinktest_LDADD = ../tools/nss/libnss_libvirt_impl.la
 nsslinktest_LDFLAGS = $(NULL)
 
+nssguestlinktest_SOURCES = nsslinktest.c
+nssguestlinktest_CFLAGS = 	\
+	-DLIBVIRT_NSS_GUEST	\
+	$(AM_CFLAGS)		\
+	-I$(top_srcdir)/tools/nss
+nssguestlinktest_LDADD = ../tools/nss/libnss_libvirt_guest_impl.la
+nssguestlinktest_LDFLAGS = $(NULL)
+
 virmacmapmock_la_SOURCES = \
 	virmacmapmock.c
 virmacmapmock_la_CFLAGS = $(AM_CFLAGS)

tests/nssdata/virbr0.macs

+[
+  {
+    "domain": "fedora",
+    "macs": [
+      "52:54:00:a4:6f:91",
+      "52:54:00:a4:6f:92"
+    ]
+  },
+  {
+    "domain": "gentoo",
+    "macs": [
+      "52:54:00:3a:b5:0c"
+    ]
+  },
+  {
+    "domain": "debian",
+    "macs": [
+      "52:54:00:11:22:33",
+      "52:54:00:a2:37:4c",
+      "52:54:00:f8:5b:1d"
+    ]
+  }
+]

tests/nssdata/virbr0.status

@@ -16,5 +16,10 @@
         "mac-address": "52:54:00:3a:b5:0c",
         "hostname": "gentoo",
         "expiry-time": 2000000000
+    },
+    {
+        "ip-address": "192.168.122.2",
+        "mac-address": "52:54:00:11:22:33",
+        "expiry-time": 2000000000
     }
 ]

tests/nssdata/virbr1.macs

+[
+  {
+    "domain": "fedora",
+    "macs": [
+      "52:54:00:a4:6f:93",
+      "52:54:00:a4:6f:94"
+    ]
+  },
+  {
+   "domain": "gentoo",
+   "macs": [
+      "52:54:00:04:be:64"
+    ]
+  },
+  {
+   "domain": "suse",
+   "macs": [
+      "52:54:00:aa:bb:cc"
+    ]
+  }
+]

tests/nssdata/virbr1.status

@@ -16,5 +16,10 @@
         "mac-address": "52:54:00:a4:6f:94",
         "hostname": "fedora",
         "expiry-time": 1
+    },
+    {
+        "ip-address": "192.168.122.3",
+        "mac-address": "52:54:00:aa:bb:cc",
+        "expiry-time": 2000000000
     }
 ]

tests/nssmock.c

@@ -26,6 +26,7 @@
 # include <dirent.h>
 # include <sys/stat.h>
 # include <fcntl.h>
+# include <unistd.h>
 
 # include "configmake.h"
 # include "virstring.h"
@@ -33,6 +34,7 @@
 
 static int (*real_open)(const char *path, int flags, ...);
 static DIR * (*real_opendir)(const char *name);
+static int (*real_access)(const char *path, int mode);
 
 # define LEASEDIR LOCALSTATEDIR "/lib/libvirt/dnsmasq/"
 
@@ -47,6 +49,7 @@ init_syms(void)
 
     VIR_MOCK_REAL_INIT(open);
     VIR_MOCK_REAL_INIT(opendir);
+    VIR_MOCK_REAL_INIT(access);
 }
 
 static int
@@ -112,6 +115,24 @@ opendir(const char *path)
     free(newpath);
     return ret;
 }
+
+int
+access(const char *path, int mode)
+{
+    int ret;
+    char *newpath = NULL;
+
+    init_syms();
+
+    if (STRPREFIX(path, LEASEDIR) &&
+        getrealpath(&newpath, path) < 0)
+        return -1;
+
+    ret = real_access(newpath ? newpath : path, mode);
+
+    free(newpath);
+    return ret;
+}
 #else
 /* Nothing to override if NSS plugin is not enabled */
 #endif

tests/nsstest.c

@@ -184,11 +184,16 @@ mymain(void)
             ret = -1;                                           \
     } while (0)
 
+# if !defined(LIBVIRT_NSS_GUEST)
     DO_TEST("fedora", AF_INET, "192.168.122.197", "192.168.122.198", "192.168.122.199");
     DO_TEST("gentoo", AF_INET, "192.168.122.254");
     DO_TEST("gentoo", AF_INET6, "2001:1234:dead:beef::2");
     DO_TEST("gentoo", AF_UNSPEC, "192.168.122.254");
     DO_TEST("non-existent", AF_UNSPEC, NULL);
+# else /* defined(LIBVIRT_NSS_GUEST) */
+    DO_TEST("debian", AF_INET, "192.168.122.2");
+    DO_TEST("suse", AF_INET, "192.168.122.3");
+# endif /* defined(LIBVIRT_NSS_GUEST) */
 
     return ret == 0 ? EXIT_SUCCESS : EXIT_FAILURE;
 }

tools/Makefile.am

@@ -436,18 +436,26 @@ endif WITH_WIRESHARK_DISSECTOR
 if WITH_BSD_NSS
 LIBVIRT_NSS_SYMBOL_FILE = \
 	$(srcdir)/nss/libvirt_nss_bsd.syms
+LIBVIRT_GUEST_NSS_SYMBOL_FILE = \
+	$(LIBVIRT_NSS_SYMBOL_FILE)
 NSS_SO_VER = 1
 
 install-nss:
 	( cd $(DESTDIR)$(libdir) && \
 	  rm -f nss_libvirt.so.$(NSS_SO_VER) && \
-	  $(LN_S) libnss_libvirt.so.$(NSS_SO_VER) nss_libvirt.so.$(NSS_SO_VER) )
+	  $(LN_S) libnss_libvirt.so.$(NSS_SO_VER) nss_libvirt.so.$(NSS_SO_VER) && \
+	  rm -f nss_libvirt_guest.so.$(NSS_SO_VER) && \
+	  $(LN_S) libnss_libvirt_guest.so.$(NSS_SO_VER) \
+	  nss_libvirt_guest.so.$(NSS_SO_VER))
 
 uninstall-nss:
 	-rm -f $(DESTDIR)$(libdir)/nss_libvirt.so.$(NSS_SO_VER)
+	-rm -f $(DESTDIR)$(libdir)/nss_libvirt_guest.so.$(NSS_SO_VER)
 else ! WITH_BSD_NSS
 LIBVIRT_NSS_SYMBOL_FILE = \
 	$(srcdir)/nss/libvirt_nss.syms
+LIBVIRT_GUEST_NSS_SYMBOL_FILE = \
+	$(srcdir)/nss/libvirt_guest_nss.syms
 NSS_SO_VER = 2
 
 install-nss:
@@ -488,14 +496,46 @@ nss_libnss_libvirt_la_LDFLAGS = \
 nss_libnss_libvirt_la_LIBADD =  \
 	nss/libnss_libvirt_impl.la
 
+noinst_LTLIBRARIES += nss/libnss_libvirt_guest_impl.la
+nss_libnss_libvirt_guest_impl_la_SOURCES = \
+	$(LIBVIRT_NSS_SOURCES)
+
+nss_libnss_libvirt_guest_impl_la_CFLAGS = \
+	-DLIBVIRT_NSS		\
+	-DLIBVIRT_NSS_GUEST	\
+	$(AM_CFLAGS)		\
+	$(WARN_CFLAGS)		\
+	$(PIE_CFLAGS)		\
+	$(COVERAGE_CFLAGS)	\
+	$(LIBXML_CFLAGS)
+
+nss_libnss_libvirt_guest_impl_la_LIBADD = \
+	../gnulib/lib/libgnu.la		\
+	../src/libvirt-nss.la
+
+nss_libnss_libvirt_guest_la_SOURCES =
+nss_libnss_libvirt_guest_la_LDFLAGS = \
+	$(VERSION_SCRIPT_FLAGS)$(LIBVIRT_GUEST_NSS_SYMBOL_FILE)	\
+	$(AM_LDFLAGS) \
+	-module \
+	-export-dynamic \
+	-avoid-version \
+	-shared \
+	-shrext .so.$(NSS_SO_VER)
+
+nss_libnss_libvirt_guest_la_LIBADD =  \
+	nss/libnss_libvirt_guest_impl.la
+
 lib_LTLIBRARIES = \
-	nss/libnss_libvirt.la
+	nss/libnss_libvirt.la \
+	nss/libnss_libvirt_guest.la
 
 endif WITH_NSS
 
 EXTRA_DIST += $(LIBVIRT_NSS_SOURCES) \
 	$(srcdir)/nss/libvirt_nss.syms \
-	$(srcdir)/nss/libvirt_nss_bsd.syms
+	$(srcdir)/nss/libvirt_nss_bsd.syms	\
+	$(srcdir)/nss/libvirt_guest_nss.syms
 
 clean-local:
 	-rm -rf wireshark/src/libvirt

tools/nss/libvirt_guest_nss.syms

+#
+# Officially exported symbols.
+#
+
+{
+global:
+    _nss_libvirt_guest_gethostbyname_r;
+    _nss_libvirt_guest_gethostbyname2_r;
+    _nss_libvirt_guest_gethostbyname3_r;
+    _nss_libvirt_guest_gethostbyname4_r;
+local: *;
+};

tools/nss/libvirt_nss.c

@@ -47,6 +47,8 @@
 #include "virstring.h"
 #include "virsocketaddr.h"
 #include "configmake.h"
+#include "virmacmap.h"
+#include "virobject.h"
 
 #if 0
 # define ERROR(...)                                             \
@@ -147,6 +149,7 @@ findLeaseInJSON(leaseAddress **tmpAddress,
                 virJSONValuePtr leases_array,
                 size_t nleases,
                 const char *name,
+                const char **macs,
                 int af,
                 bool *found)
 {
@@ -162,7 +165,6 @@ findLeaseInJSON(leaseAddress **tmpAddress,
 
     for (i = 0; i < nleases; i++) {
         virJSONValuePtr lease = virJSONValueArrayGet(leases_array, i);
-        const char *lease_name;
 
         if (!lease) {
             /* This should never happen (TM) */
@@ -170,10 +172,23 @@ findLeaseInJSON(leaseAddress **tmpAddress,
             goto cleanup;
         }
 
-        lease_name = virJSONValueObjectGetString(lease, "hostname");
+        if (macs) {
+            const char *macAddr;
 
-        if (STRNEQ_NULLABLE(name, lease_name))
-            continue;
+            macAddr = virJSONValueObjectGetString(lease, "mac-address");
+            if (!macAddr)
+                continue;
+
+            if (!virStringListHasString(macs, macAddr))
+                continue;
+        } else {
+            const char *lease_name;
+
+            lease_name = virJSONValueObjectGetString(lease, "hostname");
+
+            if (STRNEQ_NULLABLE(name, lease_name))
+                continue;
+        }
 
         if (virJSONValueObjectGetNumberLong(lease, "expiry-time", &expirytime) < 0) {
             /* A lease cannot be present without expiry-time */
@@ -236,6 +251,8 @@ findLease(const char *name,
     ssize_t nleases;
     leaseAddress *tmpAddress = NULL;
     size_t ntmpAddress = 0;
+    virMacMapPtr *macmaps = NULL;
+    size_t nMacmaps = 0;
 
     *address = NULL;
     *naddress = 0;
@@ -246,7 +263,6 @@ findLease(const char *name,
         goto cleanup;
     }
 
-
     if (virDirOpenQuiet(&dir, leaseDir) < 0) {
         ERROR("Failed to open dir '%s'", leaseDir);
         goto cleanup;
@@ -261,33 +277,64 @@ findLease(const char *name,
     while ((ret = virDirRead(dir, &entry, leaseDir)) > 0) {
         char *path;
 
-        if (!virFileHasSuffix(entry->d_name, ".status"))
-            continue;
-
-        if (!(path = virFileBuildPath(leaseDir, entry->d_name, NULL)))
-            goto cleanup;
-
-        DEBUG("Processing %s", path);
+        if (virFileHasSuffix(entry->d_name, ".status")) {
+            if (!(path = virFileBuildPath(leaseDir, entry->d_name, NULL)))
+                goto cleanup;
 
-        if (virLeaseReadCustomLeaseFile(leases_array, path, NULL, NULL) < 0) {
-            ERROR("Unable to parse %s", path);
+            DEBUG("Processing %s", path);
+            if (virLeaseReadCustomLeaseFile(leases_array, path, NULL, NULL) < 0) {
+                ERROR("Unable to parse %s", path);
+                VIR_FREE(path);
+                goto cleanup;
+            }
+            VIR_FREE(path);
+        } else if (virFileHasSuffix(entry->d_name, ".macs")) {
+            if (!(path = virFileBuildPath(leaseDir, entry->d_name, NULL)))
+                goto cleanup;
+
+            if (VIR_REALLOC_N_QUIET(macmaps, nMacmaps + 1) < 0) {
+                VIR_FREE(path);
+                goto cleanup;
+            }
+
+            DEBUG("Processing %s", path);
+            if (!(macmaps[nMacmaps] = virMacMapNew(path))) {
+                ERROR("Unable to parse %s", path);
+                VIR_FREE(path);
+                goto cleanup;
+            }
+            nMacmaps++;
             VIR_FREE(path);
-            goto cleanup;
         }
-
-        VIR_FREE(path);
     }
-
     VIR_DIR_CLOSE(dir);
 
     nleases = virJSONValueArraySize(leases_array);
     DEBUG("Read %zd leases", nleases);
 
+#if !defined(LIBVIRT_NSS_GUEST)
     if (findLeaseInJSON(&tmpAddress, &ntmpAddress,
                         leases_array, nleases,
-                        name, af, found) < 0)
+                        name, NULL, af, found) < 0)
         goto cleanup;
 
+#else /* defined(LIBVIRT_NSS_GUEST) */
+
+    size_t i;
+    for (i = 0; i < nMacmaps; i++) {
+        const char **macs = (const char **) virMacMapLookup(macmaps[i], name);
+
+        if (!macs)
+            continue;
+
+        if (findLeaseInJSON(&tmpAddress, &ntmpAddress,
+                            leases_array, nleases,
+                            name, macs, af, found) < 0)
+            goto cleanup;
+    }
+
+#endif /* defined(LIBVIRT_NSS_GUEST) */
+
     *address = tmpAddress;
     *naddress = ntmpAddress;
     tmpAddress = NULL;
@@ -300,6 +347,9 @@ findLease(const char *name,
     VIR_FREE(tmpAddress);
     virJSONValueFree(leases_array);
     VIR_DIR_CLOSE(dir);
+    while (nMacmaps)
+        virObjectUnref(macmaps[--nMacmaps]);
+    VIR_FREE(macmaps);
     return ret;
 }
 

tools/nss/libvirt_nss.h

@@ -32,7 +32,11 @@
 # include <nss.h>
 # include <netdb.h>
 
-# define NSS_NAME(s) _nss_libvirt_##s##_r
+# if !defined(LIBVIRT_NSS_GUEST)
+#  define NSS_NAME(s) _nss_libvirt_##s##_r
+# else
+#  define NSS_NAME(s) _nss_libvirt_guest_##s##_r
+# endif
 
 enum nss_status
 NSS_NAME(gethostbyname)(const char *name, struct hostent *result,