mountd: Support junction management plug-ins

To support FedFS and NFS junctions without introducing additional build-time or run-time dependencies on nfs-utils, the community has chosen to use a dynamically loadable library to handle junction resolution. There is one plug-in library for mountd that will handle any NFS- related junction type. Currently there are two types: o nfs-basic locally stored file set location data, and o nfs-fedfs file set location data stored on an LDAP server mountd's support for this library is enabled at build time by the presence of the junction API definition header: /usr/include/nfs-plugin.h If this header is not found on the build system, mountd will build without junction support, and will operate as before. Note that mountd does not cache junction resolution results. NFSD already caches these results in its exports cache. Thus each time NFSD calls up to mountd, it is, in essence, requesting a fresh junction resolution operation, not a cached response. Signed-off-by: Chuck Lever <[email protected]> Signed-off-by: Steve Dickson <[email protected]>
kouril · Jan 5, 2012 · ab74900 · ab74900
1 parent 652f1c2
commit ab74900
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Showing 3 changed files with 229 additions and 3 deletions.
diff --git a/configure.ac b/configure.ac
@@ -248,6 +248,8 @@ AC_CHECK_FUNC([getservbyname], ,
 
 AC_CHECK_LIB([crypt], [crypt], [LIBCRYPT="-lcrypt"])
 
+AC_CHECK_LIB([dl], [dlclose], [LIBDL="-ldl"])
+
 if test "$enable_nfsv4" = yes; then
   dnl check for libevent libraries and headers
   AC_LIBEVENT
@@ -298,6 +300,7 @@ AC_SUBST(LIBSOCKET)
 AC_SUBST(LIBCRYPT)
 AC_SUBST(LIBBSD)
 AC_SUBST(LIBBLKID)
+AC_SUBST(LIBDL)
 
 if test "$enable_libmount" != no; then
    AC_CHECK_LIB(mount, mnt_context_do_mount, [LIBMOUNT="-lmount"], AC_MSG_ERROR([libmount needed]))
@@ -335,7 +338,7 @@ AC_CHECK_HEADERS([arpa/inet.h fcntl.h libintl.h limits.h \
                  stdlib.h string.h sys/file.h sys/ioctl.h sys/mount.h \
                  sys/param.h sys/socket.h sys/time.h sys/vfs.h \
                  syslog.h unistd.h com_err.h et/com_err.h \
-                 ifaddrs.h])
+                 ifaddrs.h nfs-plugin.h])
 
 dnl *************************************************************
 dnl Checks for typedefs, structures, and compiler characteristics

diff --git a/utils/mountd/Makefile.am b/utils/mountd/Makefile.am
@@ -12,7 +12,7 @@ mountd_SOURCES = mountd.c mount_dispatch.c auth.c rmtab.c cache.c \
 mountd_LDADD = ../../support/export/libexport.a \
 	       ../../support/nfs/libnfs.a \
 	       ../../support/misc/libmisc.a \
-	       $(LIBBSD) $(LIBWRAP) $(LIBNSL) $(LIBBLKID)
+	       $(LIBBSD) $(LIBWRAP) $(LIBNSL) $(LIBBLKID) $(LIBDL)
 mountd_CPPFLAGS = $(AM_CPPFLAGS) $(CPPFLAGS) \
 		  -I$(top_builddir)/support/include \
 		  -I$(top_srcdir)/support/export

diff --git a/utils/mountd/cache.c b/utils/mountd/cache.c
@@ -802,6 +802,229 @@ lookup_export(char *dom, char *path, struct addrinfo *ai)
 	return found;
 }
 
+#ifdef HAVE_NFS_PLUGIN_H
+#include <dlfcn.h>
+#include <nfs-plugin.h>
+
+/*
+ * Walk through a set of FS locations and build a set of export options.
+ * Returns true if all went to plan; otherwise, false.
+ */
+static _Bool
+locations_to_options(struct jp_ops *ops, nfs_fsloc_set_t locations,
+		char *options, size_t remaining, int *ttl)
+{
+	char *server, *last_path, *rootpath, *ptr;
+	_Bool seen = false;
+
+	last_path = NULL;
+	rootpath = NULL;
+	server = NULL;
+	ptr = options;
+	*ttl = 0;
+
+	for (;;) {
+		enum jp_status status;
+		int len;
+
+		status = ops->jp_get_next_location(locations, &server,
+							&rootpath, ttl);
+		if (status == JP_EMPTY)
+			break;
+		if (status != JP_OK) {
+			xlog(D_GENERAL, "%s: failed to parse location: %s",
+				__func__, ops->jp_error(status));
+			goto out_false;
+		}
+		xlog(D_GENERAL, "%s: Location: %s:%s",
+			__func__, server, rootpath);
+
+		if (last_path && strcmp(rootpath, last_path) == 0) {
+			len = snprintf(ptr, remaining, "+%s", server);
+			if (len < 0) {
+				xlog(D_GENERAL, "%s: snprintf: %m", __func__);
+				goto out_false;
+			}
+			if ((size_t)len >= remaining) {
+				xlog(D_GENERAL, "%s: options buffer overflow", __func__);
+				goto out_false;
+			}
+			remaining -= (size_t)len;
+			ptr += len;
+		} else {
+			if (last_path == NULL)
+				len = snprintf(ptr, remaining, "refer=%s@%s",
+							rootpath, server);
+			else
+				len = snprintf(ptr, remaining, ":%s@%s",
+							rootpath, server);
+			if (len < 0) {
+				xlog(D_GENERAL, "%s: snprintf: %m", __func__);
+				goto out_false;
+			}
+			if ((size_t)len >= remaining) {
+				xlog(D_GENERAL, "%s: options buffer overflow",
+					__func__);
+				goto out_false;
+			}
+			remaining -= (size_t)len;
+			ptr += len;
+			last_path = rootpath;
+		}
+
+		seen = true;
+		free(rootpath);
+		free(server);
+	}
+
+	xlog(D_CALL, "%s: options='%s', ttl=%d",
+		__func__, options, *ttl);
+	return seen;
+
+out_false:
+	free(rootpath);
+	free(server);
+	return false;
+}
+
+/*
+ * Walk through the set of FS locations and build an exportent.
+ * Returns pointer to an exportent if "junction" refers to a junction.
+ *
+ * Returned exportent points to static memory.
+ */
+static struct exportent *do_locations_to_export(struct jp_ops *ops,
+		nfs_fsloc_set_t locations, const char *junction,
+		char *options, size_t options_len)
+{
+	struct exportent *exp;
+	int ttl;
+
+	if (!locations_to_options(ops, locations, options, options_len, &ttl))
+		return NULL;
+
+	exp = mkexportent("*", (char *)junction, options);
+	if (exp == NULL) {
+		xlog(L_ERROR, "%s: Failed to construct exportent", __func__);
+		return NULL;
+	}
+
+	exp->e_uuid = NULL;
+	exp->e_ttl = ttl;
+	return exp;
+}
+
+/*
+ * Convert set of FS locations to an exportent.  Returns pointer to
+ * an exportent if "junction" refers to a junction.
+ *
+ * Returned exportent points to static memory.
+ */
+static struct exportent *locations_to_export(struct jp_ops *ops,
+		nfs_fsloc_set_t locations, const char *junction)
+{
+	struct exportent *exp;
+	char *options;
+
+	options = malloc(BUFSIZ);
+	if (options == NULL) {
+		xlog(D_GENERAL, "%s: failed to allocate options buffer",
+			__func__);
+		return NULL;
+	}
+	options[0] = '\0';
+
+	exp = do_locations_to_export(ops, locations, junction,
+						options, BUFSIZ);
+
+	free(options);
+	return exp;
+}
+
+/*
+ * Retrieve locations information in "junction" and dump it to the
+ * kernel.  Returns pointer to an exportent if "junction" refers
+ * to a junction.
+ *
+ * Returned exportent points to static memory.
+ */
+static struct exportent *invoke_junction_ops(void *handle,
+		const char *junction)
+{
+	nfs_fsloc_set_t locations;
+	struct exportent *exp;
+	enum jp_status status;
+	struct jp_ops *ops;
+	char *error;
+
+	ops = (struct jp_ops *)dlsym(handle, "nfs_junction_ops");
+	error = dlerror();
+	if (error != NULL) {
+		xlog(D_GENERAL, "%s: dlsym(jp_junction_ops): %s",
+			__func__, error);
+		return NULL;
+	}
+	if (ops->jp_api_version != JP_API_VERSION) {
+		xlog(D_GENERAL, "%s: unrecognized junction API version: %u",
+			__func__, ops->jp_api_version);
+		return NULL;
+	}
+
+	status = ops->jp_init(false);
+	if (status != JP_OK) {
+		xlog(D_GENERAL, "%s: failed to resolve %s: %s",
+			__func__, junction, ops->jp_error(status));
+		return NULL;
+	}
+
+	status = ops->jp_get_locations(junction, &locations);
+	if (status != JP_OK) {
+		xlog(D_GENERAL, "%s: failed to resolve %s: %s",
+			__func__, junction, ops->jp_error(status));
+		return NULL;
+	}
+
+	exp = locations_to_export(ops, locations, junction);
+
+	ops->jp_put_locations(locations);
+	ops->jp_done();
+	return exp;
+}
+
+/*
+ * Load the junction plug-in, then try to resolve "pathname".
+ * Returns pointer to an initialized exportent if "junction"
+ * refers to a junction, or NULL if not.
+ *
+ * Returned exportent points to static memory.
+ */
+static struct exportent *lookup_junction(const char *pathname)
+{
+	struct exportent *exp;
+	void *handle;
+
+	handle = dlopen("libnfsjunct.so", RTLD_NOW);
+	if (handle == NULL) {
+		xlog(D_GENERAL, "%s: dlopen: %s", __func__, dlerror());
+		return NULL;
+	}
+	(void)dlerror();	/* Clear any error */
+
+	exp = invoke_junction_ops(handle, pathname);
+
+	/* We could leave it loaded to make junction resolution
+	 * faster next time.  However, if we want to replace the
+	 * library, that would require restarting mountd. */
+	(void)dlclose(handle);
+	return exp;
+}
+#else	/* !HAVE_NFS_PLUGIN_H */
+static inline struct exportent *lookup_junction(const char *UNUSED(pathname))
+{
+	return NULL;
+}
+#endif	/* !HAVE_NFS_PLUGIN_H */
+
 static void nfsd_export(FILE *f)
 {
 	/* requests are:
@@ -854,7 +1077,7 @@ static void nfsd_export(FILE *f)
 			dump_to_cache(f, dom, path, NULL);
 		}
 	} else {
-		dump_to_cache(f, dom, path, NULL);
+		dump_to_cache(f, dom, path, lookup_junction(path));
 	}
  out:
 	xlog(D_CALL, "nfsd_export: found %p path %s", found, path ? path : NULL);