Implement reexport= export option

When re-exporting a NFS volume it is mandatory to specify
either a UUID or numerical fsid= option because nfsd is unable
to derive an identifier on its own.

For NFS cross mounts this becomes a problem because nfsd also
needs an identifier for every crossed mount.
A common workaround is stating every single subvolume in the
exports list too.
But this defeats the purpose of the crossmnt option and is tedious.

This is where the reexport= tries to help.
It offers various strategies to automatically derive a identifier
for NFS volumes and sub volumes.

Currently two strategies are implemented:

1. auto-fsidnum
    In this mode mountd/exportd will create a new numerical fsid
    for a NFS volume and subvolume. The numbers are stored in a database,
    via fsidd, such that the server will always use the same fsid.
    The entry in the exports file allowed to skip the fsid= option but
    stating a UUID is allowed, if needed.

    This mode has the obvious downside that load balancing is by default not
    possible since multiple re-exporting NFS servers would generate
    different ids.
    It is possible if all load balancers use the same database.
    This can be achieved by using nfs-utils' fsidd and placing it's sqlit
    database on a network share which supports file locks or by implementing
    your own fsidd which is able to provide consistent fsids across multiple
    re-exporting nfs servers.

2. predefined-fsidnum
    This mode works just like auto-fsidnum but does not generate ids
    for you. It helps in the load balancing case. A system administrator
    has to manually maintain the database and install it on all re-exporting
    NFS servers. If you have a massive amount of subvolumes this mode
    will help because you don't have to bloat the exports list.

Signed-off-by: Richard Weinberger <richard@nod.at>
Signed-off-by: Steve Dickson <steved@redhat.com>

9 files changed, 106 insertions, 2 deletions

diff --git a/support/export/export.c b/support/export/export.c
index 03390df..3e48c42 100644
--- a/support/export/export.c
+++ b/support/export/export.c
@@ -25,6 +25,7 @@
 #include "exportfs.h"
 #include "nfsd_path.h"
 #include "xlog.h"
+#include "reexport.h"
 
 exp_hash_table exportlist[MCL_MAXTYPES] = {{NULL, {{NULL,NULL}, }}, }; 
 static int export_hash(char *);
@@ -115,6 +116,7 @@ export_read(char *fname, int ignore_hosts)
 	nfs_export		*exp;
 
 	int volumes = 0;
+	int reexport_found = 0;
 
 	setexportent(fname, "r");
 	while ((eep = getexportent(0,1)) != NULL) {
@@ -126,7 +128,25 @@ export_read(char *fname, int ignore_hosts)
 		}
 		else
 			warn_duplicated_exports(exp, eep);
+
+		if (eep->e_reexport)
+			reexport_found = 1;
 	}
+
+	if (reexport_found) {
+		for (int i = 0; i < MCL_MAXTYPES; i++) {
+			for (exp = exportlist[i].p_head; exp; exp = exp->m_next) {
+				if (exp->m_export.e_reexport)
+					continue;
+
+				if (exp->m_export.e_flags & NFSEXP_FSID) {
+					xlog(L_ERROR, "When a reexport= option is present no manully assigned numerical fsid= options are allowed");
+					return -1;
+				}
+			}
+		}
+	}
+
 	endexportent();
 
 	return volumes;
diff --git a/support/nfs/Makefile.am b/support/nfs/Makefile.am
index 67e3a8e..2e1577c 100644
--- a/support/nfs/Makefile.am
+++ b/support/nfs/Makefile.am
@@ -9,6 +9,7 @@ libnfs_la_SOURCES = exports.c rmtab.c xio.c rpcmisc.c rpcdispatch.c \
 		   svc_socket.c cacheio.c closeall.c nfs_mntent.c \
 		   svc_create.c atomicio.c strlcat.c strlcpy.c
 libnfs_la_LIBADD = libnfsconf.la
+libnfs_la_CPPFLAGS = $(AM_CPPFLAGS) $(CPPFLAGS) -I$(top_srcdir)/support/reexport
 
 libnfsconf_la_SOURCES = conffile.c xlog.c
 
diff --git a/support/nfs/exports.c b/support/nfs/exports.c
index da8ace3..72e632f 100644
--- a/support/nfs/exports.c
+++ b/support/nfs/exports.c
@@ -31,6 +31,7 @@
 #include "xlog.h"
 #include "xio.h"
 #include "pseudoflavors.h"
+#include "reexport.h"
 
 #define EXPORT_DEFAULT_FLAGS	\
   (NFSEXP_READONLY|NFSEXP_ROOTSQUASH|NFSEXP_GATHERED_WRITES|NFSEXP_NOSUBTREECHECK)
@@ -104,6 +105,7 @@ static void init_exportent (struct exportent *ee, int fromkernel)
 	ee->e_nsqgids = 0;
 	ee->e_uuid = NULL;
 	ee->e_ttl = default_ttl;
+	ee->e_reexport = REEXP_NONE;
 }
 
 struct exportent *
@@ -313,6 +315,23 @@ putexportent(struct exportent *ep)
 	}
 	if (ep->e_uuid)
 		fprintf(fp, "fsid=%s,", ep->e_uuid);
+
+	if (ep->e_reexport) {
+		fprintf(fp, "reexport=");
+		switch (ep->e_reexport) {
+			case REEXP_AUTO_FSIDNUM:
+				fprintf(fp, "auto-fsidnum");
+				break;
+			case REEXP_PREDEFINED_FSIDNUM:
+				fprintf(fp, "predefined-fsidnum");
+				break;
+			default:
+				xlog(L_ERROR, "unknown reexport method %i", ep->e_reexport);
+				fprintf(fp, "none");
+		}
+		fprintf(fp, ",");
+	}
+
 	if (ep->e_mountpoint)
 		fprintf(fp, "mountpoint%s%s,",
 			ep->e_mountpoint[0]?"=":"", ep->e_mountpoint);
@@ -619,6 +638,7 @@ parseopts(char *cp, struct exportent *ep, int warn, int *had_subtree_opt_ptr)
 	char 	*flname = efname?efname:"command line";
 	int	flline = efp?efp->x_line:0;
 	unsigned int active = 0;
+	int saw_reexport = 0;
 
 	squids = ep->e_squids; nsquids = ep->e_nsquids;
 	sqgids = ep->e_sqgids; nsqgids = ep->e_nsqgids;
@@ -725,6 +745,13 @@ bad_option:
 			}
 		} else if (strncmp(opt, "fsid=", 5) == 0) {
 			char *oe;
+
+			if (saw_reexport) {
+				xlog(L_ERROR, "%s:%d: 'fsid=' has to be before 'reexport=' %s\n",
+				     flname, flline, opt);
+				goto bad_option;
+			}
+
 			if (strcmp(opt+5, "root") == 0) {
 				ep->e_fsid = 0;
 				setflags(NFSEXP_FSID, active, ep);
@@ -772,6 +799,41 @@ bad_option:
 		} else if (strncmp(opt, "xprtsec=", 8) == 0) {
 			if (!parse_xprtsec(opt + 8, ep))
 				goto bad_option;
+		} else if (strncmp(opt, "reexport=", 9) == 0) {
+			char *strategy = strchr(opt, '=');
+
+			if (!strategy) {
+				xlog(L_ERROR, "%s:%d: bad option %s\n",
+				     flname, flline, opt);
+				goto bad_option;
+			}
+			strategy++;
+
+			if (saw_reexport) {
+				xlog(L_ERROR, "%s:%d: only one 'reexport=' is allowed%s\n",
+				     flname, flline, opt);
+				goto bad_option;
+			}
+
+			if (strcmp(strategy, "auto-fsidnum") == 0) {
+				ep->e_reexport = REEXP_AUTO_FSIDNUM;
+			} else if (strcmp(strategy, "predefined-fsidnum") == 0) {
+				ep->e_reexport = REEXP_PREDEFINED_FSIDNUM;
+			} else if (strcmp(strategy, "none") == 0) {
+				ep->e_reexport = REEXP_NONE;
+			} else {
+				xlog(L_ERROR, "%s:%d: bad option %s\n",
+				     flname, flline, strategy);
+				goto bad_option;
+			}
+
+			if (reexpdb_apply_reexport_settings(ep, flname, flline) != 0)
+				goto bad_option;
+
+			if (ep->e_fsid)
+				setflags(NFSEXP_FSID, active, ep);
+
+			saw_reexport = 1;
 		} else {
 			xlog(L_ERROR, "%s:%d: unknown keyword \"%s\"\n",
 					flname, flline, opt);
diff --git a/systemd/Makefile.am b/systemd/Makefile.am
index 577c6a2..2e250dc 100644
--- a/systemd/Makefile.am
+++ b/systemd/Makefile.am
@@ -70,8 +70,10 @@ rpc_pipefs_generator_SOURCES = $(COMMON_SRCS) rpc-pipefs-generator.c
 nfs_server_generator_LDADD = ../support/export/libexport.a \
 			     ../support/nfs/libnfs.la \
 			     ../support/misc/libmisc.a \
+			     ../support/reexport/libreexport.a \
 			     $(LIBPTHREAD)
 
+
 rpc_pipefs_generator_LDADD = ../support/nfs/libnfs.la
 
 if INSTALL_SYSTEMD
diff --git a/utils/exportd/Makefile.am b/utils/exportd/Makefile.am
index c95bdee..26078c9 100644
--- a/utils/exportd/Makefile.am
+++ b/utils/exportd/Makefile.am
@@ -16,7 +16,9 @@ exportd_SOURCES = exportd.c
 exportd_LDADD = ../../support/export/libexport.a \
 			../../support/nfs/libnfs.la \
 			../../support/misc/libmisc.a \
-			$(OPTLIBS) $(LIBBLKID) $(LIBPTHREAD) -luuid
+			../../support/reexport/libreexport.a \
+			$(OPTLIBS) $(LIBBLKID) $(LIBPTHREAD) \
+			-luuid
 
 exportd_CPPFLAGS = $(AM_CPPFLAGS) $(CPPFLAGS) \
 		-I$(top_srcdir)/support/export
diff --git a/utils/exportfs/Makefile.am b/utils/exportfs/Makefile.am
index 96524c7..7f8ce9f 100644
--- a/utils/exportfs/Makefile.am
+++ b/utils/exportfs/Makefile.am
@@ -10,6 +10,9 @@ exportfs_SOURCES = exportfs.c
 exportfs_LDADD = ../../support/export/libexport.a \
 	       	 ../../support/nfs/libnfs.la \
 		 ../../support/misc/libmisc.a \
+		 ../../support/reexport/libreexport.a \
 		 $(LIBWRAP) $(LIBNSL) $(LIBPTHREAD)
 
+exportfs_CPPFLAGS = $(AM_CPPFLAGS) $(CPPFLAGS) -I$(top_srcdir)/support/reexport
+
 MAINTAINERCLEANFILES = Makefile.in
diff --git a/utils/exportfs/exportfs.c b/utils/exportfs/exportfs.c
index 37b9e4b..b03a047 100644
--- a/utils/exportfs/exportfs.c
+++ b/utils/exportfs/exportfs.c
@@ -38,6 +38,7 @@
 #include "exportfs.h"
 #include "xlog.h"
 #include "conffile.h"
+#include "reexport.h"
 
 static void	export_all(int verbose);
 static void	exportfs(char *arg, char *options, int verbose);
@@ -719,6 +720,16 @@ dump(int verbose, int export_format)
 				c = dumpopt(c, "fsid=%d", ep->e_fsid);
 			if (ep->e_uuid)
 				c = dumpopt(c, "fsid=%s", ep->e_uuid);
+			if (ep->e_reexport) {
+				switch (ep->e_reexport) {
+					case REEXP_AUTO_FSIDNUM:
+						c = dumpopt(c, "reexport=%s", "auto-fsidnum");
+						break;
+					case REEXP_PREDEFINED_FSIDNUM:
+						c = dumpopt(c, "reexport=%s", "predefined-fsidnum");
+						break;
+				}
+			}
 			if (ep->e_mountpoint)
 				c = dumpopt(c, "mountpoint%s%s",
 					    ep->e_mountpoint[0]?"=":"",
diff --git a/utils/mount/Makefile.am b/utils/mount/Makefile.am
index 3101f7a..5ff1148 100644
--- a/utils/mount/Makefile.am
+++ b/utils/mount/Makefile.am
@@ -29,8 +29,9 @@ endif
 
 mount_nfs_LDADD = ../../support/nfs/libnfs.la \
 		  ../../support/export/libexport.a \
+		  ../../support/reexport/libreexport.a \
 		  ../../support/misc/libmisc.a \
-		  $(LIBTIRPC)
+		   $(LIBTIRPC) $(LIBPTHREAD)
 
 mount_nfs_SOURCES = $(mount_common)
 
diff --git a/utils/mountd/Makefile.am b/utils/mountd/Makefile.am
index 13b25c9..197ef29 100644
--- a/utils/mountd/Makefile.am
+++ b/utils/mountd/Makefile.am
@@ -17,9 +17,11 @@ mountd_SOURCES = mountd.c mount_dispatch.c rmtab.c \
 mountd_LDADD = ../../support/export/libexport.a \
 	       ../../support/nfs/libnfs.la \
 	       ../../support/misc/libmisc.a \
+	       ../../support/reexport/libreexport.a \
 	       $(OPTLIBS) \
 	       $(LIBBSD) $(LIBWRAP) $(LIBNSL) $(LIBBLKID) -luuid $(LIBTIRPC) \
 	       $(LIBPTHREAD)
+
 mountd_CPPFLAGS = $(AM_CPPFLAGS) $(CPPFLAGS) \
 		  -I$(top_builddir)/support/include \
 		  -I$(top_srcdir)/support/export