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>

5 files changed, 21 insertions, 2 deletions

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