storage: Turn storage backends into dynamic modules

If driver modules are enabled turn storage driver backends into
dynamically loadable objects. This will allow greater modularity for
binary distributions, where heavyweight dependencies as rbd and gluster
can be avoided by selecting only a subset of drivers if the rest is not
necessary.

The storage modules are installed into 'LIBDIR/libvirt/storage-backend/'
and users can override the location by using
'LIBVIRT_STORAGE_BACKEND_DIR' environment variable.

rpm based distros will at this point install all the backends when
libvirt-daemon-driver-storage package is installed.

libvirt.spec.in

@@ -1239,6 +1239,8 @@ rm -f $RPM_BUILD_ROOT%{_libdir}/libvirt/lock-driver/*.la
 rm -f $RPM_BUILD_ROOT%{_libdir}/libvirt/lock-driver/*.a
 rm -f $RPM_BUILD_ROOT%{_libdir}/libvirt/connection-driver/*.la
 rm -f $RPM_BUILD_ROOT%{_libdir}/libvirt/connection-driver/*.a
+rm -f $RPM_BUILD_ROOT%{_libdir}/libvirt/storage-backend/*.la
+rm -f $RPM_BUILD_ROOT%{_libdir}/libvirt/storage-backend/*.a
 %if %{with_wireshark}
     %if 0%{fedora} >= 24
 rm -f $RPM_BUILD_ROOT%{_libdir}/wireshark/plugins/libvirt.la
@@ -1694,6 +1696,21 @@ exit 0
 %files daemon-driver-storage
 %attr(0755, root, root) %{_libexecdir}/libvirt_parthelper
 %{_libdir}/%{name}/connection-driver/libvirt_driver_storage.so
+%{_libdir}/%{name}/storage-backend/libvirt_storage_backend_fs.so
+%{_libdir}/%{name}/storage-backend/libvirt_storage_backend_disk.so
+%{_libdir}/%{name}/storage-backend/libvirt_storage_backend_logical.so
+%{_libdir}/%{name}/storage-backend/libvirt_storage_backend_scsi.so
+%{_libdir}/%{name}/storage-backend/libvirt_storage_backend_iscsi.so
+%{_libdir}/%{name}/storage-backend/libvirt_storage_backend_mpath.so
+%if %{with_storage_gluster}
+%{_libdir}/%{name}/storage-backend/libvirt_storage_backend_gluster.so
+%endif
+%if %{with_storage_rbd}
+%{_libdir}/%{name}/storage-backend/libvirt_storage_backend_rbd.so
+%endif
+%if %{with_storage_sheepdog}
+%{_libdir}/%{name}/storage-backend/libvirt_storage_backend_sheepdog.so
+%endif
 
 %if %{with_qemu}
 %files daemon-driver-qemu

src/Makefile.am

@@ -972,9 +972,12 @@ SECRET_DRIVER_SOURCES =						\
 		secret/secret_driver.h secret/secret_driver.c
 
 # Storage backend specific impls
+STORAGE_DRIVER_BACKEND_SOURCES = \
+		storage/storage_backend.h storage/storage_backend.c
+
 STORAGE_DRIVER_SOURCES =						\
 		storage/storage_driver.h storage/storage_driver.c	\
-		storage/storage_backend.h storage/storage_backend.c \
+		$(STORAGE_DRIVER_BACKEND_SOURCES) \
 		storage/storage_util.h storage/storage_util.c
 
 STORAGE_DRIVER_FS_SOURCES =					\
@@ -1661,6 +1664,12 @@ if WITH_BLKID
 libvirt_driver_storage_impl_la_CFLAGS += $(BLKID_CFLAGS)
 libvirt_driver_storage_impl_la_LIBADD += $(BLKID_LIBS)
 endif WITH_BLKID
+
+if WITH_DRIVER_MODULES
+storagebackenddir = $(libdir)/libvirt/storage-backend
+storagebackend_LTLIBRARIES =
+endif WITH_DRIVER_MODULES
+
 if WITH_STORAGE
 noinst_LTLIBRARIES += libvirt_driver_storage_impl.la
 libvirt_driver_storage_la_SOURCES =
@@ -1682,8 +1691,14 @@ libvirt_storage_backend_fs_la_CFLAGS =	\
 	-I$(srcdir)/conf \
 	$(AM_CFLAGS)
 
+if WITH_DRIVER_MODULES
+storagebackend_LTLIBRARIES += libvirt_storage_backend_fs.la
+libvirt_storage_backend_fs_la_LDFLAGS = \
+	-module -avoid-version $(AM_LDFLAGS)
+else ! WITH_DRIVER_MODULES
 noinst_LTLIBRARIES += libvirt_storage_backend_fs.la
 libvirt_driver_storage_impl_la_LIBADD += libvirt_storage_backend_fs.la
+endif ! WITH_DRIVER_MODULES
 endif WITH_STORAGE
 
 if WITH_STORAGE_LVM
@@ -1693,9 +1708,15 @@ libvirt_storage_backend_logical_la_CFLAGS = \
 	-I$(srcdir)/conf \
 	$(AM_CFLAGS)
 
+if WITH_DRIVER_MODULES
+storagebackend_LTLIBRARIES += libvirt_storage_backend_logical.la
+libvirt_storage_backend_logical_la_LDFLAGS = \
+	-module -avoid-version $(AM_LDFLAGS)
+else ! WITH_DRIVER_MODULES
 noinst_LTLIBRARIES += libvirt_storage_backend_logical.la
 libvirt_driver_storage_impl_la_LIBADD += \
 	libvirt_storage_backend_logical.la
+endif ! WITH_DRIVER_MODULES
 endif WITH_STORAGE_LVM
 
 if WITH_STORAGE_ISCSI
@@ -1706,9 +1727,15 @@ libvirt_storage_backend_iscsi_la_CFLAGS = \
 	-I$(srcdir)/secret \
 	$(AM_CFLAGS)
 
+if WITH_DRIVER_MODULES
+storagebackend_LTLIBRARIES += libvirt_storage_backend_iscsi.la
+libvirt_storage_backend_iscsi_la_LDFLAGS = \
+	-module -avoid-version $(AM_LDFLAGS)
+else ! WITH_DRIVER_MODULES
 noinst_LTLIBRARIES += libvirt_storage_backend_iscsi.la
 libvirt_driver_storage_impl_la_LIBADD += \
 	libvirt_storage_backend_iscsi.la
+endif ! WITH_DRIVER_MODULES
 endif WITH_STORAGE_ISCSI
 
 if WITH_STORAGE_SCSI
@@ -1717,8 +1744,14 @@ libvirt_storage_backend_scsi_la_CFLAGS = \
 	-I$(srcdir)/conf \
 	$(AM_CFLAGS)
 
+if WITH_DRIVER_MODULES
+storagebackend_LTLIBRARIES += libvirt_storage_backend_scsi.la
+libvirt_storage_backend_scsi_la_LDFLAGS = \
+	-module -avoid-version $(AM_LDFLAGS)
+else ! WITH_DRIVER_MODULES
 noinst_LTLIBRARIES += libvirt_storage_backend_scsi.la
 libvirt_driver_storage_impl_la_LIBADD += libvirt_storage_backend_scsi.la
+endif ! WITH_DRIVER_MODULES
 endif WITH_STORAGE_SCSI
 
 if WITH_STORAGE_MPATH
@@ -1730,9 +1763,15 @@ libvirt_storage_backend_mpath_la_CFLAGS =	\
 	$(DEVMAPPER_CFLAGS) \
 	$(AM_CFLAGS)
 
+if WITH_DRIVER_MODULES
+storagebackend_LTLIBRARIES += libvirt_storage_backend_mpath.la
+libvirt_storage_backend_mpath_la_LDFLAGS = \
+	-module -avoid-version $(AM_LDFLAGS)
+else ! WITH_DRIVER_MODULES
 noinst_LTLIBRARIES += libvirt_storage_backend_mpath.la
 libvirt_driver_storage_impl_la_LIBADD += \
 	libvirt_storage_backend_mpath.la
+endif ! WITH_DRIVER_MODULES
 endif WITH_STORAGE_MPATH
 
 if WITH_STORAGE_DISK
@@ -1741,8 +1780,14 @@ libvirt_storage_backend_disk_la_CFLAGS =	\
 	-I$(srcdir)/conf \
 	$(AM_CFLAGS)
 
+if WITH_DRIVER_MODULES
+storagebackend_LTLIBRARIES += libvirt_storage_backend_disk.la
+libvirt_storage_backend_disk_la_LDFLAGS = \
+	-module -avoid-version $(AM_LDFLAGS)
+else ! WITH_DRIVER_MODULES
 noinst_LTLIBRARIES += libvirt_storage_backend_disk.la
 libvirt_driver_storage_impl_la_LIBADD += libvirt_storage_backend_disk.la
+endif ! WITH_DRIVER_MODULES
 endif WITH_STORAGE_DISK
 
 if WITH_STORAGE_RBD
@@ -1753,8 +1798,14 @@ libvirt_storage_backend_rbd_la_CFLAGS = \
 	-I$(srcdir)/secret \
 	$(AM_CFLAGS)
 
+if WITH_DRIVER_MODULES
+storagebackend_LTLIBRARIES += libvirt_storage_backend_rbd.la
+libvirt_storage_backend_rbd_la_LDFLAGS = \
+	-module -avoid-version $(AM_LDFLAGS)
+else ! WITH_DRIVER_MODULES
 noinst_LTLIBRARIES += libvirt_storage_backend_rbd.la
 libvirt_driver_storage_impl_la_LIBADD += libvirt_storage_backend_rbd.la
+endif ! WITH_DRIVER_MODULES
 endif WITH_STORAGE_RBD
 
 if WITH_STORAGE_SHEEPDOG
@@ -1764,9 +1815,23 @@ libvirt_storage_backend_sheepdog_la_CFLAGS = \
 	-I$(srcdir)/conf \
 	$(AM_CFLAGS)
 
+libvirt_storage_backend_sheepdog_priv_la_SOURCES = \
+	$(STORAGE_DRIVER_SHEEPDOG_SOURCES) \
+	$(STORAGE_DRIVER_BACKEND_SOURCES)
+libvirt_storage_backend_sheepdog_priv_la_CFLAGS = \
+	-I$(srcdir)/conf \
+	$(AM_CFLAGS)
+noinst_LTLIBRARIES += libvirt_storage_backend_sheepdog_priv.la
+
+if WITH_DRIVER_MODULES
+storagebackend_LTLIBRARIES += libvirt_storage_backend_sheepdog.la
+libvirt_storage_backend_sheepdog_la_LDFLAGS = \
+	-module -avoid-version $(AM_LDFLAGS)
+else ! WITH_DRIVER_MODULES
 noinst_LTLIBRARIES += libvirt_storage_backend_sheepdog.la
 libvirt_driver_storage_impl_la_LIBADD += \
 	libvirt_storage_backend_sheepdog.la
+endif ! WITH_DRIVER_MODULES
 endif WITH_STORAGE_SHEEPDOG
 
 if WITH_STORAGE_GLUSTER
@@ -1778,9 +1843,15 @@ libvirt_storage_backend_gluster_la_CFLAGS = \
 	$(GLUSTERFS_CFLAGS) \
 	$(AM_CFLAGS)
 
+if WITH_DRIVER_MODULES
+storagebackend_LTLIBRARIES += libvirt_storage_backend_gluster.la
+libvirt_storage_backend_gluster_la_LDFLAGS = \
+	-module -avoid-version $(AM_LDFLAGS)
+else ! WITH_DRIVER_MODULES
 noinst_LTLIBRARIES += libvirt_storage_backend_gluster.la
 libvirt_driver_storage_impl_la_LIBADD += \
 	libvirt_storage_backend_gluster.la
+endif ! WITH_DRIVER_MODULES
 endif WITH_STORAGE_GLUSTER
 
 if WITH_STORAGE_ZFS
@@ -1789,8 +1860,14 @@ libvirt_storage_backend_zfs_la_CFLAGS =	\
 	-I$(srcdir)/conf \
 	$(AM_CFLAGS)
 
+if WITH_DRIVER_MODULES
+storagebackend_LTLIBRARIES += libvirt_storage_backend_zfs.la
+libvirt_storage_backend_zfs_la_LDFLAGS = \
+	-module -avoid-version $(AM_LDFLAGS)
+else ! WITH_DRIVER_MODULES
 noinst_LTLIBRARIES += libvirt_storage_backend_zfs.la
 libvirt_driver_storage_impl_la_LIBADD += libvirt_storage_backend_zfs.la
+endif ! WITH_DRIVER_MODULES
 endif WITH_STORAGE_ZFS
 
 if WITH_STORAGE_VSTORAGE
@@ -1800,9 +1877,15 @@ libvirt_storage_backend_vstorage_la_CFLAGS =	\
 	-I$(srcdir)/conf \
 	$(AM_CFLAGS)
 
+if WITH_DRIVER_MODULES
+storagebackend_LTLIBRARIES += libvirt_storage_backend_vstorage.la
+libvirt_storage_backend_vstorage_la_LDFLAGS = \
+	-module -avoid-version $(AM_LDFLAGS)
+else ! WITH_DRIVER_MODULES
 noinst_LTLIBRARIES += libvirt_storage_backend_vstorage.la
 libvirt_driver_storage_impl_la_LIBADD += \
 	libvirt_storage_backend_vstorage.la
+endif ! WITH_DRIVER_MODULES
 endif WITH_STORAGE_VSTORAGE
 
 if WITH_NODE_DEVICES

src/storage/storage_backend.c

@@ -33,6 +33,8 @@
 #include "virstoragefile.h"
 #include "storage_backend.h"
 #include "virlog.h"
+#include "virfile.h"
+#include "configmake.h"
 
 #if WITH_STORAGE_LVM
 # include "storage_backend_logical.h"
@@ -79,45 +81,77 @@ static size_t virStorageBackendsCount;
 static virStorageFileBackendPtr virStorageFileBackends[VIR_STORAGE_BACKENDS_MAX];
 static size_t virStorageFileBackendsCount;
 
-#define VIR_STORAGE_BACKEND_REGISTER(name)                                     \
-    if (name() < 0)                                                            \
+#if WITH_DRIVER_MODULES
+
+# define STORAGE_BACKEND_MODULE_DIR LIBDIR "/libvirt/storage-backend"
+
+static int
+virStorageDriverLoadBackendModule(const char *name,
+                                  const char *regfunc)
+{
+    char *modfile = NULL;
+    int ret;
+
+    if (!(modfile = virFileFindResourceFull(name,
+                                            "libvirt_storage_backend_",
+                                            ".so",
+                                            abs_topbuilddir "/src/.libs",
+                                            STORAGE_BACKEND_MODULE_DIR,
+                                            "LIBVIRT_STORAGE_BACKEND_DIR")))
+        return 1;
+
+    ret = virDriverLoadModuleFull(modfile, regfunc, NULL);
+
+    VIR_FREE(modfile);
+
+    return ret;
+}
+
+
+# define VIR_STORAGE_BACKEND_REGISTER(func, module)                            \
+    if (virStorageDriverLoadBackendModule(module, #func) < 0)                  \
+        return -1
+#else
+# define VIR_STORAGE_BACKEND_REGISTER(func, module)                            \
+    if (func() < 0)                                                            \
         return -1
+#endif
 
 int
 virStorageBackendDriversRegister(void)
 {
 #if WITH_STORAGE_DIR || WITH_STORAGE_FS
-    VIR_STORAGE_BACKEND_REGISTER(virStorageBackendFsRegister);
+    VIR_STORAGE_BACKEND_REGISTER(virStorageBackendFsRegister, "fs");
 #endif
 #if WITH_STORAGE_LVM
-    VIR_STORAGE_BACKEND_REGISTER(virStorageBackendLogicalRegister);
+    VIR_STORAGE_BACKEND_REGISTER(virStorageBackendLogicalRegister, "logical");
 #endif
 #if WITH_STORAGE_ISCSI
-    VIR_STORAGE_BACKEND_REGISTER(virStorageBackendISCSIRegister);
+    VIR_STORAGE_BACKEND_REGISTER(virStorageBackendISCSIRegister, "iscsi");
 #endif
 #if WITH_STORAGE_SCSI
-    VIR_STORAGE_BACKEND_REGISTER(virStorageBackendSCSIRegister);
+    VIR_STORAGE_BACKEND_REGISTER(virStorageBackendSCSIRegister, "scsi");
 #endif
 #if WITH_STORAGE_MPATH
-    VIR_STORAGE_BACKEND_REGISTER(virStorageBackendMpathRegister);
+    VIR_STORAGE_BACKEND_REGISTER(virStorageBackendMpathRegister, "mpath");
 #endif
 #if WITH_STORAGE_DISK
-    VIR_STORAGE_BACKEND_REGISTER(virStorageBackendDiskRegister);
+    VIR_STORAGE_BACKEND_REGISTER(virStorageBackendDiskRegister, "disk");
 #endif
 #if WITH_STORAGE_RBD
-    VIR_STORAGE_BACKEND_REGISTER(virStorageBackendRBDRegister);
+    VIR_STORAGE_BACKEND_REGISTER(virStorageBackendRBDRegister, "rbd");
 #endif
 #if WITH_STORAGE_SHEEPDOG
-    VIR_STORAGE_BACKEND_REGISTER(virStorageBackendSheepdogRegister);
+    VIR_STORAGE_BACKEND_REGISTER(virStorageBackendSheepdogRegister, "sheepdog");
 #endif
 #if WITH_STORAGE_GLUSTER
-    VIR_STORAGE_BACKEND_REGISTER(virStorageBackendGlusterRegister);
+    VIR_STORAGE_BACKEND_REGISTER(virStorageBackendGlusterRegister, "gluster");
 #endif
 #if WITH_STORAGE_ZFS
-    VIR_STORAGE_BACKEND_REGISTER(virStorageBackendZFSRegister);
+    VIR_STORAGE_BACKEND_REGISTER(virStorageBackendZFSRegister, "zfs");
 #endif
 #if WITH_STORAGE_VSTORAGE
-    VIR_STORAGE_BACKEND_REGISTER(virStorageBackendVstorageRegister);
+    VIR_STORAGE_BACKEND_REGISTER(virStorageBackendVstorageRegister, "vstorage");
 #endif
 
     return 0;

tests/Makefile.am

@@ -805,7 +805,9 @@ storagebackendsheepdogtest_SOURCES = \
 	storagebackendsheepdogtest.c \
 	testutils.c testutils.h
 storagebackendsheepdogtest_LDADD = \
-	../src/libvirt_driver_storage_impl.la $(LDADDS)
+	../src/libvirt_driver_storage_impl.la \
+	../src/libvirt_storage_backend_sheepdog_priv.la \
+	$(LDADDS)
 else ! WITH_STORAGE_SHEEPDOG
 EXTRA_DIST += storagebackendsheepdogtest.c
 endif ! WITH_STORAGE_SHEEPDOG