util: Export virStorageFileSupportsBackingChainTraversal

The function will be reused in the qemu snapshot code. The argument is
turned into const similarly to the other virStorageFileSupports*
functions.
Signed-off-by: NPeter Krempa <pkrempa@redhat.com>
Reviewed-by: NJán Tomko <jtomko@redhat.com>

src/libvirt_private.syms

@@ -2994,6 +2994,7 @@ virStorageFileReportBrokenChain;
 virStorageFileResize;
 virStorageFileStat;
 virStorageFileSupportsAccess;
+virStorageFileSupportsBackingChainTraversal;
 virStorageFileSupportsCreate;
 virStorageFileSupportsSecurityDriver;
 virStorageFileUnlink;

src/util/virstoragefile.c

@@ -4450,8 +4450,8 @@ virStorageFileGetBackendForSupportCheck(const virStorageSource *src,
 }
 
 
-static int
-virStorageFileSupportsBackingChainTraversal(virStorageSourcePtr src)
+int
+virStorageFileSupportsBackingChainTraversal(const virStorageSource *src)
 {
     virStorageFileBackendPtr backend;
     int rv;

src/util/virstoragefile.h

@@ -533,6 +533,7 @@ int virStorageFileChown(const virStorageSource *src, uid_t uid, gid_t gid);
 int virStorageFileSupportsSecurityDriver(const virStorageSource *src);
 int virStorageFileSupportsAccess(const virStorageSource *src);
 int virStorageFileSupportsCreate(const virStorageSource *src);
+int virStorageFileSupportsBackingChainTraversal(const virStorageSource *src);
 
 int virStorageFileGetMetadata(virStorageSourcePtr src,
                               uid_t uid, gid_t gid,