storage: Return backing format from virStorageFileGetMetadataFromFD

Add argument to return backing file format of a file probed by
virStorageFileGetMetadataFromFD so that it can be used in place of
virStorageFileGetMetadataFromBuf.

src/qemu/qemu_driver.c

@@ -10364,7 +10364,7 @@ qemuDomainGetBlockInfo(virDomainPtr dom,
         }
     }
 
-    if (!(meta = virStorageFileGetMetadataFromFD(path, fd, format)))
+    if (!(meta = virStorageFileGetMetadataFromFD(path, fd, format, NULL)))
         goto cleanup;
 
     /* Get info for normal formats */

src/util/virstoragefile.c

@@ -1091,14 +1091,16 @@ virStorageFileGetMetadataFromFDInternal(virStorageSourcePtr meta,
 virStorageSourcePtr
 virStorageFileGetMetadataFromFD(const char *path,
                                 int fd,
-                                int format)
+                                int format,
+                                int *backingFormat)
+
 {
     virStorageSourcePtr ret = NULL;
 
     if (!(ret = virStorageFileMetadataNew(path, format)))
         goto cleanup;
 
-    if (virStorageFileGetMetadataFromFDInternal(ret, fd, NULL) < 0) {
+    if (virStorageFileGetMetadataFromFDInternal(ret, fd, backingFormat) < 0) {
         virStorageSourceFree(ret);
         ret = NULL;
     }

src/util/virstoragefile.h

@@ -271,7 +271,8 @@ int virStorageFileGetMetadata(virStorageSourcePtr src,
     ATTRIBUTE_NONNULL(1);
 virStorageSourcePtr virStorageFileGetMetadataFromFD(const char *path,
                                                     int fd,
-                                                    int format);
+                                                    int format,
+                                                    int *backingFormat);
 virStorageSourcePtr virStorageFileGetMetadataFromBuf(const char *path,
                                                      char *buf,
                                                      size_t len,