storage: Switch metadata crawler to use storage driver to read headers

Use virStorageFileReadHeader() to read headers of storage files possibly
on remote storage to retrieve the image metadata.

The backend information is now parsed by
virStorageFileGetMetadataInternal which is now exported from the util
source and virStorageFileGetMetadataFromFDInternal now doesn't need to
be exported.

src/libvirt_private.syms

@@ -1865,7 +1865,7 @@ virStorageFileFormatTypeToString;
 virStorageFileGetLVMKey;
 virStorageFileGetMetadataFromBuf;
 virStorageFileGetMetadataFromFD;
-virStorageFileGetMetadataFromFDInternal;
+virStorageFileGetMetadataInternal;
 virStorageFileGetSCSIKey;
 virStorageFileIsClusterFS;
 virStorageFileParseChainIndex;

src/storage/storage_driver.c

@@ -3132,10 +3132,11 @@ virStorageFileGetMetadataRecurse(virStorageSourcePtr src,
                                  bool allow_probe,
                                  virHashTablePtr cycle)
 {
-    int fd;
     int ret = -1;
     struct stat st;
     const char *uniqueName;
+    char *buf = NULL;
+    ssize_t headerLen;
     virStorageSourcePtr backingStore = NULL;
     int backingFormat;
 
@@ -3163,26 +3164,13 @@ virStorageFileGetMetadataRecurse(virStorageSourcePtr src,
     if (virHashAddEntry(cycle, uniqueName, (void *)1) < 0)
         goto cleanup;
 
-    if (virStorageSourceGetActualType(src) != VIR_STORAGE_TYPE_NETWORK) {
-        if ((fd = virFileOpenAs(src->path, O_RDONLY, 0, uid, gid, 0)) < 0) {
-            virReportSystemError(-fd, _("Failed to open file '%s'"),
-                                 src->path);
-            goto cleanup;
-        }
-
-        if (virStorageFileGetMetadataFromFDInternal(src, fd,
-                                                    &backingFormat) < 0) {
-            VIR_FORCE_CLOSE(fd);
-            goto cleanup;
-        }
+    if ((headerLen = virStorageFileReadHeader(src, VIR_STORAGE_MAX_HEADER,
+                                              &buf)) < 0)
+        goto cleanup;
 
-        if (VIR_CLOSE(fd) < 0)
-            VIR_WARN("could not close file %s", src->path);
-    } else {
-        /* TODO: currently we call this only for local storage */
-        ret = 0;
+    if (virStorageFileGetMetadataInternal(src, buf, headerLen,
+                                          &backingFormat) < 0)
         goto cleanup;
-    }
 
     /* check whether we need to go deeper */
     if (!src->backingStoreRaw) {

src/util/virstoragefile.c

@@ -740,8 +740,7 @@ qcow2GetFeatures(virBitmapPtr *features,
  * with information about the file and its backing store. Return format
  * of the backing store as BACKING_FORMAT. PATH and FORMAT have to be
  * pre-populated in META */
-static int ATTRIBUTE_NONNULL(1) ATTRIBUTE_NONNULL(2)
-ATTRIBUTE_NONNULL(4)
+int
 virStorageFileGetMetadataInternal(virStorageSourcePtr meta,
                                   char *buf,
                                   size_t len,
@@ -955,7 +954,7 @@ virStorageFileGetMetadataFromBuf(const char *path,
 
 
 /* Internal version that also supports a containing directory name.  */
-int
+static int
 virStorageFileGetMetadataFromFDInternal(virStorageSourcePtr meta,
                                         int fd,
                                         int *backingFormat)

src/util/virstoragefile.h

@@ -265,9 +265,12 @@ struct _virStorageSource {
 
 int virStorageFileProbeFormat(const char *path, uid_t uid, gid_t gid);
 
-int virStorageFileGetMetadataFromFDInternal(virStorageSourcePtr meta,
-                                            int fd,
-                                            int *backingFormat);
+int virStorageFileGetMetadataInternal(virStorageSourcePtr meta,
+                                      char *buf,
+                                      size_t len,
+                                      int *backingFormat)
+    ATTRIBUTE_NONNULL(1) ATTRIBUTE_NONNULL(2) ATTRIBUTE_NONNULL(4);
+
 virStorageSourcePtr virStorageFileGetMetadataFromFD(const char *path,
                                                     int fd,
                                                     int format,