On Sun, Aug 25, 2019 at 07:46:50PM -0700, harshad shirwadkar wrote: > If last is an intermediate dx node, is there a way to find out if it > actually is an intermediate dx node? Because an empty dirent block and > an intermediate dx block look the same. Unless we do dx_probe() there > is no way to know if a block is an intermediate dx block. Is that > right or am I missing something? You can simply look at the first hash value in the intermediate dx_node (remember, an empty intermediate node is not allowed), and then do a dx_probe to search from the root and validate that we find our way back to the last block. > Looking at your following comment, if metadata_csum feature is > enabled, then we can distinguish if a block is an empty dirent block > or an index block based on dentry->rec_len. If metadata csum is > enabled, then for index blocks, fake_dentry->rec_len is set to > blocksize while for a dirent not dentry->rec_len is set to blocksize - > sizeof(ext4_dir_entry_tail). Is my understanding correct? Yes. Although even if the metadata_csum feature is enabled, it's a good idea to search from the root to make sure this really is the intermediate dx node block that you are looking for. You need to do the dx_probe() to find its parent block anyway, in order to update it. And if you don't find a pointer to that intermediate node, then it must not be an a dx node --- or the htree pointers are corrupted. In the case of metadata_csum and a dx_tail, that sequence should never occur normally, so if you don't find an entry for that block when doing a dx_probe(), it's likely the directory structures have gotten corrupted. - Ted
