exfat: finding dentry faster

We don't need to read all the dentry and compare them
one by one. Skip reading the useless dentries to fast
the dentry finding speed.

Also add back the name_hash to compare it more faster.

Signed-off-by: Lianwei Wang <lianwei.wang@gmail.com>

exfat_core.c

@@ -3758,7 +3758,7 @@ s32 fat_find_dir_entry(struct super_block *sb, CHAIN_T *p_dir, UNI_NAME_T *p_uni
    -2 : entry with the name does not exist */
 s32 exfat_find_dir_entry(struct super_block *sb, CHAIN_T *p_dir, UNI_NAME_T *p_uniname, s32 num_entries, DOS_NAME_T *p_dosname, u32 type)
 {
-	int i, dentry = 0, num_ext_entries = 0, len;
+	int i = 0, dentry = 0, num_ext_entries = 0, len, step;
 	s32 order = 0, is_feasible_entry = FALSE;
 	s32 dentries_per_clu, num_empty = 0;
 	u32 entry_type;
@@ -3792,12 +3792,13 @@ s32 exfat_find_dir_entry(struct super_block *sb, CHAIN_T *p_dir, UNI_NAME_T *p_u
 		if (p_fs->dev_ejected)
 			break;
-		for (i = 0; i < dentries_per_clu; i++, dentry++) {
+		while (i < dentries_per_clu) {
 			ep = get_entry_in_dir(sb, &clu, i, NULL);
 			if (!ep)
 				return -2;
 			entry_type = p_fs->fs_func->get_entry_type(ep);
+			step = 1;
 			if ((entry_type == TYPE_UNUSED) || (entry_type == TYPE_DELETED)) {
 				is_feasible_entry = FALSE;
@@ -3820,20 +3821,23 @@ s32 exfat_find_dir_entry(struct super_block *sb, CHAIN_T *p_dir, UNI_NAME_T *p_u
 				num_empty = 0;
 				if ((entry_type == TYPE_FILE) || (entry_type == TYPE_DIR)) {
+					file_ep = (FILE_DENTRY_T *) ep;
 					if ((type == TYPE_ALL) || (type == entry_type)) {
-						file_ep = (FILE_DENTRY_T *) ep;
 						num_ext_entries = file_ep->num_ext;
 						is_feasible_entry = TRUE;
 					} else {
 						is_feasible_entry = FALSE;
+						step = file_ep->num_ext + 1;
 					}
 				} else if (entry_type == TYPE_STREAM) {
 					if (is_feasible_entry) {
 						strm_ep = (STRM_DENTRY_T *) ep;
-						if (p_uniname->name_len == strm_ep->name_len) {
+						if (p_uniname->name_hash == GET16_A(strm_ep->name_hash) &&
+						    p_uniname->name_len == strm_ep->name_len) {
 							order = 1;
 						} else {
 							is_feasible_entry = FALSE;
+							step = num_ext_entries;
 						}
 					}
 				} else if (entry_type == TYPE_EXTEND) {
@@ -3852,6 +3856,7 @@ s32 exfat_find_dir_entry(struct super_block *sb, CHAIN_T *p_dir, UNI_NAME_T *p_u
 						if (nls_uniname_cmp(sb, uniname, entry_uniname)) {
 							is_feasible_entry = FALSE;
+							step = num_ext_entries - order + 1;
 						} else if (order == num_ext_entries) {
 							p_fs->hint_uentry.dir = CLUSTER_32(~0);
 							p_fs->hint_uentry.entry = -1;
@@ -3864,8 +3869,13 @@ s32 exfat_find_dir_entry(struct super_block *sb, CHAIN_T *p_dir, UNI_NAME_T *p_u
 					is_feasible_entry = FALSE;
 				}
 			}
+
+			i += step;
+			dentry += step;
 		}
+		i -= dentries_per_clu;
+
 		if (p_dir->dir == CLUSTER_32(0))
 			break; /* FAT16 root_dir */