DAOS-15069 dfs: use memcpy instead of snprintf for readdir (#13654)

- memcpy is more efficient to avoid scanning the entire kds string.
- remove an assert and replace with error when looking up "."


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Signed-off-by: Mohamad Chaarawi <[email protected]>

src/client/dfs/dfs.c

@@ -568,7 +568,7 @@ fetch_entry(dfs_layout_ver_t ver, daos_handle_t oh, daos_handle_t th, const char
 
 	/** TODO - not supported yet */
 	if (strcmp(name, ".") == 0)
-		D_ASSERT(0);
+		return ENOTSUP;
 
 	if (xnr) {
 		D_ALLOC_ARRAY(pxnames, xnr);
@@ -3790,11 +3790,8 @@ readdir_int(dfs_t *dfs, dfs_obj_t *obj, daos_anchor_t *anchor, uint32_t *nr,
 			D_GOTO(out, rc = daos_der2errno(rc));
 
 		for (ptr = enum_buf, i = 0; i < number; i++) {
-			int len;
-
-			len = snprintf(dirs[key_nr].d_name,
-				       kds[i].kd_key_len + 1, "%s", ptr);
-			D_ASSERT(len >= kds[i].kd_key_len);
+			memcpy(dirs[key_nr].d_name, ptr, kds[i].kd_key_len);
+			dirs[key_nr].d_name[kds[i].kd_key_len] = '\0';
 			ptr += kds[i].kd_key_len;
 
 			/** stat the entry if requested */
@@ -6542,8 +6539,6 @@ dfs_listxattr(dfs_t *dfs, dfs_obj_t *obj, char *list, daos_size_t *size)
 			continue;
 
 		for (ptr = enum_buf, i = 0; i < number; i++) {
-			int len;
-
 			if (strncmp("x:", ptr, 2) != 0) {
 				ptr += kds[i].kd_key_len;
 				continue;
@@ -6556,10 +6551,8 @@ dfs_listxattr(dfs_t *dfs, dfs_obj_t *obj, char *list, daos_size_t *size)
 			if (list_size < kds[i].kd_key_len - 2)
 				continue;
 
-			len = snprintf(ptr_list, kds[i].kd_key_len - 1, "%s",
-				       ptr + 2);
-			D_ASSERT(len >= kds[i].kd_key_len - 2);
-
+			memcpy(ptr_list, ptr + 2, kds[i].kd_key_len - 2);
+			ptr_list[kds[i].kd_key_len - 2] = '\0';
 			list_size -= kds[i].kd_key_len - 1;
 			ptr_list += kds[i].kd_key_len - 1;
 			ptr += kds[i].kd_key_len;