From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-9.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,UNPARSEABLE_RELAY, USER_AGENT_GIT autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 02B2EC4360F for ; Mon, 18 Mar 2019 20:28:42 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D015E20989 for ; Mon, 18 Mar 2019 20:28:41 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727737AbfCRU2k (ORCPT ); Mon, 18 Mar 2019 16:28:40 -0400 Received: from bhuna.collabora.co.uk ([46.235.227.227]:33120 "EHLO bhuna.collabora.co.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727393AbfCRU2k (ORCPT ); Mon, 18 Mar 2019 16:28:40 -0400 Received: from [127.0.0.1] (localhost [127.0.0.1]) (Authenticated sender: krisman) with ESMTPSA id E4ADB2811A2 From: Gabriel Krisman Bertazi To: tytso@mit.edu Cc: linux-ext4@vger.kernel.org, sfrench@samba.org, darrick.wong@oracle.com, jlayton@kernel.org, bfields@fieldses.org, paulus@samba.org, linux-fsdevel@vger.kernel.org, Gabriel Krisman Bertazi Subject: [PATCH RFC v6 11/11] docs: ext4.rst: Document encoding and case-insensitive Date: Mon, 18 Mar 2019 16:27:45 -0400 Message-Id: <20190318202745.5200-12-krisman@collabora.com> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20190318202745.5200-1-krisman@collabora.com> References: <20190318202745.5200-1-krisman@collabora.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org From: Gabriel Krisman Bertazi Introduces the encoding-awareness and case-insensitive features on ext4 for system administrators. Explain the minimum of design decisions that are important for sysadmins wanting to enable this feature. Signed-off-by: Gabriel Krisman Bertazi --- Documentation/admin-guide/ext4.rst | 41 ++++++++++++++++++++++++++++++ 1 file changed, 41 insertions(+) diff --git a/Documentation/admin-guide/ext4.rst b/Documentation/admin-guide/ext4.rst index e506d3dae510..4e08d0309f1e 100644 --- a/Documentation/admin-guide/ext4.rst +++ b/Documentation/admin-guide/ext4.rst @@ -91,10 +91,51 @@ Currently Available * large block (up to pagesize) support * efficient new ordered mode in JBD2 and ext4 (avoid using buffer head to force the ordering) +* Encoding aware file names +* Case insensitive file name lookups [1] Filesystems with a block size of 1k may see a limit imposed by the directory hash tree having a maximum depth of two. +Encoding-aware file names and case-insensitive lookups +====================================================== + +Ext4 optionally supports filesystem-wide charset knowledge when handling +file names, which allows the user to perform file system lookups using +charset equivalent versions of the same file name, and optionally ensure +that no invalid names are held by the filesystem. charset encoding +awareness is also essential for performing case-insensitive lookups, +because it is what defines the casefold operation. + +The case-insensitive file name lookup feature is supported in a smaller +granularity, on a per-directory basis, allowing the user to mix +case-insensitive and case-sensitive directories in the same filesystem. +It is enabled by flipping a file attribute on an empty directory. For +the reason stated above, the filesystem must have encoding enabled to +use this feature. + +Both encoding-awareness and case-awareness are name-preserving on the +disk, meaning that the file name provided by userspace is a +byte-per-byte match to what is actually written in the disk. The +Unicode normalization format used by the kernel is thus an internal +representation, and not exposed to the userspace nor to the disk, with +the important exception of disk hashes, used on large directories with +DX feature. On DX directories, the hash must be calculated using the +normalized version of the filename, meaning that the normalization +format used actually has an impact on where the directory entry is +stored. + +When we change from viewing filenames as opaque byte sequences to seeing +them as encoded strings we need to address what happens when a program +tries to create a file with an invalid name. The Unicode subsystem +within the kernel leaves the decision of what to do in this case to the +filesystem, which select its preferred behavior by enabling/disabling +the strict mode. When Ext4 encounters one of those strings and the +filesystem did not require strict mode, it falls back to considering the +entire string as an opaque byte sequence, which still allows the user to +operate on that file but the case-insensitive and equivalent sequence +lookups won't work. + Options ======= -- 2.20.1