From patchwork Wed Aug 4 16:06:12 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Gabriel Krisman Bertazi X-Patchwork-Id: 12419389 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=-16.7 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,UNPARSEABLE_RELAY,URIBL_BLOCKED, USER_AGENT_GIT autolearn=ham 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 474C1C4338F for ; Wed, 4 Aug 2021 16:10:43 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 2EC5460F41 for ; Wed, 4 Aug 2021 16:10:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233805AbhHDQKh (ORCPT ); Wed, 4 Aug 2021 12:10:37 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:50092 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229603AbhHDQIU (ORCPT ); Wed, 4 Aug 2021 12:08:20 -0400 Received: from bhuna.collabora.co.uk (bhuna.collabora.co.uk [IPv6:2a00:1098:0:82:1000:25:2eeb:e3e3]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 112DAC0613D5; Wed, 4 Aug 2021 09:08:08 -0700 (PDT) Received: from [127.0.0.1] (localhost [127.0.0.1]) (Authenticated sender: krisman) with ESMTPSA id AD91C1F4369A From: Gabriel Krisman Bertazi To: jack@suse.com, amir73il@gmail.com Cc: djwong@kernel.org, tytso@mit.edu, david@fromorbit.com, dhowells@redhat.com, khazhy@google.com, linux-fsdevel@vger.kernel.org, linux-ext4@vger.kernel.org, linux-api@vger.kernel.org, Gabriel Krisman Bertazi , kernel@collabora.com Subject: [PATCH v5 23/23] docs: Document the FAN_FS_ERROR event Date: Wed, 4 Aug 2021 12:06:12 -0400 Message-Id: <20210804160612.3575505-24-krisman@collabora.com> X-Mailer: git-send-email 2.32.0 In-Reply-To: <20210804160612.3575505-1-krisman@collabora.com> References: <20210804160612.3575505-1-krisman@collabora.com> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org Document the FAN_FS_ERROR event for user administrators and user space developers. Reviewed-by: Amir Goldstein Signed-off-by: Gabriel Krisman Bertazi --- Changes Since v4: - Update documentation about reporting non-file error. Changes Since v3: - Move FAN_FS_ERROR notification into a subsection of the file. Changes Since v2: - NTR Changes since v1: - Drop references to location record - Explain that the inode field is optional - Explain we are reporting only the first error --- .../admin-guide/filesystem-monitoring.rst | 70 +++++++++++++++++++ Documentation/admin-guide/index.rst | 1 + 2 files changed, 71 insertions(+) create mode 100644 Documentation/admin-guide/filesystem-monitoring.rst diff --git a/Documentation/admin-guide/filesystem-monitoring.rst b/Documentation/admin-guide/filesystem-monitoring.rst new file mode 100644 index 000000000000..d03a2e54ae2a --- /dev/null +++ b/Documentation/admin-guide/filesystem-monitoring.rst @@ -0,0 +1,70 @@ +.. SPDX-License-Identifier: GPL-2.0 + +==================================== +File system Monitoring with fanotify +==================================== + +File system Error Reporting +=========================== + +fanotify supports the FAN_FS_ERROR mark for file system-wide error +reporting. It is meant to be used by file system health monitoring +daemons who listen on that interface and take actions (notify sysadmin, +start recovery) when a file system problem is detected by the kernel. + +By design, A FAN_FS_ERROR notification exposes sufficient information for a +monitoring tool to know a problem in the file system has happened. It +doesn't necessarily provide a user space application with semantics to +verify an IO operation was successfully executed. That is outside of +scope of this feature. Instead, it is only meant as a framework for +early file system problem detection and reporting recovery tools. + +When a file system operation fails, it is common for dozens of kernel +errors to cascade after the initial failure, hiding the original failure +log, which is usually the most useful debug data to troubleshoot the +problem. For this reason, FAN_FS_ERROR only reports the first error that +occurred since the last notification, and it simply counts addition +errors. This ensures that the most important piece of error information +is never lost. + +FAN_FS_ERROR requires the fanotify group to be setup with the +FAN_REPORT_FID flag. + +At the time of this writing, the only file system that emits FAN_FS_ERROR +notifications is Ext4. + +A user space example code is provided at ``samples/fanotify/fs-monitor.c``. + +A FAN_FS_ERROR Notification has the following format:: + + [ Notification Metadata (Mandatory) ] + [ Generic Error Record (Mandatory) ] + [ FID record (Mandatory) ] + +Generic error record +-------------------- + +The generic error record provides enough information for a file system +agnostic tool to learn about a problem in the file system, without +providing any additional details about the problem. This record is +identified by ``struct fanotify_event_info_header.info_type`` being set +to FAN_EVENT_INFO_TYPE_ERROR. + + struct fanotify_event_info_error { + struct fanotify_event_info_header hdr; + __s32 error; + __u32 error_count; + }; + +The `error` field identifies the type of error. `error_count` count +tracks the number of errors that occurred and were suppressed to +preserve the original error, since the last notification. + +FID record +---------- + +The FID record can be used to uniquely identify the inode that triggered +the error through the combination of fsid and file handler. A +filesystem specific handler can use that information to attempt a +recovery procedure. Errors that are not related to an inode are +reported with an empty file handler, with type FILEID_INVALID. diff --git a/Documentation/admin-guide/index.rst b/Documentation/admin-guide/index.rst index dc00afcabb95..1bedab498104 100644 --- a/Documentation/admin-guide/index.rst +++ b/Documentation/admin-guide/index.rst @@ -82,6 +82,7 @@ configure specific aspects of kernel behavior to your liking. edid efi-stub ext4 + filesystem-monitoring nfs/index gpio/index highuid