From patchwork Thu Oct 14 21:36:46 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: 12559487 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id F0AB1C4332F for ; Thu, 14 Oct 2021 21:40:16 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D077760524 for ; Thu, 14 Oct 2021 21:40:16 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234111AbhJNVmV (ORCPT ); Thu, 14 Oct 2021 17:42:21 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53564 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232249AbhJNVmT (ORCPT ); Thu, 14 Oct 2021 17:42:19 -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 7F9C2C061570; Thu, 14 Oct 2021 14:40:14 -0700 (PDT) Received: from localhost (unknown [IPv6:2804:14c:124:8a08::1007]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) (Authenticated sender: krisman) by bhuna.collabora.co.uk (Postfix) with ESMTPSA id 9249B1F415A6; Thu, 14 Oct 2021 22:40:12 +0100 (BST) From: Gabriel Krisman Bertazi To: jack@suse.com, amir73il@gmail.com Cc: djwong@kernel.org, tytso@mit.edu, dhowells@redhat.com, khazhy@google.com, linux-fsdevel@vger.kernel.org, linux-ext4@vger.kernel.org, linux-api@vger.kernel.org, repnop@google.com, Gabriel Krisman Bertazi , kernel@collabora.com Subject: [PATCH v7 28/28] docs: Document the FAN_FS_ERROR event Date: Thu, 14 Oct 2021 18:36:46 -0300 Message-Id: <20211014213646.1139469-29-krisman@collabora.com> X-Mailer: git-send-email 2.33.0 In-Reply-To: <20211014213646.1139469-1-krisman@collabora.com> References: <20211014213646.1139469-1-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 v7: - Update semantics Changes Since v6: - English fixes (jan) - Proper document error field (jan) 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 | 76 +++++++++++++++++++ Documentation/admin-guide/index.rst | 1 + 2 files changed, 77 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..f1f6476fa4f3 --- /dev/null +++ b/Documentation/admin-guide/filesystem-monitoring.rst @@ -0,0 +1,76 @@ +.. SPDX-License-Identifier: GPL-2.0 + +==================================== +File system Monitoring with fanotify +==================================== + +File system Error Reporting +=========================== + +Fanotify supports the FAN_FS_ERROR event type for file system-wide error +reporting. It is meant to be used by file system health monitoring +daemons, which listen for these events and take actions (notify +sysadmin, start recovery) when a file system problem is detected. + +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 out of +scope for 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 tries to report only the first +error that occurred for a process since the last notification, and it +simply counts additional errors. This ensures that the most important +pieces of information are 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 error in a file-system specific way. +Ext4, for instance, which is the only file system implementing this +interface at the time of this writing, exposes EXT4_ERR_ values in this +field. Please refer to the file system documentation for the meaning of +specific error codes. + +`error_count` tracks the number of errors that occurred and were +suppressed to preserve the original error information, 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 handle. A file system +specific application can use that information to attempt a recovery +procedure. Errors that are not related to an inode are reported with an +empty file handle of 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