linux-ext4 - [PATCH 11/11] Documentation: Document the FAN

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Date:   Thu, 20 May 2021 22:41:34 -0400
From:   Gabriel Krisman Bertazi <krisman@...labora.com>
To:     amir73il@...il.com
Cc:     Gabriel Krisman Bertazi <krisman@...labora.com>,
        kernel@...labora.com, "Darrick J . Wong" <djwong@...nel.org>,
        Theodore Ts'o <tytso@....edu>,
        Dave Chinner <david@...morbit.com>, jack@...e.com,
        dhowells@...hat.com, khazhy@...gle.com,
        linux-fsdevel@...r.kernel.org, linux-ext4@...r.kernel.org
Subject: [PATCH 11/11] Documentation: Document the FAN_ERROR event

Signed-off-by: Gabriel Krisman Bertazi <krisman@...labora.com>
---
 .../admin-guide/filesystem-monitoring.rst     | 52 +++++++++++++++++++
 Documentation/admin-guide/index.rst           |  1 +
 2 files changed, 53 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..81e632f8e1de
--- /dev/null
+++ b/Documentation/admin-guide/filesystem-monitoring.rst
@@ -0,0 +1,52 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+====================================
+File system Monitoring with fanotify
+====================================
+
+fanotify supports the FAN_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_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.
+
+At the time of this writing, the only file system that emits this
+FAN_ERROR notifications is ext4.
+
+A user space example code is provided at ``samples/fanotify/fs-monitor.c``.
+
+Usage
+=====
+
+Notification structure
+======================
+
+A FAN_ERROR Notification has the following format::
+
+  [ Notification Metadata (Mandatory) ]
+  [ Generic Error Record  (Mandatory) ]
+
+With the exception of the notification metadata and the generic
+information, all information records are optional.  Each record type is
+identified by its unique ``struct fanotify_event_info_header.info_type``.
+
+Generic error Location
+----------------------
+
+The Generic error record provides enough information for a file system
+agnostic tool to learn about a problem in the file system, without
+requiring any details about the problem.::
+
+  struct fanotify_event_info_error {
+	struct fanotify_event_info_header hdr;
+	int error;
+	__kernel_fsid_t fsid;
+	unsigned long inode;
+	__u32 error_count;
+  };
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
-- 
2.31.0