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authorLinus Torvalds <torvalds@linux-foundation.org>2021-11-07 02:43:20 +0300
committerLinus Torvalds <torvalds@linux-foundation.org>2021-11-07 02:43:20 +0300
commit2acda7549e7081f75bac6e1e51518eb8a3bf5d5d (patch)
tree8a7398b46377afb15b856c6376b0602285d52ea6 /Documentation
parentd8b4e5bd4889e6568e8c3db983b4320f06091594 (diff)
parent15c72660fe9a3fddb301ac90175860b14c63ff03 (diff)
downloadlinux-2acda7549e7081f75bac6e1e51518eb8a3bf5d5d.tar.xz
Merge tag 'fsnotify_for_v5.16-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/jack/linux-fs
Pull fsnotify updates from Jan Kara: "Support for reporting filesystem errors through fanotify so that system health monitoring daemons can watch for these and act instead of scraping system logs" * tag 'fsnotify_for_v5.16-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/jack/linux-fs: (34 commits) samples: remove duplicate include in fs-monitor.c samples: Fix warning in fsnotify sample docs: Fix formatting of literal sections in fanotify docs samples: Make fs-monitor depend on libc and headers docs: Document the FAN_FS_ERROR event samples: Add fs error monitoring example ext4: Send notifications on error fanotify: Allow users to request FAN_FS_ERROR events fanotify: Emit generic error info for error event fanotify: Report fid info for file related file system errors fanotify: WARN_ON against too large file handles fanotify: Add helpers to decide whether to report FID/DFID fanotify: Wrap object_fh inline space in a creator macro fanotify: Support merging of error events fanotify: Support enqueueing of error events fanotify: Pre-allocate pool of error events fanotify: Reserve UAPI bits for FAN_FS_ERROR fsnotify: Support FS_ERROR event type fanotify: Require fid_mode for any non-fd event fanotify: Encode empty file handle when no inode is provided ...
Diffstat (limited to 'Documentation')
-rw-r--r--Documentation/admin-guide/filesystem-monitoring.rst78
-rw-r--r--Documentation/admin-guide/index.rst1
2 files changed, 79 insertions, 0 deletions
diff --git a/Documentation/admin-guide/filesystem-monitoring.rst b/Documentation/admin-guide/filesystem-monitoring.rst
new file mode 100644
index 000000000000..ab8dba76283c
--- /dev/null
+++ b/Documentation/admin-guide/filesystem-monitoring.rst
@@ -0,0 +1,78 @@
+.. 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 file system 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 FAN_FS_ERROR Notification has the following format::
+
+ ::
+
+ [ Notification Metadata (Mandatory) ]
+ [ Generic Error Record (Mandatory) ]
+ [ FID record (Mandatory) ]
+
+The order of records is not guaranteed, and new records might be added
+in the future. Therefore, applications must not rely on the order and
+must be prepared to skip over unknown records. Please refer to
+``samples/fanotify/fs-monitor.c`` for an example parser.
+
+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 using errno values.
+`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