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Date:   Tue, 20 Jul 2021 11:59:28 -0400
From:   Gabriel Krisman Bertazi <>
        Gabriel Krisman Bertazi <>,
Subject: [PATCH v4 00/16] File system wide monitoring


This is the fourth version of the FAN_FS_ERROR patches.  This applies
the feedback from last version (thanks Amir, Jan), in particular how we
report file handlers for errors not related to a file.  Now it is
reported as an invalid, empty fh.

This was tested with LTP for regressions, and also using the sample on
the last patch, with a corrupted image.  I can publish the bad image
upon request.

In addition, I wrote a man-page that can be pulled from: -b fan-fs-error

And I'm sending it shortly for review.

I'm automating my tests in LTP next and will be sharing shortly.

I also pushed the full series to: -b fanotify-notifications-single-slot

Thank you

Original cover letter

This series follow up on my previous proposal [1] to support file system
wide monitoring.  As suggested by Amir, this proposal drops the ring
buffer in favor of a single slot associated with each mark.  This
simplifies a bit the implementation, as you can see in the code.

As a reminder, This proposal is limited to an interface for
administrators to monitor the health of a file system, instead of a
generic inteface for file errors.  Therefore, this doesn't solve the
problem of writeback errors or the need to watch a specific subtree.

In comparison to the previous RFC, this implementation also drops the
per-fs data and location, and leave those as future extensions.

* Implementation

The feature is implemented on top of fanotify, as a new type of fanotify
mark, FAN_ERROR, which a file system monitoring tool can register to
receive error notifications.  When an error occurs a new notification is
generated, in addition followed by this info field:

 - FS generic data: A file system agnostic structure that has a generic
 error code and identifies the filesystem.  Basically, it let's
 userspace know something happened on a monitored filesystem.  Since
 only the first error is recorded since the last read, this also
 includes a counter of errors that happened since the last read.

* Testing

This was tested by watching notifications flowing from an intentionally
corrupted filesystem in different places.  In addition, other events
were watched in an attempt to detect regressions.

Is there a specific testsuite for fanotify I should be running?

* Patches

This patchset is divided as follows: Patch 1 through 5 are refactoring
to fsnotify/fanotify in preparation for FS_ERROR/FAN_ERROR; patch 6 and
7 implement the FS_ERROR API for filesystems to report error; patch 8
add support for FAN_ERROR in fanotify; Patch 9 is an example
implementation for ext4; patch 10 and 11 provide a sample userspace code
and documentation.

I also pushed the full series to: -b fanotify-notifications-single-slot


Cc: Darrick J. Wong <>
Cc: Theodore Ts'o <>
Cc: Dave Chinner <>

Amir Goldstein (1):
  fsnotify: pass arguments of fsnotify() in struct fsnotify_event_info

Gabriel Krisman Bertazi (15):
  fsnotify: Don't insert unmergeable events in hashtable
  fanotify: Fold event size calculation to its own function
  fanotify: Split fsid check from other fid mode checks
  fsnotify: Reserve mark bits for backends
  fanotify: Split superblock marks out to a new cache
  inotify: Don't force FS_IN_IGNORED
  fsnotify: Add helper to detect overflow_event
  fsnotify: Add wrapper around fsnotify_add_event
  fsnotify: Support passing argument to insert callback on add_event
  fsnotify: Support FS_ERROR event type
  fsnotify: Introduce helpers to send error_events
  fanotify: Introduce FAN_FS_ERROR event
  ext4: Send notifications on error
  samples: Add fs error monitoring example
  docs: Document the FAN_FS_ERROR event

 .../admin-guide/filesystem-monitoring.rst     |  70 +++++
 Documentation/admin-guide/index.rst           |   1 +
 fs/ext4/super.c                               |   8 +
 fs/notify/fanotify/fanotify.c                 | 217 ++++++++++----
 fs/notify/fanotify/fanotify.h                 |  79 ++++-
 fs/notify/fanotify/fanotify_user.c            | 278 +++++++++++++++---
 fs/notify/fsnotify.c                          |  75 ++---
 fs/notify/inotify/inotify_fsnotify.c          |   2 +-
 fs/notify/inotify/inotify_user.c              |   6 +-
 fs/notify/notification.c                      |  16 +-
 include/linux/fanotify.h                      |   8 +-
 include/linux/fsnotify.h                      |  13 +
 include/linux/fsnotify_backend.h              | 140 +++++++--
 include/uapi/linux/fanotify.h                 |   8 +
 samples/Kconfig                               |   9 +
 samples/Makefile                              |   1 +
 samples/fanotify/Makefile                     |   5 +
 samples/fanotify/fs-monitor.c                 | 134 +++++++++
 18 files changed, 897 insertions(+), 173 deletions(-)
 create mode 100644 Documentation/admin-guide/filesystem-monitoring.rst
 create mode 100644 samples/fanotify/Makefile
 create mode 100644 samples/fanotify/fs-monitor.c


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