linux-kernel - [PATCH 2/6] Adjust watch_queue documentation to mention mount and superblock watches. [ver #5]

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Message-ID: <156173703546.15650.14319137940607993268.stgit@warthog.procyon.org.uk>
Date:   Fri, 28 Jun 2019 16:50:35 +0100
From:   David Howells <dhowells@...hat.com>
To:     viro@...iv.linux.org.uk
Cc:     dhowells@...hat.com, Casey Schaufler <casey@...aufler-ca.com>,
        Stephen Smalley <sds@...ho.nsa.gov>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        nicolas.dichtel@...nd.com, raven@...maw.net,
        Christian Brauner <christian@...uner.io>, dhowells@...hat.com,
        keyrings@...r.kernel.org, linux-usb@...r.kernel.org,
        linux-security-module@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-api@...r.kernel.org,
        linux-block@...r.kernel.org, linux-security-module@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH 2/6] Adjust watch_queue documentation to mention mount and
 superblock watches. [ver #5]

Signed-off-by: David Howells <dhowells@...hat.com>
---

 Documentation/watch_queue.rst |   20 +++++++++++++++++++-
 drivers/misc/Kconfig          |    5 +++--
 2 files changed, 22 insertions(+), 3 deletions(-)

diff --git a/Documentation/watch_queue.rst b/Documentation/watch_queue.rst
index 4087a8e670a8..1bec2018d549 100644
--- a/Documentation/watch_queue.rst
+++ b/Documentation/watch_queue.rst
@@ -13,6 +13,10 @@ receive notifications from the kernel.  This can be used in conjunction with::
 
     * USB subsystem event notifications
 
+  * Mount topology change notifications
+
+  * Superblock event notifications
+
 
 The notifications buffers can be enabled by:
 
@@ -324,6 +328,19 @@ Any particular buffer can be fed from multiple sources.  Sources include:
     for buses and devices.  Watchpoints of this type are set on the global
     device watch list.
 
+  * WATCH_TYPE_MOUNT_NOTIFY
+
+    Notifications of this type indicate mount tree topology changes and mount
+    attribute changes.  A watch can be set on a particular file or directory
+    and notifications from the path subtree rooted at that point will be
+    intercepted.
+
+  * WATCH_TYPE_SB_NOTIFY
+
+    Notifications of this type indicate superblock events, such as quota limits
+    being hit, I/O errors being produced or network server loss/reconnection.
+    Watches of this type are set directly on superblocks.
+
 
 Event Filtering
 ===============
@@ -365,7 +382,8 @@ Where:
 	(watch.info & info_mask) == info_filter
 
     This could be used, for example, to ignore events that are not exactly on
-    the watched point in a mount tree.
+    the watched point in a mount tree by specifying NOTIFY_MOUNT_IN_SUBTREE
+    must be 0.
 
   * ``subtype_filter`` is a bitmask indicating the subtypes that are of
     interest.  Bit 0 of subtype_filter[0] corresponds to subtype 0, bit 1 to
diff --git a/drivers/misc/Kconfig b/drivers/misc/Kconfig
index e53f88783fe7..8b13103b17c0 100644
--- a/drivers/misc/Kconfig
+++ b/drivers/misc/Kconfig
@@ -11,8 +11,9 @@ config WATCH_QUEUE
 	help
 	  This is a general notification queue for the kernel to pass events to
 	  userspace through a mmap()'able ring buffer.  It can be used in
-	  conjunction with watches for key/keyring change notifications and device
-	  notifications.
+	  conjunction with watches for key/keyring change notifications, device
+	  notifications, mount topology change notifications, and superblock
+	  change notifications.
 
 	  Note that in theory this should work fine with NOMMU, but I'm not
 	  sure how to make that work.