[PATCH] fanotify: Document mount namespace events

[Amir Goldstein <amir73il@gmail.com>]

Used to subscribe for notifications for when mounts
are attached/detached from a mount namespace.

Cc: Jan Kara <jack@suse.cz>
Cc: Miklos Szeredi <mszeredi@redhat.com>
Cc: Christian Brauner <brauner@kernel.org>
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
---

Alejandro,

This feature was also added (by Miklos) in v6.14.

The man page patch can be merged independently of the
FAN_PRE_ACCESS patch.

However, this patch depends on the FAN_FS_ERROR cleanup patch
that I just posted, because of the reordering of event entries.

Thanks,
Amir.

 man/man2/fanotify_init.2 | 20 ++++++++++++++++++++
 man/man2/fanotify_mark.2 | 35 ++++++++++++++++++++++++++++++++++-
 man/man7/fanotify.7      | 39 +++++++++++++++++++++++++++++++++++++++
 3 files changed, 93 insertions(+), 1 deletion(-)

diff --git a/man/man2/fanotify_init.2 b/man/man2/fanotify_init.2
index 699b6f054..26289c496 100644
--- a/man/man2/fanotify_init.2
+++ b/man/man2/fanotify_init.2
@@ -330,6 +330,26 @@ that the directory entry is referring to.
 This is a synonym for
 .RB ( FAN_REPORT_DFID_NAME | FAN_REPORT_FID | FAN_REPORT_TARGET_FID ).
 .TP
+.BR FAN_REPORT_MNT " (since Linux 6.14)"
+.\" commit 0f46d81f2bce970b1c562aa3c944a271bbec2729
+This value allows the receipt of events which contain additional information
+about the underlying mount correlated to an event.
+An additional record of type
+.B FAN_EVENT_INFO_TYPE_MNT
+encapsulates the information about the mount and is included alongside the
+generic event metadata structure.
+The use of
+.BR FAN_CLASS_CONTENT ,
+.BR FAN_CLASS_PRE_CONTENT,
+or any of the
+.B FAN_REPORT_DFID_NAME_TARGET
+flags along with this flag is not permitted
+and will result in the error
+.BR EINVAL .
+See
+.BR fanotify (7)
+for additional details.
+.TP
 .BR FAN_REPORT_PIDFD " (since Linux 5.15 and 5.10.220)"
 .\" commit af579beb666aefb17e9a335c12c788c92932baf1
 Events for fanotify groups initialized with this flag will contain
diff --git a/man/man2/fanotify_mark.2 b/man/man2/fanotify_mark.2
index da569279b..b843c1f9a 100644
--- a/man/man2/fanotify_mark.2
+++ b/man/man2/fanotify_mark.2
@@ -67,7 +67,8 @@ contains
 all marks for filesystems are removed from the group.
 Otherwise, all marks for directories and files are removed.
 No flag other than, and at most one of, the flags
-.B FAN_MARK_MOUNT
+.BR FAN_MARK_MNTNS ,
+.BR FAN_MARK_MOUNT ,
 or
 .B FAN_MARK_FILESYSTEM
 can be used in conjunction with
@@ -99,6 +100,20 @@ If the filesystem object to be marked is not a directory, the error
 .B ENOTDIR
 shall be raised.
 .TP
+.BR FAN_MARK_MNTNS " (since Linux 6.14)"
+.\" commit 0f46d81f2bce970b1c562aa3c944a271bbec2729
+Mark the mount namespace of the path specified by
+.IR pathname .
+If
+.I pathname
+is not itself a mount point,
+the mount namespace of the mount containing
+.I pathname
+will be marked.
+An fanotify group that is initialized with flag
+.B FAN_REPORT_MNT
+is required.
+.TP
 .B FAN_MARK_MOUNT
 Mark the mount specified by
 .IR pathname .
@@ -395,6 +410,24 @@ Create an event when a marked file or directory itself has been moved.
 An fanotify group that identifies filesystem objects by file handles
 is required.
 .TP
+.BR FAN_MNT_ATTACH ", " FAN_MNT_DETACH " (since Linux 6.14)"
+.\" commit 0f46d81f2bce970b1c562aa3c944a271bbec2729
+Create an event when a mount was attached to or detached from a marked mount namespace.
+An attempt to set this flag on an inode, mount or filesystem mark
+will result in the error
+.BR EINVAL .
+An fanotify group that is initialized with flag
+.B FAN_REPORT_MNT
+and the mark flag
+.B FAN_MARK_MNTNS
+are required.
+An additional information record of type
+.B FAN_EVENT_INFO_TYPE_MNT
+is returned with the event.
+See
+.BR fanotify (7)
+for additional details.
+.TP
 .BR FAN_FS_ERROR " (since Linux 5.16, 5.15.154, and 5.10.220)"
 .\" commit 9709bd548f11a092d124698118013f66e1740f9b
 Create an event when a filesystem error
diff --git a/man/man7/fanotify.7 b/man/man7/fanotify.7
index 77dcb8aa5..98705c3c7 100644
--- a/man/man7/fanotify.7
+++ b/man/man7/fanotify.7
@@ -228,6 +228,23 @@ struct fanotify_event_info_pidfd {
 .EE
 .in
 .P
+In cases where an fanotify group is initialized with
+.BR FAN_REPORT_MNT ,
+event listeners should expect to receive the below
+information record object alongside the generic
+.I fanotify_event_metadata
+structure within the read buffer.
+This structure is defined as follows:
+.P
+.in +4n
+.EX
+struct fanotify_event_info_mnt {
+    struct fanotify_event_info_header hdr;
+    __u64 mnt_id;
+};
+.EE
+.in
+.P
 In case of a
 .B FAN_FS_ERROR
 event,
@@ -442,6 +459,12 @@ A file or directory that was opened read-only
 .RB ( O_RDONLY )
 was closed.
 .TP
+.BR FAN_MNT_ATTACH
+A mount was attached to mount namespace.
+.TP
+.BR FAN_MNT_DETACH
+A mount was detached to mount namespace.
+.TP
 .B FAN_FS_ERROR
 A filesystem error was detected.
 .TP
@@ -540,6 +563,7 @@ The value of this field can be set to one of the following:
 .BR FAN_EVENT_INFO_TYPE_FID ,
 .BR FAN_EVENT_INFO_TYPE_DFID ,
 .BR FAN_EVENT_INFO_TYPE_DFID_NAME ,
+.BR FAN_EVENT_INFO_TYPE_MNT ,
 .BR FAN_EVENT_INFO_TYPE_ERROR ,
 .BR FAN_EVENT_INFO_TYPE_RANGE ,
 or
@@ -727,6 +751,21 @@ in case of a terminated process, the value will be
 .BR \-ESRCH .
 .P
 The fields of the
+.I fanotify_event_info_mnt
+structure are as follows:
+.TP
+.I .hdr
+This is a structure of type
+.IR fanotify_event_info_header .
+The
+.I .info_type
+field is set to
+.BR FAN_EVENT_INFO_TYPE_MNT .
+.TP
+.I .mnt_id
+Identifies the mount associated with the event.
+.P
+The fields of the
 .I fanotify_event_info_error
 structure are as follows:
 .TP
-- 
2.34.1