[RFC][PATCH 1/6] fanotify: add a super block root watch

[Amir Goldstein <amir73il@gmail.com>]

Set a watch on the super block's root inode including the
mask bit FAN_EVENT_ON_SB to get notified on the events
of all the inodes on the same super block.

When requesting to add a super block root watch, any
file on the file system can be passed as input argument
for fanotify_mark(). The mark will be added to the root
inode of the file system that file belongs to.

The super block watch cannot be set with FAN_MARK_MOUNT flag,
because a super block watch is an inode mark, not a mount mark.

Signed-off-by: Amir Goldstein <amir73il@gmail.com>
---
 fs/notify/fanotify/fanotify.c      |  1 +
 fs/notify/fanotify/fanotify_user.c | 15 ++++++++++++---
 include/uapi/linux/fanotify.h      |  3 +++
 3 files changed, 16 insertions(+), 3 deletions(-)

diff --git a/fs/notify/fanotify/fanotify.c b/fs/notify/fanotify/fanotify.c
index a647e7b..67feeb6 100644
--- a/fs/notify/fanotify/fanotify.c
+++ b/fs/notify/fanotify/fanotify.c
@@ -237,6 +237,7 @@ static int fanotify_handle_event(struct fsnotify_group *group,
 	BUILD_BUG_ON(FAN_DELETE_SELF != FS_DELETE_SELF);
 	BUILD_BUG_ON(FAN_MOVE_SELF != FS_MOVE_SELF);
 	BUILD_BUG_ON(FAN_EVENT_ON_CHILD != FS_EVENT_ON_CHILD);
+	BUILD_BUG_ON(FAN_EVENT_ON_SB != FS_EVENT_ON_SB);
 	BUILD_BUG_ON(FAN_Q_OVERFLOW != FS_Q_OVERFLOW);
 	BUILD_BUG_ON(FAN_OPEN_PERM != FS_OPEN_PERM);
 	BUILD_BUG_ON(FAN_ACCESS_PERM != FS_ACCESS_PERM);
diff --git a/fs/notify/fanotify/fanotify_user.c b/fs/notify/fanotify/fanotify_user.c
index 13015ee..e57c82a 100644
--- a/fs/notify/fanotify/fanotify_user.c
+++ b/fs/notify/fanotify/fanotify_user.c
@@ -902,9 +902,9 @@ SYSCALL_DEFINE5(fanotify_mark, int, fanotify_fd, unsigned int, flags,
 	}
 
 #ifdef CONFIG_FANOTIFY_ACCESS_PERMISSIONS
-	if (mask & ~(FAN_ALL_EVENTS | FAN_ALL_PERM_EVENTS | FAN_EVENT_ON_CHILD))
+	if (mask & ~(FAN_ALL_EVENTS | FAN_ALL_PERM_EVENTS | FAN_EVENT_ON_DESCENDANT))
 #else
-	if (mask & ~(FAN_ALL_EVENTS | FAN_EVENT_ON_CHILD))
+	if (mask & ~(FAN_ALL_EVENTS | FAN_EVENT_ON_DESCENDANT))
 #endif
 		return -EINVAL;
 
@@ -927,6 +927,12 @@ SYSCALL_DEFINE5(fanotify_mark, int, fanotify_fd, unsigned int, flags,
 	    group->priority == FS_PRIO_0)
 		goto fput_and_out;
 
+	/* Super block root watch is not a mount watch */
+	ret = -EINVAL;
+	if ((mask & FAN_EVENT_ON_SB) &&
+	    (flags & FAN_MARK_MOUNT))
+		goto fput_and_out;
+
 	if (flags & FAN_MARK_FLUSH) {
 		ret = 0;
 		if (flags & FAN_MARK_MOUNT)
@@ -941,7 +947,9 @@ SYSCALL_DEFINE5(fanotify_mark, int, fanotify_fd, unsigned int, flags,
 		goto fput_and_out;
 
 	/* inode held in place by reference to path; group by fget on fd */
-	if (!(flags & FAN_MARK_MOUNT))
+	if (mask & FAN_EVENT_ON_SB)
+		inode = path.dentry->d_sb->s_root->d_inode;
+	else if (!(flags & FAN_MARK_MOUNT))
 		inode = path.dentry->d_inode;
 
 	/*
@@ -950,6 +958,7 @@ SYSCALL_DEFINE5(fanotify_mark, int, fanotify_fd, unsigned int, flags,
 	 * even if the events happened on another mount point.
 	 */
 	if ((flags & FAN_MARK_MOUNT) ||
+	    (mask & FAN_EVENT_ON_SB) ||
 	    group->fanotify_data.flags & FAN_EVENT_INFO_PARENT)
 		mnt = path.mnt;
 
diff --git a/include/uapi/linux/fanotify.h b/include/uapi/linux/fanotify.h
index 95b8335..b202e09 100644
--- a/include/uapi/linux/fanotify.h
+++ b/include/uapi/linux/fanotify.h
@@ -25,8 +25,11 @@
 
 #define FAN_ONDIR		0x40000000	/* event occurred against dir */
 
+#define FAN_EVENT_ON_SB		0x01000000	/* interested in all sb inodes */
 #define FAN_EVENT_ON_CHILD	0x08000000	/* interested in child events */
 
+#define FAN_EVENT_ON_DESCENDANT	(FAN_EVENT_ON_CHILD | FAN_EVENT_ON_SB)
+
 /* helper events */
 #define FAN_CLOSE		(FAN_CLOSE_WRITE | FAN_CLOSE_NOWRITE) /* close */
 #define FAN_MOVE		(FAN_MOVED_FROM | FAN_MOVED_TO) /* moves */
-- 
2.7.4