[PATCH v6 11/17] fanotify: add a helper to check for pre content events

[Josef Bacik <josef@toxicpanda.com>]

We want to emit events during page fault, and calling into fanotify
could be expensive, so add a helper to allow us to skip calling into
fanotify from page fault.  This will also be used to disable readahead
for content watched files which will be handled in a subsequent patch.

Reviewed-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
---
 fs/notify/fsnotify.c             | 16 ++++++++++++++++
 include/linux/fsnotify_backend.h | 14 ++++++++++++++
 2 files changed, 30 insertions(+)

diff --git a/fs/notify/fsnotify.c b/fs/notify/fsnotify.c
index 0696c1771b2a..a49c42c6ce01 100644
--- a/fs/notify/fsnotify.c
+++ b/fs/notify/fsnotify.c
@@ -203,6 +203,22 @@ static inline bool fsnotify_object_watched(struct inode *inode, __u32 mnt_mask,
 	return mask & marks_mask & ALL_FSNOTIFY_EVENTS;
 }
 
+#ifdef CONFIG_FANOTIFY_ACCESS_PERMISSIONS
+bool fsnotify_file_has_pre_content_watches(struct file *file)
+{
+	struct inode *inode = file_inode(file);
+	__u32 mnt_mask = real_mount(file->f_path.mnt)->mnt_fsnotify_mask;
+
+	if (!(inode->i_sb->s_iflags & SB_I_ALLOW_HSM))
+		return false;
+
+	return fsnotify_object_watched(inode, mnt_mask,
+				       FSNOTIFY_PRE_CONTENT_EVENTS);
+}
+EXPORT_SYMBOL_GPL(fsnotify_file_has_pre_content_watches);
+#endif
+
+
 /*
  * Notify this dentry's parent about a child's events with child name info
  * if parent is watching or if inode/sb/mount are interested in events with
diff --git a/include/linux/fsnotify_backend.h b/include/linux/fsnotify_backend.h
index abd292edb48c..e3a4a8e06fa0 100644
--- a/include/linux/fsnotify_backend.h
+++ b/include/linux/fsnotify_backend.h
@@ -896,6 +896,15 @@ static inline void fsnotify_init_event(struct fsnotify_event *event)
 	INIT_LIST_HEAD(&event->list);
 }
 
+#ifdef CONFIG_FANOTIFY_ACCESS_PERMISSIONS
+bool fsnotify_file_has_pre_content_watches(struct file *file);
+#else
+static inline bool fsnotify_file_has_pre_content_watches(struct file *file)
+{
+	return false;
+}
+#endif /* CONFIG_FANOTIFY_ACCESS_PERMISSIONS */
+
 #else
 
 static inline int fsnotify(__u32 mask, const void *data, int data_type,
@@ -934,6 +943,11 @@ static inline u32 fsnotify_get_cookie(void)
 static inline void fsnotify_unmount_inodes(struct super_block *sb)
 {}
 
+static inline bool fsnotify_file_has_pre_content_watches(struct file *file)
+{
+	return false;
+}
+
 #endif	/* CONFIG_FSNOTIFY */
 
 #endif	/* __KERNEL __ */
-- 
2.43.0