fanotify: prepare for setting event flags in ignore mask

Setting flags FAN_ONDIR FAN_EVENT_ON_CHILD in ignore mask has no effect.
The FAN_EVENT_ON_CHILD flag in mask implicitly applies to ignore mask and
ignore mask is always implicitly applied to events on directories.

Define a mark flag that replaces this legacy behavior with logic of
applying the ignore mask according to event flags in ignore mask.

Implement the new logic to prepare for supporting an ignore mask that
ignores events on children and ignore mask that does not ignore events
on directories.

To emphasize the change in terminology, also rename ignored_mask mark
member to ignore_mask and use accessors to get only the effective
ignored events or the ignored events and flags.

This change in terminology finally aligns with the "ignore mask"
language in man pages and in most of the comments.

Link: https://lore.kernel.org/r/20220629144210.2983229-2-amir73il@gmail.com
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Jan Kara <jack@suse.cz>

1 files changed, 83 insertions, 6 deletions

diff --git a/include/linux/fsnotify_backend.h b/include/linux/fsnotify_backend.h
index 9560734759fa..d7d96c806bff 100644
--- a/include/linux/fsnotify_backend.h
+++ b/include/linux/fsnotify_backend.h
@@ -518,8 +518,8 @@ struct fsnotify_mark {
 	struct hlist_node obj_list;
 	/* Head of list of marks for an object [mark ref] */
 	struct fsnotify_mark_connector *connector;
-	/* Events types to ignore [mark->lock, group->mark_mutex] */
-	__u32 ignored_mask;
+	/* Events types and flags to ignore [mark->lock, group->mark_mutex] */
+	__u32 ignore_mask;
 	/* General fsnotify mark flags */
 #define FSNOTIFY_MARK_FLAG_ALIVE		0x0001
 #define FSNOTIFY_MARK_FLAG_ATTACHED		0x0002
@@ -529,6 +529,7 @@ struct fsnotify_mark {
 	/* fanotify mark flags */
 #define FSNOTIFY_MARK_FLAG_IGNORED_SURV_MODIFY	0x0100
 #define FSNOTIFY_MARK_FLAG_NO_IREF		0x0200
+#define FSNOTIFY_MARK_FLAG_HAS_IGNORE_FLAGS	0x0400
 	unsigned int flags;		/* flags [mark->lock] */
 };
 
@@ -655,15 +656,91 @@ extern void fsnotify_remove_queued_event(struct fsnotify_group *group,
 
 /* functions used to manipulate the marks attached to inodes */
 
-/* Get mask for calculating object interest taking ignored mask into account */
+/*
+ * Canonical "ignore mask" including event flags.
+ *
+ * Note the subtle semantic difference from the legacy ->ignored_mask.
+ * ->ignored_mask traditionally only meant which events should be ignored,
+ * while ->ignore_mask also includes flags regarding the type of objects on
+ * which events should be ignored.
+ */
+static inline __u32 fsnotify_ignore_mask(struct fsnotify_mark *mark)
+{
+	__u32 ignore_mask = mark->ignore_mask;
+
+	/* The event flags in ignore mask take effect */
+	if (mark->flags & FSNOTIFY_MARK_FLAG_HAS_IGNORE_FLAGS)
+		return ignore_mask;
+
+	/*
+	 * Legacy behavior:
+	 * - Always ignore events on dir
+	 * - Ignore events on child if parent is watching children
+	 */
+	ignore_mask |= FS_ISDIR;
+	ignore_mask &= ~FS_EVENT_ON_CHILD;
+	ignore_mask |= mark->mask & FS_EVENT_ON_CHILD;
+
+	return ignore_mask;
+}
+
+/* Legacy ignored_mask - only event types to ignore */
+static inline __u32 fsnotify_ignored_events(struct fsnotify_mark *mark)
+{
+	return mark->ignore_mask & ALL_FSNOTIFY_EVENTS;
+}
+
+/*
+ * Check if mask (or ignore mask) should be applied depending if victim is a
+ * directory and whether it is reported to a watching parent.
+ */
+static inline bool fsnotify_mask_applicable(__u32 mask, bool is_dir,
+					    int iter_type)
+{
+	/* Should mask be applied to a directory? */
+	if (is_dir && !(mask & FS_ISDIR))
+		return false;
+
+	/* Should mask be applied to a child? */
+	if (iter_type == FSNOTIFY_ITER_TYPE_PARENT &&
+	    !(mask & FS_EVENT_ON_CHILD))
+		return false;
+
+	return true;
+}
+
+/*
+ * Effective ignore mask taking into account if event victim is a
+ * directory and whether it is reported to a watching parent.
+ */
+static inline __u32 fsnotify_effective_ignore_mask(struct fsnotify_mark *mark,
+						   bool is_dir, int iter_type)
+{
+	__u32 ignore_mask = fsnotify_ignored_events(mark);
+
+	if (!ignore_mask)
+		return 0;
+
+	/* For non-dir and non-child, no need to consult the event flags */
+	if (!is_dir && iter_type != FSNOTIFY_ITER_TYPE_PARENT)
+		return ignore_mask;
+
+	ignore_mask = fsnotify_ignore_mask(mark);
+	if (!fsnotify_mask_applicable(ignore_mask, is_dir, iter_type))
+		return 0;
+
+	return ignore_mask & ALL_FSNOTIFY_EVENTS;
+}
+
+/* Get mask for calculating object interest taking ignore mask into account */
 static inline __u32 fsnotify_calc_mask(struct fsnotify_mark *mark)
 {
 	__u32 mask = mark->mask;
 
-	if (!mark->ignored_mask)
+	if (!fsnotify_ignored_events(mark))
 		return mask;
 
-	/* Interest in FS_MODIFY may be needed for clearing ignored mask */
+	/* Interest in FS_MODIFY may be needed for clearing ignore mask */
 	if (!(mark->flags & FSNOTIFY_MARK_FLAG_IGNORED_SURV_MODIFY))
 		mask |= FS_MODIFY;
 
@@ -671,7 +748,7 @@ static inline __u32 fsnotify_calc_mask(struct fsnotify_mark *mark)
 	 * If mark is interested in ignoring events on children, the object must
 	 * show interest in those events for fsnotify_parent() to notice it.
 	 */
-	return mask | (mark->ignored_mask & ALL_FSNOTIFY_EVENTS);
+	return mask | mark->ignore_mask;
 }
 
 /* Get mask of events for a list of marks */