fsnotify: add FSNOTIFY_EVENT_RENAME data type

Add a new fsnotify_rename_data struct and FSNOTIFY_EVENT_RENAME data
type that carries both the moved dentry and the inode that was
overwritten by the rename (if any).

Update fsnotify_data_inode(), fsnotify_data_dentry(), and
fsnotify_data_sb() to handle the new type, and add a new
fsnotify_data_rename_target() helper for extracting the overwritten
target inode.

Update fsnotify_move() to use the new data type for FS_RENAME and
FS_MOVED_TO events, passing the overwritten target inode through the
event data. FS_MOVED_FROM is unchanged since the source directory
doesn't need overwrite information.

This is done so that fsnotify consumers like nfsd can atomically
observe the overwritten file when a rename replaces an existing entry,
without needing a separate FS_DELETE event.

Assisted-by: Claude (Anthropic Claude Code)
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Jeff Layton <jlayton@kernel.org>
Link: https://patch.msgid.link/20260428-dir-deleg-v3-7-5a0780ba9def@kernel.org
Acked-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>

2 files changed, 26 insertions, 2 deletions

diff --git a/include/linux/fsnotify.h b/include/linux/fsnotify.h
index 079c18bcdbde..bda798bc67bc 100644
--- a/include/linux/fsnotify.h
+++ b/include/linux/fsnotify.h
@@ -257,6 +257,10 @@ static inline void fsnotify_move(struct inode *old_dir, struct inode *new_dir,
 	__u32 new_dir_mask = FS_MOVED_TO;
 	__u32 rename_mask = FS_RENAME;
 	const struct qstr *new_name = &moved->d_name;
+	struct fsnotify_rename_data rd = {
+		.moved = moved,
+		.target = target,
+	};
 
 	if (isdir) {
 		old_dir_mask |= FS_ISDIR;
@@ -265,12 +269,12 @@ static inline void fsnotify_move(struct inode *old_dir, struct inode *new_dir,
 	}
 
 	/* Event with information about both old and new parent+name */
-	fsnotify_name(rename_mask, moved, FSNOTIFY_EVENT_DENTRY,
+	fsnotify_name(rename_mask, &rd, FSNOTIFY_EVENT_RENAME,
 		      old_dir, old_name, 0);
 
 	fsnotify_name(old_dir_mask, source, FSNOTIFY_EVENT_INODE,
 		      old_dir, old_name, fs_cookie);
-	fsnotify_name(new_dir_mask, source, FSNOTIFY_EVENT_INODE,
+	fsnotify_name(new_dir_mask, &rd, FSNOTIFY_EVENT_RENAME,
 		      new_dir, new_name, fs_cookie);
 
 	if (target)
diff --git a/include/linux/fsnotify_backend.h b/include/linux/fsnotify_backend.h
index 66e185bd1b1b..f8c8fb7f34ae 100644
--- a/include/linux/fsnotify_backend.h
+++ b/include/linux/fsnotify_backend.h
@@ -311,6 +311,7 @@ enum fsnotify_data_type {
 	FSNOTIFY_EVENT_DENTRY,
 	FSNOTIFY_EVENT_MNT,
 	FSNOTIFY_EVENT_ERROR,
+	FSNOTIFY_EVENT_RENAME,
 };
 
 struct fs_error_report {
@@ -335,6 +336,11 @@ struct fsnotify_mnt {
 	u64 mnt_id;
 };
 
+struct fsnotify_rename_data {
+	struct dentry *moved;	/* the dentry that was renamed */
+	struct inode *target;	/* inode overwritten by rename, or NULL */
+};
+
 static inline struct inode *fsnotify_data_inode(const void *data, int data_type)
 {
 	switch (data_type) {
@@ -348,6 +354,8 @@ static inline struct inode *fsnotify_data_inode(const void *data, int data_type)
 		return d_inode(file_range_path(data)->dentry);
 	case FSNOTIFY_EVENT_ERROR:
 		return ((struct fs_error_report *)data)->inode;
+	case FSNOTIFY_EVENT_RENAME:
+		return d_inode(((const struct fsnotify_rename_data *)data)->moved);
 	default:
 		return NULL;
 	}
@@ -363,6 +371,8 @@ static inline struct dentry *fsnotify_data_dentry(const void *data, int data_typ
 		return ((const struct path *)data)->dentry;
 	case FSNOTIFY_EVENT_FILE_RANGE:
 		return file_range_path(data)->dentry;
+	case FSNOTIFY_EVENT_RENAME:
+		return ((struct fsnotify_rename_data *)data)->moved;
 	default:
 		return NULL;
 	}
@@ -395,6 +405,8 @@ static inline struct super_block *fsnotify_data_sb(const void *data,
 		return file_range_path(data)->dentry->d_sb;
 	case FSNOTIFY_EVENT_ERROR:
 		return ((struct fs_error_report *) data)->sb;
+	case FSNOTIFY_EVENT_RENAME:
+		return ((const struct fsnotify_rename_data *)data)->moved->d_sb;
 	default:
 		return NULL;
 	}
@@ -430,6 +442,14 @@ static inline struct fs_error_report *fsnotify_data_error_report(
 	}
 }
 
+static inline struct inode *fsnotify_data_rename_target(const void *data,
+							int data_type)
+{
+	if (data_type == FSNOTIFY_EVENT_RENAME)
+		return ((const struct fsnotify_rename_data *)data)->target;
+	return NULL;
+}
+
 static inline const struct file_range *fsnotify_data_file_range(
 							const void *data,
 							int data_type)