fs: new helper: simple_rename_timestamp

A rename potentially involves updating 4 different inode timestamps. Add
a function that handles the details sanely, and convert the libfs.c
callers to use it.
Signed-off-by: Jeff Layton <jlayton@kernel.org>
Reviewed-by: Jan Kara <jack@suse.cz>
Message-Id: <20230705185812.579118-3-jlayton@kernel.org>
Signed-off-by: Christian Brauner <brauner@kernel.org>

fs/libfs.c

@@ -444,6 +444,31 @@ int simple_rmdir(struct inode *dir, struct dentry *dentry)
 }
 EXPORT_SYMBOL(simple_rmdir);
 
+/**
+ * simple_rename_timestamp - update the various inode timestamps for rename
+ * @old_dir: old parent directory
+ * @old_dentry: dentry that is being renamed
+ * @new_dir: new parent directory
+ * @new_dentry: target for rename
+ *
+ * POSIX mandates that the old and new parent directories have their ctime and
+ * mtime updated, and that inodes of @old_dentry and @new_dentry (if any), have
+ * their ctime updated.
+ */
+void simple_rename_timestamp(struct inode *old_dir, struct dentry *old_dentry,
+			     struct inode *new_dir, struct dentry *new_dentry)
+{
+	struct inode *newino = d_inode(new_dentry);
+
+	old_dir->i_mtime = inode_set_ctime_current(old_dir);
+	if (new_dir != old_dir)
+		new_dir->i_mtime = inode_set_ctime_current(new_dir);
+	inode_set_ctime_current(d_inode(old_dentry));
+	if (newino)
+		inode_set_ctime_current(newino);
+}
+EXPORT_SYMBOL_GPL(simple_rename_timestamp);
+
 int simple_rename_exchange(struct inode *old_dir, struct dentry *old_dentry,
 			   struct inode *new_dir, struct dentry *new_dentry)
 {
@@ -459,11 +484,7 @@ int simple_rename_exchange(struct inode *old_dir, struct dentry *old_dentry,
 			inc_nlink(old_dir);
 		}
 	}
-	old_dir->i_ctime = old_dir->i_mtime =
-	new_dir->i_ctime = new_dir->i_mtime =
-	d_inode(old_dentry)->i_ctime =
-	d_inode(new_dentry)->i_ctime = current_time(old_dir);
-
+	simple_rename_timestamp(old_dir, old_dentry, new_dir, new_dentry);
 	return 0;
 }
 EXPORT_SYMBOL_GPL(simple_rename_exchange);
@@ -472,7 +493,6 @@ int simple_rename(struct mnt_idmap *idmap, struct inode *old_dir,
 		  struct dentry *old_dentry, struct inode *new_dir,
 		  struct dentry *new_dentry, unsigned int flags)
 {
-	struct inode *inode = d_inode(old_dentry);
 	int they_are_dirs = d_is_dir(old_dentry);
 
 	if (flags & ~(RENAME_NOREPLACE | RENAME_EXCHANGE))
@@ -495,9 +515,7 @@ int simple_rename(struct mnt_idmap *idmap, struct inode *old_dir,
 		inc_nlink(new_dir);
 	}
 
-	old_dir->i_ctime = old_dir->i_mtime = new_dir->i_ctime =
-		new_dir->i_mtime = inode->i_ctime = current_time(old_dir);
-
+	simple_rename_timestamp(old_dir, old_dentry, new_dir, new_dentry);
 	return 0;
 }
 EXPORT_SYMBOL(simple_rename);

include/linux/fs.h

@@ -2977,6 +2977,8 @@ extern int simple_open(struct inode *inode, struct file *file);
 extern int simple_link(struct dentry *, struct inode *, struct dentry *);
 extern int simple_unlink(struct inode *, struct dentry *);
 extern int simple_rmdir(struct inode *, struct dentry *);
+void simple_rename_timestamp(struct inode *old_dir, struct dentry *old_dentry,
+			     struct inode *new_dir, struct dentry *new_dentry);
 extern int simple_rename_exchange(struct inode *old_dir, struct dentry *old_dentry,
 				  struct inode *new_dir, struct dentry *new_dentry);
 extern int simple_rename(struct mnt_idmap *, struct inode *,