fs: new helper: simple_rename_timestamp

JIRA: https://issues.redhat.com/browse/RHEL-27743
Conflicts:
  * include/linux/fs.h: minor context difference due to RHEL9 missing
      upstream commit e18275a ("fs: port ->rename() to pass mnt_idmap")

This patch is a backport of the following upstream commit:
commit 0c47679
Author: Jeff Layton <[email protected]>
Date:   Wed Jul 5 14:58:11 2023 -0400

    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 <[email protected]>
    Reviewed-by: Jan Kara <[email protected]>
    Message-Id: <[email protected]>
    Signed-off-by: Christian Brauner <[email protected]>

Signed-off-by: Rafael Aquini <[email protected]>

Author: Rafael Aquini

fs/libfs.c

@@ -446,6 +446,31 @@ 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)
 {
@@ -461,11 +486,7 @@ 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);
@@ -474,7 +495,6 @@ int simple_rename(struct user_namespace *mnt_userns, 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))
@@ -497,9 +517,7 @@ int simple_rename(struct user_namespace *mnt_userns, 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

@@ -3424,6 +3424,8 @@ 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 user_namespace *, struct inode *,