ext4: add cross rename support

Implement RENAME_EXCHANGE flag in renameat2 syscall.
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Reviewed-by: Jan Kara <jack@suse.cz>

fs/ext4/namei.c

@@ -3004,6 +3004,8 @@ struct ext4_renament {
 	struct inode *dir;
 	struct dentry *dentry;
 	struct inode *inode;
+	bool is_dir;
+	int dir_nlink_delta;
 
 	/* entry for "dentry" */
 	struct buffer_head *bh;
@@ -3135,6 +3137,17 @@ static void ext4_rename_delete(handle_t *handle, struct ext4_renament *ent)
 	}
 }
 
+static void ext4_update_dir_count(handle_t *handle, struct ext4_renament *ent)
+{
+	if (ent->dir_nlink_delta) {
+		if (ent->dir_nlink_delta == -1)
+			ext4_dec_count(handle, ent->dir);
+		else
+			ext4_inc_count(handle, ent->dir);
+		ext4_mark_inode_dirty(handle, ent->dir);
+	}
+}
+
 /*
  * Anybody can rename anything with this: the permission checks are left to the
  * higher-level routines.
@@ -3274,13 +3287,137 @@ static int ext4_rename(struct inode *old_dir, struct dentry *old_dentry,
 	return retval;
 }
 
+static int ext4_cross_rename(struct inode *old_dir, struct dentry *old_dentry,
+			     struct inode *new_dir, struct dentry *new_dentry)
+{
+	handle_t *handle = NULL;
+	struct ext4_renament old = {
+		.dir = old_dir,
+		.dentry = old_dentry,
+		.inode = old_dentry->d_inode,
+	};
+	struct ext4_renament new = {
+		.dir = new_dir,
+		.dentry = new_dentry,
+		.inode = new_dentry->d_inode,
+	};
+	u8 new_file_type;
+	int retval;
+
+	dquot_initialize(old.dir);
+	dquot_initialize(new.dir);
+
+	old.bh = ext4_find_entry(old.dir, &old.dentry->d_name,
+				 &old.de, &old.inlined);
+	/*
+	 *  Check for inode number is _not_ due to possible IO errors.
+	 *  We might rmdir the source, keep it as pwd of some process
+	 *  and merrily kill the link to whatever was created under the
+	 *  same name. Goodbye sticky bit ;-<
+	 */
+	retval = -ENOENT;
+	if (!old.bh || le32_to_cpu(old.de->inode) != old.inode->i_ino)
+		goto end_rename;
+
+	new.bh = ext4_find_entry(new.dir, &new.dentry->d_name,
+				 &new.de, &new.inlined);
+
+	/* RENAME_EXCHANGE case: old *and* new must both exist */
+	if (!new.bh || le32_to_cpu(new.de->inode) != new.inode->i_ino)
+		goto end_rename;
+
+	handle = ext4_journal_start(old.dir, EXT4_HT_DIR,
+		(2 * EXT4_DATA_TRANS_BLOCKS(old.dir->i_sb) +
+		 2 * EXT4_INDEX_EXTRA_TRANS_BLOCKS + 2));
+	if (IS_ERR(handle))
+		return PTR_ERR(handle);
+
+	if (IS_DIRSYNC(old.dir) || IS_DIRSYNC(new.dir))
+		ext4_handle_sync(handle);
+
+	if (S_ISDIR(old.inode->i_mode)) {
+		old.is_dir = true;
+		retval = ext4_rename_dir_prepare(handle, &old);
+		if (retval)
+			goto end_rename;
+	}
+	if (S_ISDIR(new.inode->i_mode)) {
+		new.is_dir = true;
+		retval = ext4_rename_dir_prepare(handle, &new);
+		if (retval)
+			goto end_rename;
+	}
+
+	/*
+	 * Other than the special case of overwriting a directory, parents'
+	 * nlink only needs to be modified if this is a cross directory rename.
+	 */
+	if (old.dir != new.dir && old.is_dir != new.is_dir) {
+		old.dir_nlink_delta = old.is_dir ? -1 : 1;
+		new.dir_nlink_delta = -old.dir_nlink_delta;
+		retval = -EMLINK;
+		if ((old.dir_nlink_delta > 0 && EXT4_DIR_LINK_MAX(old.dir)) ||
+		    (new.dir_nlink_delta > 0 && EXT4_DIR_LINK_MAX(new.dir)))
+			goto end_rename;
+	}
+
+	new_file_type = new.de->file_type;
+	retval = ext4_setent(handle, &new, old.inode->i_ino, old.de->file_type);
+	if (retval)
+		goto end_rename;
+
+	retval = ext4_setent(handle, &old, new.inode->i_ino, new_file_type);
+	if (retval)
+		goto end_rename;
+
+	/*
+	 * Like most other Unix systems, set the ctime for inodes on a
+	 * rename.
+	 */
+	old.inode->i_ctime = ext4_current_time(old.inode);
+	new.inode->i_ctime = ext4_current_time(new.inode);
+	ext4_mark_inode_dirty(handle, old.inode);
+	ext4_mark_inode_dirty(handle, new.inode);
+
+	if (old.dir_bh) {
+		retval = ext4_rename_dir_finish(handle, &old, new.dir->i_ino);
+		if (retval)
+			goto end_rename;
+	}
+	if (new.dir_bh) {
+		retval = ext4_rename_dir_finish(handle, &new, old.dir->i_ino);
+		if (retval)
+			goto end_rename;
+	}
+	ext4_update_dir_count(handle, &old);
+	ext4_update_dir_count(handle, &new);
+	retval = 0;
+
+end_rename:
+	brelse(old.dir_bh);
+	brelse(new.dir_bh);
+	brelse(old.bh);
+	brelse(new.bh);
+	if (handle)
+		ext4_journal_stop(handle);
+	return retval;
+}
+
 static int ext4_rename2(struct inode *old_dir, struct dentry *old_dentry,
 			struct inode *new_dir, struct dentry *new_dentry,
 			unsigned int flags)
 {
-	if (flags & ~RENAME_NOREPLACE)
+	if (flags & ~(RENAME_NOREPLACE | RENAME_EXCHANGE))
 		return -EINVAL;
 
+	if (flags & RENAME_EXCHANGE) {
+		return ext4_cross_rename(old_dir, old_dentry,
+					 new_dir, new_dentry);
+	}
+	/*
+	 * Existence checking was done by the VFS, otherwise "RENAME_NOREPLACE"
+	 * is equivalent to regular rename.
+	 */
 	return ext4_rename(old_dir, old_dentry, new_dir, new_dentry);
 }