linux-kernel - Re: [PATCH 04/11] vfs: add renameat2 syscall

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Message-Id: <201401150711.AHB52169.VMSFFLtHQFOOOJ@I-love.SAKURA.ne.jp>
Date:	Wed, 15 Jan 2014 07:11:16 +0900
From:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:	miklos@...redi.hu
Cc:	torvalds@...ux-foundation.org, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, hch@...radead.org,
	akpm@...ux-foundation.org, dhowells@...hat.com, zab@...hat.com,
	jack@...e.cz, luto@...capital.net, mszeredi@...e.cz
Subject: Re: [PATCH 04/11] vfs: add renameat2 syscall

Miklos Szeredi wrote:
> +
> +	if (flags)
> +		return -EOPNOTSUPP;
> +

If (at least for now) only ext4 interprets renameat2() flags,
I think adding a new member to "struct inode_operations" and
check it like

	if (!old_dir->i_op->swapname)
		return -EOPNOTSUPP;

or

	if (!(old_dir->i_op->supported_features & flags))
		return -EOPNOTSUPP;

earlier is smarter than scattering


	if (flags)
		return -EOPNOTSUPP;

into individual rename function.
If we do above change, LSM can omit checking permission for cross rename
operation which after all fails with -EOPNOTSUPP.
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