linux-kernel - Re: [PATCH 05/11] vfs: add RENAME

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Date:	Wed, 15 Jan 2014 19:35:04 +0100
From:	Miklos Szeredi <miklos@...redi.hu>
To:	"J. Bruce Fields" <bfields@...ldses.org>
Cc:	Al Viro <viro@...iv.linux.org.uk>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Linux-Fsdevel <linux-fsdevel@...r.kernel.org>,
	Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Christoph Hellwig <hch@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	David Howells <dhowells@...hat.com>,
	Zach Brown <zab@...hat.com>, Jan Kara <jack@...e.cz>,
	Andy Lutomirski <luto@...capital.net>,
	"mszeredi@...e.cz" <mszeredi@...e.cz>
Subject: Re: [PATCH 05/11] vfs: add RENAME_NOREPLACE flag

On Wed, Jan 15, 2014 at 7:19 PM, J. Bruce Fields <bfields@...ldses.org> wrote:
> On Wed, Jan 08, 2014 at 11:10:09PM +0100, Miklos Szeredi wrote:
>> From: Miklos Szeredi <mszeredi@...e.cz>
>>
>> If this flag is specified and the target of the rename exists then the
>> rename syscall fails with EEXIST.
>
> Why is this useful?
>
> (I'm sure it is, it'd just be useful to have the reasons recorded
> someplace.)
>
>> The VFS does the existence checking, so it is trivial to enable for most
>> local filesystems.  This patch only enables it in ext4.
>>
>> For network filesystems the VFS check is not enough as there may be a race
>> between a remote create and the rename, so these filesystems need to handle
>> this flag in their ->rename() implementations to ensure atomicity.
>
> Till that's done this should probably result in -EOPNOTSUPP on those
> filesystems?
>
> I think this would need new protocol in the NFS case.

Yes, it needs to be enabled on a case-by-case basis.  Only enabled for
ext4 now, but trivial to do for most fs.

Thanks,
Miklos
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