linux-kernel - Re: New copyfile system call

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Date:	Sat, 30 Mar 2013 19:21:07 -0400
From:	Ric Wheeler <rwheeler@...hat.com>
To:	"Myklebust, Trond" <Trond.Myklebust@...app.com>
CC:	Pavel Machek <pavel@....cz>, Andreas Dilger <adilger@...ger.ca>,
	Jörn Engel <joern@...fs.org>,
	Andy Lutomirski <luto@...capital.net>,
	Zach Brown <zab@...hat.com>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Linux FS Devel <linux-fsdevel@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Chris L. Mason" <clmason@...ionio.com>,
	Christoph Hellwig <hch@...radead.org>,
	Alexander Viro <aviro@...hat.com>,
	"Martin K. Petersen" <mkp@....net>, Hannes Reinecke <hare@...e.de>,
	Joel Becker <jlbec@...lplan.org>
Subject: Re: New copyfile system call - discuss before LSF?

On 03/30/2013 05:57 PM, Myklebust, Trond wrote:
> On Mar 30, 2013, at 5:45 PM, Pavel Machek <pavel@....cz>
>   wrote:
>
>> On Sat 2013-03-30 13:08:39, Andreas Dilger wrote:
>>> On 2013-03-30, at 12:49 PM, Pavel Machek wrote:
>>>> Hmm, really? AFAICT it would be simple to provide an
>>>> open_deleted_file("directory") syscall. You'd open_deleted_file(),
>>>> copy source file into it, then fsync(), then link it into filesystem.
>>>>
>>>> That should have atomicity properties reflected.
>>> Actually, the open_deleted_file() syscall is quite useful for many
>>> different things all by itself.  Lots of applications need to create
>>> temporary files that are unlinked at application failure (without a
>>> race if app crashes after creating the file, but before unlinking).
>>> It also avoids exposing temporary files into the namespace if other
>>> applications are accessing the directory.
>> Hmm. open_deleted_file() will still need to get a directory... so it
>> will still need a path. Perhaps open("/foo/bar/mnt", O_DELETED) would
>> be acceptable interface?
>> 									Pavel
> ...and what's the big plan to make this work on anything other than ext4 and btrfs?
>
> Cheers,
>    Trond

I know that change can be a good thing, but are we really solving a pressing 
problem given that application developers have dealt with open/rename as the way 
to get "atomic" file creation for several decades now ?

Regards,

Ric

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