linux-kernel - Re: New copyfile system call

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Message-Id: <BF9B5AA3-79C2-424F-8969-53269338F049@gmail.com>
Date:	Sat, 30 Mar 2013 22:38:35 -0700
From:	AEDilger Gmail <aedilger@...il.com>
To:	Pavel Machek <pavel@....cz>
Cc:	Andreas Dilger <adilger@...ger.ca>,
	Jörn Engel <joern@...fs.org>,
	Andy Lutomirski <luto@...capital.net>,
	Zach Brown <zab@...hat.com>,
	"Myklebust, Trond" <Trond.Myklebust@...app.com>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Ric Wheeler <rwheeler@...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 2013-03-30, at 14:45, 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?

Yes, that would be reasonable, and/or possibly openat(fd, NULL, AT_FDCWD|AT_UNLINKED)?

Cheers, Andreas--
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