linux-kernel - Re: New copyfile system call

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Message-ID: <20130331082548.GA15385@amd.pavel.ucw.cz>
Date:	Sun, 31 Mar 2013 10:25:48 +0200
From:	Pavel Machek <pavel@....cz>
To:	AEDilger Gmail <aedilger@...il.com>
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?

Hi!
On Sat 2013-03-30 22:38:35, AEDilger Gmail wrote:
> 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)?

openat() is better interface for this, I'd say.

BTW... I don't think this has to be done at the same time as splice()
[or how it ends up being called] changes...

									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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