linux-kernel - Re: New copyfile system call

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Message-ID: <1364754452.4771.10.camel@leira.trondhjem.org>
Date:	Sun, 31 Mar 2013 18:27:32 +0000
From:	"Myklebust, Trond" <Trond.Myklebust@...app.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>,
	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 Sun, 2013-03-31 at 09:36 +0200, Pavel Machek wrote:
> Hi!
> 
> > >>> 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?
> > 
> > ...and what's the big plan to make this work on anything other than ext4 and btrfs?
> 
> Deleted but open files are from original unix, so it should work on
> anything unixy (minix, ext, ext2, ...).
> 								Pavel

minix, ext, ext2... are not under active development and haven't been
for more than a decade.

Take a look at how many actively used filesystems out there that have
some variant of sillyrename(), and explain what you want to do in those
cases.

-- 
Trond Myklebust
Linux NFS client maintainer

NetApp
Trond.Myklebust@...app.com
www.netapp.com
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