Re: New reflink(2) syscall

[Joel Becker <Joel.Becker@oracle.com>]

On Mon, May 04, 2009 at 12:59:39PM -0400, Stephen Smalley wrote:
> On Tue, 2009-05-05 at 01:35 +1000, James Morris wrote:
> > What's fundamentally different, though, that the process would only be 
> > able to then modify the data in a subsequent syscall?
> 
> Since the data doesn't flow through the process at all, it can neither
> be leaked nor modified by the process.  Whereas normally the data would
> be copied into the memory of the process (and potentially leaked
> elsewhere) and the process could write any arbitrary data it liked to
> the new file.  As a result, one might be willing to allow reflink(2) in
> situations where one would not be willing to allow a userspace file
> copy.

	Oh, that's a good point.  A process using reflink(2) to make a
snapshot can do the snap but not modify.  That's neat.

Joel

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Joel Becker
Principal Software Developer
Oracle
E-mail: joel.becker@oracle.com
Phone: (650) 506-8127