Subject: Re: checkpoint/restart ABI
From: Dave Hansen <dave@linux.vnet.ibm.com>
To: Oren Laadan <orenl@cs.columbia.edu>
Cc: Jeremy Fitzhardinge <jeremy@goop.org>, Theodore Tso <tytso@mit.edu>,
       Daniel Lezcano <daniel.lezcano@fr.ibm.com>,
       Arnd Bergmann <arnd@arndb.de>, containers@lists.linux-foundation.org,
       linux-kernel@vger.kernel.org, Peter Chubb <peterc@gelato.unsw.edu.au>
In-Reply-To: <48AC929C.9030901@cs.columbia.edu>
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Date: Wed, 20 Aug 2008 15:11:54 -0700
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On Wed, 2008-08-20 at 17:54 -0400, Oren Laadan wrote:
> > Me, personally, I think I'd probably "re-link" the thing, mark it as
> > such, ship it across like a normal file, then unlink it after the
> > restore.  I don't know what we'd choose when actually implementing
> it.  
> 
> Re-linking works well when the file system supports that - some do not
> allow this, in which case you need to silently rename instead of really
> un-linking (even with NFS), or copy the entire contents.

Yeah, it will certainly be fs-dependent.

This might be a good application for splice.

	open("/tmp/linked-newfile", O_RDONLY, perms);
	splice(unlinked_fd, NULL, new_fd, NULL, MAX_INT, SPLICE_F_MOVE);

I'm not sure if it can re-use the blocks on the fs for this, but it
probably doesn't matter.  

-- Dave

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