linux-kernel - Re: [RFC][PATCH 1/4] checkpoint-restart: general infrastructure

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Message-ID: <20080814055301.GH6995@ucw.cz>
Date:	Thu, 14 Aug 2008 07:53:02 +0200
From:	Pavel Machek <pavel@...e.cz>
To:	"Serge E. Hallyn" <serue@...ibm.com>
Cc:	Dave Hansen <dave@...ux.vnet.ibm.com>,
	Arnd Bergmann <arnd@...db.de>,
	containers@...ts.linux-foundation.org,
	Theodore Tso <tytso@....edu>, linux-kernel@...r.kernel.org
Subject: Re: [RFC][PATCH 1/4] checkpoint-restart: general infrastructure

Hi!

> > > > I have to wonder if this is just a symptom of us trying to do this the
> > > > wrong way.  We're trying to talk the kernel into writing internal gunk
> > > > into a FD.  You're right, it is like a splice where one end of the pipe
> > > > is in the kernel.
> > > > 
> > > > Any thoughts on a better way to do this?  
> > > 
> > > Maybe you can invert the logic and let the new syscalls create a file
> > > descriptor, and then have user space read or splice the checkpoint
> > > data from it, and restore it by writing to the file descriptor.
> > > It's probably easy to do using anon_inode_getfd() and would solve this
> > > problem, but at the same time make checkpointing the current thread
> > > hard if not impossible.
> > 
> > Yeah, it does seem kinda backwards.  But, instead of even having to
> > worry about the anon_inode stuff, why don't we just put it in a fs like
> > everything else?  checkpointfs!
> 
> One reason is that I suspect that stops us from being able to send that
> data straight to a pipe to compress and/or send on the network, without
> hitting local disk.  Though if the checkpointfs was ram-based maybe not?
> 
> As Oren has pointed out before, passing in an fd means we can pass a
> socket into the syscall.

If you do pass a socket, will it handle blocking correctly? Getting
deadlocked task would be bad. What happens if I try to snapshot into
/proc/self/fd/0 ? Or maybe restore from /proc/cmdline?

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