linux-kernel - Re: [PATCH 10/30] cr: core stuff

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Message-ID: <20090414154139.GA8085@us.ibm.com>
Date:	Tue, 14 Apr 2009 10:41:39 -0500
From:	"Serge E. Hallyn" <serue@...ibm.com>
To:	Alexey Dobriyan <adobriyan@...il.com>
Cc:	akpm@...ux-foundation.org, containers@...ts.linux-foundation.org,
	xemul@...allels.com, dave@...ux.vnet.ibm.com, mingo@...e.hu,
	orenl@...columbia.edu, hch@...radead.org,
	torvalds@...ux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 10/30] cr: core stuff

Quoting Alexey Dobriyan (adobriyan@...il.com):
> On Mon, Apr 13, 2009 at 04:47:01PM -0500, Serge E. Hallyn wrote:
> > Quoting Alexey Dobriyan (adobriyan@...il.com):
> > 
> > Hi Alexey,
> > 
> > as far as I can see, the main differences between this patch and the
> > equivalent in Oren's tree are:
> > 
> > 1. kernel auto-selects container init to freeze
> 
> Note, auto-select part was dropped, userspace is required to pass pid of
> container init exactly. This was done to keep semantic of checkpoint(2)
> small and extendable.

sys_checkpoint() in this patch still finds the child_reaper of the
passed-in pid, doesn't it?  Or are you saying that a later patch in
this set removes that?

> > 2. kernel freezes tasks
> > 3. no objhash taking references
> 
> That's because none needed.

Right while I have opinions on some things in this list, I didn't
mean to imply positions on these items.  My question was:  are
there are differences you want to call out?

> > 4. no hbuf
> 
> hbuf is an optimization to not allocate/free memory for every image.
> For a start it's unnecessary complication, I just kzalloc/dump/kfree.
> 
> > 5. always require CAP_SYS_ADMIN
> > 
> > Are there other differences which you would consider meaningful?  Which
> > do you consider the most important?
> > 
> > Also, since Dave introduced the fops->checkpoint(), we (or at least I)
> > have been struck by the ugly assymetry with checkpoint() being in fops,
> > and restart() not.  Do you have an idea for fixing that?
> 
> Module can legally support C/R for its files.
> In the end it most certainly will end up with module registering restart

Which module?  The module defining a filesystem?

In that case I'm just not clear on how the restart code will know which
fs's file_operations to use to pick a fops->restart() fn.

> hook for file type N.
> 
> Or module registering hook to restart object type N.
> 
> This is for discussion.

Ok, it's just something I've wondered (with both patchsets).

thanks,
-serge
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