linux-kernel - Re: [PATCH 2.6.25-rc2 3/9] Kconfig: Improve init/Kconfig help descriptions

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Date:	Fri, 22 Feb 2008 21:45:39 -0600
From:	"Serge E. Hallyn" <serue@...ibm.com>
To:	Nick Andrew <nick@...k-andrew.net>
Cc:	"Serge E. Hallyn" <serue@...ibm.com>, trivial@...nel.org,
	linux-kernel@...r.kernel.org, Pavel Emelyanov <xemul@...nvz.org>,
	Randy Dunlap <randy.dunlap@...cle.com>,
	Paul Menage <menage@...gle.com>, Paul Jackson <pj@....com>,
	Valdis Kletnieks <Valdis.Kletnieks@...edu>
Subject: Re: [PATCH 2.6.25-rc2 3/9] Kconfig: Improve init/Kconfig help
	descriptions - NAMESPACES

Quoting Nick Andrew (nick@...k-andrew.net):
> On Fri, Feb 22, 2008 at 04:14:12PM -0600, Serge E. Hallyn wrote:
> > Quoting Nick Andrew (nick@...k-andrew.net):
> > >  config UTS_NS
> > >  	bool "UTS namespace"
> > >  	depends on NAMESPACES
> > >  	help
> > > -	  In this namespace tasks see different info provided with the
> > > -	  uname() system call
> > > +	  Enable support for multiple UTS system attributes.
> > > +
> > > +	  Each UTS namespace provides an individual view of the
> > > +	  information returned by the uname() system call including
> > > +	  hostname, kernel version and domain name.
> > > +
> > > +	  This is used by container systems (e.g. vservers) so that
> > > +	  each container has its own hostname and other attributes.
> > > +	  Tasks in the container are placed in the UTS namespace
> > > +	  corresponding to the container.
> > 
> > this paragraph reads a little weird...  really what happens is that
> > each forked task is in the same UTS namespace as its parent, unless
> > it was cloned with CLONE_NEWUTS or has done unshare(CLONE_NEWUTS),
> > in which case it receives a copy.
> 
> You mean only the third paragraph, right? I hope the other two are
> accurate.
> 
> I'm trying to describe how the feature is used by container systems
> and my description is obviously inaccurate. There are subtle semantic
> differences between the way the different namespaces work, which you've
> pointed out. I think mentioning CLONE_NEWUTS or other flags is too
> technical for help descriptions.
> 
> For UTS_NS and IPC_NS I think I could remove that paragraph because
> the end user hint "Answer Y if you will be using a container system"
> remains. For USER_NS and PID_NS however, these features are tagged
> EXPERIMENTAL so the hint is "If unsure, say N" and I think I need
> to at least mention the use in container systems or find some better
> clarifying description which doesn't get too technical.
> 
> > > +	  This is used by container systems (e.g. vservers).
> > > +	  Tasks in the container are placed in the IPC namespace
> > > +	  corresponding to the container.
> > 
> > Same as with UTS, except that upon CLONE_NEWIPC the task receives a
> > blank new ipc namespace, not a copy of the original.
> 
> Per above my response is to remove the paragraph.
> 
> > >  config PID_NS
> > > [...]
> > >  	default n
> > >  	depends on NAMESPACES && EXPERIMENTAL
> > >  	help
> > > -	  Suport process id namespaces.  This allows having multiple
> > > -	  process with the same pid as long as they are in different
> > > -	  pid namespaces.  This is a building block of containers.
> > > +	  Enable experimental support for hierarchical process id namespaces.
> > > 
> > > -	  Unless you want to work with an experimental feature
> > > -	  say N here.
> > > +	  This is a function used by container-based virtualisation
> > > +	  systems (e.g. vservers).  Each process will have a distinct
> > > +	  Process ID in each PID namespace which the process is in.
> > > +	  Processes in the container are placed in the PID namespace
> > > +	  corresponding to the container, and cannot see or affect
> > > +	  processes in any parent PID namespace.
> > 
> > A cloned process inherits the pid namespace hierarchy from its
> > parent.  If it was cloned with CLONE_NEWPID, the hierarchy is
> > topped with one additional newly created pid namespace.  This
> > is the only pid namespace in which the new process will be able
> > to see processes, while it will be visible in all namespaces in
> > its pidns hierarchy.
> 
> Yes, I understand that. Would you agree that your problem is with the
> wording "Processes in the container are placed in the PID namespace
> corresponding to the container"? And that this is the part that needs
> to be fixed?

Yup.

thanks,
-serge

> ... todo = revisit these descriptions soon, not today though
> 
> Nick.
> -- 
> PGP Key ID = 0x418487E7                      http://www.nick-andrew.net/
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