linux-kernel - Re: sysfs: tagged directories not merged completely yet

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Message-ID: <20081008003834.GA8680@kroah.com>
Date:	Tue, 7 Oct 2008 17:38:34 -0700
From:	Greg KH <greg@...ah.com>
To:	"Serge E. Hallyn" <serue@...ibm.com>
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Al Viro <viro@...IV.linux.org.uk>,
	Benjamin Thery <benjamin.thery@...l.net>,
	linux-kernel@...r.kernel.org, Al Viro <viro@....linux.org.uk>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Tejun Heo <tj@...nel.org>
Subject: Re: sysfs: tagged directories not merged completely yet

On Tue, Oct 07, 2008 at 07:12:03PM -0500, Serge E. Hallyn wrote:
> Quoting Greg KH (greg@...ah.com):
> > On Tue, Oct 07, 2008 at 05:54:24PM -0500, Serge E. Hallyn wrote:
> > > Quoting Greg KH (greg@...ah.com):
> > > > On Tue, Oct 07, 2008 at 01:27:17AM -0700, Eric W. Biederman wrote:
> > > > > Unless someone will give an example of how having multiple superblocks
> > > > > sharing inodes is a problem in practice for sysfs and call it good
> > > > > for 2.6.28.  Certainly it shouldn't be an issue if the network namespace
> > > > > code is compiled out.  And it should greatly improve testing of the
> > > > > network namespace to at least have access to sysfs.
> > > > 
> > > > But if the network namespace code is in?  THen we have problems, right?
> > > > And that's the whole point here.
> > > > 
> > > > The fact that you are trying to limit userspace view of in-kernel data
> > > > structures, based on that specific user, is, in my opinion, crazy.
> > > > 
> > > > Why not just keep all users from seeing sysfs, and then have a user
> > > > daemon doing something on top of FUSE if you really want to see this
> > > > kind of stuff.
> > > 
> > > Well the blocker is really that when you create a new network namespace,
> > > it wants to create a new loopback interface, but
> > > /sys/devices/virtual/net/lo already exists.  That's the same issue with
> > > user namespace when the fair scheduler is enabled, which tries to
> > > re-create /sys/kernel/uids/0.
> > > 
> > > Otherwise yeah at least for my own uses, containers wouldn't need to
> > > look at /sys at all.
> > > 
> > > Heck you wouldn't even need FUSE, just mount -t tmpfs /sys/class/net
> > > and manually link the right devices from /sys/devices/virtual/net.
> > 
> > Great, that sounds like a solution.
> > 
> > So tell me again why we need these huge sysfs reworks? :)
> 
> Because :
> 
> > > Well the blocker is really that when you create a new network namespace,

No, wait.  Why would you want to do such a thing in the first place?

> > > it wants to create a new loopback interface, but
> > > /sys/devices/virtual/net/lo already exists.  That's the same issue with
> 
> So at least we'd have to do something to allow creation of 'duplicate'
> devices in different namespaces.  It might be fine if we just ended up
> with /sys/devices/virtual/net/lo, if created in a child net namespace,
> be named /sys/devices/virtual/net/lo.childXYZ.  Then userspace can
> mount -t tmpfs none /sys/class/net and ln -s
> /sys/devices/virtual/net/lo.childXYZ /sys/class/net/lo.

ick.

I agree with Tejun here, what's this whole network namespace stuff, what
problems is it trying to solve and what are its goals?

thanks,

greg k-h
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