linux-kernel - Re: Is configfs the right solution for configuration based fs?

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Date:	Wed, 11 Jun 2008 08:12:58 +1000
From:	Ben Nizette <bn@...sdigital.com>
To:	Johannes Berg <johannes@...solutions.net>
Cc:	"Luis R. Rodriguez" <mcgrof@...il.com>,
	linux-wireless <linux-wireless@...r.kernel.org>,
	linux kernel <linux-kernel@...r.kernel.org>,
	Greg KH <greg@...ah.com>, Joel Becker <joel.becker@...cle.com>,
	Satyam Sharma <ssatyam@....iitk.ac.in>,
	Felix Fietkau <nbd@...nwrt.org>,
	Al Viro <viro@....linux.org.uk>,
	"H. Peter Anvin" <hpa@...nel.org>
Subject: Re: Is configfs the right solution for configuration based fs?


On Tue, 2008-06-10 at 10:01 +0200, Johannes Berg wrote:
> On Tue, 2008-06-10 at 10:12 +1000, Ben Nizette wrote:
> > On Mon, 2008-06-09 at 11:03 +0200, Johannes Berg wrote:
> > 
> > > Personally, I have a few issues with this:
> > >  1) why bother with a second configuration interface that we have to
> > >     maintain, adjust, ...? if we need scriptable access, then make a
> > >     good userspace tool that is scriptable.
> > 
> > What's the first one, sysfs..?  ioctl (eww..)?  
> 
> netlink.

Ah right.  Netlink is indeed a nice interface for this kind of network
device configuration, I'd probably use that for this task too.

Of course, it isn't a general solution to the problem.  If I were
answering the question in $(SUBJECT) I'd say configfs is a good choice.
In the specific case of network devices, you're lucky enough to have
something more specifically tailored to your needs already.

> 
> > >  2) string-based stuff is often messy, especially the varying attributes
> > >     like MAC addresses etc. Unless we just use binary files again, which
> > >     is not very useful again. Take, for example, the monitor flags. If
> > >     we use the same flags then nobody really knows what's up 
> > >     (echo 0x3 > mntr_flags?) and if we use strings then we cannot easily
> > >     ever rename the flag while keeping ABI/API compatibility.
> > 
> > Not sure I see the argument here, why would you want to change the flag
> > name?  If you decide the old name is stupid then can't you just alias
> > the old name to the new one?
> 
> Sure can do, but it just adds a lot of complexity to the kernel. I don't
> see the point, it's not like you need a lot of code to build netlink
> messages. Heck, I've done it by _hand_ and used just netlink sockets.
> It's not a lot of code.
> 
> > String handling is always a bit iffy, though it has to be done
> > somewhere, either in kernel or in your "good userspace tool which is
> > scriptable".  I'd prefer to have it done once, well, in the kernel and
> > not have to ship more software than necessary.
> 
> I personally prefer to put it into userspace.

Yeah, personal preference here.  I come from an embedded background and
have an aversion to tracking more userspace tools than I have to.  This
mainly comes from the fact uClibc (an embedded C library) doesn't
maintain binary compatibility across releases; each time a bugfix comes
out for that my entire userspace needs to be recompiled.  Each userspace
tool I add to my build scripts makes me die a little inside ;-)


	--Ben.


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