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

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Date:	Tue, 10 Jun 2008 10:01:20 +0200
From:	Johannes Berg <johannes@...solutions.net>
To:	Ben Nizette <bn@...sdigital.com>
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 10:12 +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.

> >  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.

> >  3) afaik configfs doesn't actually support the mkdir, ... stuff yet
> >     that you want for virtual interfaces.
> 
> It has all the  mkdir stuff I can think of, can you elaborate?  It
> doesn't have the commitable object support but I just have an 'enabled'
> attribute in there to switch the thing on and off.

I don't remember the specifics, it's been a while, I guess I could be
thinking of the commitable object support; mostly we'd want to configure
many things in one go, even on a live object. Without disabling that
object first, obviously.

johannes

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