> On Fri, Oct 08, 1999, danielt@digi.com <danielt@digi.com> wrote:
> > On Fri, 8 Oct 1999, Theodore Y. Ts'o wrote:
> >
> > >
> > > With a /devfs approach, you will still need to readdir() through all of
> > > /devfs, figure out what changed, and then stat the device to see what
> > > has differed. This also limits the information you can read out to what
> > > is the stat()-style interface can provide, and that may not be enough to
> > > give you the USB topology information. I suppose you could use
> > > directories to represent USB hubs, but now you will have to recursively
> > > search a directory tree to find the new devices! See what I mean? It's
> > > a bad way of communicating this kind of information to the user process.
> > >
> > > The advantage of /devfs is that for folks who don't care, they can
> > > simply overmount /dev and be done with it. But in the long term, if you
> > > accept the supposition that you *need* a user-mode daemon, /devfs is an
> > > inefficient interface.
> > >
> > Um, with devfs you do not need a user space daemon, so that daemon does
> > not need to keep track of all the changes to the /dev directory, which
> > promptly renders the rest of the argument irrelevent.
> >
> > If the user plugs in a USB modem, the user knows they plugged in a modem,
> > they run their getty/pppd/minicom on the new modem device.
>
> No, no, no. No one seems to understand the issues at stake here.
>
> I have 2 modems, I plug modem A in first, it becomes (hypothetical)
> device /dev/modem1. I plug in modem B second, it becomes /dev/modem2.
>
> Now, I unplug both and plug modem B in first, it becomes modem1 now with
> the current naming system.
>
> This is completely unacceptable.
>
> Does devfs solve this problem right now? No. Will it be easy to solve
> this problem with devfs when an appropriate algorithm to name PnP
> devices is created. Yes.
>
OK, I think I understand. This is a problem that is more difficult
to solve from a userspace daemon than it is from within the USB
driver itself. All a userspace component would be able to do
here is assign the appropriate name to the device, and with
devfs the USB driver can do that directly. The problem is strictly
with USB device naming so devfs is merely one possible solution.
> > I personally think devfsd is a major mistake. Those who do not
> > use it assume that its features are limited to a set that can
> > apparently be addressed with an rc script. They also assume that
> > it is necessary to use devfs.
>
> Please solve the above problem with an rc script. I have yet to see one
> created and if you could do so, you would greatly advance adoption of
> PnP in Linux.
>
Since devfsd is irrelevant to this problem, so too would be an rc script.
-- Daniel Taylor Senior Test Engineer Digi International danielt@digi.com Open systems win.
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