Re: hotpluggable ide cd-rom drive?

["Kari Karhi" <karhi@hotmail.com>]

Hi,
so let me try to summarize for my own understanding.  Comments are welcome.

1. The mechanism used to probe the hardware for new devices during boot can
not be used later during normal operation of the os.  This prevents linux
from running the ide-probe again and updating the device maps.  Therefore
there can be no user level commands one could run after plugging in a
hot-pluggable device, that would find the device and add it to the device
maps.

2. The hot-plug mechanism is specific to the system hardware and is not
standardised.  This prevents linux from finding out that new hardware has
been added, and automagically adding the hot-plugged devices.

3. It is not possible to guess the device map and to build it from some
static file at boot time (e.g. boot hdc=hotplug fd0=hotplug).  This would
allow the device to always be there, but if you try to access it before it
is plugged in, you would get failures and time-outs.

So none of the above mechanisms would work?
Cheers,
    Kari

----- Original Message -----
From: "Oliver Neukum" <oliver@neukum.name>
To: "Greg KH" <greg@kroah.com>
Cc: "Kari Karhi" <karhi@hotmail.com>;
<linux-hotplug-devel@lists.sourceforge.net>
Sent: Monday, March 17, 2003 2:44 PM
Subject: Re: hotpluggable ide cd-rom drive?


Am Montag, 17. März 2003 20:09 schrieb Greg KH:
> On Mon, Mar 17, 2003 at 08:05:21PM +0100, Oliver Neukum wrote:
> > Am Montag, 17. März 2003 18:50 schrieb Greg KH:
> > > On Mon, Mar 17, 2003 at 06:56:28AM -0600, Kari Karhi wrote:
> > > > Is there a user level command to kick the ide-probe module into
> > > > probing the ide bus again?  Or is work going on to get the kernel to
> > > > support hot-pluggable ide drives?  Or am I just missing some
> > > > configuration parameter?
> > >
> > > Unfortunately this is usually done in a hardware specific way, and
> > > since neither Dell, nor any other laptop manufacturer has provided the
> > > specs for how to detect and do this kind of hot-swap, Linux does not
> > > support it.
> >
> > Not entirely true. It's supported in Apple Powerbooks.
>
> Oh, forgot, some laptops support this if you suspend to ram, swap out
> the drive, and then resume.  Works for some APM based laptops, don't
> know about ACPI based ones.

Powerbooks do it on a live system. Look at drivers/macintosh/mediabay.c.

> > What happens if we suspend to disk and wake up with a changed drive ?
>
> Heh, I don't want to think about that :)

Let me guess, you have an aversion against horror movies? ;-)

Seriously, looking power.c::device_resume()  the code assumes that
resumption
is always successful. That is bad. Error codes need to be returned and
evaluated.

Regards
Oliver




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