Re: usb-mount (hotplug + desktop hooks)

[Ajay <a_ajay_sr@yahoo.com>]

I've been thinking of a linux automount utility for
USB MSD compliant devices that works in conjunction
with hotplug. I basically read /proc/bus/usb/devices,
get the vid-pid-serial, read /proc/scsi/scsi to check
for SCSI devices, then read /proc/scsi/usb-storage-*/*
for the vid-pid-serial match (from the GUID). Now
since the serial match is vital for device
identification, this sort of shakes me up a bit.

> > The larger problem is that there are lots of USB
> storage devices
> > that don't have (or require) a serial number at
> all.  How are you
> > handling those?

AFAIK MSD Devices all need a serial number. Is that
right?

> Things get a little more confusing because, if a
> usb-device's serial
> changes when ever the device is unplugged and
> replugged, it will 
> march down the scsi bus.  For example, plug it in
> once and
> it appears as /dev/sda, unplug it and plug it in
> again and it will
> be /dev/sdb, then /dev/sdc, and so on. I suspect
> this is because 
> the usb-serial keeps changing.  

Again, AFAIK the serial can be changed only if the
Device firmware is flashed. Assuming a user will flash
it before plugging it in each time seems to be an
overkill.

> The only way I found
> to clear this 
> up is to unload the usb-storage module.

Also, the fact is that /dev/sda, etc. are only
'relative labels' - i.e. if you had plugged in a
device before the one you're using, _that_ would have
been /dev/sda and your device /dev/sdb, even if the
serial hasn't changed (this after unloading - loading
the usb-storage module). 

Thanks and regards
Ajay
--------------------------------
  I'm not
> sure if the kernel 
> can deal with this nicely - because, if it did, I
> think it would
> exhibit bad behaviour for devices that do have a
> constant serial.
> On the other hand, should a device hold onto
> /dev/sda a week after
> you unplugged it just because you haven't rebooted
> since - I guess
> the it should have a lease that times out.  
> 
> This is a messy business. I suspect the best that
> can be done 
> is to create a desktop folder where USB devices come
> and go.  
> Each device should named as meaningfully as possible
> and have 
> a tool-tip with as much info as can be retrieved
> about he 
> identity of the device (Manufacturer, Name, etc).
> But ultimately 
> the user must figure out which device is which by
> inspection.
> 
> Yeah - volume labels aren't likely - but if Linux
> becomes the
> the platform of choice, we can try and make it so.
> 
> I haven't had time to check out what 2.5 is up to in
> respect to
> the above issues - has anyone seen a good summary
> anywhere?
> 
> Michael
> 
> On Tue, 05 Nov 2002 05:38, Gary_Lerhaupt@Dell.com
> wrote:
> > Are these physically separate USB storage devices
> made by the same
> > manufacturer?  Or is this device more like a USB
> card reader and you are
> > having problems differentiating between the cards
> that you put into the
> > reader?  I have a feeling its the first case,
> which is unfortunate because
> > with a bad ID like "1f00" for both, devlabel won't
> work for you.  Or, at
> > least it would work for you if you only plugged in
> one at a time.
> >
> > If you do go with the one-at-a-time approach, then
> you could create a
> > symlink name to be shared by both like
> /dev/neodio_storage and then go
> > about automounting with /etc/fstab, etc.  However,
> this won't work for both
> > at the same time (as you've seen).
> >
> > I'm interested in the usb-serial idea, though.  
> Where are these kept? 
> > Even if they aren't implemented on many devices,
> I'd still like to add any
> > possible identifier to make devlabel work in more
> scenarios.  You also
> > mention a volume label, but with USB storage
> devices, this isn't likely.
> > Well, at least not on my smart card reader.
> > -Gary
> >
> 
> 
> 
>
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