usb hotplug problems with 2.6.10

usb hotplug problems with 2.6.10

[Jack Howarth]

Alan,
   I had mentioned a couple weeks back that with kernel 2.6.10, 
the ability to hotplug usb keys in Fedora Core 2 and 3 has been broken.
There is actually a bugzilla report on this with some useful information
on manifestation of the problem....

https://bugzilla.redhat.com/beta/show_bug.cgi?id=119140

The problem can be hacked around for the moment in hotplug by
repeatedly calling updfstab until the device appears in both
/proc/scsi/scsi and /sys/bus/usb/drivers/usb-storage but it 
would be nice is this could be fixed in the kernel. Hasn't any
distributions other than Fedora run into this yet?
                     Jack
The hack recommended by Jason Tibbitts that works around this problem
is...

--- /root/hotplug.functions.sav 2005-02-03 09:17:28.433643468 -0500
+++ hotplug.functions   2005-02-03 09:21:32.336895753 -0500
@@ -146,6 +146,7 @@
                # parameters ... handle per-device parameters in apps
                # (ioctls etc) not in setup scripts or modules.conf
                LOADED=true
+               JUST_LOADED=true
            fi
        else
            # This module is already loaded
@@ -167,7 +168,18 @@
            mesg "missing kernel or user mode driver $MODULE "
        fi
        if echo "$MODULE" | grep -q "usb-storage" > /dev/null 2>&1 ; then
-           [ -x /usr/sbin/updfstab ] &&  /usr/sbin/updfstab
+               if [ -x /usr/sbin/updfstab ]; then
+                       INITIAL_SCSI=$(cat /proc/scsi/scsi | wc -l)
+                       COUNT=10   # (big) upper bound of the loop
+                       while [ $COUNT -gt 0 ]; do
+                               sleep 1
+                               [ "$(cat /proc/scsi/scsi | wc -l)" -gt
+                               "$INITIAL_SCSI" ] && break
+                               COUNT=$(($COUNT - 1))
+                       done
+               fi
+               /usr/sbin/updfstab
+#          [ -x /usr/sbin/updfstab ] &&  /usr/sbin/updfstab
        fi
     done
 }

...its ugly of course but at least hotplugging usb keys work again
under 2.6.10.

Re: usb hotplug problems with 2.6.10

[Greg KH]

On Thu, Feb 03, 2005 at 10:03:10AM -0500, Jack Howarth wrote:
> Alan,
>    I had mentioned a couple weeks back that with kernel 2.6.10, 
> the ability to hotplug usb keys in Fedora Core 2 and 3 has been broken.
> There is actually a bugzilla report on this with some useful information
> on manifestation of the problem....
> 
> https://bugzilla.redhat.com/beta/show_bug.cgi?id=119140
> 
> The problem can be hacked around for the moment in hotplug by
> repeatedly calling updfstab until the device appears in both
> /proc/scsi/scsi and /sys/bus/usb/drivers/usb-storage but it 
> would be nice is this could be fixed in the kernel.

How do you propose "fixing" this in the kernel?  Userspace needs to be
changed to go off of the /dev node showing up, not the usb hotplug event
(which can happen much sooner, as you have found out.)

I would recommend bringing this up with the Fedora developers.

thanks,

greg k-h

Re: usb hotplug problems with 2.6.10

[Jason L Tibbitts III]

>>>>> "JH" == Jack Howarth <howarth@bromo.msbb.uc.edu> writes:

JH> Alan, I had mentioned a couple weeks back that with kernel 2.6.10,
JH> the ability to hotplug usb keys in Fedora Core 2 and 3 has been
JH> broken.

The true issue is a little more complicated than that.  The kernel
issue here is that under 2.6.9 (or Red Hat's versions thereof)
usb-storage devices would be picked up by the SCSI layer immediately
after the usb-storage module became aware of them.  Under Red Hat's
2.6.10 (which currently includes -ac11) there is a delay of
five or ten seconds between the device appearing in
/sys/bus/usb/drivers/usb-storage and it showing up as a SCSI device.

This delay has broken some stuff.  Yes, Red Hat's userland hotplugging
bits made incorrect assumptions and should be fixed.  The question is
whether this kernel delay is intended and, if not, how to fix it.
Even after I've hacked around the userland problems I still have
people asking why it takes so long for their USB keys to show up.

 - J<