On Sun, Nov 28, 2010 at 11:02:52AM -, Alkis Georgopoulos wrote:
Public bug reported:
In /etc/init.d/nbd-client, I don't see any way that would permit me to
use an nbd-mounted root filesystem and have a clean shutdown process.
With the current code, rmmod nbd is executed and then the client gets
a bunch of read errors instead of shutting down.
It's not the rmmod that is at fault.
When the module is still in use (i.e., the device is still connected),
rmmod will fail since the kernel knows that the driver is still needed.
However, there is no way for nbd-client to know for sure whether a block
device is still in use (as swapspace, with a filesystem, whatever), so
it can't check for that very well. As such, the 'nbd-client -d' might
succeed, even if the block device is still in use.
The initscript has some logic to prevent an 'nbd-client -d' to occur on
a device that is still in use; that's what the KILLALL and the OMITKILL
variables are for.
Test case:
* In /etc/nbd-server/config on the server, I export a whole partition with
an OS in it:
[generic]
[sda2]
exportname = /dev/sda2
port = 10809
Note that port 10809 is supposed to be for name-based exports of the NBD
device, not for the oldstyle exports. What you're doing will work for
now, but will start to fail when you upgrade to an NBD version of 2.9.18
or above.
* In pxelinux.cfg/default on the server, I pass these kernel parameters to
netboot a client:
APPEND ro initrd=nbdclient/initrd.img root=/dev/nbd0
nbdroot=10.160.31.14,10809
ip=10.160.31.101:10.160.31.1:10.160.31.1:255.255.255.0:nbd101:eth0:none
* In the client /etc/network/interfaces (i.e. in /dev/sda2), I put a
manual eth0 to prevent network manager to break the existing
connection.
Then I need the following 2 workarounds so cleanly shutdown:
1) In the client /etc/fstab, I put the following *commented* entry,
just to prevent /etc/init.d/nbd-client from unmounting the root
filesystem on shutdown. Some documentation for a better way to do
that would be appreciated:
Did you find /usr/share/doc/nbd-client/README.Debian ?
#/dev/nbd0/ ext4_netdev,errors=remount-ro 0
1
This should not be necessary (and the grep line that checks for the
device in was changed in a more recent version of the package, so this
will break once you upgrade to natty or beyond)
2) In the client /etc/init.d/nbd-client, I move the marked if after the
rmmod command:
if [ $KILLALL != false ]
then
if [ -d /dev/nbd ]
then
DEVICES=/dev/nbd/*
else
DEVICES=/dev/nb*
fi
- fi
echo Invoking swapoff on NBD devices...
swapoff $DEVICES 2/dev/null
echo Disconnecting $DESCes...
for i in $DEVICES
do
$DAEMON -d $i 2/dev/null /dev/null
done
rmmod nbd
+ fi
If you have set KILLALL=false in the configuration file, then the above
should not be necessary, due to the fact that nbd-client will then not
yank the root device from under your nose anymore.
If you have in fact done so and it still does not work, then something
fishy is going on. In that case, please send your configuration file to
the bugreport, too.
Regards,
--
The biometric identification system at the gates of the CIA headquarters
works because there's a guard with a large gun making sure no one is
trying to fool the system.
http://www.schneier.com/blog/archives/2009/01/biometrics.html
--
Unable to cleanly shutdown with an nbd root filesystem
https://bugs.launchpad.net/bugs/682328
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