On loopback device creation

I was having some problems with loop back device creating & almost immediately detaching; it seems sometimes a kernel thread holds on to the device and the detach fails.
I decided to have a look what's going on so I created a script which automates the creation, attaching and detaching of loopback devices:

# ./test.sh

Creating sparse 4TB file: Done
----START----
Loopback devices currently in use:
Checking for free loopback device: /dev/loop0
Setting up loopback device: Done
Sleeping for 0 seconds.
Breaking down loopback device:
----NEXT PASS----
Loopback devices currently in use:
/dev/loop0
Checking for free loopback device: /dev/loop1
Setting up loopback device: Done
Sleeping for 0 seconds.
Breaking down loopback device:
----NEXT PASS----
Loopback devices currently in use:
/dev/loop0
/dev/loop1
Checking for free loopback device: /dev/loop2
Setting up loopback device: Done
Sleeping for 0 seconds.
Breaking down loopback device:
----NEXT PASS----
Loopback devices currently in use:
/dev/loop0
/dev/loop1
/dev/loop2
Checking for free loopback device: /dev/loop3
Setting up loopback device: Done
Sleeping for 0 seconds.
Breaking down loopback device:
----NEXT PASS----
Loopback devices currently in use:
/dev/loop0
/dev/loop1
/dev/loop2
/dev/loop3
Checking for free loopback device: /dev/loop4
Setting up loopback device: Done
Sleeping for 0 seconds.
Breaking down loopback device:
----NEXT PASS----
Loopback devices currently in use:
/dev/loop0
/dev/loop1
/dev/loop2
/dev/loop3
/dev/loop4
Checking for free loopback device: /dev/loop5
Setting up loopback device: Done
Sleeping for 0 seconds.
Breaking down loopback device:
----NEXT PASS----
Loopback devices currently in use:
/dev/loop0
/dev/loop1
/dev/loop2
/dev/loop3
/dev/loop4
/dev/loop5
Checking for free loopback device: /dev/loop6
Setting up loopback device: Done
Sleeping for 0 seconds.
Breaking down loopback device:
----NEXT PASS----
Loopback devices currently in use:
/dev/loop0
/dev/loop1
/dev/loop2
/dev/loop3
/dev/loop4
/dev/loop5
/dev/loop6
Checking for free loopback device: /dev/loop7
Setting up loopback device: Done
Sleeping for 0 seconds.
Breaking down loopback device:
----NEXT PASS----
Loopback devices currently in use:
/dev/loop0
/dev/loop1
/dev/loop2
/dev/loop3
/dev/loop4
/dev/loop5
/dev/loop6
/dev/loop7
Checking for free loopback device: losetup: could not find any free loop device
Exiting, couldn't find any free device any more.

So if done fast enough the pool quickly gets depleted as giving back (detaching) the device fails. A second or so later it might work, though. But let's test how much time exactly is needed to free the device? I modified the script to keep trying to detach/free the loopback device and see what happens:

Loopback devices currently in use:
Checking for free loopback device: /dev/loop0
Setting up loopback device: Done
Sleeping for 0 seconds.
Breaking down loopback device:
loop: can't delete device /dev/loop0: Device or resource busy
loop: can't delete device /dev/loop0: Device or resource busy
loop: can't delete device /dev/loop0: Device or resource busy
loop: can't delete device /dev/loop0: Device or resource busy
Loopback device broken down after 4 tries.
----NEXT PASS----
Loopback devices currently in use:
Checking for free loopback device: /dev/loop0
Setting up loopback device: Done
Sleeping for 0 seconds.
Breaking down loopback device:
loop: can't delete device /dev/loop0: Device or resource busy
loop: can't delete device /dev/loop0: Device or resource busy
Loopback device broken down after 2 tries.
----NEXT PASS----
Loopback devices currently in use:
Checking for free loopback device: /dev/loop0
Setting up loopback device: Done
Sleeping for 0 seconds.
Breaking down loopback device:
loop: can't delete device /dev/loop0: Device or resource busy
loop: can't delete device /dev/loop0: Device or resource busy
loop: can't delete device /dev/loop0: Device or resource busy
loop: can't delete device /dev/loop0: Device or resource busy
loop: can't delete device /dev/loop0: Device or resource busy
loop: can't delete device /dev/loop0: Device or resource busy
Loopback device broken down after 6 tries.
----NEXT PASS----
Loopback devices currently in use:
Checking for free loopback device: /dev/loop0
Setting up loopback device: Done
Sleeping for 0 seconds.
Breaking down loopback device:
loop: can't delete device /dev/loop0: Device or resource busy
Loopback device broken down after 1 tries.
----NEXT PASS----
Loopback devices currently in use:
Checking for free loopback device: /dev/loop0
Setting up loopback device: Done
Sleeping for 0 seconds.
Breaking down loopback device:
loop: can't delete device /dev/loop0: Device or resource busy
loop: can't delete device /dev/loop0: Device or resource busy
loop: can't delete device /dev/loop0: Device or resource busy
Loopback device broken down after 3 tries.
----NEXT PASS----
Loopback devices currently in use:
Checking for free loopback device: /dev/loop0
Setting up loopback device: Done
Sleeping for 0 seconds.
Breaking down loopback device:
loop: can't delete device /dev/loop0: Device or resource busy
loop: can't delete device /dev/loop0: Device or resource busy
loop: can't delete device /dev/loop0: Device or resource busy
Loopback device broken down after 3 tries.
----NEXT PASS----
Loopback devices currently in use:
Checking for free loopback device: /dev/loop0
Setting up loopback device: Done
Sleeping for 0 seconds.

Breaking down loopback device:
loop: can't delete device /dev/loop0: Device or resource busy
loop: can't delete device /dev/loop0: Device or resource busy
Loopback device broken down after 2 tries.
----NEXT PASS----
Loopback devices currently in use:
Checking for free loopback device: /dev/loop0
Setting up loopback device: Done
Sleeping for 0 seconds.
Breaking down loopback device:
loop: can't delete device /dev/loop0: Device or resource busy
loop: can't delete device /dev/loop0: Device or resource busy
loop: can't delete device /dev/loop0: Device or resource busy
Loopback device broken down after 3 tries.
----NEXT PASS----
Loopback devices currently in use:
Checking for free loopback device: /dev/loop0
Setting up loopback device: Done
Sleeping for 0 seconds.
Breaking down loopback device:
loop: can't delete device /dev/loop0: Device or resource busy
loop: can't delete device /dev/loop0: Device or resource busy
Loopback device broken down after 2 tries.
----NEXT PASS----
Loopback devices currently in use:
Checking for free loopback device: /dev/loop0
Setting up loopback device: Done
Sleeping for 0 seconds.
Breaking down loopback device:
loop: can't delete device /dev/loop0: Device or resource busy
loop: can't delete device /dev/loop0: Device or resource busy
loop: can't delete device /dev/loop0: Device or resource busy
loop: can't delete device /dev/loop0: Device or resource busy
Loopback device broken down after 4 tries.
----NEXT PASS----
Loopback devices currently in use:
Checking for free loopback device: /dev/loop0
Setting up loopback device: Done
Sleeping for 0 seconds.
Breaking down loopback device:
loop: can't delete device /dev/loop0: Device or resource busy
loop: can't delete device /dev/loop0: Device or resource busy
loop: can't delete device /dev/loop0: Device or resource busy
loop: can't delete device /dev/loop0: Device or resource busy
Loopback device broken down after 4 tries.
----NEXT PASS----
Loopback devices currently in use:

Checking for free loopback device: /dev/loop0
Setting up loopback device: Done
Sleeping for 0 seconds.
Breaking down loopback device:
loop: can't delete device /dev/loop0: Device or resource busy
Loopback device broken down after 1 tries.
----NEXT PASS----
Loopback devices currently in use:
Checking for free loopback device: /dev/loop0
Setting up loopback device: Done
Sleeping for 0 seconds.
Breaking down loopback device:
loop: can't delete device /dev/loop0: Device or resource busy
loop: can't delete device /dev/loop0: Device or resource busy
loop: can't delete device /dev/loop0: Device or resource busy
loop: can't delete device /dev/loop0: Device or resource busy
loop: can't delete device /dev/loop0: Device or resource busy
Loopback device broken down after 5 tries.
----NEXT PASS----
Loopback devices currently in use:
Checking for free loopback device: /dev/loop0
Setting up loopback device: Done
Sleeping for 0 seconds.
Breaking down loopback device:
loop: can't delete device /dev/loop0: Device or resource busy
loop: can't delete device /dev/loop0: Device or resource busy
loop: can't delete device /dev/loop0: Device or resource busy
loop: can't delete device /dev/loop0: Device or resource busy
loop: can't delete device /dev/loop0: Device or resource busy
loop: can't delete device /dev/loop0: Device or resource busy
loop: can't delete device /dev/loop0: Device or resource busy
loop: can't delete device /dev/loop0: Device or resource busy
loop: can't delete device /dev/loop0: Device or resource busy
loop: can't delete device /dev/loop0: Device or resource busy
Loopback device broken down after 10 tries.
----NEXT PASS----
Loopback devices currently in use:
Checking for free loopback device: /dev/loop0
Setting up loopback device: Done
Sleeping for 0 seconds.
Breaking down loopback device:
loop: can't delete device /dev/loop0: Device or resource busy
loop: can't delete device /dev/loop0: Device or resource busy
Loopback device broken down after 2 tries.
----NEXT PASS----
Loopback devices currently in use:
Checking for free loopback device: /dev/loop0
Setting up loopback device: Done
Sleeping for 0 seconds.
Breaking down loopback device:
loop: can't delete device /dev/loop0: Device or resource busy
loop: can't delete device /dev/loop0: Device or resource busy
loop: can't delete device /dev/loop0: Device or resource busy
loop: can't delete device /dev/loop0: Device or resource busy
Loopback device broken down after 4 tries.
----NEXT PASS----
Loopback devices currently in use:
Checking for free loopback device: /dev/loop0
Setting up loopback device: Done
Sleeping for 0 seconds.
Breaking down loopback device:
loop: can't delete device /dev/loop0: Device or resource busy
loop: can't delete device /dev/loop0: Device or resource busy
loop: can't delete device /dev/loop0: Device or resource busy
loop: can't delete device /dev/loop0: Device or resource busy
Loopback device broken down after 4 tries.
----NEXT PASS----
Loopback devices currently in use:
Checking for free loopback device: /dev/loop0
Setting up loopback device: Done
Sleeping for 0 seconds.
Breaking down loopback device:
loop: can't delete device /dev/loop0: Device or resource busy
loop: can't delete device /dev/loop0: Device or resource busy
loop: can't delete device /dev/loop0: Device or resource busy
Loopback device broken down after 3 tries.
----NEXT PASS----
Loopback devices currently in use:
Checking for free loopback device: /dev/loop0
Setting up loopback device: Done
Sleeping for 0 seconds.
Breaking down loopback device:
Loopback device broken down after 0 tries.
----NEXT PASS----
Loopback devices currently in use:
Checking for free loopback device: /dev/loop0
Setting up loopback device: Done
Sleeping for 0 seconds.
Breaking down loopback device:
loop: can't delete device /dev/loop0: Device or resource busy
loop: can't delete device /dev/loop0: Device or resource busy
loop: can't delete device /dev/loop0: Device or resource busy
loop: can't delete device /dev/loop0: Device or resource busy
Loopback device broken down after 4 tries.
----NEXT PASS----
Loopback devices currently in use:
Checking for free loopback device: /dev/loop0
Setting up loopback device: Done
Sleeping for 0 seconds.
Breaking down loopback device:
loop: can't delete device /dev/loop0: Device or resource busy
loop: can't delete device /dev/loop0: Device or resource busy
loop: can't delete device /dev/loop0: Device or resource busy
Loopback device broken down after 3 tries.
----NEXT PASS----
Loopback devices currently in use:
Checking for free loopback device: /dev/loop0
Setting up loopback device: Done
Sleeping for 0 seconds.
Breaking down loopback device:
loop: can't delete device /dev/loop0: Device or resource busy
loop: can't delete device /dev/loop0: Device or resource busy
Loopback device broken down after 2 tries.
----NEXT PASS----
Loopback devices currently in use:
Checking for free loopback device: /dev/loop0
Setting up loopback device: Done
Sleeping for 0 seconds.
Breaking down loopback device:
Loopback device broken down after 0 tries.
----NEXT PASS----
Loopback devices currently in use:
Checking for free loopback device: /dev/loop0
Setting up loopback device: Done
Sleeping for 0 seconds.
Breaking down loopback device:
loop: can't delete device /dev/loop0: Device or resource busy
Loopback device broken down after 1 tries.
----NEXT PASS----
Loopback devices currently in use:
Checking for free loopback device: /dev/loop0
Setting up loopback device: Done
Sleeping for 0 seconds.
Breaking down loopback device:
loop: can't delete device /dev/loop0: Device or resource busy
loop: can't delete device /dev/loop0: Device or resource busy
loop: can't delete device /dev/loop0: Device or resource busy
Loopback device broken down after 3 tries.
----NEXT PASS----
Loopback devices currently in use:
Checking for free loopback device: /dev/loop0
Setting up loopback device: Done
Sleeping for 0 seconds.
Breaking down loopback device:
loop: can't delete device /dev/loop0: Device or resource busy
loop: can't delete device /dev/loop0: Device or resource busy
Loopback device broken down after 2 tries.
----NEXT PASS----
Loopback devices currently in use:
Checking for free loopback device: /dev/loop0
Setting up loopback device: Done
Sleeping for 0 seconds.
Breaking down loopback device:
loop: can't delete device /dev/loop0: Device or resource busy
Loopback device broken down after 1 tries.
----NEXT PASS----
Loopback devices currently in use:
Checking for free loopback device: /dev/loop0
Setting up loopback device: Done
Sleeping for 0 seconds.
Breaking down loopback device:
loop: can't delete device /dev/loop0: Device or resource busy
loop: can't delete device /dev/loop0: Device or resource busy
Loopback device broken down after 2 tries.
----NEXT PASS----
Loopback devices currently in use:
Checking for free loopback device: /dev/loop0
Setting up loopback device: Done
Sleeping for 0 seconds.
Breaking down loopback device:
loop: can't delete device /dev/loop0: Device or resource busy
Loopback device broken down after 1 tries.
----NEXT PASS----
Loopback devices currently in use:
Checking for free loopback device: /dev/loop0
Setting up loopback device: Done
Sleeping for 0 seconds.
Breaking down loopback device:
loop: can't delete device /dev/loop0: Device or resource busy
Loopback device broken down after 1 tries.
----NEXT PASS----
Loopback devices currently in use:
Checking for free loopback device: /dev/loop0
Setting up loopback device: ^C

So it varies. The device might get released instantaneously, but that doesn't happen too often, or it might take 10 consecutive tries. Let's see if allowing half a second's worth of pause in between creating and detaching fix the problem,

# ./test.sh
Creating sparse 4TB file: Done
----START----
Loopback devices currently in use:
Checking for free loopback device: /dev/loop0
Setting up loopback device: Done
Sleeping for 0.5 seconds.
Breaking down loopback device:
Loopback device broken down after 0 tries.
----NEXT PASS----
Loopback devices currently in use:
Checking for free loopback device: /dev/loop0
Setting up loopback device: Done
Sleeping for 0.5 seconds.
Breaking down loopback device:
Loopback device broken down after 0 tries.
----NEXT PASS----
Loopback devices currently in use:
Checking for free loopback device: /dev/loop0
Setting up loopback device: Done
Sleeping for 0.5 seconds.
Breaking down loopback device:
Loopback device broken down after 0 tries.
----NEXT PASS----
Loopback devices currently in use:
Checking for free loopback device: /dev/loop0
Setting up loopback device: Done
Sleeping for 0.5 seconds.
Breaking down loopback device:
Loopback device broken down after 0 tries.
----NEXT PASS----
Loopback devices currently in use:
Checking for free loopback device: /dev/loop0
Setting up loopback device: Done
Sleeping for 0.5 seconds.

^C

It does, but what's holding on to the device exactly? I modified the script again to look up the did in the process table. This takes time of course, so the detaching phase took less tries to complete:

# ./test.sh
Creating sparse 4TB file: Done
----START----
Loopback devices currently in use:
Checking for free loopback device: /dev/loop0
Setting up loopback device: Done
Sleeping for 0 seconds.
Breaking down loopback device:
loop: can't delete device /dev/loop0: Device or resource busy
root     25417  0.0  0.0      0     0 ?        S<   13:25   0:00 [loop0]
Loopback device broken down after 1 tries.
----NEXT PASS----
Loopback devices currently in use:
Checking for free loopback device: /dev/loop0
Setting up loopback device: Done
Sleeping for 0 seconds.
Breaking down loopback device:
loop: can't delete device /dev/loop0: Device or resource busy
root     25437  0.0  0.0      0     0 ?        S<   13:25   0:00 [loop0]
Loopback device broken down after 1 tries.
----NEXT PASS----
Loopback devices currently in use:
^C

Right, so it's Linux that's holding on to it and I'm not sure if I like this behavior. I realize losetup can only request Linux to free up the device and it does cleanly report a 'Device or resource busy' but I don't understand why it just doesn't wait a bit until the resource is cleared from the kernel, or at least provides the option to the user to do so. I thought about pathing losetup but now I can't be bothered anymore, so I'm just putting it out there :)

On bypassing mdadm's interactive mode

So I wanted mdadm to not go interactive, ever, but instead just bail out whenever something happens it doesn't understand; you'd think the developers would have thought of that, right? Turns out they haven't.
The 'fix' is easy enough though: pipe /bin/false through mdadm by default so it'll get a 'false' every time it would be looking for user input; effectively making it bail out whenever something's off:

alias mdadm="/bin/false | /sbin/mdadm"

On quickly creating sparse and large files

I've been using dd(1) for as long as I can remember to create sparse files but for some reason I keep forgetting how to use dd's argument options so I set out to find something better... and found it: truncate(1):

From the man page: "Shrink or extend the size of each FILE to the specified size. A FILE argument that does not exist is created." -looking good:

root@debian64:~# time truncate -s 10T testfile

real0m0.003s
user0m0.000s
sys 0m0.004s

root@debian64:~# ls -l testfile
-rw-r--r-- 1 root root 10995116277760 Dec4 10:27 testfile

root@debian64:~# du -hs testfile
0 testfile

Awesome!
So then I set out to find me something to quickly allocate 'real' files:

fallocate(1):
"fallocate  is used to preallocate blocks to a file.  For filesystems which support the fallocate system call, this is done quickly by allocating blocks and marking them as uninitialized, requiring no IO to the data blocks.  This is much faster than creating a file by filling it with zeros."

And it truly is fast:

root@debian64:~# time fallocate -l 1G testfile

real    0m0.004s
user    0m0.000s
sys     0m0.000s

root@debian64:~# du -hs testfile
1.1G    testfile

root@debian64:~# ls -l testfile
-rw-r--r-- 1 root root 1073741824 Dec  4 10:34 testfile

On OverlayFS and distilling patches (or: how to get OverlayFS)

So, I was looking at unionfs alternatives and I wanted to try overlayfs.
You'd think a project almost begging to be merged into mainline Linux would be interested in getting some traction amongst the "regular" Linux crowd and actually provide some patches making it relatively easy to try out the code until the time finally comes they're part of mainline, right?
Well, apparently you'd be wrong assuming that: getting a clean OverlayFS patch requires distilling a diff from a patched Linux source tree on git and that is left as an exercise to the user... or simply use Ubuntu's or SuSE's kernels (no...fucking...way) as those are already patched it seems.
Anyways, this is how to do it:

Branch overlayfs.v18 is intended to work with Linux 3.10.x:

https://git.kernel.org/cgit/linux/kernel/git/mszeredi/vfs.git/tree/Makefile?h=overlayfs.v18

Git clone the overlayfs.v18 branch:

git clone git://git.kernel.org/pub/scm/linux/kernel/git/mszeredi/vfs.git -b overlayfs.v18 overlayfs.v18

From the git log I got they merged Linux 3.10-rc7 so that's the branch we're going to diff to. Adding a new remote repo to the overlayfs.v18 local repo and fetching the v3.10-rc7 branch from it (git fetching won't actually change the local code!):

cd overlayfs.v18
git remote add v3.10-rc7 git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux
git fetch v3.10-rc7

Now all we have to do is the actual git diff:

git diff v3.10-rc7/master...HEAD > ../overlayfs-v18.patch

So let's try to patch our Linux 3.10.12 tree :

root@bob:/usr/src/linux# patch -p1 --dry-run < ../overlayfs-v18.patch 
patching file Documentation/filesystems/Locking
patching file Documentation/filesystems/overlayfs.txt
patching file Documentation/filesystems/vfs.txt
patching file MAINTAINERS
patching file fs/Kconfig
patching file fs/Makefile
patching file fs/ecryptfs/main.c
patching file fs/internal.h
patching file fs/namei.c
patching file fs/namespace.c
patching file fs/open.c
patching file fs/overlayfs/Kconfig
patching file fs/overlayfs/Makefile
patching file fs/overlayfs/copy_up.c
patching file fs/overlayfs/dir.c
patching file fs/overlayfs/inode.c
patching file fs/overlayfs/overlayfs.h
patching file fs/overlayfs/readdir.c
patching file fs/overlayfs/super.c
patching file fs/splice.c
Hunk #1 succeeded at 1313 (offset 1 line).
patching file include/linux/fs.h
patching file include/linux/mount.h
root@bob:/usr/src/linux#

Lookin' good, w00t!

On Linux patches and diffs

So you're running your own customized Linux, and want to stay up-to-date a bit, right?

root@box:/usr/src/linux# patch -p1 --dry-run < ../patch-3.10.4
patching file Documentation/i2c/busses/i2c-piix4
Reversed (or previously applied) patch detected!  Assume -R? [n] ^C

So what's happening here is that 'patch-3.10.4' from kernel.org actually is a diff from 3.10 to 3.10.4, not from 3.10.3 to 3.10.4.
This'd be fine except that you've already applied patch-3.10.3 the day before yesterday and you don't want to keep track of which patches are already applied and stuff, you just want to see whether or not the new 3.10.4 patches apply without problems.
Plus you've got other patches applied as well so you really just want to have a patch with the changes form one minor release to the other, right?
So that's where interdiff comes into play:

interdiff patch-3.10.3 patch-3.10.4 > patch-3.10.3-to-3.10.4

Now we have a patch that only includes the changes from 3.10.3 to 3.10.4 and that can be applied directly and cleanly to our already patched-with-the-previous-version-and-other-stuff-as-well Linux tree.

On apache's mod_proxy

Another short one, a warning; a 'heads up' if you will.

Took me some time to figure out that Apache's mod_proxy actually requires the proxied service to be accessible when Apache itself starts.

It seems logical enough writing it down now, but when I was configuring mod_proxy to work with apt-cacher it sure wasn't clear looking at the log files.

So when you're playing around with mod_proxy and a random to-be-proxied service, make sure to reload/restart the service first (and verify everything working alright) and only then reload Apache to take the new mod_proxy settings into effect.

Debugging a slow KDE session.

KDE (from the Kubuntu repo) and all QT applications were slow as hell after an update so I set out to investigate:

The most obvious one to start with was kopete (sloooooooooooooow), so I straced (strace -s 500 -f kopete) and it hung on this:

11574 recvmsg(6, 0x7fffb90ddde0, MSG_CMSG_CLOEXEC) = -1 EAGAIN (Resource temporarily unavailable)
11574 sendmsg(6, {msg_name(0)=NULL, msg_iov(2)=[{"l\1\0\1\0\0\0\0\t\0\0\0o\0\0\0\1\1o\0\26\0\0\0/modules/networkstatus\0\0\6\1s\0\f\0\0\0org.kde.kded\0\0\0\0\2\1s\0\37\0\0\0org.kde.Solid.Networking.Client\0\3\1s\0\6\0\0\0status\0\0", 128}, {"", 0}], msg_controllen=0, msg_flags=0}, MSG_NOSIGNAL) = 128
11574 poll([{fd=6, events=POLLIN}], 1, 25000

It's hanging on handler 6, going up in the output I found what 6 is:

11368 socket(PF_FILE, SOCK_STREAM|SOCK_CLOEXEC, 0) = 6
11368 connect(6, {sa_family=AF_FILE, path=@"/tmp/dbus-TNffZVatPK"}, 23) = 0
11368 fcntl(6, F_GETFL)                 = 0x2 (flags O_RDWR)
11368 fcntl(6, F_SETFL, O_RDWR|O_NONBLOCK) = 0
11368 geteuid()                         = 1000
11368 getsockname(6, {sa_family=AF_FILE, NULL}, [2]) = 0

Right, so kopete is slow because it's waiting to receive something sent through dbus to kded.
Let's try to use dbus to contact kopete manually:

timothy@xps:~$ time qdbus org.kde.kopete                                         Error: org.freedesktop.DBus.Error.NoReply
Did not receive a reply. Possible causes include: the remote application did not send a reply, the message bus security policy blocked the reply, the reply timeout expired, or the network connection was broken.
real    0m25.018s
user    0m0.004s
sys     0m0.008s

It timed out, let's try it again:

timothy@xps:~$ time qdbus org.kde.kopete
/
/KDebug
/KIO
/KIO/Scheduler
/Kopete
/MainApplication
/ManagerIface_contact
/Statistics
/kopete
/kopete/MainWindow_1
/kopete/MainWindow_1/actions
/kopete/MainWindow_1/actions/settings_prefs
/kopete/MainWindow_1/actions/file_quit
/kopete/MainWindow_1/actions/settings_showmenubar
/kopete/MainWindow_1/actions/settings_showstatusbar
/kopete/MainWindow_1/actions/settings_keys
/kopete/MainWindow_1/actions/options_configure_toolbars
/kopete/MainWindow_1/actions/settings_notifications
/kopete/MainWindow_1/actions/AddGroup
/kopete/MainWindow_1/actions/contactSendMessage
/kopete/MainWindow_1/actions/contactStartChat
/kopete/MainWindow_1/actions/contactMove
/kopete/MainWindow_1/actions/contactCopy
/kopete/MainWindow_1/actions/makeMetaContact
/kopete/MainWindow_1/actions/contactRemove
/kopete/MainWindow_1/actions/contactSendEmail
/kopete/MainWindow_1/actions/contactSendFile
/kopete/MainWindow_1/actions/contactAddContact
/kopete/MainWindow_1/actions/contactAddTemporaryContact
/kopete/MainWindow_1/actions/contactProperties

real    0m3.720s
user    0m0.028s
sys     0m0.004s

So now it works. Consistent with what I'm experiencing in the KDE session right now.
Everything works, more or less, but it's all extremely slow.
Let's have a look at kded:

timothy@xps:~$ qdbus org.kde.kded
Error: org.freedesktop.DBus.Error.NoReply                                        Did not receive a reply. Possible causes include: the remote application did not send a reply, the message bus security policy blocked the reply, the reply timeout expired, or the network connection was broken.                         

I want to see what's kded's problem, let's look at it's status:

timothy@xps:~$ ps aux | grep kded
timothy  10298  0.0  0.3 793672 29280 ?        Sl   10:06   0:00 kdeinit4: kded4 [kdeinit]                     
timothy  10455  0.0  0.1 414756 11236 ?        Sl   10:06   0:00 kdeinit4: kio_trash [kdeinit] trash local:/tmp/ksocket-timothy/klauncherT10296.slave-socket local:/tmp/ksocket-timothy/kdeda10298.slave-socket

Sleeping eh, could be worse. Let's see what's it actually is doing/hanging on:

timothy@xps:~$ gdb kdeinit `pidof kded4`
[... lots of stuff...]
(gdb) bt
#0  0x00007f6aa1952023 in select () at ../sysdeps/unix/syscall-template.S:82
#1  0x00007f6aa2d99366 in qt_safe_select(int, fd_set*, fd_set*, fd_set*, timeval const*) () from /usr/lib/x86_64-linux-gnu/libQtCore.so.4
#2  0x00007f6aa2d466da in ?? () from /usr/lib/x86_64-linux-gnu/libQtCore.so.4
#3  0x00007f6aa2d47fab in ?? () from /usr/lib/x86_64-linux-gnu/libQtCore.so.4
#4  0x00007f6aa2d0248e in QProcess::waitForFinished(int) () from /usr/lib/x86_64-linux-gnu/libQtCore.so.4
#5  0x00007f6aa31def32 in KProcess::execute(int) () from /usr/lib/libkdecore.so.5
#6  0x00007f6a80f3f1a5 in ?? () from /usr/lib/kde4/kded_notificationhelper.so
#7  0x00007f6a80f3bca5 in ?? () from /usr/lib/kde4/kded_notificationhelper.so
#8  0x00007f6a80f39ad4 in ?? () from /usr/lib/kde4/kded_notificationhelper.so
#9  0x00007f6a80f39d24 in ?? () from /usr/lib/kde4/kded_notificationhelper.so
#10 0x00007f6aa2d86446 in QObject::event(QEvent*) () from /usr/lib/x86_64-linux-gnu/libQtCore.so.4
#11 0x00007f6aa20ef894 in QApplicationPrivate::notify_helper(QObject*, QEvent*) () from /usr/lib/x86_64-linux-gnu/libQtGui.so.4
#12 0x00007f6aa20f4713 in QApplication::notify(QObject*, QEvent*) () from /usr/lib/x86_64-linux-gnu/libQtGui.so.4
#13 0x00007f6aa3b063f6 in KApplication::notify(QObject*, QEvent*) () from /usr/lib/libkdeui.so.5
#14 0x00007f6aa2d6ce9c in QCoreApplication::notifyInternal(QObject*, QEvent*) () from /usr/lib/x86_64-linux-gnu/libQtCore.so.4
#15 0x00007f6aa2d70c6a in QCoreApplicationPrivate::sendPostedEvents(QObject*, int, QThreadData*) () from /usr/lib/x86_64-linux-gnu/libQtCore.so.4
#16 0x00007f6aa2d9bf93 in ?? () from /usr/lib/x86_64-linux-gnu/libQtCore.so.4
#17 0x00007f6a9ea5fd53 in g_main_context_dispatch () from /lib/x86_64-linux-gnu/libglib-2.0.so.0
#18 0x00007f6a9ea600a0 in ?? () from /lib/x86_64-linux-gnu/libglib-2.0.so.0
#19 0x00007f6a9ea60164 in g_main_context_iteration () from /lib/x86_64-linux-gnu/libglib-2.0.so.0
#20 0x00007f6aa2d9c3bf in QEventDispatcherGlib::processEvents(QFlags) ()
   from /usr/lib/x86_64-linux-gnu/libQtCore.so.4
#21 0x00007f6aa2197d5e in ?? () from /usr/lib/x86_64-linux-gnu/libQtGui.so.4
#22 0x00007f6aa2d6bc82 in QEventLoop::processEvents(QFlags) () from /usr/lib/x86_64-linux-gnu/libQtCore.so.4
#23 0x00007f6aa2d6bed7 in QEventLoop::exec(QFlags) () from /usr/lib/x86_64-linux-gnu/libQtCore.so.4
#24 0x00007f6aa2d70f67 in QCoreApplication::exec() () from /usr/lib/x86_64-linux-gnu/libQtCore.so.4
#25 0x00007f6a8f4fde55 in kdemain () from /usr/lib/kde4/libkdeinit/libkdeinit4_kded4.so
#26 0x00000000004086a4 in _start ()

So we're in the kded_notificationhelper.so module. Let's see what I've got on my system mathing that name:

timothy@xps:~$ dpkg -l | grep "notification-helper"
ii  kubuntu-notification-helper            11.10ubuntu1                            Kubuntu system notification helper

Seems fishy.

timothy@xps:~$ apt-cache show kubuntu-notification-helper
Package: kubuntu-notification-helper
Priority: optional
Section: kde
Installed-Size: 212
Maintainer: Kubuntu Developers
Original-Maintainer: Jonathan Thomas
Architecture: amd64
Version: 11.10ubuntu1
Depends: libc6 (>= 2.4), libkdecore5 (>= 4:4.4.95), libkdeui5 (>= 4:4.4.0), libqt4-dbus (>= 4:4.5.3), libqtcore4 (>= 4:4.7.0~beta1), libqtgui4 (>= 4:4.5.3), libstdc++6 (>= 4.1.1), konsole | x-terminal-emulator, qapt-batch
Recommends: apport-kde | apport-gtk
Filename: pool/main/k/kubuntu-notification-helper/kubuntu-notification-helper_11.10ubuntu1_amd64.deb
Size: 38114
MD5sum: 0c6b775a0f78cbdb138149ea0e32b60b
SHA1: 2f2c37f9d16a094ac6f215c22c6cb558f6e5eada
SHA256: 8a96a2b822e825d3d56d7dcba732061576b690077bd73ff5ddcfd896192399bf
Description-en: Kubuntu system notification helper
 Kubuntu Notification Helper is a daemon that presents various notifications
 to the user. It uses the KDE Daemon system as a base and presents the
 notifications using the KDE Notification system. It also includes a
 System Settings module for configuring the daemon. Kubuntu Notification
 Helper is lightweight and fully integrated with KDE.
 .
 Current features include:
  - Notifications for Apport crashes.
  - Notifications for upgrade information, when available.
- Notifications for the availability restrictively-licensed packages.
  - Notifications for when upgrades require a reboot to complete.
  - All notifications can be hidden temporarily or permanently.
Homepage: https://launchpad.net/kubuntu-notification-helper
Description-md5: cfe41fe07651879c49f8ca54be0c1170
Bugs: https://bugs.launchpad.net/ubuntu/+filebug
Origin: Ubuntu
Supported: 5y
Task: kubuntu-desktop, kubuntu-full, kubuntu-active-desktop, kubuntu-active-full, kubuntu-active, edubuntu-desktop-kde

Ubuntu bloatware I can perfectly do without, check.

timothy@xps:~$ sudo apt-get remove --purge kubuntu-notification-helper
Reading package lists... Done
Building dependency tree     
Reading state information... Done
The following packages will be REMOVED:
  kubuntu-notification-helper*
0 upgraded, 0 newly installed, 1 to remove and 0 not upgraded.
After this operation, 217 kB disk space will be freed.
Do you want to continue [Y/n]?
(Reading database ... 296995 files and directories currently installed.)
Removing kubuntu-notification-helper ...

After a KDM restart everything is back to normal AND that annoying pop up 'there's are X software updates' thing is gone...