So, in the example the cpu stats are collected within a function
called do_top. At the beginning of the function we ask the daemon for
how much vCPUs can we get stats, and how many stats for a vCPU can we
get. This is because it's how our API works - users are required to
preallocate a chunk of memory for the results. Now, at the end, we try
to free the allocated array, but we are not doing it correctly.
There's this virTypedParamsFree() function which gets a pointer to the
array and the length of the array. However, if there was an error in
getting vCPU stats we pass a negative number instead of the originally
computed value. This flaw results in SIGSEGV:
libvirt: QEMU Driver error : Requested operation is not valid: domain is not running
ERROR do_top:333 : Unable to get cpu stats
==29201== Invalid read of size 4
==29201== at 0x4F1DF8B: virTypedParamsClear (virtypedparam.c:1145)
==29201== by 0x4F1DFEB: virTypedParamsFree (virtypedparam.c:1165)
==29201== by 0x4023C3: do_top (domtop.c:349)
==29201== by 0x40260B: main (domtop.c:386)
==29201== Address 0x131cd7c0 is 16 bytes after a block of size 768 alloc'd
==29201== at 0x4C2C070: calloc (in /usr/lib64/valgrind/vgpreload_memcheck-amd64-linux.so)
==29201== by 0x401FF1: do_top (domtop.c:295)
==29201== by 0x40260B: main (domtop.c:386)
Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Wikipedia's list of common misspellings [1] has a machine-readable
version. This patch fixes those misspellings mentioned in the list
which don't have multiple right variants (as e.g. "accension", which can
be both "accession" and "ascension"), such misspellings are left
untouched. The list of changes was manually re-checked for false
positives.
[1] https://en.wikipedia.org/wiki/Wikipedia:Lists_of_common_misspellings/For_machines
Signed-off-by: Martin Kletzander <mkletzan@redhat.com>
Apparmor must not prevent access to required helper programs. The following
helpers should be allowed to run in unconfined execution mode:
- libvirt_parthelper
- libvirt_iohelper
The network and nwfilter tests contained in the libvirt-TCK testkit can fail
unless access to raw network packets is granted. Without this access, the
following apparmor error can be seen while running the tests:
apparmor="DENIED" operation="create" parent=1 profile="/usr/sbin/libvirtd"
pid=94731 comm="libvirtd" family="packet" sock_type="raw" protocol=768
In order for apparmor to work properly in Xen environments, the following
access rights need to be allowed:
- Allow CAP_SYS_PACCT, which is required when resetting some multi-port
Broadcom cards by writting to the PCI config space
- Allow CAP_IPC_LOCK, which is required to lock/unlock memory. Without
this setting, an error 'Resource temporarily unavailable' can be seen
while attempting to mmap memory. At the same time, the following
apparmor message is seen:
apparmor="DENIED" operation="capable" parent=1 profile="/usr/sbin/libvirtd"
pid=2097 comm="libvirtd" pid=2097 comm="libvirtd" capability=14
capname="ipc_lock"
- Allow access to distribution specific directories:
/usr/{lib,lib64}/xen/bin
As discussed before, this simple script should help with debugging
deadlocks, although there are still some caveats. RWLocks are not
handled by this and if your deadlock if very racy, it may not lock
up when running with this script due to the slowdown.
Signed-off-by: Martin Kletzander <mkletzan@redhat.com>
When building on mingw the format string for long long/unsigned long
long have to be I64d/I64u instead of lld/llu.
Signed-off-by: Pavel Hrdina <phrdina@redhat.com>
libcap-ng >= 0.7.4 fails when it can't read /sys/kernel/cap_last_cap
and thus running a qemu guest fails.
Allow reading cap_last_cap in the libvirt-qemu apparmor abstraction.
Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
On some places in the libvirt code we have:
f(a,z)
instead of
f(a, z)
This trivial patch fixes couple of such occurrences.
Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
The "maxMemory" element was never supported by libvirt. Remove it from
the test XMLs. (Found while actually trying to add support for a
identically named element).
The variable 'k' in the print_cpu_usage function is not used anywhere
and can fire a warning on some compilers.
Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Currently, the function follows the usual pattern used in our code:
int ret = -1;
...
ret = 0;
cleanup:
return ret;
However, the function always call exit() on error, so the cleanup
label is never jumped onto. Therefore, it doesn't make any sense to
have the parse_argv function return an integer value, if it
effectively can return only value of zero.
Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Firstly, there's no sigaction() nor struct sigaction on mingw. We have
to use the one implemented by gnulib (and hence link with gnulib).
Then, for some reason one header file from windows defines ERROR
symbol. Yes it does. Sigh.
Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Use the virTypedParamsFree unconditionally as it handles NULL well and
has the benefit of freeing a typed parameter array even if it wasn't yet
assigned, but only allocated.
There's this question on the list that is asked over and over again.
How do I get {cpu, memory, ...} usage in percentage? Or its modified
version: How do I plot nice graphs like virt-manager does?
It would be nice if we have an example to inspire people. And that's
what domtop should do. Yes, it could be written in different ways, but
I've chosen this one as I think it show explicitly what users need to
implement in order to imitate virt-manager's graphing.
Note: The usage is displayed from host perspective. That is, how much
host CPUs the domain is using. But it should be fairly simple to
switch do just guest CPU usage if needed.
Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Rework the apparmor lxc profile abstraction to mimic ubuntu's container-default.
This profile allows quite a lot, but strives to restrict access to
dangerous resources.
Removing the explicit authorizations to bash, systemd and cron files,
forces them to keep the lxc profile for all applications inside the
container. PUx permissions where leading to running systemd (and others
tasks) unconfined.
Put the generic files, network and capabilities restrictions directly
in the TEMPLATE.lxc: this way, users can restrict them on a per
container basis.
Tiny fix for virt-lxc-convert: we are setting memory values in bytes, while
free may give us values in a different unit by default: force free to output
bytes with -b flag.
This commit adds a new example to illustrate peer to
peer domain migration with virDomainMigrateToURI.
Signed-off-by: Sahid Orentino Ferdjaoui <sahid.ferdjaoui@cloudwatt.com>
See lp#1276719 for the bug description. As virt-aa-helper doesn't know
the VFIO groups to use for the guest, allow access to all
/dev/vfio/[0-9]* and /dev/vfio/vfio files if there is a potential need
for vfio
Signed-off-by: Eric Blake <eblake@redhat.com>
use_apparmor() was first designed to be called from withing libvirtd,
but libvirt_lxc also uses it. in libvirt_lxc, there is no need to check
whether to use apparmor or not: just use it if possible.
The security driver expects /etc/apparmor.d/libvirt/TEMPLATE but we
installed it to /etc/apparmor.d/libvirtd/TEMPLATE. Move the template to
the expected place since that code was here long before.
Make it easy to install the shipped examples. The aim is to have
reasonably working templates so that distros only need to minimally
patch these and can feed things upstream more easily.
This was prompted by http://bugs.debian.org/725144
When registering a close callback, the connection refcount is increased
as the connection object is passed to the callback and hence we must
prevent deleting it too soon. However, when closing the connection, the
connection object is just unrefed. So whenever a connection with a close
callback is closed, we end up with the connection object which has
exactly one reference. Leaving the code as-is doesn't mean the end of
the world as we know it, but why give a bad example?
==14531== 288 bytes in 1 blocks are still reachable in loss record 695 of 762
==14531== at 0x4C2BDE4: calloc (in /usr/lib64/valgrind/vgpreload_memcheck-amd64-linux.so)
==14531== by 0x4E9FE09: virAllocVar (viralloc.c:558)
==14531== by 0x4EDBE45: virObjectNew (virobject.c:190)
==14531== by 0x4F71AAC: virGetConnect (datatypes.c:116)
==14531== by 0x4F78511: do_open (libvirt.c:1136)
==14531== by 0x4F7B3AC: virConnectOpenAuth (libvirt.c:1481)
==14531== by 0x4011D2: main (event-test.c:499)
(and other leaks tied to virGetConnect())
Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
This partially reverts 5eb4b04211 and 62774afb6b.
Rewrite the domsuspend example from scratch. This time do it right.
Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
The domain events demo program isn't really tied to domain
events anymore, so rename it to object events.
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
The domsuspend example code is a really old and bad exmample of (how not
to use) the libvirt API. Remove it as it's apparent that nobody tried to
use it. It was broken and nobody complained.
The python binding now lives in
http://libvirt.org/git/?p=libvirt-python.git
that repo also provides an RPM which is upgrade compatible
with the old libvirt-python sub-RPM.
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
The libvirt.so library has far too many library deps to allow
linking against it from setuid programs. Those libraries can
do stuff in __attribute__((constructor) functions which is
not setuid safe.
The virt-login-shell needs to link directly against individual
files that it uses, with all library deps turned off except
for libxml2 and libselinux.
Create a libvirt-setuid-rpc-client.la library which is linked
to by virt-login-shell. A config-post.h file allows this library
to disable all external deps except libselinux and libxml2.
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
'make rpm' with client_local set to 1 (by manual modification,
or with RHEL 5 on s390) warns:
RPM build errors:
Installed (but unpackaged) file(s) found:
/etc/libvirt/nwfilter/allow-arp.xml
/etc/libvirt/nwfilter/allow-dhcp-server.xml
/etc/libvirt/nwfilter/allow-dhcp.xml
/etc/libvirt/nwfilter/allow-incoming-ipv4.xml
/etc/libvirt/nwfilter/allow-ipv4.xml
/etc/libvirt/nwfilter/clean-traffic.xml
/etc/libvirt/nwfilter/no-arp-ip-spoofing.xml
/etc/libvirt/nwfilter/no-arp-mac-spoofing.xml
/etc/libvirt/nwfilter/no-arp-spoofing.xml
/etc/libvirt/nwfilter/no-ip-multicast.xml
/etc/libvirt/nwfilter/no-ip-spoofing.xml
/etc/libvirt/nwfilter/no-mac-broadcast.xml
/etc/libvirt/nwfilter/no-mac-spoofing.xml
/etc/libvirt/nwfilter/no-other-l2-traffic.xml
/etc/libvirt/nwfilter/no-other-rarp-traffic.xml
/etc/libvirt/nwfilter/qemu-announce-self-rarp.xml
/etc/libvirt/nwfilter/qemu-announce-self.xml
/usr/share/polkit-1/actions/org.libvirt.api.policy
The bulk of these are fixed with this patch.
* examples/xml/nwfilter/Makefile.am (install-data-local)
(uninstall-local): Make conditional.
Signed-off-by: Eric Blake <eblake@redhat.com>
Consistently use "is" or "is not" to compare variables to None,
because doing so is preferrable, as per PEP 8
(http://www.python.org/dev/peps/pep-0008/#programming-recommendations):
> Comparisons to singletons like None should always be done with is or
> is not, never the equality operators.
Mingw *printf is a moving target; newer mingw now provides a version
of asprintf() that fails to understand %lld:
CC event_test-event-test.o
../../../../examples/domain-events/events-c/event-test.c: In function 'myDomainEventRTCChangeCallback':
../../../../examples/domain-events/events-c/event-test.c:270:18: error: unknown conversion type character 'l' in format [-Werror=format=]
virDomainGetID(dom), offset) < 0)
^
But since our examples already admitted that they were hacking around
a mingw deficiency, it is easier to just use printf() directly, coupled
with <inttypes.h> macros, for a more portable work-around.
* examples/domain-events/events-c/event-test.c
(myDomainEventRTCChangeCallback): Use PRIdMAX instead of asprintf.
Signed-off-by: Eric Blake <eblake@redhat.com>
Convert the type of loop iterators named 'i', 'j', k',
'ii', 'jj', 'kk', to be 'size_t' instead of 'int' or
'unsigned int', also santizing 'ii', 'jj', 'kk' to use
the normal 'i', 'j', 'k' naming
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
I noticed several unusual spacings in for loops, and decided to
fix them up. See the next commit for the syntax check that found
all of these.
* examples/domsuspend/suspend.c (main): Fix spacing.
* python/libvirt-override.c: Likewise.
* src/conf/interface_conf.c: Likewise.
* src/security/virt-aa-helper.c: Likewise.
* src/util/virconf.c: Likewise.
* src/util/virhook.c: Likewise.
* src/util/virlog.c: Likewise.
* src/util/virsocketaddr.c: Likewise.
* src/util/virsysinfo.c: Likewise.
* src/util/viruuid.c: Likewise.
* src/vbox/vbox_tmpl.c: Likewise.
* src/xen/xen_hypervisor.c: Likewise.
* tools/virsh-domain-monitor.c (vshDomainStateToString): Drop
default case, to let compiler check us.
* tools/virsh-domain.c (vshDomainVcpuStateToString): Likewise.
Signed-off-by: Eric Blake <eblake@redhat.com>
Update the hellolibvirt example program to demonstrate use of
the virGetLastErrorMessage() API for quick error reporting
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
In the domain-events example C code virEventRegisterDefaultImpl was being
called before virConnectOpen without first calling virInitialize. While this
code worked, it is incorrect. Adding a call to g_string_new prior to the call
to virEventRegisterDefaultImpl would cause the code to break. This fix will
help avoid unintentional misue of the API.
Relates to: Ret Hat Bugzilla - Bug 961155
When converting to virObject, the probes on the 'Free' functions
were removed on the basis that there is a probe on virObjectFree
that suffices. This puts a burden on people writing probe scripts
to identify which object is being dispose. This adds back probes
in the 'Dispose' functions and updates the rpc monitor systemtap
example to use them
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
Change the order of some conditions and use the AllDomains API to get
a list of all the active and defined domains, then use the Active and
Name API's in order to print.
This changes here adjust the output from:
Attempting to connect to hypervisor
Connected to hypervisor at "qemu:///system"
Hypervisor: "QEMU" version: 0.32.656
There are 0 active and 2 inactive domains
Inactive domains:
foo
bar
Disconnected from hypervisor
to
Attempting to connect to hypervisor
Connected to hypervisor at "qemu:///system"
Hypervisor: "QEMU" version: 0.32.656
There are 0 active and 2 inactive domains
foo (non-active)
bar (non-active)
Disconnected from hypervisor
Add code in the python binding to cope with the new APIs
virConnectRegisterCloseCallback and
virConnectUnregisterCloseCallback. Also demonstrate their
use in the python domain events demo
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
This is supposed to be thrown every time we need to pause domain
because of API execution (e.g. qemuDomainSaveInternal) but fails
to restore it back after. In this case, domain remains paused,
however, none of existing reasons can fit this scenario.
This patch adds support for SUSPEND_DISK event; both lifecycle and
separated. The support is added for QEMU, machines are changed to
PMSUSPENDED, but as QEMU sends SHUTDOWN afterwards, the state changes
to shut-off. This and much more needs to be done in order for libvirt
to work with transient devices, wake-ups etc. This patch is not
aiming for that functionality.
https://www.gnu.org/licenses/gpl-howto.html recommends that
the 'If not, see <url>.' phrase be a separate sentence.
* tests/securityselinuxhelper.c: Remove doubled line.
* tests/securityselinuxtest.c: Likewise.
* globally: s/; If/. If/
If there is only one detail string for a particular event, we need to pu
comma after the string otherwise the string itself will be taken as a
list and only its first character will be printed out. For example,
myDomainEventCallback1 EVENT: Domain fedora17(12) Shutdown F
instead of the desired
myDomainEventCallback1 EVENT: Domain fedora17(12) Shutdown Finished
The unused reason parameter of PM{Suspend,Wakeup} event callbacks was
completely ignored in lot of places and those events were not actually
working at all.
This patch provides AppArmor policy updates for the QEMU bridge helper.
The QEMU bridge helper is a SUID executable exec'd by QEMU that drops
capabilities to CAP_NET_ADMIN and adds a tap device to a network bridge.
Signed-off-by: Richa Marwaha <rmarwah@linux.vnet.ibm.com>
Signed-off-by: Corey Bryant<coreyb@linux.vnet.ibm.com>
some system call and signal will interrupt poll,
making event loop stops and fails to react events and keepalive message
from libvirt.
adding handling EINTR to poll to make it more robust
Signed-off-by: Royce Lv <lvroyce@linux.vnet.ibm.com>
When the guest changes its memory balloon applications may want
to know what the new value is, without having to periodically
poll on XML / domain info. Introduce a "balloon change" event
to let apps see this
* include/libvirt/libvirt.h.in: Define the
virConnectDomainEventBalloonChangeCallback callback
and VIR_DOMAIN_EVENT_ID_BALLOON_CHANGE constant
* python/libvirt-override-virConnect.py,
python/libvirt-override.c: Wire up helpers for new event
* daemon/remote.c: Helper for serializing balloon event
* examples/domain-events/events-c/event-test.c,
examples/domain-events/events-python/event-test.py: Add
example of balloon event usage
* src/conf/domain_event.c, src/conf/domain_event.h: Handling
of balloon events
* src/remote/remote_driver.c: Add handler of balloon events
* src/remote/remote_protocol.x: Define wire protocol for
balloon events
* src/remote_protocol-structs: Likewise.
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
A while back I wrote the attached code to demonstrate how to use
events and serial console to create a serial console that stays up
even when the VM is down. It might need some work, as I am not
terribly strong with Python.
* examples/python/consolecallback.py: New file.
* examples/python/Makefile.am (EXTRA_DIST): Ship it.
* libvirt.spec.in: Remove obsolete --with-remote-pid-file arg.
Add missing %{without_libxl} statement. Fix handling of docs
in client only build. Put systemtap files in -client RPM
instead of -daemon RPM
* examples/xml/nwfilter/Makefile.am: Don't install examples if
nwfilter is disabled.
The code is splattered with a mix of
sizeof foo
sizeof (foo)
sizeof(foo)
Standardize on sizeof(foo) and add a syntax check rule to
enforce it
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
Return statements with parameter enclosed in parentheses were modified
and parentheses were removed. The whole change was scripted, here is how:
List of files was obtained using this command:
git grep -l -e '\<return\s*([^()]*\(([^()]*)[^()]*\)*)\s*;' | \
grep -e '\.[ch]$' -e '\.py$'
Found files were modified with this command:
sed -i -e \
's_^\(.*\<return\)\s*(\(\([^()]*([^()]*)[^()]*\)*\))\s*\(;.*$\)_\1 \2\4_' \
-e 's_^\(.*\<return\)\s*(\([^()]*\))\s*\(;.*$\)_\1 \2\3_'
Then checked for nonsense.
The whole command looks like this:
git grep -l -e '\<return\s*([^()]*\(([^()]*)[^()]*\)*)\s*;' | \
grep -e '\.[ch]$' -e '\.py$' | xargs sed -i -e \
's_^\(.*\<return\)\s*(\(\([^()]*([^()]*)[^()]*\)*\))\s*\(;.*$\)_\1 \2\4_' \
-e 's_^\(.*\<return\)\s*(\([^()]*\))\s*\(;.*$\)_\1 \2\3_'
This introduces a new running reason VIR_DOMAIN_RUNNING_WAKEUP,
and new suspend event type VIR_DOMAIN_EVENT_STARTED_WAKEUP.
While a wakeup event is emitted, the domain which entered into
VIR_DOMAIN_PMSUSPENDED will be transferred to "running"
with reason VIR_DOMAIN_RUNNING_WAKEUP, and a new domain lifecycle
event emitted with type VIR_DOMAIN_EVENT_STARTED_WAKEUP.
This patch introduces a new event type for the QMP event
SUSPEND:
VIR_DOMAIN_EVENT_ID_PMSUSPEND
The event doesn't take any data, but considering there might
be reason for wakeup in future, the callback definition is:
typedef void
(*virConnectDomainEventSuspendCallback)(virConnectPtr conn,
virDomainPtr dom,
int reason,
void *opaque);
"reason" is unused currently, always passes "0".
This patch introduces a new event type for the QMP event
WAKEUP:
VIR_DOMAIN_EVENT_ID_PMWAKEUP
The event doesn't take any data, but considering there might
be reason for wakeup in future, the callback definition is:
typedef void
(*virConnectDomainEventWakeupCallback)(virConnectPtr conn,
virDomainPtr dom,
int reason,
void *opaque);
"reason" is unused currently, always passes "0".
This patch introduces a new event type for the QMP event
DEVICE_TRAY_MOVED, which occurs when the tray of a removable
disk is moved (i.e opened or closed):
VIR_DOMAIN_EVENT_ID_TRAY_CHANGE
The event's data includes the device alias and the reason
for tray status' changing, which indicates why the tray
status was changed. Thus the callback definition for the event
is:
enum {
VIR_DOMAIN_EVENT_TRAY_CHANGE_OPEN = 0,
VIR_DOMAIN_EVENT_TRAY_CHANGE_CLOSE,
\#ifdef VIR_ENUM_SENTINELS
VIR_DOMAIN_EVENT_TRAY_CHANGE_LAST
\#endif
} virDomainEventTrayChangeReason;
typedef void
(*virConnectDomainEventTrayChangeCallback)(virConnectPtr conn,
virDomainPtr dom,
const char *devAlias,
int reason,
void *opaque);
Unlike .cvsignore under CVS, git allows for ignoring nested
names. We weren't very consistent where new tests were
being ignored (some in .gitignore, some in tests/.gitignore),
and I found it easier to just consolidate everything.
* .gitignore: Subsume entries from subdirectories.
* daemon/.gitignore: Delete.
* docs/.gitignore: Likewise.
* docs/devhelp/.gitignore: Likewise.
* docs/html/.gitignore: Likewise.
* examples/dominfo/.gitignore: Likewise.
* examples/domsuspend/.gitignore: Likewise.
* examples/hellolibvirt/.gitignore: Likewise.
* examples/openauth/.gitignore: Likewise.
* examples/domain-events/events-c/.gitignore: Likewise.
* include/libvirt/.gitignore: Likewise.
* src/.gitignore: Likewise.
* src/esx/.gitignore: Likewise.
* tests/.gitignore: Likewise.
* tools/.gitignore: Likewise.
Execute bit on *.stp files in examples/systemtap/ caused dependency when
building RPM packages. Disabling execute permission should help the auto
dependency resolver to see that systemtap is not needed.
Fix a typing error in the no-ip-spoofing filter.
Return DHCP request packets passing through this filter. Have
the user use another filter to actually allow DHCP requests to be
sent (action='accept').
With fragments borrowed from David Steven's previous submission and some
further modifications:
A set of modifications to filters to handle multiple IP addresses
(and MAC addresses) per interface.
Also:
- enable DHCP traffic from VM to any DHCP server
- will require an update to a libvirt-tck data file
Signed-off-by: David L Stevens <dlstevens@us.ibm.com>
Signed-off-by: Stefan Berger <stefanb@linux.vnet.ibm.com>
Add APIs to the virNetSocket object, to allow file descriptors
to be sent/received over UNIX domain socket connections
* src/rpc/virnetsocket.c, src/rpc/virnetsocket.h,
src/libvirt_private.syms: Add APIs for FD send/recv
This change adds some systemtap/dtrace probes to the QEMU monitor
client code. In particular it allows watching of all operations
for a VM
* examples/systemtap/qemu-monitor.stp: Watch all monitor commands
* src/Makefile.am: Passing libdir/bindir/sbindir to dtrace2systemtap.pl
* src/dtrace2systemtap.pl: Accept libdir/bindir/sbindir as args
and look for '# binary:' comment to mark probes against libvirtd
vs libvirt.so
* src/qemu/qemu_monitor.c, src/qemu/qemu_monitor_json.c,
src/qemu/qemu_monitor_text.c: Add probes for key functions
If a disk source gets dropped because it is not accessible,
mgmt application might want to be informed about this. Therefore
we need to emit an event. The event presented in this patch
is however a bit superset of what written above. The reason is simple:
an intention to be easily expanded, e.g. on 'user ejected disk
in guest' events. Therefore, callback gets source string and disk alias
(which should be unique among a domain) and reason (an integer);
