Move the code for matching hostdev instances out of virDomainHostdevFind
and into virDomainHostdevMatch method, which in turn calls out to other
helper methods depending on the type of hostdev.
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
Rename virDomainHostdevPartsParse to virDomainHostdevDefParseSubsys
to reflect the fact that it only deals with hostdevs uing the
traditional mode=subsystem, and not mode=capabilities
Rename virDomainHostSourceFormat to virDomainHostdevDefFormatSubsys
for the same reason.
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
Interfaces keeps a class_id, which is an ID from which bridge
part of QoS settings is derived. We need to store class_id
in domain status file, so we can later pass it to
virNetDevBandwidthUnplug.
Currently, we are only keeping a inactive XML configuration
in status dir. This is no longer enough as we need to keep
this class_id attribute so we don't overwrite old entries
when the daemon restarts. However, since there has already
been release which has just <network/> as root element,
and we want to keep things compatible, detect that loaded
status file is older one, and don't scream about it.
Network should be notified if we plug in or unplug an
interface, so it can perform some action, e.g. set/unset
network part of QoS. However, we are doing this in very
early stage, so iface->ifname isn't filled in yet. So
whenever we want to report an error, we must use a different
identifier, e.g. the MAC address.
This is however supported only on domain interfaces with
type='network'. Moreover, target network needs to have at least
inbound QoS set. This is required by hierarchical traffic shaping.
From now on, the required attribute for <inbound/> is either 'average'
(old) or 'floor' (new). This new attribute can be used just for
interfaces type of network (<interface type='network'/>) currently.
The DHCPv6 support includes IPV6 dhcp-range and dhcp-host for one
IPv6 subnetwork on one interface. This support will only work
if dnsmasq version >= 2.64; otherwise an error occurs if
dhcp-range or dhcp-host is specified for an IPv6 address.
Essentially, this change provides the same DHCP support for IPv6
that has been available for IPv4.
With dnsmasq >= 2.64, support for the RA service is also now provided
by dnsmasq (radvd is no longer used/started). (Although at least one
version of dnsmasq prior to 2.64 "supported" IPv6 Router
Advertisement, there were bugs (fixed in 2.64) that rendered it
unusable.)
Documentation and the network schema has been updated
to reflect the new support.
virNetworkDefUpdateForward requires separate functions to parse and
clear a virNetworkForwardDef by itself, but they were previously just
inlined in the virNetworkDef parse and free functions. This patch
makes them into separate functions.
The attributes of a <network> element's <forward> element were
previously stored directly in the virNetworkDef object, but
virNetworkUpdateForward() needs to operate on a <forward> in
isolation, so this patchs pulls out all those attributes into a
separate virNetworkForwardDef struct (and shortens their names
appropriately). This new object is contained in the virNetworkDef, not
pointed to by it, so there is no extra memory management.
This patch makes no functional changes, it only changes, e.g.,
"nForwardIfs" to "forward.nifs".
The other clear functions in network_conf.c that clear out arrays of
sub-objects do so by using the n[itemname]s value as a counter going
down to 0. Make this one consistent. There's no functional value, just
makes the style more consistent with the rest of the file.
This makes some function names and arg lists for consistent with other
parse functions in network_conf.c. While modifying
virNetworkIPParseXML(), also change its "error" label to "cleanup",
since the code at that label is executed on success as well as
failure.
These three functions are very similar - none allow a MODIFY
operation; you can only add or delete.
The biggest difference between them (other than the data itself) is in
the criteria for determining a match, and whether or not multiple
matches are possible:
1) for HOST records, it's considered a match if the IP address or any
of the hostnames of an existing record matches.
2) for SRV records, it's a match if all of
domain+service+protocol+target *which have been specified* are
matched.
3) for TXT records, there is only a single field to match - name
(value can be the same for multiple records, and isn't considered a
search term), so by definition there can be no ambiguous matches.
In all three cases, if any matches are found, ADD will fail; if
multiple matches are found, it means the search term was ambiguous,
and a DELETE will fail.
The upper level code in bridge_driver.c is already implemented for
these functions - appropriate conf files will be re-written, and
dnsmasq will be SIGHUPed or restarted as appropriate.
Since there is only a single virNetworkDNSDef for any virNetworkDef,
and it's trivial to determine whether or not it contains any real
data, it's much simpler (and fits more uniformly with the parse
function calling sequence of the parsers for many other objects that
are subordinates of virNetworkDef) if virNetworkDef *contains* an
virNetworkDNSDef rather than pointing to one.
Since it is now just a part of another object rather than its own
object, it no longer makes sense to have a *Free() function, so that
is changed to a *Clear() function.
More importantly though, ParseXML and Clear functions are needed for
the individual items contained in a virNetworkDNSDef (srv, txt, and
host records), but none of them have a *Clear(), and only two of the
three had *ParseXML() functions (both of which used a non-uniform
arglist). Those problems are cleared up by this patch - it splits the
higher-level Clear function into separate functions for each of the
three, creates a parse for txt records, and cleans up the srv and host
parsers, so we now have all the utility functions necessary to
implement virNetworkDefUpdateDNS(Host|Srv|Txt).
This shortens the name of the structs for srv and txt, and their
instances in virNetworkDNSDef, to be more compact and uniform with the
naming of the dns host array. It also changes the type of ntxts, etc
from unsigned int to size_t, so that they can be used directly as args
to VIR_*_ELEMENT.
The already-written backend functions for virNetworkUpdate that add
and delete items into lists within the a network were already debugged
to work properly, but future such functions will use
VIR_(INSERT|DELETE)_ELEMENT instead, so these are changed for
uniformity.
QEMU supports setting vendor and product strings for disk since
1.2.0 (only scsi-disk, scsi-hd, scsi-cd support it), this patch
exposes it with new XML elements <vendor> and <product> of disk
device.
This resolves: https://bugzilla.redhat.com/show_bug.cgi?id=767057
It was possible to define a network with <forward mode='bridge'> that
had both a bridge device and a forward device defined. These two are
mutually exclusive by definition (if you are using a bridge device,
then this is a host bridge, and if you have a forward dev defined,
this is using macvtap). It was also possible to put <ip>, <dns>, and
<domain> elements in this definition, although those aren't supported
by the current driver (although it's conceivable that some other
driver might support that).
The items that are invalid by definition, are now checked in the XML
parser (since they will definitely *always* be wrong), and the others
are checked in networkValidate() in the network driver (since, as
mentioned, it's possible that some other network driver, or even this
one, could some day support setting those).
This patch adds the capability for virtual guests to do IPv6
communication via a virtual network interface with no IPv6 (gateway)
addresses specified. This capability has always been enabled by
default for IPv4, but disabled for IPv6 for security concerns, and
because it requires the ip6tables command to be operational (which
isn't the case on a system with the ipv6 module completely disabled).
This patch adds a new attribute "ipv6" at the toplevel of a <network>
object. If ipv6='yes', the extra ip6tables rules required to permite
inter-guest communications are added when the network is started. If
it is 'no', or not present, those rules will not be added; thus the
default behavior doesn't change, so there should be no compatibility
issues with any existing installations.
Note that virtual guests cannot communication with the virtualization
host via this interface, because the following kernel tunable has
been set:
net.ipv6.conf.<bridge_interface_name>.disable_ipv6 = 1
This assures that the bridge interface will not have an IPv6
link-local (fe80::) address.
To control this behavior so that it is not enabled by default, the parameter
ipv6='yes' on the <network> statement has been added.
Documentation related to this patch has been updated.
The network schema has also been updated.
Since we can't (currently) rely on the ability to provide blanket
support for all possible network changes by calling the toplevel
netdev hostside disconnect/connect functions (due to qemu only
supporting a lockstep between initialization of host side and guest
side of devices), in order to support live change of an interface's
nwfilter we need to make a special purpose function to only call the
nwfilter teardown and setup functions if the filter for an interface
(or its parameters) changes. The pattern is nearly identical to that
used to change the bridge that an interface is connected to.
This patch was inspired by a request from Guido Winkelmann
<guido@sagersystems.de>, who tested an earlier version.
To detect if an interface's nwfilter has changed, we need to also
compare the filterparams, which is a hashtable of virNWFilterVarValue.
virHashEqual can do this nicely, but requires a pointer to a function
that will compare two of the items being stored in the hashes.
This resolves:
https://bugzilla.redhat.com/show_bug.cgi?id=881480
These three functions:
virDomainNetGetActualBridgeName
virDomainNetGetActualDirectDev
virDomainNetGetActualDirectMode
return attributes that are in a union whose contents are interpreted
differently depending on the actual->type and so they should only
return non-0 when actual->type is 'bridge' (in the first case) or
'direct' (in the other two cases, but I had neglected to do that, so
...DirectDev() was returning bridge.brname (which happens to share the
same spot in the union with direct.linkdev) if actual->type was
'bridge', and ...BridgeName was returning direct.linkdev when
actual->type was 'direct'.
How does this involve Bug 881480 (which was about the inability to
switch between two networks that both have "<forward mode='bridge'/>
<bridge name='xxx'/>"? Whenever the return value of
virDomainNetGetActualDirectDev() for the new and old network
definitions doesn't match, qemuDomainChangeNet() requires a "complete
reconnect" of the device, which qemu currently doesn't
support. ...DirectDev() *should* have been returning NULL for old and
new, but was instead returning the old and new bridge names, which
differ.
(The other two functions weren't causing any behavioral problems in
virDomainChangeNet(), but their problem and fix was identical, so I
included them in this same patch).
Fix the null pointer access when UUID is not specified.
Introduce a bool 'uuidUsable' to virStoragePoolAuthCephx that indicates
if uuid was specified or not and use it instead of the pointless
comparison of the static UUID array to NULL.
Add an error message if both uuid and usage are specified.
Fixes:
Error: FORWARD_NULL (CWE-476):
libvirt-0.10.2/src/conf/storage_conf.c:461: var_deref_model: Passing
null pointer "uuid" to function "virUUIDParse(char const *, unsigned
char *)", which dereferences it. (The dereference is assumed on the
basis of the 'nonnull' parameter attribute.)
Error: NO_EFFECT (CWE-398):
libvirt-0.10.2/src/conf/storage_conf.c:979: array_null: Comparing an
array to null is not useful: "src->auth.cephx.secret.uuid != NULL".
Found by coverity:
Error: REVERSE_INULL (CWE-476):
libvirt-0.10.2/src/conf/netdev_bandwidth_conf.c:99: deref_ptr:
Directly dereferencing pointer "node".
libvirt-0.10.2/src/conf/netdev_bandwidth_conf.c:107:
check_after_deref: Null-checking "node" suggests that it may be
null, but it has already been dereferenced on all paths leading to
the check.
This resolves: https://bugzilla.redhat.com/show_bug.cgi?id=879473
The name attribute is required for portgroup elements (yes, the RNG
specifies that), and there is code in libvirt that assumes it is
non-null. Unfortunately, the portgroup parsing function wasn't
checking for lack of portgroup. One adverse result of this was that
attempts to update a network by adding a portgroup with no name would
cause libvirtd to segfault. For example:
virsh net-update default add portgroup "<portgroup default='yes'/>"
This patch causes virNetworkPortGroupParseXML to fail if no name is
specified, thus avoiding any later problems.
In a few places, the return value could get passed to VIR_ALLOC_N without
being checked, resulting in a request to allocate a lot of memory if the
return value was negative.
This patch introduces the RNG schema and updates necessary data strucutures
to allow various hypervisors to make use of Gluster protocol as one of the
supported network disk backend. Next patch will add support to make use of
this feature in Qemu since it now supports Gluster protocol as one of the
network based storage backend.
Two new optional attributes for <host> element are introduced - 'transport'
and 'socket'. Valid transport values are tcp, unix or rdma. If none specified,
tcp is assumed. If transport is unix, socket specifies path to unix socket.
This patch allows users to specify disks on gluster backends like this:
<disk type='network' device='disk'>
<driver name='qemu' type='raw'/>
<source protocol='gluster' name='Volume1/image'>
<host name='example.org' port='6000' transport='tcp'/>
</source>
<target dev='vda' bus='virtio'/>
</disk>
<disk type='network' device='disk'>
<driver name='qemu' type='raw'/>
<source protocol='gluster' name='Volume2/image'>
<host transport='unix' socket='/path/to/sock'/>
</source>
<target dev='vdb' bus='virtio'/>
</disk>
Signed-off-by: Harsh Prateek Bora <harsh@linux.vnet.ibm.com>
This will simplify the refactoring of the ESX storage driver to support
a VMFS and an iSCSI backend.
One of the tasks the storage driver needs to do is to decide which backend
driver needs to be invoked for a given request. This approach extends
virStoragePool and virStorageVol to store extra parameters:
1. privateData: stores pointer to respective backend storage driver.
2. privateDataFreeFunc: stores cleanup function pointer.
virGetStoragePool and virGetStorageVol are modfied to accept these extra
parameters as user params. virStoragePoolDispose and virStorageVolDispose
checks for cleanup operation if available.
The private data pointer allows the ESX storage driver to store a pointer
to the used backend with each storage pool and volume. This avoids the need
to detect the correct backend in each storage driver function call.
The error "... but the cause is unknown" appeared for XMLs similar to
this:
<disk type='file' device='cdrom'>
<driver name='qemu' type='raw'/>
<source file='/dev/zero'/>
<target dev='sr0'/>
</disk>
Notice unsupported disk type (for the driver), but also no address
specified. The first part is not a problem and we should not abort
immediately because of that, but the combination with the address
unknown was causing an unspecified error.
While fixing this, I added an error to one place where this return
value was not managed properly.
Currently the LXC driver logs audit messages when a container
is started or stopped. These audit messages, however, contain
the PID of the libvirt_lxc supervisor process. To enable
sysadmins to correlate with audit messages generated by
processes /inside/ the container, we need to include the
container init process PID.
We can't do this in the main 'start' audit message, since
the init PID is not available at that point. Instead we output
a completely new audit record, that lists both PIDs.
type=VIRT_CONTROL msg=audit(1353433750.071:363): pid=20180 uid=0 auid=501 ses=3 subj=unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023 msg='virt=lxc op=init vm="busy" uuid=dda7b947-0846-1759-2873-0f375df7d7eb vm-pid=20371 init-pid=20372 exe="/home/berrange/src/virt/libvirt/daemon/.libs/lt-libvirtd" hostname=? addr=? terminal=pts/6 res=success'
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
Commit a4c19459aa only added the
QEMU capability flag, command line option and added the boot element
for redirdev's in the XML schema.
This patch adds support for parsing and writing the XML with redirdevs
with the boot flag. It also ignores unknown XML elements in redirdev
instead of failing with:
"error: An error occurred, but the cause is unknown"
Bug: https://bugzilla.redhat.com/show_bug.cgi?id=805414
Upcoming patches for revert-and-clone branching of snapshots need
to be able to copy a domain definition; make this step reusable.
* src/conf/domain_conf.h (virDomainDefCopy): New prototype.
* src/conf/domain_conf.c (virDomainObjCopyPersistentDef): Split...
(virDomainDefCopy): ...into new function.
(virDomainObjSetDefTransient): Use it.
* src/libvirt_private.syms (domain_conf.h): Export it.
* src/qemu/qemu_driver.c (qemuDomainRevertToSnapshot): Use it.
Relatively straight-forward. And since qemu was already using
VIR_DOMAIN_SNAPSHOT_FILTERS_ALL, with 6 different APIs all calling
into this common code, I've instantly added all 5 flags to 6 APIs.
* src/conf/snapshot_conf.h (VIR_DOMAIN_SNAPSHOT_FILTERS_ALL):
Enable new filters.
* src/conf/snapshot_conf.c (virDomainSnapshotObjListGetNames):
Prep the new flags.
(virDomainSnapshotObjListCopyNames): Actually do the filtering.
As we enable more modes of snapshot creation, it becomes more important
to be able to quickly filter based on snapshot properties. This patch
introduces new filter flags; subsequent patches will introduce virsh
back-compat filtering, as well as actual libvirt filtering.
* include/libvirt/libvirt.h.in (virDomainSnapshotListFlags): Add
five new flags in two new groups.
* src/libvirt.c (virDomainSnapshotNum, virDomainSnapshotListNames)
(virDomainListAllSnapshots, virDomainSnapshotNumChildren)
(virDomainSnapshotListChildrenNames)
(virDomainSnapshotListAllChildren): Document them.
* src/conf/snapshot_conf.h (VIR_DOMAIN_SNAPSHOT_FILTERS_STATUS)
(VIR_DOMAIN_SNAPSHOT_FILTERS_LOCATION): Add new convenience filter
collection macros.
* tools/virsh-snapshot.c (cmdSnapshotList): Add 5 new flags.
* tools/virsh.pod (snapshot-list): Document them.
This resolves:
https://bugzilla.redhat.com/show_bug.cgi?id=873134
The reported problem is that an attempt to restore a saved domain that
was configured with <currentMemory> and <memory> set to some (same for
both) number that's not a multiple of 4096KiB results in an error like
this:
error: Failed to start domain libvirt_test_api
error: XML error: current memory '4001792k' exceeds maximum '4000768k'
(in this case, currentMemory was set to 4000000KiB).
The reason for this failure is:
1) a saved image contains the "live xml" of the domain at the time of
the save.
2) the live xml of a running domain gets its currentMemory
(a.k.a. cur_balloon) directly from the qemu monitor rather than from
the configuration of the domain.
3) the value reported by qemu is (sometimes) not exactly what was
originally given to qemu when the domain was started, but is rounded
up to [some indeterminate granularity] - in some versions of qemu that
granularity is apparently 1MiB, and in others it is 4MiB.
4) When the XML is parsed to setup the state of the restored domain,
the XML parser for <currentMemory> compares it to <memory> (which is
the maximum allowed memory size for the domain) and if <currentMemory>
is greater than the next 1024KiB boundary above <memory>, it spits out
an error and fails.
For example (from the BZ) if you start qemu on RHEL6 with both
<currentMemory> and <memory> of 4000000 (this number is in KiB),
libvirt's dominfo or dumpxml will report "4001792" back (rounded up to
next 4MiB) for 10-20 seconds after the start, then revert to reporting
"4000000". On Fedora 16 (which uses qemu-1.0), it will instead report
"4000768" (rounded up to next 1MiB). On Fedora 17 (qemu-1.2), it seems
to always report "4000000". ("4000000" is of course okay, and
"4000768" is also okay since that's the next 1024KiB boundary above
"4000000" and the parser was already allowing for that. But "4001792
is *not* okay and produces the error message.)
This patch solves the problem by changing the allowed "fudge factor"
when parsing from 1024KiB to 4096KiB to match the maximum up-rounding
that could be done in qemu.
(I had earlier thought to fix this by up-rounding <memory> in the
dumpxml that's put into the saved image, but that wouldn't have fixed
the case where the save image was produced by an "unfixed"
libvirtd.)
For disk snapshots, the user could request an external snapshot
but not supply a filename; later on, we would check this condition
and generate a suitable name if possible, or gracefully error out
when not possible (such as when the original file was a block
device). But unless we come up with a suitable way to generate
external memory file names, we have no later code point that was
checking for NULL, so we should forbid this up front.
* src/conf/snapshot_conf.c (virDomainSnapshotDefParseString):
Avoid NULL deref, since we don't generate names yet.
This patch adds a helper to determine if snapshots are external and uses
the helper to fix detection of those in snapshot deletion code.
Snapshots are external if they have an external memory image or if the
disk locations are external. As mixed snapshots are forbidden for now
we need to check just one disk to know.
For S390, the default console target type cannot be of type 'serial'.
It is necessary to at least interpret the 'arch' attribute
value of the os/type element to produce the correct default type.
Therefore we need to extend the signature of defaultConsoleTargetType
to account for architecture. As a consequence all the drivers
supporting this capability function must be updated.
Despite the amount of changed files, the only change in behavior is
that for S390 the default console target type will be 'virtio'.
N.B.: A more future-proof approach could be to to use hypervisor
specific capabilities to determine the best possible console type.
For instance one could add an opaque private data pointer to the
virCaps structure (in case of QEMU to hold capsCache) which could
then be passed to the defaultConsoleTargetType callback to determine
the console target type.
Seems to be however a bit overengineered for the use case...
Signed-off-by: Viktor Mihajlovski <mihajlov@linux.vnet.ibm.com>
There were not previous callers with require_match set to true.
I originally implemented this bool with the intent of supporting
ESX snapshot semantics, where the choice of internal vs. external
vs. non-checkpointable must be made at domain start, but as ESX
has not been wired up to use it yet, we might as well fix it to
work with our next qemu patch for now, and worry about any further
improvements (changing the bool to a flags argument) if the ESX
driver decides to use this function in the future.
* src/conf/snapshot_conf.c (virDomainSnapshotAlignDisks): Alter
logic when require_match is true to deal with new XML.
Each <domainsnapshot> can now contain an optional <memory>
element that describes how the VM state was handled, similar
to disk snapshots. The new element will always appear in
output; for back-compat, an input that lacks the element will
assume 'no' or 'internal' according to the domain state.
Along with this change, it is now possible to pass <disks> in
the XML for an offline snapshot; this also needs to be wired up
in a future patch, to make it possible to choose internal vs.
external on a per-disk basis for each disk in an offline domain.
At that point, using the --disk-only flag for an offline domain
will be able to work.
For some examples below, remember that qemu supports the
following snapshot actions:
qemu-img: offline external and internal disk
savevm: online internal VM and disk
migrate: online external VM
transaction: online external disk
=====
<domainsnapshot>
<memory snapshot='no'/>
...
</domainsnapshot>
implies that there is no VM state saved (mandatory for
offline and disk-only snapshots, not possible otherwise);
using qemu-img for offline domains and transaction for online.
=====
<domainsnapshot>
<memory snapshot='internal'/>
...
</domainsnapshot>
state is saved inside one of the disks (as in qemu's 'savevm'
system checkpoint implementation). If needed in the future,
we can also add an attribute pointing out _which_ disk saved
the internal state; maybe disk='vda'.
=====
<domainsnapshot>
<memory snapshot='external' file='/path/to/state'/>
...
</domainsnapshot>
This is not wired up yet, but future patches will allow this to
control a combination of 'virsh save /path/to/state' plus disk
snapshots from the same point in time.
=====
So for 1.0.1 (and later, as needed), I plan to implement this table
of combinations, with '*' designating new code and '+' designating
existing code reached through new combinations of xml and/or the
existing DISK_ONLY flag:
domain memory disk disk-only | result
-----------------------------------------
offline omit omit any | memory=no disk=int, via qemu-img
offline no omit any |+memory=no disk=int, via qemu-img
offline omit/no no any | invalid combination (nothing to snapshot)
offline omit/no int any |+memory=no disk=int, via qemu-img
offline omit/no ext any |*memory=no disk=ext, via qemu-img
offline int/ext any any | invalid combination (no memory to save)
online omit omit off | memory=int disk=int, via savevm
online omit omit on | memory=no disk=default, via transaction
online omit no/ext off | unsupported for now
online omit no on | invalid combination (nothing to snapshot)
online omit ext on | memory=no disk=ext, via transaction
online omit int off |+memory=int disk=int, via savevm
online omit int on | unsupported for now
online no omit any |+memory=no disk=default, via transaction
online no no any | invalid combination (nothing to snapshot)
online no int any | unsupported for now
online no ext any |+memory=no disk=ext, via transaction
online int/ext any on | invalid combination (disk-only vs. memory)
online int omit off |+memory=int disk=int, via savevm
online int no/ext off | unsupported for now
online int int off |+memory=int disk=int, via savevm
online ext omit off |*memory=ext disk=default, via migrate+trans
online ext no off |+memory=ext disk=no, via migrate
online ext int off | unsupported for now
online ext ext off |*memory=ext disk=ext, via migrate+transaction
* docs/schemas/domainsnapshot.rng (memory): New RNG element.
* docs/formatsnapshot.html.in: Document it.
* src/conf/snapshot_conf.h (virDomainSnapshotDef): New fields.
* src/conf/domain_conf.c (virDomainSnapshotDefFree)
(virDomainSnapshotDefParseString, virDomainSnapshotDefFormat):
Manage new fields.
* tests/domainsnapshotxml2xmltest.c: New test.
* tests/domainsnapshotxml2xmlin/*.xml: Update existing tests.
* tests/domainsnapshotxml2xmlout/*.xml: Likewise.
The libvirt coding standard is to use 'function(...args...)'
instead of 'function (...args...)'. A non-trivial number of
places did not follow this rule and are fixed in this patch.
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
In the XML warning, we print a virsh command line that can be used to
edit that XML. This patch prints UUIDs if the entity name contains
special characters (like shell metacharacters, or "--" that would break
parsing of the XML comment). If the entity doesn't have a UUID, just
print the virsh command that can be used to edit it.
