[libvirt] Supporting vhost-net and macvtap in libvirt for QEMU
by Anthony Liguori
Disclaimer: I am neither an SR-IOV nor a vhost-net expert, but I've CC'd
people that are who can throw tomatoes at me for getting bits wrong :-)
I wanted to start a discussion about supporting vhost-net in libvirt.
vhost-net has not yet been merged into qemu but I expect it will be soon
so it's a good time to start this discussion.
There are two modes worth supporting for vhost-net in libvirt. The
first mode is where vhost-net backs to a tun/tap device. This is
behaves in very much the same way that -net tap behaves in qemu today.
Basically, the difference is that the virtio backend is in the kernel
instead of in qemu so there should be some performance improvement.
Current, libvirt invokes qemu with -net tap,fd=X where X is an already
open fd to a tun/tap device. I suspect that after we merge vhost-net,
libvirt could support vhost-net in this mode by just doing -net
vhost,fd=X. I think the only real question for libvirt is whether to
provide a user visible switch to use vhost or to just always use vhost
when it's available and it makes sense. Personally, I think the later
makes sense.
The more interesting invocation of vhost-net though is one where the
vhost-net device backs directly to a physical network card. In this
mode, vhost should get considerably better performance than the current
implementation. I don't know the syntax yet, but I think it's
reasonable to assume that it will look something like -net
tap,dev=eth0. The effect will be that eth0 is dedicated to the guest.
On most modern systems, there is a small number of network devices so
this model is not all that useful except when dealing with SR-IOV
adapters. In that case, each physical device can be exposed as many
virtual devices (VFs). There are a few restrictions here though. The
biggest is that currently, you can only change the number of VFs by
reloading a kernel module so it's really a parameter that must be set at
startup time.
I think there are a few ways libvirt could support vhost-net in this
second mode. The simplest would be to introduce a new tag similar to
<source network='br0'>. In fact, if you probed the device type for the
network parameter, you could probably do something like <source
network='eth0'> and have it Just Work.
Another model would be to have libvirt see an SR-IOV adapter as a
network pool whereas it handled all of the VF management. Considering
how inflexible SR-IOV is today, I'm not sure whether this is the best model.
Has anyone put any more thought into this problem or how this should be
modeled in libvirt? Michael, could you share your current thinking for
-net syntax?
--
Regards,
Anthony Liguori
1 year
[libvirt] JNA Error Callback could cause core dump.
by Benjamin Wang (gendwang)
Hi,
When I changed code as following:
public class Connect {
// Load the native part
static {
Libvirt.INSTANCE.virInitialize();
try {
ErrorHandler.processError(Libvirt.INSTANCE);
} catch (Exception e) {
e.printStackTrace();
}
+ Libvirt.INSTANCE.virSetErrorFunc(null, new ErrorCallback());
}
The server will generate the following core dump:
Program terminated with signal 6, Aborted.
#0 0x0000003f9b030265 in raise () from /lib64/libc.so.6
(gdb) where
#0 0x0000003f9b030265 in raise () from /lib64/libc.so.6
#1 0x0000003f9b031d10 in abort () from /lib64/libc.so.6
#2 0x0000003f9b06a84b in __libc_message () from /lib64/libc.so.6
#3 0x0000003f9b07230f in _int_free () from /lib64/libc.so.6
#4 0x0000003f9b07276b in free () from /lib64/libc.so.6
#5 0x00002aaaacf46868 in ?? ()
#6 0x0000000000000000 in ?? ()
The problem was caused that when JNA call setErrorFunc, it will create ErrorCallback object. But when GC is executed, the object is GCed. But even I change code as following.
When GC is excuted, the callback object will be moved. Then C can't find this object. Both of scenarios will cause core dump. It seems that JNA mustn't provide ErrorCallback Class,
Because nobody can use this.
Please correct me.
public class Connect {
+ private static final ErrorCallback callback = new ErrorCallback();
// Load the native part
static {
Libvirt.INSTANCE.virInitialize();
try {
ErrorHandler.processError(Libvirt.INSTANCE);
} catch (Exception e) {
e.printStackTrace();
}
+ Libvirt.INSTANCE.virSetErrorFunc(null, callback);
}
B.R.
Benjamin Wang
10 years, 11 months
[libvirt] [PATCH 0/2] qemu: Rework CD/DVD changing
by Michal Privoznik
The first patch is bare bug fix (without any bug reported though).
The second is again a bug fix, but not so easy to spot. Basically, when we
change a media, we should issue 'eject' first, then wait until the tray gets
open, after which we can finally issue 'change' command. Even for bare 'eject'
we ought to check status, shouldn't we?
Michal Privoznik (2):
qemu_monitor: Fix tray-open attribute in query-block
qemu_hotplug: Rework media changing process
src/qemu/qemu_hotplug.c | 51 +++++++++++++++++++++++++++++++++++++++++---
src/qemu/qemu_monitor_json.c | 2 +-
src/qemu/qemu_monitor_text.c | 6 +++---
3 files changed, 52 insertions(+), 7 deletions(-)
--
1.8.0.2
11 years, 6 months
[libvirt] New application
by Maciej Nabożny
Hello,
I'm developer of CC1 project in Institute of Nuclear Physics in
Cracow. We are creating cloud computing system based on Libvirt. Is it
possible to add link to our project at yours website in applications
section?
Title: CC1 Project (http://cc1.ifj.edu.pl)
Description: The Cloud Computing for Science and Economy project
At this time we are using version 0.8.3, but as soon as debian 7 will
we stable, we are going to migrate to newer version of Libvirt.
Regards,
Maciej Nabożny
11 years, 6 months
[libvirt] [PATCH] ESX: Fix DISPATCH_FREE generation code to free all extended objects
by Ata E Husain Bohra
Python code generator "generate_source" section that handles
code generation to "free" inherited objects needs to generate
DISPATCH_FREE calls for all extended_by objects.
---
src/esx/esx_vi_generator.py | 21 ++++++++++++++++++---
1 file changed, 18 insertions(+), 3 deletions(-)
diff --git a/src/esx/esx_vi_generator.py b/src/esx/esx_vi_generator.py
index af4e7e8..7a7cf76 100755
--- a/src/esx/esx_vi_generator.py
+++ b/src/esx/esx_vi_generator.py
@@ -4,6 +4,7 @@
# esx_vi_generator.py: generates most of the SOAP type mapping code
#
# Copyright (C) 2010-2012 Matthias Bolte <matthias.bolte(a)googlemail.com>
+# Copyright (C) 2013 Ata E Husain Bohra <ata.husain(a)hotmail.com>
#
# This library is free software; you can redistribute it and/or
# modify it under the terms of the GNU Lesser General Public
@@ -785,9 +786,7 @@ class Object(Type):
source += "ESX_VI__TEMPLATE__DYNAMIC_FREE(%s,\n" % self.name
source += "{\n"
- for extended_by in self.extended_by:
- source += " ESX_VI__TEMPLATE__DISPATCH__FREE(%s)\n" \
- % extended_by
+ source += recurse_dispatch(self, "ESX_VI__TEMPLATE__DISPATCH__FREE")
source += "},\n"
source += "{\n"
@@ -1285,6 +1284,22 @@ class ManagedObject(Type):
+def recurse_dispatch(object, text):
+
+ source = ""
+
+ if object.extended_by is None:
+ return source
+
+ for extended_by in object.extended_by:
+ source += " %s(%s)\n" % (text, extended_by)
+ child = objects_by_name[extended_by]
+ source += recurse_dispatch(child, text)
+
+ return source
+
+
+
class Enum(Type):
FEATURE__ANY_TYPE = (1 << 1)
FEATURE__SERIALIZE = (1 << 2)
--
1.7.9.5
11 years, 6 months
[libvirt] [RFC] New API to retrieve node CPU map
by Viktor Mihajlovski
Hi,
in order to use the APIs listed below it is necessary for a client to
know the maximum number of node CPUs which is passed via the maplen
argument.
virDomainGetEmulatorPinInfo
virDomainGetVcpuPinInfo
virDomainGetVcpus
virDomainPinEmulator
virDomainPinVcpu
virDomainPinVcpuFlags
The current approach uses virNodeGetInfo to determine the maximum CPU
number. This can lead to incorrect results if not all node CPUs are
online. The maximum CPU number should always be the number of CPUs
present on the host, regardless of their online/offline state.
The following example illustrates the issue:
Host has 3 logical CPUs, 1 socket, 3 cores, 1 thread.
Guest has 1 virtual CPU and is started while all 3 host CPUs are
online.
$ virsh vcpuinfo guest
VCPU: 0
CPU: 0
State: running
CPU time: 35.4s
CPU Affinity: yyy
$ echo 0 > /sys/devices/system/cpu/cpu1/online
$ virsh vcpuinfo guest
VCPU: 0
CPU: 0
State: running
CPU time: 35.5s
CPU Affinity: y-
The correct display for CPU affinity would have been y-y, as the guest
continues to use CPUs 0 and 2.
This is not a display problem only, because it is also not possible to
explicitly pin the virtual CPU to host CPUs 0 and 2, due to the
truncated CPU mask.
PROPOSAL:
To help solve the issue above I suggest two new public API functions:
int
virNodeGetCpuNum(virConnectPtr conn);
returning the number of present CPUs on the host or -1 upon failure
and
int
virNodeGetCpuMap(virConnectPtr conn, unsigned char * cpumap, int maplen);
returning the number of present CPUs or -1 on failure and storing a bit
map of real CPUs as described in virDomainPinVcpu in cpumap. The bits in
the bit map are set to 1 for online CPUs and set to 0 for offline CPUs.
Implementation is facilitated by the function nodeGetCPUmap in nodeinfo.c.
Clients can use virNodeGetCpuNum to properly determine the maximum
number of node CPUs and the online/offline information.
Thanks for your comments.
--
Mit freundlichen Grüßen/Kind Regards
Viktor Mihajlovski
IBM Deutschland Research & Development GmbH
Vorsitzender des Aufsichtsrats: Martin Jetter
Geschäftsführung: Dirk Wittkopp
Sitz der Gesellschaft: Böblingen
Registergericht: Amtsgericht Stuttgart, HRB 243294
11 years, 6 months
[libvirt] [PATCHv2] Configure native vlan modes on Open vSwitch ports
by james robson
This patch adds functionality to allow libvirt to configure the
'native-tagged' and 'native-untagged' modes on openvswitch networks.
v2 changes:
Fix problems reported by Eric Blake
---
diff --git a/docs/formatdomain.html.in b/docs/formatdomain.html.in
index ffcc33e..a5054cc 100644
--- a/docs/formatdomain.html.in
+++ b/docs/formatdomain.html.in
@@ -3209,6 +3209,12 @@ qemu-kvm -net nic,model=? /dev/null
<parameters
interfaceid='09b11c53-8b5c-4eeb-8f00-d84eaa0aaa4f'/>
</virtualport>
</interface>
+ <interface type='bridge'>
+ <b><vlan trunk='yes' native_mode='tagged'
native_tag='123'></b>
+ <b><tag id='42'/></b>
+ <b></vlan></b>
+ ...
+ </interface>
<devices>
...</pre>
@@ -3234,7 +3240,17 @@ qemu-kvm -net nic,model=? /dev/null
attribute <code>trunk='yes'</code> can be added to the toplevel
vlan element.
</p>
-
+ <p>
+ For network connections using openvswitch it is possible to
+ configure the 'native-tagged' and 'native-untagged' vlan modes
+ <span class="since">(Since 1.0.3).</span> This uses the optional
+ <code>native_mode</code> and <code>native_tag</code> attributes
+ on the <code><vlan></code> element:
<code>native_mode</code>
+ may be set to 'tagged' or 'untagged', <code>native_tag</code>
+ sets the id of the native vlan. Setting a native vlan implies
+ this is a trunk port, so <code>trunk='yes'</code> will be added
if not
+ explicitly set.
+ </p>
<h5><a name="elementLink">Modifying virtual link state</a></h5>
<pre>
...
diff --git a/docs/formatnetwork.html.in b/docs/formatnetwork.html.in
index 7b42529..68c562b 100644
--- a/docs/formatnetwork.html.in
+++ b/docs/formatnetwork.html.in
@@ -396,6 +396,12 @@
<parameters
interfaceid='09b11c53-8b5c-4eeb-8f00-d84eaa0aaa4f'/>
</virtualport>
</interface>
+ <interface type='bridge'>
+ <b><vlan trunk='yes' native_mode='tagged'
native_tag='123'></b>
+ <b><tag id='42'/></b>
+ <b></vlan></b>
+ ...
+ </interface>
<devices>
...</pre>
diff --git a/docs/schemas/networkcommon.rng
b/docs/schemas/networkcommon.rng
index 51ff759..4696f43 100644
--- a/docs/schemas/networkcommon.rng
+++ b/docs/schemas/networkcommon.rng
@@ -197,6 +197,21 @@
<value>yes</value>
</attribute>
</optional>
+ <optional>
+ <attribute name="native_mode">
+ <choice>
+ <value>tagged</value>
+ <value>untagged</value>
+ </choice>
+ </attribute>
+ </optional>
+ <optional>
+ <attribute name="native_tag">
+ <data type="unsignedInt">
+ <param name="maxInclusive">4095</param>
+ </data>
+ </attribute>
+ </optional>
<oneOrMore>
<element name="tag">
<attribute name="id">
diff --git a/src/conf/netdev_vlan_conf.c b/src/conf/netdev_vlan_conf.c
index 13ba8c6..618eb4c 100644
--- a/src/conf/netdev_vlan_conf.c
+++ b/src/conf/netdev_vlan_conf.c
@@ -17,6 +17,7 @@
*
* Authors:
* Laine Stump <laine(a)redhat.com>
+ * James Robson <jrobson(a)websense.com>
*/
#include <config.h>
@@ -33,6 +34,8 @@ virNetDevVlanParse(xmlNodePtr node, xmlXPathContextPtr
ctxt, virNetDevVlanPtr de
int ret = -1;
xmlNodePtr save = ctxt->node;
const char *trunk = NULL;
+ const char *nativeMode;
+ unsigned int nativeTag;
xmlNodePtr *tagNodes = NULL;
int nTags, ii;
@@ -73,16 +76,44 @@ virNetDevVlanParse(xmlNodePtr node,
xmlXPathContextPtr ctxt, virNetDevVlanPtr de
def->nTags = nTags;
- /* now that we know how many tags there are, look for an explicit
- * trunk setting.
- */
- if (nTags > 1)
- def->trunk = true;
+ def->nativeMode = 0;
+ def->nativeTag = 0;
ctxt->node = node;
+ if ((nativeMode = virXPathString("string(./@native_mode)", ctxt)) !
= NULL) {
+ if (STRCASENEQ(nativeMode, "tagged") && STRCASENEQ(nativeMode,
"untagged")) {
+ virReportError(VIR_ERR_XML_ERROR,
+ _("invalid \"native_mode='%s'\" in <vlan> -
"
+ "native_mode must be 'tagged' or
'untagged'"), nativeMode);
+ goto error;
+ }
+ if (virXPathUInt("string(./@native_tag)", ctxt, &nativeTag) <
0) {
+ virReportError(VIR_ERR_XML_ERROR, "%s",
+ _("missing or invalid native_tag
attribute"));
+ goto error;
+ }
+ if (nativeTag > 4095) {
+ virReportError(VIR_ERR_XML_ERROR,
+ _("native_tag %u too large (maximum 4095)"),
nativeTag);
+ goto error;
+ }
+ def->nativeMode = STRCASEEQ(nativeMode, "tagged") ? 1 : 2;
+ def->nativeTag = nativeTag;
+ }
+
+ /* def->trunk will be set to true if:
+ * "trunk='yes'" is set in xml
+ * a native-* vlan mode has been set
+ * >1 tag has been set */
if ((trunk = virXPathString("string(./@trunk)", ctxt)) != NULL) {
def->trunk = STRCASEEQ(trunk, "yes");
if (!def->trunk) {
+ if (def->nativeMode > 0) {
+ virReportError(VIR_ERR_XML_ERROR, "%s",
+ _("invalid configuration in <vlan> -
\"trunk='no'\" is "
+ "not allowed with native_mode"));
+ goto error;
+ }
if (nTags > 1) {
virReportError(VIR_ERR_XML_ERROR,
_("invalid \"trunk='%s'\" in <vlan> -
trunk='yes' "
@@ -97,6 +128,8 @@ virNetDevVlanParse(xmlNodePtr node,
xmlXPathContextPtr ctxt, virNetDevVlanPtr de
goto error;
}
}
+ } else if (nTags > 1 || def->nativeMode > 0) {
+ def->trunk = true;
}
ret = 0;
@@ -122,8 +155,11 @@ virNetDevVlanFormat(virNetDevVlanPtr def,
virBufferPtr buf)
_("missing vlan tag data"));
return -1;
}
-
- virBufferAsprintf(buf, "<vlan%s>\n", def->trunk ? " trunk='yes'" :
"");
+ if (def->nativeMode == 0) {
+ virBufferAsprintf(buf, "<vlan%s>\n", def->trunk ? "
trunk='yes'" : "");
+ } else {
+ virBufferAsprintf(buf, "<vlan trunk='yes' native_mode='%s'
native_tag='%u'>\n", def->nativeMode == 1 ? "tagged" : "untagged",
def->nativeTag);
+ }
for (ii = 0; ii < def->nTags; ii++) {
virBufferAsprintf(buf, " <tag id='%u'/>\n", def->tag[ii]);
}
diff --git a/src/util/virnetdevopenvswitch.c
b/src/util/virnetdevopenvswitch.c
index 4fe077a..87122b0 100644
--- a/src/util/virnetdevopenvswitch.c
+++ b/src/util/virnetdevopenvswitch.c
@@ -19,6 +19,7 @@
* Dan Wendlandt <dan(a)nicira.com>
* Kyle Mestery <kmestery(a)cisco.com>
* Ansis Atteka <aatteka(a)nicira.com>
+ * James Robson <jrobson(a)websense.com>
*/
#include <config.h>
@@ -108,9 +109,13 @@ int virNetDevOpenvswitchAddPort(const char *brname,
const char *ifname,
virCommandAddArgList(cmd, "--timeout=5", "--", "--may-exist",
"add-port",
brname, ifname, NULL);
- if (virBufferUse(&buf) != 0)
+ if (virBufferUse(&buf) != 0) {
+ if (virtVlan->nativeMode > 0) {
+ virCommandAddArgFormat(cmd, "vlan_mode=%s",
virtVlan->nativeMode == 1 ? "native-tagged" : "native-untagged");
+ virCommandAddArgFormat(cmd, "tag=%d", virtVlan->nativeTag);
+ }
virCommandAddArgList(cmd, virBufferCurrentContent(&buf), NULL);
-
+ }
if (ovsport->profileID[0] == '\0') {
virCommandAddArgList(cmd,
"--", "set", "Interface", ifname,
attachedmac_ex_id,
diff --git a/src/util/virnetdevvlan.c b/src/util/virnetdevvlan.c
index 2fe2017..298673d 100644
--- a/src/util/virnetdevvlan.c
+++ b/src/util/virnetdevvlan.c
@@ -17,6 +17,7 @@
*
* Authors:
* Laine Stump <laine(a)redhat.com>
+ * James Robson <jrobson(a)websense.com>
*/
#include <config.h>
@@ -33,6 +34,8 @@ virNetDevVlanClear(virNetDevVlanPtr vlan)
{
VIR_FREE(vlan->tag);
vlan->nTags = 0;
+ vlan->nativeMode = 0;
+ vlan->nativeTag = -1;
}
void
@@ -54,7 +57,9 @@ virNetDevVlanEqual(const virNetDevVlanPtr a, const
virNetDevVlanPtr b)
return false;
if (a->trunk != b->trunk ||
- a->nTags != b->nTags) {
+ a->nTags != b->nTags ||
+ a->nativeMode != b->nativeMode ||
+ a->nativeTag != b->nativeTag) {
return false;
}
@@ -89,6 +94,8 @@ virNetDevVlanCopy(virNetDevVlanPtr dst, const
virNetDevVlanPtr src)
dst->trunk = src->trunk;
dst->nTags = src->nTags;
+ dst->nativeMode = src->nativeMode;
+ dst->nativeTag = src->nativeTag;
memcpy(dst->tag, src->tag, src->nTags * sizeof(*src->tag));
return 0;
}
diff --git a/src/util/virnetdevvlan.h b/src/util/virnetdevvlan.h
index c6b16ef..f0f78f0 100644
--- a/src/util/virnetdevvlan.h
+++ b/src/util/virnetdevvlan.h
@@ -17,6 +17,7 @@
*
* Authors:
* Laine Stump <laine(a)redhat.com>
+ * James Robson <jrobson(a)websense.com>
*/
#ifndef __VIR_NETDEV_VLAN_H__
@@ -25,6 +26,8 @@
typedef struct _virNetDevVlan virNetDevVlan;
typedef virNetDevVlan *virNetDevVlanPtr;
struct _virNetDevVlan {
+ short int nativeMode; /* 0=off, 1=tagged, 2=untagged */
+ unsigned int nativeTag;
bool trunk; /* true if this is a trunk */
int nTags; /* number of tags in array */
unsigned int *tag; /* pointer to array of tags */
diff --git a/tests/networkxml2xmlin/openvswitch-net.xml
b/tests/networkxml2xmlin/openvswitch-net.xml
index a3d82b1..93c49d5 100644
--- a/tests/networkxml2xmlin/openvswitch-net.xml
+++ b/tests/networkxml2xmlin/openvswitch-net.xml
@@ -21,4 +21,13 @@
<parameters profileid='alice-profile'/>
</virtualport>
</portgroup>
+ <portgroup name='tagged'>
+ <vlan native_mode='tagged' native_tag='123'>
+ <tag id='555'/>
+ <tag id='444'/>
+ </vlan>
+ <virtualport>
+ <parameters profileid='tagged-profile'/>
+ </virtualport>
+ </portgroup>
</network>
diff --git a/tests/networkxml2xmlout/openvswitch-net.xml
b/tests/networkxml2xmlout/openvswitch-net.xml
index a3d82b1..ab3d797 100644
--- a/tests/networkxml2xmlout/openvswitch-net.xml
+++ b/tests/networkxml2xmlout/openvswitch-net.xml
@@ -21,4 +21,13 @@
<parameters profileid='alice-profile'/>
</virtualport>
</portgroup>
+ <portgroup name='tagged'>
+ <vlan trunk='yes' native_mode='tagged' native_tag='123'>
+ <tag id='555'/>
+ <tag id='444'/>
+ </vlan>
+ <virtualport>
+ <parameters profileid='tagged-profile'/>
+ </virtualport>
+ </portgroup>
</network>
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11 years, 7 months
[libvirt] [PATCH] docs: Add detailed notes snapshots, blockcommit, blockpull
by Kashyap Chamarthy
More elaborate notes on snapshots, blockpull, blockcommit. Much of this
is derived from various dicussions with Eric Blake, Jeff Cody, Kevin Wolf
(thanks a lot!) & several others on IRC and mailing lists and a lot of adhoc
testing. I didn't wanted this to get lost.
I also plan to add notes for 'blockcopy' once I complete testing with upstream
libvirt/qemu git.
NOTE: This document is formatted using reStructuredText. And can be trivially
converted to HTML using:
# rst2html snapshots-blockcommit-blockpull.rst > snapshots-blockcommit-blockpull.html
('rst2html' is part of python-docutils package.)
I didn't send an html PATCH directly, as I thought, this'd be more readable.
Any comments, criticisms more than welcome.
---
docs/snapshots-blockcommit-blockpull.rst | 646 ++++++++++++++++++++++++++++++
1 files changed, 646 insertions(+), 0 deletions(-)
create mode 100644 docs/snapshots-blockcommit-blockpull.rst
diff --git a/docs/snapshots-blockcommit-blockpull.rst b/docs/snapshots-blockcommit-blockpull.rst
new file mode 100644
index 0000000000000000000000000000000000000000..99c30223a004ee5291e2914b788ac7fe04eee3c8
--- /dev/null
+++ b/docs/snapshots-blockcommit-blockpull.rst
@@ -0,0 +1,646 @@
+.. ----------------------------------------------------------------------
+ Note: All these tests were performed with latest qemu-git,libvirt-git (as of
+ 20-Oct-2012 on a Fedora-18 alpha machine
+.. ----------------------------------------------------------------------
+
+
+Introduction
+============
+
+A virtual machine snapshot is a view of a virtual machine(its OS & all its
+applications) at a given point in time. So that, one can revert to a known sane
+state, or take backups while the guest is running live. So, before we dive into
+snapshots, let's have an understanding of backing files and overlays.
+
+
+
+QCOW2 backing files & overlays
+------------------------------
+
+In essence, QCOW2(Qemu Copy-On-Write) gives you an ability to create a base-image,
+and create several 'disposable' copy-on-write overlay disk images on top of the
+base image(also called backing file). Backing files and overlays are
+extremely useful to rapidly instantiate thin-privisoned virtual machines(more on
+it below). Especially quite useful in development & test environments, so that
+one could quickly revert to a known state & discard the overlay.
+
+**Figure-1**
+
+::
+
+ .--------------. .-------------. .-------------. .-------------.
+ | | | | | | | |
+ | RootBase |<---| Overlay-1 |<---| Overlay-1A <--- | Overlay-1B |
+ | (raw/qcow2) | | (qcow2) | | (qcow2) | | (qcow2) |
+ '--------------' '-------------' '-------------' '-------------'
+
+The above figure illustrates - RootBase is the backing file for Overlay-1, which
+in turn is backing file for Overlay-2, which in turn is backing file for
+Overlay-3.
+
+**Figure-2**
+::
+
+ .-----------. .-----------. .------------. .------------. .------------.
+ | | | | | | | | | |
+ | RootBase |<--- Overlay-1 |<--- Overlay-1A <--- Overlay-1B <--- Overlay-1C |
+ | | | | | | | | | (Active) |
+ '-----------' '-----------' '------------' '------------' '------------'
+ ^ ^
+ | |
+ | | .-----------. .------------.
+ | | | | | |
+ | '-------| Overlay-2 |<---| Overlay-2A |
+ | | | | (Active) |
+ | '-----------' '------------'
+ |
+ |
+ | .-----------. .------------.
+ | | | | |
+ '------------| Overlay-3 |<---| Overlay-3A |
+ | | | (Active) |
+ '-----------' '------------'
+
+The above figure is just another representation which indicates, we can use a
+'single' backing file, and create several overlays -- which can be used further,
+to create overlays on top of them.
+
+
+**NOTE**: Backing files are always opened **read-only**. In other words, once
+ an overlay is created, its backing file should not be modified(as the
+ overlay depends on a particular state of the backing file). Refer
+ below ('blockcommit' section) for relevant info on this.
+
+
+**Example** :
+
+::
+
+ [FedoraBase.img] ----- <- [Fedora-guest-1.qcow2] <- [Fed-w-updates.qcow2] <- [Fedora-guest-with-updates-1A]
+ \
+ \--- <- [Fedora-guest-2.qcow2] <- [Fed-w-updates.qcow2] <- [Fedora-guest-with-updates-2A]
+
+(Arrow to be read as Fed-w-updates.qcow2 has Fedora-guest-1.qcow2 as its backing file.)
+
+In the above example, say, *FedoraBase.img* has a freshly installed Fedora-17 OS on it,
+and let's establish it as our backing file. Now, FedoraBase can be used as a
+read-only 'template' to quickly instantiate two(or more) thinly provisioned
+Fedora-17 guests(say Fedora-guest-1.qcow2, Fedora-guest-2.qcow2) by creating
+QCOW2 overlay files pointing to our backing file. Also, the example & *Figure-2*
+above illustrate that a single root-base image(FedoraBase.img) can be used
+to create multiple overlays -- which can subsequently have their own overlays.
+
+
+ To create two thinly-provisioned Fedora clones(or overlays) using a single
+ backing file, we can invoke qemu-img as below: ::
+
+
+ # qemu-img create -b /export/vmimages/RootBase.img -f qcow2 \
+ /export/vmimages/Fedora-guest-1.qcow2
+
+ # qemu-img create -b /export/vmimages/RootBase.img -f qcow2 \
+ /export/vmimages/Fedora-guest-2.qcow2
+
+ Now, both the above images *Fedora-guest-1* & *Fedora-guest-2* are ready to
+ boot. Continuting with our example, say, now you want to instantiate a
+ Fedora-17 guest, but this time, with full Fedora updates. This can be
+ accomplished by creating another overlay(Fedora-guest-with-updates-1A) - but
+ this overly would point to 'Fed-w-updates.qcow2' as its backing file (which
+ has the full Fedora updates) ::
+
+ # qemu-img create -b /export/vmimages/Fed-w-updates.qcow2 -f qcow2 \
+ /export/vmimages/Fedora-guest-with-updates-1A.qcow2
+
+
+ Information about a disk image, like virtual size, disk size, backing file(if it
+ exists) can be obtained by using 'qemu-img' as below:
+ ::
+
+ # qemu-img info /export/vmimages/Fedora-guest-with-updates-1A.qcow2
+
+ NOTE: With latest qemu, an entire backing chain can be recursively
+ enumerated by doing:
+ ::
+
+ # qemu-img info --backing-chain /export/vmimages/Fedora-guest-with-updates-1A.qcow2
+
+
+
+Snapshot Terminology:
+---------------------
+
+ - **Internal Snapshots** -- A single qcow2 image file holds both the saved state
+ & the delta since that saved point. This can be further classified as :-
+
+ (1) **Internal disk snapshot**: The state of the virtual disk at a given
+ point in time. Both the snapshot & delta since the snapshot are
+ stored in the same qcow2 file. Can be taken when the guest is 'live'
+ or 'offline'.
+
+ - Libvirt uses QEMU's 'qemu-img' command when the guest is 'offline'.
+ - Libvirt uses QEMU's 'savevm' command when the guest is 'live'.
+
+ (2) **Internal system checkpoint**: RAM state, device state & the
+ disk-state of a running guest, are all stored in the same originial
+ qcow2 file. Can be taken when the guest is running 'live'.
+
+ - Libvirt uses QEMU's 'savevm' command when the guest is 'live'
+
+
+ - **External Snapshots** -- Here, when a snapshot is taken, the saved state will
+ be stored in one file(from that point, it becomes a read-only backing
+ file) & a new file(overlay) will track the deltas from that saved state.
+ This can be further classified as :-
+
+ (1) **External disk snapshot**: The snapshot of the disk is saved in one
+ file, and the delta since the snapshot is tracked in a new qcow2
+ file. Can be taken when the guest is 'live' or 'offline'.
+
+ - Libvirt uses QEMU's 'transaction' cmd under the hood, when the
+ guest is 'live'.
+
+ - Libvirt uses QEMU's 'qemu-img' cmd under the hood when the
+ guest is 'offline'(this implementation is in progress, as of
+ writing this).
+
+ (2) **External system checkpoint**: Here, the guest's disk-state will be
+ saved in one file, its RAM & device-state will be saved in another
+ new file (This implementation is in progress upstream libvirt, as of
+ writing this).
+
+
+
+ - **VM State**: Saves the RAM & device state of a running guest(not 'disk-state') to
+ a file, so that it can be restored later. This simliar to doing hibernate
+ of the system. (NOTE: The disk-state should be unmodified at the time of
+ restoration.)
+
+ - Libvirt uses QEMU's 'migrate' (to file) cmd under the hood.
+
+
+
+Creating snapshots
+==================
+ - Whenever an 'external' snapshot is issued, a /new/ overlay image is
+ created to facilitate guest writes, and the previous image becomes a
+ snapshot.
+
+ - **Create a disk-only internal snapshot**
+
+ (1) If I have a guest named 'f17vm1', to create an offline or online
+ 'internal' snapshot called 'snap1' with description 'snap1-desc' ::
+
+ # virsh snapshot-create-as f17vm1 snap1 snap1-desc
+
+ (2) List the snapshot ; and query using *qemu-img* tool to view
+ the image info & its internal snapshot details ::
+
+ # virsh snapshot-list f17vm1
+ # qemu-img info /home/kashyap/vmimages/f17vm1.qcow2
+
+
+
+ - **Create a disk-only external snapshot** :
+
+ (1) List the block device associated with the guest. ::
+
+ # virsh domblklist f17-base
+ Target Source
+ ---------------------------------------------
+ vda /export/vmimages/f17-base.qcow2
+
+ #
+
+ (2) Create external disk-only snapshot (while the guest is *running*). ::
+
+ # virsh snapshot-create-as --domain f17-base snap1 snap1-desc \
+ --disk-only --diskspec vda,snapshot=external,file=/export/vmimages/sn1-of-f17-base.qcow2 \
+ --atomic
+ Domain snapshot snap1 created
+ #
+
+ * Once the above command is issued, the original disk-image
+ of f17-base will become the backing_file & a new overlay
+ image is created to track the new changes. Here on, libvirt
+ will use this overlay for further write operations(while
+ using the original image as a read-only backing_file).
+
+ (3) Now, list the block device associated(use cmd from step-1, above)
+ with the guest,again, to ensure it reflects the new overlay image as
+ the current block device in use. ::
+
+ # virsh domblklist f17-base
+ Target Source
+ ----------------------------------------------------
+ vda /export/vmimages/sn1-of-f17-base.qcow2
+
+ #
+
+
+
+
+Reverting to snapshots
+======================
+As of writing this, reverting to 'Internal Snapshots'(system checkpoint or
+disk-only) is possible.
+
+ To revert to a snapshot named 'snap1' of domain f17vm1 ::
+
+ # virsh snapshot-revert --domain f17vm1 snap1
+
+Reverting to 'external disk snapshots' using *snapshot-revert* is a little more
+tricky, as it involves slightly complicated process of dealing with additional
+snapshot files - whether to merge 'base' images into 'top' or to merge other way
+round ('top' into 'base').
+
+That said, there are a couple of ways to deal with external snapshot files by
+merging them to reduce the external snapshot disk image chain by performing
+either a **blockpull** or **blockcommit** (more on this below).
+
+Further improvements on this front is in work upstream libvirt as of writing
+this.
+
+
+
+Merging snapshot files
+======================
+External snapshots are incredibly useful. But, with plenty of external snapshot
+files, there comes a problem of maintaining and tracking all these inidivdual
+files. At a later point in time, we might want to 'merge' some of these snapshot
+files (either backing_files into overlays or vice-versa) to reduce the length of
+the image chain. To accomplish that, there are two mechanisms:
+
+ + blockcommit: merges data from **top** into **base** (in other
+ words, merge overlays into backing files).
+
+
+ + blockpull: Populates a disk image with data from its backing file. Or
+ merges data from **base** into **top** (in other words, merge backing files
+ into overlays).
+
+
+blockcommit
+-----------
+
+Block Commit allows you to merge from a 'top' image(within a disk backing file
+chain) into a lower-level 'base' image. To rephrase, it allows you to
+merge overlays into backing files. Once the **blockcommit** operation is finished,
+any portion that depends on the 'top' image, will now be pointing to the 'base'.
+
+This is useful in flattening(or collapsing or reducing) backing file chain
+length after taking several external snapshots.
+
+
+Let's understand with an illustration below:
+
+We have a base image called 'RootBase', which has a disk image chain with 4
+external snapshots. With 'Active' as the current active-layer, where 'live' guest
+writes happen. There are a few possibilities of resulting image chains that we
+can end up with, using 'blockcommit' :
+
+ (1) Data from Snap-1, Snap-2 and Snap-3 can be merged into 'RootBase'
+ (resulting in RootBase becoming the backing_file of 'Active', and thus
+ invalidating Snap-1, Snap-2, & Snap-3).
+
+ (2) Data from Snap-1 and Snap-2 can be merged into RootBase(resulting in
+ Rootbase becoming the backing_file of Snap-3, and thus invalidating
+ Snap-1 & Snap-2).
+
+ (3) Data from Snap-1 can be merged into RootBase(resulting in RootBase
+ becoming the backing_file of Snap-2, and thus invalidating Snap-1).
+
+ (4) Data from Snap-2 can be merged into Snap-1(resulting in Snap-1 becoming
+ the backing_file of Snap-3, and thus invalidating Snap-2).
+
+ (5) Data from Snap-3 can be merged into Snap-2(resulting in Snap-2 becoming
+ the backing_file for 'Active', and thus invalidating Snap-3).
+
+ (6) Data from Snap-2 and Snap-3 can be merged into Snap-1(resulting in
+ Snap-1 becoming the backing_file of 'Active', and thus invalidating
+ Snap-2 & Snap-3).
+
+ NOTE: Eventually(not supported in qemu as of writing this), we can also
+ merge down the 'Active' layer(the top-most overlay) into its
+ backing_files. Once it is supported, the 'top' argument can become
+ optional, and default to active layer.
+
+
+(The below figure illustrates case (6) from the above)
+
+**Figure-3**
+::
+
+ .------------. .------------. .------------. .------------. .------------.
+ | | | | | | | | | |
+ | RootBase <--- Snap-1 <--- Snap-2 <--- Snap-3 <--- Snap-4 |
+ | | | | | | | | | (Active) |
+ '------------' '------------' '------------' '------------' '------------'
+ / |
+ / |
+ / commit data |
+ / |
+ / |
+ / |
+ v commit data |
+ .------------. .------------. <--------------------' .------------.
+ | | | | | |
+ | RootBase <--- Snap-1 |<---------------------------------| Snap-4 |
+ | | | | Backing File | (Active) |
+ '------------' '------------' '------------'
+
+For instance, if we have the below scenario:
+
+ Actual: [base] <- sn1 <- sn2 <- sn3 <- sn4(this is active)
+
+ Desired: [base] <- sn1 <- sn4 (thus invalidating sn2,sn3)
+
+ Any of the below two methods is valid (as of 17-Oct-2012 qemu-git). With
+ method-a, operation will be faster & correct if we don't care about
+ sn2(because, it'll be invalidated). Note that, method-b is slower, but sn2
+ will remain valid. (Also note that, the guest is 'live' in all these cases).
+
+ **(method-a)**:
+ ::
+
+ # virsh blockcommit --domain f17 vda --base /export/vmimages/sn1.qcow2 --top /export/vmimages/sn3.qcow2 --wait --verbose
+
+ [OR]
+
+ **(method-b)**:
+ ::
+
+ # virsh blockcommit --domain f17 vda --base /export/vmimages/sn2.qcow2 --top /export/vmimages/sn3.qcow2 --wait --verbose
+ # virsh blockcommit --domain f17 vda --base /export/vmimages/sn1.qcow2 --top /export/vmimages/sn2.qcow2 --wait --verbose
+
+ NOTE: If we had to do manually with *qemu-img* cmd, we can only do method-b at the moment.
+
+
+**Figure-4**
+::
+
+ .------------. .------------. .------------. .------------. .------------.
+ | | | | | | | | | |
+ | RootBase <--- Snap-1 <--- Snap-2 <--- Snap-3 <--- Snap-4 |
+ | | | | | | | | | (Active) |
+ '------------' '------------' '------------' '------------' '------------'
+ / | |
+ / | |
+ / | |
+ commit data / commit data | |
+ / | |
+ / | commit data |
+ v | |
+ .------------.<----------------------|-------------' .------------.
+ | |<----------------------' | |
+ | RootBase | | Snap-4 |
+ | |<-------------------------------------------------| (Active) |
+ '------------' Backing File '------------'
+
+
+The above figure is another representation of reducing the disk image chain
+using blockcommit. Data from Snap-1, Snap-2, Snap-3 are merged(/committed)
+into RootBase, & now the current 'Active' image now pointing to 'RootBase' as its
+backing file(instead of Snap-3, which was the case *before* blockcommit). Note
+that, now intermediate images Snap-1, Snap-1, Snap-3 will be invalidated(as they were
+dependent on a particular state of RootBase).
+
+blockpull
+---------
+Block Pull(also called 'Block Stream' in QEMU's paralance) allows you to merge
+into 'base' from a 'top' image(within a disk backing file chain). To rephrase it
+allows merging backing files into an overlay(active). This works in the
+opposite side of 'blockcommit' to flatten the snapshot chain. At the moment,
+**blockpull** can pull only into the active layer(the top-most image). It's
+worth noting here that, intermediate images are not invalidated once a blockpull
+operation is complete (while blockcommit, invalidates them).
+
+
+Consider the below illustration:
+
+**Figure-5**
+::
+
+ .------------. .------------. .------------. .------------. .------------.
+ | | | | | | | | | |
+ | RootBase <--- Snap-1 <--- Snap-2 <--- Snap-3 <--- Snap-4 |
+ | | | | | | | | | (Active) |
+ '------------' '------------' '------------' '------------' '------------'
+ | | \
+ | | \
+ | | \
+ | | \ stream data
+ | | stream data \
+ | stream data | \
+ | | v
+ .------------. | '---------------> .------------.
+ | | '---------------------------------> | |
+ | RootBase | | Snap-4 |
+ | | <---------------------------------------- | (Active) |
+ '------------' Backing File '------------'
+
+
+
+The above figure illustrates that, using block-copy we can pull data from
+Snap-1, Snap-2 and Snap-3 into the 'Active' layer, resulting in 'RootBase'
+becoming the backing file for the 'Active' image (instead of 'Snap-3', which was
+the case before doing the blockpull operation).
+
+The command flow would be:
+ (1) Assuming a external disk-only snapshot was created as mentioned in
+ *Creating Snapshots* section:
+
+ (2) A blockpull operation can be issued this way, to achieve the desired
+ state of *Figure-5*-- [RootBase] <- [Active]. ::
+
+ # virsh blockpull --domain RootBase --path var/lib/libvirt/images/active.qcow2 --base /var/lib/libvirt/images/RootBase.qcow2 --wait --verbose
+
+
+ As a follow up, we can do the below to clean-up the snapshot *tracking*
+ metadata by libvirt (note: the below does not 'remove' the files, it
+ just cleans up the snapshot tracking metadata). ::
+
+ # virsh snapshot-delete --domain RootBase Snap-3 --metadata
+ # virsh snapshot-delete --domain RootBase Snap-2 --metadata
+ # virsh snapshot-delete --domain RootBase Snap-1 --metadata
+
+
+
+
+**Figure-6**
+::
+
+ .------------. .------------. .------------. .------------. .------------.
+ | | | | | | | | | |
+ | RootBase <--- Snap-1 <--- Snap-2 <--- Snap-3 <--- Snap-4 |
+ | | | | | | | | | (Active) |
+ '------------' '------------' '------------' '------------' '------------'
+ | | | \
+ | | | \
+ | | | \ stream data
+ | | | stream data \
+ | | | \
+ | | stream data | \
+ | stream data | '------------------> v
+ | | .--------------.
+ | '---------------------------------> | |
+ | | Snap-4 |
+ '----------------------------------------------------> | (Active) |
+ '--------------'
+ 'Standalone'
+ (w/o backing
+ file)
+
+The above figure illustrates, once blockpull operation is complete, by
+pulling/streaming data from RootBase, Snap-1, Snap-2, Snap-3 into 'Active', all
+the backing files can be discarded and 'Active' now will be a standalone image
+without any backing files.
+
+Command flow would be:
+ (0) Assuming 4 external disk-only (live) snapshots were created as
+ mentioned in *Creating Snapshots* section,
+
+ (1) Let's check the snapshot overlay images size *before* blockpull operation (note the image of 'Active'):
+ ::
+
+ # ls -lash /var/lib/libvirt/images/RootBase.img
+ 608M -rw-r--r--. 1 qemu qemu 1.0G Oct 11 17:54 /var/lib/libvirt/images/RootBase.img
+
+ # ls -lash /var/lib/libvirt/images/*Snap*
+ 840K -rw-------. 1 qemu qemu 896K Oct 11 17:56 /var/lib/libvirt/images/Snap-1.qcow2
+ 392K -rw-------. 1 qemu qemu 448K Oct 11 17:56 /var/lib/libvirt/images/Snap-2.qcow2
+ 456K -rw-------. 1 qemu qemu 512K Oct 11 17:56 /var/lib/libvirt/images/Snap-3.qcow2
+ 2.9M -rw-------. 1 qemu qemu 3.0M Oct 11 18:10 /var/lib/libvirt/images/Active.qcow2
+
+ (2) Also, check the disk image information of 'Active'. It can noticed that
+ 'Active' has Snap-3 as its backing file. ::
+
+ # qemu-img info /var/lib/libvirt/images/Active.qcow2
+ image: /var/lib/libvirt/images/Active.qcow2
+ file format: qcow2
+ virtual size: 1.0G (1073741824 bytes)
+ disk size: 2.9M
+ cluster_size: 65536
+ backing file: /var/lib/libvirt/images/Snap-3.qcow2
+
+ (3) Do the **blockpull** operation. ::
+
+ # virsh blockpull --domain ptest2-base --path /var/lib/libvirt/images/Active.qcow2 --wait --verbose
+ Block Pull: [100 %]
+ Pull complete
+
+ (4) Let's again check the snapshot overlay images size *after*
+ blockpull operation. It can be noticed, 'Active' is now considerably larger. ::
+
+ # ls -lash /var/lib/libvirt/images/*Snap*
+ 840K -rw-------. 1 qemu qemu 896K Oct 11 17:56 /var/lib/libvirt/images/Snap-1.qcow2
+ 392K -rw-------. 1 qemu qemu 448K Oct 11 17:56 /var/lib/libvirt/images/Snap-2.qcow2
+ 456K -rw-------. 1 qemu qemu 512K Oct 11 17:56 /var/lib/libvirt/images/Snap-3.qcow2
+ 1011M -rw-------. 1 qemu qemu 3.0M Oct 11 18:29 /var/lib/libvirt/images/Active.qcow2
+
+
+ (5) Also, check the disk image information of 'Active'. It can now be
+ noticed that 'Active' is a standalone image without any backing file -
+ which is the desired state of *Figure-6*.::
+
+ # qemu-img info /var/lib/libvirt/images/Active.qcow2
+ image: /var/lib/libvirt/images/Active.qcow2
+ file format: qcow2
+ virtual size: 1.0G (1073741824 bytes)
+ disk size: 1.0G
+ cluster_size: 65536
+
+ (6) We can now clean-up the snapshot tracking metadata by libvirt to
+ reflect the new reality ::
+
+ # virsh snapshot-delete --domain RootBase Snap-3 --metadata
+
+ (7) Optionally, one can check, the guest disk contents by invoking
+ *guestfish* tool(part of *libguestfs*) **READ-ONLY** (*--ro* option
+ below does it) as below ::
+
+ # guestfish --ro -i -a /var/lib/libvirt/images/Active.qcow2
+
+
+Deleting snapshots (and 'offline commit')
+=========================================
+
+Deleting (live/offline) *Internal Snapshots* (where the originial & all the named snapshots
+are stored in a single QCOW2 file), is quite straight forward. ::
+
+ # virsh snapshot-delete --domain f17vm --snapshotname snap6
+
+ [OR]
+
+ # virsh snapshot-delete f17vm snap6
+
+Deleting External snapshots (offline), Libvirt has not acquired the capability.
+But, it can be done via *qemu-img* manipulation.
+
+Say, we have this image chain(the guest is *offline* here): **base <- sn1 <- sn2 <- sn3**
+(arrow to be read as 'sn3 has sn2 as its backing file').
+
+
+And, we want to delete the second snapshot(sn2). It's possible to do it in two
+ways:
+
+
+ - **Method (1)**: **base <- sn1 <- sn3** (by copying sn2 into sn1)
+ - **Method (2)**: **base <- sn1 <- sn3** (by copying sn2 into sn3)
+
+Method (1)
+----------
+To end up with this image chain : **base <- sn1 <- sn3** (by copying *sn2* into *sn1*)
+
+**NOTE**: This is only possible *if* sn1 isn't used by more images as their backing
+file, or they'd get corrupted!!
+
+ (a) We're doing an *offline commit* (similar to what *blockcommit* can do
+ to an *online* guest). ::
+
+ # qemu-img commit sn2.qcow2
+
+ - This will *commit* the changes from sn2 into its backing file(which is
+ sn1).
+
+ (b) Now that we've comitted changes from sn2 into sn1, let's change the
+ backing file link in sn3 to point to sn1. ::
+
+ # qemu-img rebase -u -b sn1.qcow2 sn3.qcow2
+
+ - **NOTE**: This is 'Unsafe mode' -- in this mode, only the backing file
+ name is changed w/o any checks on the file contents. The user must
+ take care of specifying the correct new backing file, or the
+ guest-visible. This mode is useful for renaming or moving the
+ backing file to somewhere else. It can be used without an
+ accessible old backing file, i.e. you can use it to fix an image
+ whose backing file has already been moved/renamed.
+
+
+ (c) Now, we can delete the sn2 disk image(as the changes are now committed
+ to sn1). ::
+
+ # rm sn2.qcow2
+
+
+Method (2)
+----------
+To end up with this image chain : **base <- sn1 <- sn3** (by copying *sn2* into *sn3*)
+
+ (a) Copy contents of sn2(the old backing file) into sn3, and change the backing file link of sn3 to sn1::
+
+ # qemu-img rebase -b sn1.qcow2 sn3.qcow2
+
+ - Apart from changing backing file link of sn3 to sn1, the above cmd
+ will it also /copy/ the contents from sn2 into sn3).
+
+ - In other words: This is 'Safe mode', which is the default --
+ any clusters that differ between the new backing_file(in this
+ case, sn1) and the old backing file(in this case, sn2) of
+ filename(in this case, sn3) are merged into filename(sn3), before
+ actually changing the backing file.
+
+ (b) Now, we can delete the sn2 disk image(as the changes are now committed to
+ sn1). ::
+
+ # rm sn2.qcow2
+
--
1.7.7.6
11 years, 7 months
