April 2022 - Devel - libvirt List Archives

[libvirt] [PATCH] Fix python error reporting for some storage operations
by Cole Robinson 07 Mar '25

07 Mar '25

In the python bindings, all vir* classes expect to be passed a virConnect object when instantiated. Before the storage stuff, these classes were only instantiated in virConnect methods, so the generator is hardcoded to pass 'self' as the connection instance to these classes. Problem is there are some methods that return pool or vol instances which aren't called from virConnect: you can lookup a storage volume's associated pool, and can lookup volumes from a pool. In these cases passing 'self' doesn't give the vir* instance a connection, so when it comes time to raise an exception crap hits the fan. Rather than rework the generator to accomodate this edge case, I just fixed the init functions for virStorage* to pull the associated connection out of the passed value if it's not a virConnect instance. Thanks, Cole diff --git a/python/generator.py b/python/generator.py index 01a17da..c706b19 100755 --- a/python/generator.py +++ b/python/generator.py @@ -962,8 +962,12 @@ def buildWrappers(): list = reference_keepers[classname] for ref in list: classes.write(" self.%s = None\n" % ref[1]) - if classname in [ "virDomain", "virNetwork", "virStoragePool", "virStorageVol" ]: + if classname in [ "virDomain", "virNetwork" ]: classes.write(" self._conn = conn\n") + elif classname in [ "virStorageVol", "virStoragePool" ]: + classes.write(" self._conn = conn\n" + \ + " if not isinstance(conn, virConnect):\n" + \ + " self._conn = conn._conn\n") classes.write(" if _obj != None:self._o = _obj;return\n") classes.write(" self._o = None\n\n"); destruct=None

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Re: [libvirt] [Qemu-devel] Qemu migration with vhost-user-blk on top of local storage
by Stefan Hajnoczi 27 Oct '23

27 Oct '23

On Wed, Jan 09, 2019 at 06:23:42PM +0800, wuzhouhui wrote: > Hi everyone, > > I'm working qemu with vhost target (e.g. spdk), and I attempt to migrate VM with > 2 local storages. One local storage is a regular file, e.g. /tmp/c74.qcow2, and > the other is a malloc bdev that spdk created. This malloc bdev will exported to > VM via vhost-user-blk. When I execute following command: > > virsh migrate --live --persistent --unsafe --undefinesource --copy-storage-all \ > --p2p --auto-converge --verbose --desturi qemu+tcp://<uri>/system vm0 > > The libvirt reports: > > qemu-2.12.1: error: internal error: unable to execute QEMU command \ > 'nbd-server-add': Cannot find device=drive-virtio-disk1 nor \ > node_name=drive-virtio-disk1 Please post your libvirt domain XML. > Does it means that qemu with spdk on top of local storage don't support migration? > > QEMU: 2.12.1 > SPDK: 18.10 vhost-user-blk bypasses the QEMU block layer, so NBD storage migration at the QEMU level will not work for the vhost-user-blk disk. Stefan

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[libvirt] [PATCH v3] openvswitch: Add new port VLAN mode "dot1q-tunnel"
by luzhipeng＠uniudc.com 27 Oct '23

27 Oct '23

From: ZhiPeng Lu <luzhipeng(a)uniudc.com> Signed-off-by: ZhiPeng Lu <luzhipeng(a)uniudc.com> --- v1->v2: 1. Fix "make syntax-check" failure v2->v3: 1. remove other_config when updating vlan docs/formatnetwork.html.in | 17 +++++++++-------- docs/schemas/networkcommon.rng | 1 + src/conf/netdev_vlan_conf.c | 2 +- src/util/virnetdevopenvswitch.c | 7 +++++++ src/util/virnetdevvlan.h | 1 + 5 files changed, 19 insertions(+), 9 deletions(-) diff --git a/docs/formatnetwork.html.in b/docs/formatnetwork.html.in index 363a72b..3c1ae62 100644 --- a/docs/formatnetwork.html.in +++ b/docs/formatnetwork.html.in @@ -688,16 +688,17 @@ For network connections using Open vSwitch it is also possible - to configure 'native-tagged' and 'native-untagged' VLAN modes + to configure 'native-tagged' and 'native-untagged' and 'dot1q-tunnel' + VLAN modes. Since 1.1.0. This is done with the - optional <code>nativeMode</code> attribute on - the <code><tag></code> subelement: <code>nativeMode</code> - may be set to 'tagged' or 'untagged'. The <code>id</code> - attribute of the <code><tag></code> subelement - containing <code>nativeMode</code> sets which VLAN is considered - to be the "native" VLAN for this interface, and + optional <code>nativeMode</code> attribute on the + <code><tag></code> subelement: <code>nativeMode</code> + may be set to 'tagged' or 'untagged' or 'dot1q-tunnel'. + The <code>id</code> attribute of the <code><tag></code> + subelement containing <code>nativeMode</code> sets which VLAN is + considered to be the "native" VLAN for this interface, and the <code>nativeMode</code> attribute determines whether or not - traffic for that VLAN will be tagged. + traffic for that VLAN will be tagged or QinQ. <code><vlan></code> elements can also be specified in diff --git a/docs/schemas/networkcommon.rng b/docs/schemas/networkcommon.rng index 2699555..11c48ff 100644 --- a/docs/schemas/networkcommon.rng +++ b/docs/schemas/networkcommon.rng @@ -223,6 +223,7 @@ <choice> <value>tagged</value> <value>untagged</value> + <value>dot1q-tunnel</value> </choice> </attribute> </optional> diff --git a/src/conf/netdev_vlan_conf.c b/src/conf/netdev_vlan_conf.c index dff49c6..79710d9 100644 --- a/src/conf/netdev_vlan_conf.c +++ b/src/conf/netdev_vlan_conf.c @@ -29,7 +29,7 @@ #define VIR_FROM_THIS VIR_FROM_NONE VIR_ENUM_IMPL(virNativeVlanMode, VIR_NATIVE_VLAN_MODE_LAST, - "default", "tagged", "untagged") + "default", "tagged", "untagged", "dot1q-tunnel") int virNetDevVlanParse(xmlNodePtr node, xmlXPathContextPtr ctxt, virNetDevVlanPtr def) diff --git a/src/util/virnetdevopenvswitch.c b/src/util/virnetdevopenvswitch.c index 8fe06fd..9fec30b 100644 --- a/src/util/virnetdevopenvswitch.c +++ b/src/util/virnetdevopenvswitch.c @@ -91,6 +91,11 @@ virNetDevOpenvswitchConstructVlans(virCommandPtr cmd, virNetDevVlanPtr virtVlan) virCommandAddArg(cmd, "vlan_mode=native-untagged"); virCommandAddArgFormat(cmd, "tag=%d", virtVlan->nativeTag); break; + case VIR_NATIVE_VLAN_MODE_DOT1Q_TUNNEL: + virCommandAddArg(cmd, "vlan_mode=dot1q-tunnel"); + virCommandAddArg(cmd, "other_config:qinq-ethtype=802.1q"); + virCommandAddArgFormat(cmd, "tag=%d", virtVlan->nativeTag); + break; case VIR_NATIVE_VLAN_MODE_DEFAULT: default: break; @@ -504,6 +509,8 @@ int virNetDevOpenvswitchUpdateVlan(const char *ifname, "--", "--if-exists", "clear", "Port", ifname, "tag", "--", "--if-exists", "clear", "Port", ifname, "trunk", "--", "--if-exists", "clear", "Port", ifname, "vlan_mode", + "--", "--if-exists", "remove", "Port", ifname, "other_config", + "qinq-ethtype", NULL, "--", "--if-exists", "set", "Port", ifname, NULL); if (virNetDevOpenvswitchConstructVlans(cmd, virtVlan) < 0) diff --git a/src/util/virnetdevvlan.h b/src/util/virnetdevvlan.h index be85f59..0667f9d 100644 --- a/src/util/virnetdevvlan.h +++ b/src/util/virnetdevvlan.h @@ -29,6 +29,7 @@ typedef enum { VIR_NATIVE_VLAN_MODE_DEFAULT = 0, VIR_NATIVE_VLAN_MODE_TAGGED, VIR_NATIVE_VLAN_MODE_UNTAGGED, + VIR_NATIVE_VLAN_MODE_DOT1Q_TUNNEL, VIR_NATIVE_VLAN_MODE_LAST } virNativeVlanMode; -- 1.8.3.1

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[libvirt] [PATCH] Fix compile error for stable 1.2.9
by Yang hongyang 27 Oct '23

27 Oct '23

Seems a backport miss. An extra member is passed to struct virLXCBasicMountInfo. Signed-off-by: Yang hongyang <hongyang.yang(a)easystack.cn> --- src/lxc/lxc_container.c | 2 +- 1 files changed, 1 insertions(+), 1 deletions(-) diff --git a/src/lxc/lxc_container.c b/src/lxc/lxc_container.c index 28dabec..1c65fa9 100644 --- a/src/lxc/lxc_container.c +++ b/src/lxc/lxc_container.c @@ -760,7 +760,7 @@ typedef struct { static const virLXCBasicMountInfo lxcBasicMounts[] = { { "proc", "/proc", "proc", MS_NOSUID|MS_NOEXEC|MS_NODEV, false, false }, - { "/proc/sys", "/proc/sys", NULL, MS_BIND|MS_NOSUID|MS_NOEXEC|MS_NODEV|MS_RDONLY, false, false, false }, + { "/proc/sys", "/proc/sys", NULL, MS_BIND|MS_NOSUID|MS_NOEXEC|MS_NODEV|MS_RDONLY, false, false }, { "sysfs", "/sys", "sysfs", MS_NOSUID|MS_NOEXEC|MS_NODEV|MS_RDONLY, false, false }, { "securityfs", "/sys/kernel/security", "securityfs", MS_NOSUID|MS_NOEXEC|MS_NODEV|MS_RDONLY, true, true }, #if WITH_SELINUX -- 1.7.1

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[libvirt] [PATCH] web docs -- macvtap mode explanation
by Stefan Berger 27 Oct '23

27 Oct '23

This adds more information about the different macvtap device modes. Regards, Stefan

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[libvirt] Supporting vhost-net and macvtap in libvirt for QEMU
by Anthony Liguori 27 Oct '23

27 Oct '23

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

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[PATCH 00/18] RFC: Remove deprecated audio features
by Martin Kletzander 15 Sep '23

15 Sep '23

I wanted to deal with https://bugzilla.redhat.com/2043498 and I got a suggesstion that removing deprecated features could actually make it easier to propagate the error. In the end (last patch) it turns out the error is still just reported with error_fatal, so it probably is not really needed, but I really wanted to dig into QEMU more and learn some of the internals for quite some time now. So I used the opportunity. The one-liner ended up being an 18 patch series which was, for someone who has just one commit in QEMU codebase, a pretty challenging task. Although I tried my best to do things properly, I am not sure whether I handled everything correctly, hence the RFC. Any comments are very much appreciated. Thanks and have a nice day ;) Martin Kletzander (18): hw/audio: Remove -soundhw support hw/input/tsc210x: Extract common init code into new function hw/audio: Simplify hda audio init hw/audio/lm4549: Add errp error reporting to init function tests/qtest: Specify audiodev= and -audiodev ui/vnc: Require audiodev= Introduce machine's default-audiodev property audio: Add easy dummy audio initialiser hw/display/xlnx_dp.c: Add audiodev property hw/input/tsc210x.c: Support machine-default audiodev with fallback hw/arm: Support machine-default audiodev with fallback hw/ppc: Support machine-default audiodev with fallback audio: Make AUD_register_card fallible and require audiodev= audio: Require AudioState in AUD_add_capture audio: Be more strict during audio backend initialisation audio: Remove legacy audio environment variables and options audio: Remove unused can_be_default audio/spiceaudio: Fail initialisation when not using spice audio/alsaaudio.c | 1 - audio/audio.c | 204 +++---- audio/audio.h | 5 +- audio/audio_int.h | 1 - audio/audio_legacy.c | 555 ------------------ audio/coreaudio.m | 1 - audio/dbusaudio.c | 1 - audio/dsoundaudio.c | 1 - audio/jackaudio.c | 1 - audio/meson.build | 1 - audio/noaudio.c | 1 - audio/ossaudio.c | 1 - audio/paaudio.c | 1 - audio/sdlaudio.c | 1 - audio/spiceaudio.c | 3 +- audio/wavaudio.c | 1 - docs/about/deprecated.rst | 24 - docs/about/removed-features.rst | 27 + docs/qdev-device-use.txt | 21 +- docs/replay.txt | 2 +- hw/arm/integratorcp.c | 8 +- hw/arm/musicpal.c | 8 +- hw/arm/omap2.c | 11 +- hw/arm/realview.c | 3 + hw/arm/spitz.c | 10 +- hw/arm/versatilepb.c | 3 + hw/arm/vexpress.c | 3 + hw/arm/xlnx-zcu102.c | 4 + hw/arm/z2.c | 12 +- hw/audio/ac97.c | 9 +- hw/audio/adlib.c | 9 +- hw/audio/cs4231a.c | 8 +- hw/audio/es1370.c | 8 +- hw/audio/gus.c | 6 +- hw/audio/hda-codec.c | 37 +- hw/audio/intel-hda.c | 25 +- hw/audio/intel-hda.h | 2 +- hw/audio/lm4549.c | 7 +- hw/audio/lm4549.h | 3 +- hw/audio/meson.build | 1 - hw/audio/pcspk.c | 15 +- hw/audio/pl041.c | 2 +- hw/audio/sb16.c | 9 +- hw/audio/soundhw.c | 177 ------ hw/audio/wm8750.c | 5 +- hw/core/machine.c | 23 + hw/display/xlnx_dp.c | 12 +- hw/input/tsc210x.c | 79 ++- hw/ppc/prep.c | 4 + hw/usb/dev-audio.c | 5 +- include/hw/audio/soundhw.h | 15 - include/hw/boards.h | 1 + qemu-options.hx | 37 -- .../codeconverter/test_regexps.py | 1 - softmmu/qdev-monitor.c | 2 - softmmu/vl.c | 10 - tests/qtest/ac97-test.c | 3 +- tests/qtest/es1370-test.c | 3 +- tests/qtest/fuzz/generic_fuzz_configs.h | 6 +- tests/qtest/intel-hda-test.c | 15 +- ui/vnc.c | 15 +- 61 files changed, 329 insertions(+), 1140 deletions(-) delete mode 100644 audio/audio_legacy.c delete mode 100644 hw/audio/soundhw.c delete mode 100644 include/hw/audio/soundhw.h -- 2.35.1

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Summary on new backup interfaces in QEMU
by Vladimir Sementsov-Ogievskiy 21 Feb '23

21 Feb '23

Hi all! Here I want to summarize new interfaces and use cases for backup in QEMU. TODO for me: convert this into good rst documentation in docs/. OK, let's begin. First, note that drive-backup qmp command is deprecated. Next, some terminology: push backup: the whole process is inside QEMU process, also may be called "internal backup" pull backup: QEMU only exports a kind of snapshot (for example by NBD), and third party software reads this export and stores it somehow, also called "external backup" copy-before-write operations: We usually do backup of active disk, guest is running and may write to the disk during the process of backup. When guest wants to rewrite data region which is not backed up yet, we must stop this guest write, and copy original data to somewhere before continuing guest write. That's a copy-before-write operation. image-fleecing: the technique that allows to export a "snapshotted" state of the active disk with help of copy-before-write operations. We create a temporary image - target for copy-before-write operations, and provide an interface to the user to read the "snapshotted" state. And for read, we do read from temporary image the data which is already changed in original active disk, and we read unchanged data directly from active disk. The temporary image itself is also called "reverse delta" or "reversed delta". == Simple push backup == Just use blockdev-backup, nothing new here. I just note some technical details, that are relatively new: 1. First, backup job inserts copy-before-write filter above source disk, to do copy-before-write operation. 2. Created copy-before-write filter shares internal block-copy state with backup job, so they work in collaboration, to not copy same things twice. == Full pull backup == Assume, we are going to do incremental backup in future, so we also need to create a dirty bitmap, to track dirtiness of active disk since full backup. 1. Create empty temporary image for fleecing. It must be of the same size as active disk. It's not necessary to be qcow2, and if it's a qcow2, you shouldn't make the original active disk a backing file for the new temporary qcow2 image (it was necessary in old fleecing scheme). Example: qemu-img create -f qcow2 temp.qcow2 64G 2. Initialize fleecing scheme and create dirty bitmap for future incremental backup. Assume, disk0 is an active disk, attached to qdev-id sda, to be backed up. qmp: transaction [ block-dirty-bitmap-add {node: disk0, name: bitmap0, persistent: true} blockdev-add* {node-name: tmp-protocol, driver: file, filename: temp.qcow2} blockdev-add {node-name: tmp, driver: qcow2, file: tmp-protocol} blockdev-add {node-name: cbw, driver: copy-before-write, file: disk0, target: tmp} blockdev-replace** {parent-type: qdev, qdev-id: sda, new-child: cbw} blockdev-add {node-name: acc, driver: snapshot-access, file: cbw} ] qmp: nbd-server-start {...} qmp: nbd-server-add {device: acc, ...} This way we create the following block-graph: [guest] [NBD export] | | | root | root v file v [copy-before-write]<------[snapshot-access] | | | file | target v v [active-disk] [temp.qcow2] * "[PATCH 0/2] blockdev-add transaction" series needed for this ** "[PATCH v3 00/11] blockdev-replace" series needed for this Note additional useful options for copy-before-write filter: "[PATCH 0/3] block: copy-before-write: on-cbw-error behavior" provides possibility of option on-cbw-error=break-snapshot, which means that on failure of CBW operation we will not break guest write, but instead all further reads by NBD client will fail, which formally means: break the backup process, not guest write. "[PATCH 0/4] block: copy-before-write: cbw-timeout" provides an option cbw-timeout, to set a timeout for CBW operations. That's very useful to avoid guest stuck. 3. Now third party backup tool can read data from NBD export NBD_CMD_TRIM (discard) operation is supported on the export, it has the following effects: 1. discard this data from temp image, if it is stored here 2. avoid further copy-before-write operation (guest is free to rewrite corresponding data with no extra latency) 3. all further read requests from discarded areas by NBD client will fail So, NBD client may discard regions that are already backed up to avoid extra latency for guest writes and to free disk space on the host. Possible TODO here is to implement NBD protocol extension, that allows to READ & DISCARD in command. In this case we avoid extra command in the wire, but lose possibility of retrying the READ operation if it failed. 4. After backup is complete, we should destroy the fleecing scheme: qmp: nbd-server-stop qmp: blockdev-del {node-name: acc} qmp: blockdev-replace {parent-type: qdev, qdev-id: sda, new-child: disk0} qmp: blockdev-del {node-name: cbw} qmp: blockdev-del {node-name: tmp} qmp: blockdev-del {node-name: tmp-protocol} 5. If backup failed, we should remove created dirty bitmap: qmp: block-dirty-bitmap-remove {node: disk0, name: bitmap0} == Incremental pull backup == OK, now we have a bitmap called bitmap0, and want to do incremental backup, accordingly to that bitmap. In short, we want: - create a new bitmap to continue dirty tracking for next incremental backup - export "snapshotted" state of disk0 through NBD - export "frozen" bitmap, so that external tool know what to copy Mostly, all points remains the same, let's go through: 1. Create empty temporary image for fleecing -- same as for full backup, no difference 2. Initialize fleecing scheme and create dirty bitmap for future incremental backup. qmp: transaction [ block-dirty-bitmap-add {node: disk0, name: bitmap1, persistent: true} block-dirty-bitmap-disable {node: disk0, name: bitmap0} blockdev-add {node-name: tmp-protocol, driver: file, filename: temp.qcow2} blockdev-add {node-name: tmp, driver: qcow2, file: tmp-protocol} blockdev-add {node-name: cbw, driver: copy-before-write, file: disk0, target: tmp, bitmap: {node: disk0, name: bitmap0}} blockdev-replace {parent-type: qdev, qdev-id: sda, new-child: cbw} blockdev-add {node-name: acc, driver: snapshot-access, file: cbw} ] qmp: nbd-server-start {...} qmp: block-export-add {type: nbd, node-name: acc, bitmaps: [{node: disk0, name: bitmap0}]} 3. Now third party backup tool can read data from NBD export - Client may negotiate meta contexts, to query exported dirty bitmap by NBD_BLOCK_STATUS commend - If client reads "not-dirty" (by bitmap0) areas, it gets an error. - NBD_CMD_TRIM (discard) works as for full backup, no difference 4. After backup is complete, we should destroy the fleecing scheme: - Same as for full backup 5. Next, we should handle dirty bitmaps: 5.1 Failure path Merge-back bitmap1 to bitmap0 and continue tracking in bitmap0: qmp: transaction [ block-dirty-bitmap-enable {node: disk0, name: bitmap0} block-dirty-bitmap-merge {node: disk0, target: bitmap0, bitmaps: ['bitmap1']} block-dirty-bitmap-remove {node: disk0, name: bitmap1} ] 5.2 Success path We have two possible user scenarios on success: 5.2.1 Continue tracking for next incremental backup in bitmap1 In this case, just remove bitmap0: qmp: block-dirty-bitmap-remove {node: disk0, name: bitmap0} Or you may not delete bitmap0 and keep it disabled, to be reused in future for differential backup (see below). 5.2.2 Continue tracking for next incremental backup in bitmap0 (assume, we always work with one bitmap and don't want any kind of differential backups, and don't associate bitmap name with stored backups) In this case, enable and clear bitmap0, merge bitmap1 to bitmap0 and remove bitmap1: qmp: transaction [ block-dirty-bitmap-enable {node: disk0, name: bitmap0} block-dirty-bitmap-clear {node: disk0, name: bitmap0} block-dirty-bitmap-merge {node: disk0, target: bitmap0, bitmaps: ['bitmap1']} block-dirty-bitmap-remove {node: disk0, name: bitmap1} ] == Push backup with fleecing full/incremental == Reasoning: the main problem of simple push backup is that guest writes may be seriously affected by copy-on-write operations, when backup target is slow. To solve this problem, we'll use the scheme like for pull backup: we create local temporary image, which is a target for copy-before-write operations, and instead of exporting the "snapshot-access" node we start internal backup from it to the target. So, the scheme and commands looks exactly the same as for full and incremental pull backup. The only difference is that we don't need to start nbd export, but instead we should add target node to qemu and start internal backup. And good thing is that it may be done in same transaction with initializing fleecing scheme: qmp: transaction [ ... initialize fleecing scheme for full or incremental backup ... # Add target node. Here is qcow2 added, but it may be nbd node or something else blockdev-add {node-name: target-protocol, driver: file, filename: target.qcow2} blockdev-add {node-name: target, driver: qcow2, file: target-protocol} # Start backup blockdev-backup {device: acc, target: target, ...} ] If it is an incremental backup, pass also bitmap parameter: blockdev-backup {..., bitmap: bitmap0, sync: incremental, bitmap-mode: never} Note bitmap-mode=never: this means that backup will do nothing with bitmap0, so we have same scheme like for pull backups (handle bitmaps by hand after backup). Still, push-backup scheme may be adopted to use other bitmap modes. What we lack here is discarding in 'acc' node after successful copying of the block to the target, to safe disk space and avoid extra copy-before-write operations. It's a TODO, should be implemented like discard-source parameter for blockdev-backup. == Differential backups == I'm not fan of this idea, but I think it should be described. Assume we have already a chain of incremental backups (represented as qcow2 chain on backup storage server, for example). They corresponds to some points in time: T0, T1, T2, T3. Assume T3 is the last backup. If we want to create usual incremental backup, it would be diff between T3 and current time (which becomes T4). Differential backup say: I want to make backup starting from T1 to current time. What's for? Maybe T2 and T3 was removed or somehow damaged.. How to do that in Qemu: on each incremental backup you start a new bitmap, and _keep_ old one as disabled. This way we have bitmap0 (which presents diff between T0 and T1), bitmap1 (diff T1 T2), bitmap2 (diff T2 T3), and bitmap3 which shows diff from T3 up to current time. bitmap3 is the only enabled bitmap and others are disabled. So, to make differential backup, use block-dirty-bitmap-merge command, to merge all bitmaps you need into one, and than use it in any backup scheme. The drawback is that all these disabled bitmaps eat RAM. Possible solution is to not keep them in RAM, it's OK to keep them in qcow2, and load only on demand. That's not realized now and that's a TODO for thous who want differential backups. -- Best regards, Vladimir

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[libvirt] Semantic change in v4.3 slows down image creation and snapshots (on ZFS)
by Christian Ehrhardt 31 Jul '22

31 Jul '22

Hi, when discussing bug [1] triggered by [2] Daniel and I have found that the change [3] which is in since v4.3 was a semantic change to the behavior of libvirt. virt-manager used and still does issue a volume XML like: <volume> <name>disk.qcow2</name> <capacity>16106127360</capacity> <allocation>16106127360</allocation> <target> <format type="qcow2"/> <features> <lazy_refcounts/> </features> </target> </volume> Up until the commit above that was using preallocation=metadata, but now uses preallocation=falloc. In many cases (read: Fileystems) that won't be very user-visible, but if you are running on ZFS (or anything else that can't fallocate well) this is made worse by [4] slowing down these operations a lot. After the POV for virt-manager seems to have settled on the bug [1] referenced the remaining question is if libvirt should revert/modify the change [3] - and that we agreed required a wider discussion to be had here, hence this mail. [1]: https://bugzilla.redhat.com/show_bug.cgi?id=1759454 [2]: https://bugs.launchpad.net/virt-manager/+bug/1847105 [3]: https://libvirt.org/git/?p=libvirt.git;a=commit;h=c9ec7088c7a3f4cd26bb471f1… [4]: https://github.com/zfsonlinux/zfs/issues/326 -- Christian Ehrhardt Software Engineer, Ubuntu Server Canonical Ltd

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[PATCH] cmdQemuMonitorCommandQMPWrap: Reset ignored errors from JSON parsing
by Peter Krempa 25 Jul '22

25 Jul '22

'cmdQemuMonitorCommandQMPWrap' is checking whether the user provided string is not valid JSON to avoid wrapping it. In cases where it's not JSON we ignore the error and add the wrapper. If the caller then reports a different non-libvirt error the error from the JSON parsing would be printed as well. Reset errors we ignore: # virsh qemu-monitor-command cd --pass-fds a asdf error: Unable to parse FD number 'a' error: internal error: cannot parse json asdf: lexical error: invalid char in json text. asdf (right here) ------^ In the above case 'asdf' is not valid JSON, but the code did wrap it into '{"execute":"asdf"}', the only problem is the argument for --pass-fds. Signed-off-by: Peter Krempa <pkrempa(a)redhat.com> --- tools/virsh-domain.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/tools/virsh-domain.c b/tools/virsh-domain.c index 9b1b14cdc2..743660e794 100644 --- a/tools/virsh-domain.c +++ b/tools/virsh-domain.c @@ -9769,6 +9769,8 @@ cmdQemuMonitorCommandQMPWrap(vshControl *ctl, if (virJSONValueIsObject(fullcmdjson)) return g_steal_pointer(&fullcmd); + vshResetLibvirtError(); + /* we try to wrap the command and possible arguments into a JSON object, if * we as fall back we pass through what we've got from the user */ @@ -9787,6 +9789,8 @@ cmdQemuMonitorCommandQMPWrap(vshControl *ctl, * JSON object wrapper and try using that */ g_auto(virBuffer) buf = VIR_BUFFER_INITIALIZER; + vshResetLibvirtError(); + virBufferAddLit(&buf, "{"); /* opt points to the _ARGV option bit containing the command so we'll * iterate through the arguments now */ -- 2.35.1

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