On Thu, Sep 24, 2020 at 01:43:50PM +0200, Peter Krempa wrote:
> To implement <transient/> disks we'll need to install an overlay on top
> of the original disk image which will be discarded after the VM is
> turned off. This was initially implemented by qemu but libvirt never > picked up this option. With blockdev the qemu feature became unsupported
> so we need to do this via the snapshot code anyways.
>
> The helpers introduced in this patch prepare a fake snapshot disk
> definition for a disk which is configured as <transient/> and use it to
> create a snapshot (without actually modifying metada or persistent def).
>
> Signed-off-by: Peter Krempa <pkrempa@xxxxxxxxxx>
> ---
> src/qemu/qemu_snapshot.c | 91 +++++++++++++++++++++++++++++++++++++++-
> src/qemu/qemu_snapshot.h | 5 +++
> 2 files changed, 95 insertions(+), 1 deletion(-)
>
> diff --git a/src/qemu/qemu_snapshot.c b/src/qemu/qemu_snapshot.c
> index ca051071aa..d10e7b6b3a 100644
> --- a/src/qemu/qemu_snapshot.c
> +++ b/src/qemu/qemu_snapshot.c
> @@ -986,6 +986,7 @@ qemuSnapshotDiskPrepareOne(virDomainObjPtr vm,
> qemuSnapshotDiskDataPtr dd,
> virHashTablePtr blockNamedNodeData,
> bool reuse,
> + bool updateConfig,
> qemuDomainAsyncJob asyncJob,
> virJSONValuePtr actions)
> {
> @@ -1008,7 +1009,8 @@ qemuSnapshotDiskPrepareOne(virDomainObjPtr vm,
> return -1;
>
> /* modify disk in persistent definition only when the source is the same */
> - if (vm->newDef &&
> + if (updateConfig &&
> + vm->newDef &&
> (persistdisk = virDomainDiskByTarget(vm->newDef, dd->disk->dst)) &&
> virStorageSourceIsSameLocation(dd->disk->src, persistdisk->src)) {
>
> @@ -1116,6 +1118,54 @@ qemuSnapshotDiskPrepareActiveExternal(virDomainObjPtr vm,
> snapctxt->dd + snapctxt->ndd++,
> blockNamedNodeData,
> reuse,
> + true,
> + asyncJob,
> + snapctxt->actions) < 0)
> + return NULL;
> + }
> +
> + return g_steal_pointer(&snapctxt);
> +}
> +
> +
> +static qemuSnapshotDiskContextPtr
> +qemuSnapshotDiskPrepareDisksTransient(virDomainObjPtr vm,
> + virQEMUDriverConfigPtr cfg,
> + virHashTablePtr blockNamedNodeData,
> + qemuDomainAsyncJob asyncJob)
> +{
> + g_autoptr(qemuSnapshotDiskContext) snapctxt = NULL;
> + size_t i;
> +
> + snapctxt = qemuSnapshotDiskContextNew(vm->def->ndisks, vm, asyncJob);
> +
> + for (i = 0; i < vm->def->ndisks; i++) {
> + virDomainDiskDefPtr domdisk = vm->def->disks[i];
> + g_autoptr(virDomainSnapshotDiskDef) snapdisk = g_new0(virDomainSnapshotDiskDef, 1);
> +
> + if (!domdisk->transient)
> + continue;
> +
> + /* validation code makes sure that we do this only for local disks
> + * with a file source */
> + snapdisk->name = g_strdup(domdisk->dst);
> + snapdisk->snapshot = VIR_DOMAIN_SNAPSHOT_LOCATION_EXTERNAL;
> + snapdisk->src = virStorageSourceNew();
> + snapdisk->src->type = VIR_STORAGE_TYPE_FILE;
> + snapdisk->src->format = VIR_STORAGE_FILE_QCOW2;
> + snapdisk->src->path = g_strdup_printf("%s.TRANSIENT", domdisk->src->path);
> + if (virFileExists(snapdisk->src->path)) {
> + virReportError(VIR_ERR_OPERATION_UNSUPPORTED,
> + _("Overlay file '%s' for transient disk '%s' already exists"),
> + snapdisk->src->path, domdisk->dst);
> + return NULL;
> + }
> +
> + if (qemuSnapshotDiskPrepareOne(vm, cfg, domdisk, snapdisk,
> + snapctxt->dd + snapctxt->ndd++,
> + blockNamedNodeData,
> + false,
> + false,
> asyncJob,
> snapctxt->actions) < 0)
> return NULL;
> @@ -1253,6 +1303,45 @@ qemuSnapshotCreateActiveExternalDisks(virDomainObjPtr vm,
> }
>
>
> +/**
> + * qemuSnapshotCreateDisksTransient:
> + * @vm: domain object
> + * @asyncJob: qemu async job type
> + *
> + * Creates overlays on top of disks which are configured as <transient/>. Note
> + * that the validation code ensures that <transient> disks have appropriate
> + * configuration.
> + */
> +int
> +qemuSnapshotCreateDisksTransient(virDomainObjPtr vm,
> + qemuDomainAsyncJob asyncJob)
> +{
> + qemuDomainObjPrivatePtr priv = vm->privateData;
> + virQEMUDriverPtr driver = priv->driver;
> + g_autoptr(virQEMUDriverConfig) cfg = virQEMUDriverGetConfig(driver);
> + g_autoptr(qemuSnapshotDiskContext) snapctxt = NULL;
> + g_autoptr(virHashTable) blockNamedNodeData = NULL;
> +
> + if (virQEMUCapsGet(priv->qemuCaps, QEMU_CAPS_BLOCKDEV)) {
> + if (!(blockNamedNodeData = qemuBlockGetNamedNodeData(vm, asyncJob)))
> + return -1;
> +
> + if (!(snapctxt = qemuSnapshotDiskPrepareDisksTransient(vm, cfg,
> + blockNamedNodeData,
> + asyncJob)))
> + return -1;
> +
> + if (qemuSnapshotDiskCreate(snapctxt, cfg) < 0)
> + return -1;
> + }
> +
> + /* the overlays are established, so they can be deleted on a shutdown */
> + priv->inhibitDiskTransientDelete = false;
> +
> + return 0;
> +}
> +
> +
> static int
> qemuSnapshotCreateActiveExternal(virQEMUDriverPtr driver,
> virDomainObjPtr vm,
> diff --git a/src/qemu/qemu_snapshot.h b/src/qemu/qemu_snapshot.h
> index 8b3ebe87b1..cf9bfec542 100644
> --- a/src/qemu/qemu_snapshot.h
> +++ b/src/qemu/qemu_snapshot.h
> @@ -21,6 +21,7 @@
> #include "virconftypes.h"
> #include "datatypes.h"
> #include "qemu_conf.h"
> +#include "qemu_domainjob.h"
>
> virDomainMomentObjPtr
> qemuSnapObjFromName(virDomainObjPtr vm,
> @@ -53,3 +54,7 @@ int
> qemuSnapshotDelete(virDomainObjPtr vm,
> virDomainSnapshotPtr snapshot,
> unsigned int flags);
> +
> +int
> +qemuSnapshotCreateDisksTransient(virDomainObjPtr vm,
> + qemuDomainAsyncJob asyncJob);
> --
Tested-by: Masayoshi Mizuma <m.mizuma@xxxxxxxxxxxxxx>
Thanks a lot!
Masa
