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Re: [PATCH v4 02/11] qemu: prepare cleanup for <transient/> disk overlays



On Thu, Sep 24, 2020 at 01:43:49PM +0200, Peter Krempa wrote:
> Later patches will implement support for <transient/> disks in libvirt
> by installing an overlay on top of the configured image. This will
> require cleanup after the VM will be stopped so that the state is
> correctly discarded.
> 
> Since the overlay will be installed only during the startup phase of the
> VM we need to ensure that qemuProcessStop doesn't delete the original
> file on some previous failure. This is solved by adding
> 'inhibitDiskTransientDelete' VM private data member which is set prior
> to any startup step and will be cleared once transient disk overlays are
> established.
> 
> Based on that we can then delete the overlays for any <transient/> disk.
> 
> Signed-off-by: Peter Krempa <pkrempa redhat com>
> ---
>  src/qemu/qemu_domain.c  |  2 ++
>  src/qemu/qemu_domain.h  |  4 ++++
>  src/qemu/qemu_process.c | 22 ++++++++++++++++++++++
>  3 files changed, 28 insertions(+)
> 
> diff --git a/src/qemu/qemu_domain.c b/src/qemu/qemu_domain.c
> index 279de2997d..dc5949edfa 100644
> --- a/src/qemu/qemu_domain.c
> +++ b/src/qemu/qemu_domain.c
> @@ -1792,6 +1792,8 @@ qemuDomainObjPrivateDataClear(qemuDomainObjPrivatePtr priv)
>      priv->dbusVMStateIds = NULL;
> 
>      priv->dbusVMState = false;
> +
> +    priv->inhibitDiskTransientDelete = false;
>  }
> 
> 
> diff --git a/src/qemu/qemu_domain.h b/src/qemu/qemu_domain.h
> index c7c3c5c073..ec776ced72 100644
> --- a/src/qemu/qemu_domain.h
> +++ b/src/qemu/qemu_domain.h
> @@ -263,6 +263,10 @@ struct _qemuDomainObjPrivate {
>      char **dbusVMStateIds;
>      /* true if -object dbus-vmstate was added */
>      bool dbusVMState;
> +
> +    /* prevent deletion of <transient> disk overlay files between startup and
> +     * succesful setup of the overlays */
> +    bool inhibitDiskTransientDelete;
>  };
> 
>  #define QEMU_DOMAIN_PRIVATE(vm) \
> diff --git a/src/qemu/qemu_process.c b/src/qemu/qemu_process.c
> index f21b8f1585..ffb3afa9c5 100644
> --- a/src/qemu/qemu_process.c
> +++ b/src/qemu/qemu_process.c
> @@ -5616,6 +5616,9 @@ qemuProcessInit(virQEMUDriverPtr driver,
>      if (virDomainObjSetDefTransient(driver->xmlopt, vm, priv->qemuCaps) < 0)
>          goto cleanup;
> 
> +    /* don't clean up files for <transient> disks until we set them up */
> +    priv->inhibitDiskTransientDelete = true;
> +
>      if (flags & VIR_QEMU_PROCESS_START_PRETEND) {
>          if (qemuDomainSetPrivatePaths(driver, vm) < 0) {
>              virDomainObjRemoveTransientDef(vm);
> @@ -7710,6 +7713,18 @@ void qemuProcessStop(virQEMUDriverPtr driver,
>              }
> 
>              qemuBlockRemoveImageMetadata(driver, vm, disk->dst, disk->src);
> +
> +            /* for now transient disks are forbidden with migration so they
> +             * can be handled here */
> +            if (disk->transient &&
> +                !priv->inhibitDiskTransientDelete) {
> +                VIR_DEBUG("Removing transient overlay '%s' of disk '%s'",
> +                          disk->src->path, disk->dst);
> +                if (qemuDomainStorageFileInit(driver, vm, disk->src, NULL) >= 0) {
> +                    virStorageFileUnlink(disk->src);
> +                    virStorageFileDeinit(disk->src);
> +                }
> +            }
>          }
>      }
> 
> @@ -8125,6 +8140,10 @@ qemuProcessReconnect(void *opaque)
>      cfg = virQEMUDriverGetConfig(driver);
>      priv = obj->privateData;
> 
> +    /* expect that libvirt might have crashed during VM start, so prevent
> +     * cleanup of transient disks */
> +    priv->inhibitDiskTransientDelete = true;
> +
>      if (qemuDomainObjBeginJob(driver, obj, QEMU_JOB_MODIFY) < 0)
>          goto error;
>      jobStarted = true;
> @@ -8228,6 +8247,9 @@ qemuProcessReconnect(void *opaque)
>          goto error;
>      }
> 
> +    /* vm startup complete, we can remove transient disks if required */
> +    priv->inhibitDiskTransientDelete = false;
> +
>      /* In case the domain shutdown while we were not running,
>       * we need to finish the shutdown process. And we need to do it after
>       * we have virQEMUCaps filled in.
> -- 

Tested-by: Masayoshi Mizuma <m mizuma jp fujitsu com>

Thanks a lot!
Masa


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