[PATCH 18/19] qemu: migration: Migrate block dirty bitmaps corresponding to checkpoints

[Jiri Denemark]

On Thu, Feb 11, 2021 at 16:37:57 +0100, Peter Krempa wrote:
> Preserve block dirty bitmaps after migration with
> QEMU_MONITOR_MIGRATE_NON_SHARED_(DISK|INC).
> 
> This patch implements functions which offer the bitmaps to the
> destination, check for eligibility on destination and then configure
> source for the migration.
> 
> Signed-off-by: Peter Krempa <pkrempa at redhat.com>
> ---
>  src/qemu/qemu_migration.c | 333 +++++++++++++++++++++++++++++++++++++-
>  1 file changed, 331 insertions(+), 2 deletions(-)
> 
> diff --git a/src/qemu/qemu_migration.c b/src/qemu/qemu_migration.c
> index 36424f8493..16bfad0390 100644
> --- a/src/qemu/qemu_migration.c
> +++ b/src/qemu/qemu_migration.c
...
> @@ -2528,6 +2619,92 @@ qemuMigrationDstPrepare(virDomainObjPtr vm,
>                                       migrateFrom, fd, NULL);
>  }
> 
> +
> +/**
> + * qemuMigrationDstPrepareAnyBlockDirtyBitmaps:
> + * @vm: domain object
> + * @mig: migration cookie
> + * @migParams: migration parameters
> + * @flags: migration flags
> + *
> + * Checks whether block dirty bitmaps offered by the migration source are
> + * to be migrated (e.g. they don't exist, the destination is compatible etc)
> + * and sets up destination qemu for migrating the bitmaps as well as updates the
> + * list of eligible bitmaps in the migration cookie to be sent back to the
> + * source.
> + */
> +static int
> +qemuMigrationDstPrepareAnyBlockDirtyBitmaps(virDomainObjPtr vm,
> +                                            qemuMigrationCookiePtr mig,
> +                                            qemuMigrationParamsPtr migParams,
> +                                            unsigned int flags)
> +{
> +    qemuDomainObjPrivatePtr priv = vm->privateData;
> +    g_autoptr(virJSONValue) mapping = NULL;
> +    g_autoptr(GHashTable) blockNamedNodeData = NULL;
> +    GSList *nextdisk;
> +
> +    if (!mig->nbd ||
> +        !mig->blockDirtyBitmaps ||
> +        !(flags & (VIR_MIGRATE_NON_SHARED_DISK | VIR_MIGRATE_NON_SHARED_INC)) ||
> +        !virQEMUCapsGet(priv->qemuCaps, QEMU_CAPS_MIGRATION_PARAM_BLOCK_BITMAP_MAPPING))
> +        return 0;

Shouldn't we report an error in case the source sent bitmaps, but local
QEMU does not support QEMU_CAPS_MIGRATION_PARAM_BLOCK_BITMAP_MAPPING?

> +
> +    if (qemuMigrationCookieBlockDirtyBitmapsMatchDisks(vm->def, mig->blockDirtyBitmaps) < 0)
> +        return -1;
> +
> +    if (!(blockNamedNodeData = qemuBlockGetNamedNodeData(vm, QEMU_ASYNC_JOB_MIGRATION_IN)))
> +        return -1;
> +
> +    for (nextdisk = mig->blockDirtyBitmaps; nextdisk; nextdisk = nextdisk->next) {
> +        qemuMigrationBlockDirtyBitmapsDiskPtr disk = nextdisk->data;
> +        qemuBlockNamedNodeDataPtr nodedata;
> +        GSList *nextbitmap;
> +
> +        if (!(nodedata = virHashLookup(blockNamedNodeData, disk->nodename))) {
> +            virReportError(VIR_ERR_INTERNAL_ERROR,
> +                           _("failed to find data for block node '%s'"),
> +                           disk->nodename);
> +            return -1;
> +        }
> +
> +        /* don't migrate bitmaps into non-qcow2v3+ images */

How about "Bitmaps can only be migrated to qcow2 v3+"?

> +        if (disk->disk->src->format != VIR_STORAGE_FILE_QCOW2 ||
> +            nodedata->qcow2v2) {
> +            disk->skip = true;

Is skipping the disk the right thing to do? Should we report an error
and abort migration instead? Just checking, maybe we can't do so for
backward compatibility...

> +            continue;
> +        }
> +
> +        for (nextbitmap = disk->bitmaps; nextbitmap; nextbitmap = nextbitmap->next) {
> +            qemuMigrationBlockDirtyBitmapsDiskBitmapPtr bitmap = nextbitmap->data;
> +            size_t k;
> +
> +            /* don't migrate into existing bitmaps */
> +            for (k = 0; k < nodedata->nbitmaps; k++) {
> +                if (STREQ(bitmap->bitmapname, nodedata->bitmaps[k]->name)) {
> +                    bitmap->skip = true;

And similar questions for bitmaps here.

> +                    break;
> +                }
> +            }
> +
> +            if (bitmap->skip)
> +                continue;
> +        }
> +    }
> +
> +    if (qemuMigrationCookieBlockDirtyBitmapsToParams(mig->blockDirtyBitmaps,
> +                                                     &mapping) < 0)
> +        return -1;
> +
> +    if (!mapping)
> +        return 0;
> +
> +    qemuMigrationParamsSetBlockDirtyBitmapMapping(migParams, &mapping);
> +    mig->flags |= QEMU_MIGRATION_COOKIE_BLOCK_DIRTY_BITMAPS;
> +    return 0;
> +}
> +
> +
>  static int
>  qemuMigrationDstPrepareAny(virQEMUDriverPtr driver,
>                             virConnectPtr dconn,
...
> +static int
> +qemuMigrationSrcRunPrepareBlockDirtyBitmaps(virDomainObjPtr vm,
> +                                            qemuMigrationCookiePtr mig,
> +                                            qemuMigrationParamsPtr migParams,
> +                                            unsigned int flags)
> +
> +{
> +    g_autoptr(virJSONValue) mapping = NULL;
> +
> +    if (!mig->blockDirtyBitmaps)
> +        return 0;
> +
> +    if (qemuMigrationCookieBlockDirtyBitmapsMatchDisks(vm->def, mig->blockDirtyBitmaps) < 0)
> +        return -1;
> +
> +    /* For QEMU_MONITOR_MIGRATE_NON_SHARED_INC we can migrate the bitmaps
> +     * directly, otherwise we must create merged bitmaps from the whole
> +     * chain */
> +
> +    if (!(flags & QEMU_MONITOR_MIGRATE_NON_SHARED_INC) &&
> +        qemuMigrationSrcRunPrepareBlockDirtyBitmapsMerge(vm, mig))

"< 0" is missing in the check.

> +        return -1;
> +
> +    if (qemuMigrationCookieBlockDirtyBitmapsToParams(mig->blockDirtyBitmaps,
> +                                                     &mapping) < 0)
> +        return -1;
> +
> +    qemuMigrationParamsSetBlockDirtyBitmapMapping(migParams, &mapping);
> +    return 0;
> +}
> +
> +
>  static int
>  qemuMigrationSrcRun(virQEMUDriverPtr driver,
>                      virDomainObjPtr vm,

Jirka