Calling bdrv_img_create() with a size of -1 means that it determines the size automatically by opening the backing file. However, in the case of live snapshots, the backing file is already opened and we must avoid opening the same image twice at the same time. Apart from that, just getting the size from the already existing BDS is a lot less overhead than opening a new instance.
Signed-off-by: Kevin Wolf <kw...@redhat.com> Reviewed-by: Jeff Cody <jc...@redhat.com> --- blockdev.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/blockdev.c b/blockdev.c index 0f20c65..e1c1540 100644 --- a/blockdev.c +++ b/blockdev.c @@ -1732,10 +1732,15 @@ static void external_snapshot_prepare(BlkActionState *common, /* create new image w/backing file */ mode = s->has_mode ? s->mode : NEW_IMAGE_MODE_ABSOLUTE_PATHS; if (mode != NEW_IMAGE_MODE_EXISTING) { + int64_t size = bdrv_getlength(state->old_bs); + if (size < 0) { + error_setg_errno(errp, -size, "bdrv_getlength failed"); + return; + } bdrv_img_create(new_image_file, format, state->old_bs->filename, state->old_bs->drv->format_name, - NULL, -1, flags, &local_err, false); + NULL, size, flags, &local_err, false); if (local_err) { error_propagate(errp, local_err); return; -- 1.8.3.1