Am 23.10.2013 um 21:40 hat Max Reitz geschrieben:
> Opening the qcow2 image with BDRV_O_NO_FLUSH prevents any flushes during
> the image creation. This means that the image has not yet been flushed
> to disk when qemu-img create exits. This flush is delayed until the next
> operation on the image involving opening it without BDRV_O_NO_FLUSH and
> closing (or directly flushing) it. For large images and/or images with a
> small cluster size and preallocated metadata, this flush may take a
> significant amount of time and may occur unexpectedly.
>
> Reopening the image without BDRV_O_NO_FLUSH right before the end of
> qcow2_create2() results in preponing the potentially costly flush into
> the image creation, which is expected to take some time (whereas
> successive image operations may be not).
>
> Signed-off-by: Max Reitz <mre...@redhat.com>
> ---
> block/qcow2.c | 10 +++++++++-
> 1 file changed, 9 insertions(+), 1 deletion(-)
>
> diff --git a/block/qcow2.c b/block/qcow2.c
> index c1abaff..8b98c3a 100644
> --- a/block/qcow2.c
> +++ b/block/qcow2.c
> @@ -1584,7 +1584,15 @@ static int qcow2_create2(const char *filename, int64_t
> total_size,
> }
> }
>
> - ret = 0;
I would prefer to keep the explicit ret = 0 there (just like the
unnecessary last 'goto out:', it just makes things more obvious and
consistent)
> + bdrv_close(bs);
> +
> + /* Reopen the image without BDRV_O_NO_FLUSH to flush it before returning
> */
> + ret = bdrv_open(bs, filename, NULL,
> + BDRV_O_RDWR | BDRV_O_CACHE_WB, drv, &local_err);
> + if (error_is_set(&local_err)) {
> + error_propagate(errp, local_err);
So a goto here wouldn't hurt either. Note how the unnecessary goto in
the block before allowed you to just add your new code without modifying
existing parts.
> + }
> +
> out:
> bdrv_unref(bs);
> return ret;
Kevin
