Re: [Qemu-devel] [PATCH alt 4/7] block/qcow2: Implement status CB for amend

[Eric Blake <eblake@redhat.com>]

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On 07/26/2014 01:22 PM, Max Reitz wrote:
> The only really time-consuming operation potentially performed by
> qcow2_amend_options() is zero cluster expansion when downgrading qcow2
> images from compat=1.1 to compat=0.10, so report status of that
> operation and that operation only through the status CB.
> 
> For this, approximate the progress as the number of L1 entries visited
> during the operation.
> 
> Signed-off-by: Max Reitz <mreitz@redhat.com>
> ---
>  block/qcow2-cluster.c | 36 ++++++++++++++++++++++++++++++++----
>  block/qcow2.c         |  9 ++++-----
>  block/qcow2.h         |  3 ++-
>  3 files changed, 38 insertions(+), 10 deletions(-)

Seems like a reasonable approximation.  The progress may appear to
change non-linearly (slower when a sequence of L1 entries visit all-zero
data, faster when the entries visit normal data), but we never promised
linear growth.

> 
> diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c
> index 4208dc0..f8bec6f 100644
> --- a/block/qcow2-cluster.c
> +++ b/block/qcow2-cluster.c
> @@ -1548,10 +1548,17 @@ fail:
>   * zero expansion (i.e., has been filled with zeroes and is referenced from an
>   * L2 table). nb_clusters contains the total cluster count of the image file,
>   * i.e., the number of bits in expanded_clusters.
> + *
> + * l1_entries and *visited_l1_entries are ued to keep track of progress for

s/ued/used/

Definitely looks simpler than your other approach.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org


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