Re: [Qemu-devel] [PATCH V11 05/17] block: add snapshot info query function bdrv_query_snapshot_info_list()

[Eric Blake]

On 04/02/2013 05:47 AM, Wenchao Xia wrote:
>   This patch adds function bdrv_query_snapshot_info_list(), which will
> retrieve snapshot info of an image in qmp object format. The implementation
> is based on the code moved from qemu-img.c with modification to fit more
> for qmp based block layer API.
> 
> Signed-off-by: Wenchao Xia <address@hidden>
> ---
>  block/qapi.c         |   55 ++++++++++++++++++++++++++++++++++++++-----------
>  include/block/qapi.h |    4 ++-
>  qemu-img.c           |    5 +++-
>  3 files changed, 49 insertions(+), 15 deletions(-)

> +/*
> + * return 0 on success, @p_list will be set only on success, and caller need 
> to

s/need/needs/

> + * check *p_list on success.

I wonder if this wording would be any better:

Returns 0 on success, with *p_list either set to describe snapshot
information, or NULL because there are no snapshots.  Returns -1 on
error, with *p_list untouched.

> + */
> +int bdrv_query_snapshot_info_list(BlockDriverState *bs,
> +                                  SnapshotInfoList **p_list,
> +                                  Error **errp)
>  {

At any rate, my only commentary was on grammar and a possible wording
for a comment, while the code itself is fine from my viewpoint; so feel
free to add:

Reviewed-by: Eric Blake <address@hidden>

> +++ b/qemu-img.c
> @@ -1735,7 +1735,10 @@ static ImageInfoList *collect_image_info_list(const 
> char *filename,
>  
>          info = g_new0(ImageInfo, 1);
>          bdrv_collect_image_info(bs, info, filename);
> -        bdrv_collect_snapshots(bs, info);
> +        if (!bdrv_query_snapshot_info_list(bs, &info->snapshots, NULL) &&
> +            info->snapshots) {
> +            info->has_snapshots = true;
> +        }

Hmm.  info->snapshots starts life as NULL (thanks to g_new0), and is
untouched on error.  Since you are ignoring any errors, you technically
could write:

bdrv_query_snapshot_info_list(bs, &info->snapshots, NULL);
if (info->snapshots) {
    info->has_snapshots = true;
}

for the same semantics.  That means that as of this commit, no caller
cares about the return value of bdrv_query_snapshot_info_list (they only
care about whether info->snapshots was changed to non-null), so it could
return void for a slightly simpler implementation.

But I don't know if any later patches in the series start to care about
which error was returned.

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

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