Re: [Qemu-devel] [PATCH 04/11] snapshot: new function bdrv_snapshot_find_by_id_and_name()

[Fam Zheng <famz@redhat.com>]

On Sat, 06/08 14:58, Wenchao Xia wrote:
> To make it clear about id and name in searching, add this API
> to distinguish them. Caller can choose to search by id or name,
> *errp will be set only for exception.
> 
> Some code are modified based on Pavel's patch.
> 
> Signed-off-by: Wenchao Xia <xiawenc@linux.vnet.ibm.com>
> Signed-off-by: Pavel Hrdina <phrdina@redhat.com>
> ---
>  block/snapshot.c         |   74 ++++++++++++++++++++++++++++++++++++++++++++++
>  include/block/snapshot.h |    6 ++++
>  2 files changed, 80 insertions(+), 0 deletions(-)
> 
> diff --git a/block/snapshot.c b/block/snapshot.c
> index 6c6d9de..0a9af4e 100644
> --- a/block/snapshot.c
> +++ b/block/snapshot.c
> @@ -48,6 +48,80 @@ int bdrv_snapshot_find(BlockDriverState *bs, QEMUSnapshotInfo *sn_info,
>      return ret;
>  }
>  
> +/**
> + * Look up an internal snapshot by @id and @name.
> + * @bs: block device to search
> + * @id: unique snapshot ID, or NULL
> + * @name: snapshot name, or NULL
> + * @sn_info: location to store information on the snapshot found
> + * @errp: location to store error, will be set only for exception
> + *
> + * This function will traverse snapshot list in @bs to search the matching
> + * one, @id and @name are the matching condition:
> + * If both @id and @name are specified, find the first one with id @id and
> + * name @name.
> + * If only @id is specified, find the first one with id @id.
> + * If only @name is specified, find the first one with name @name.
> + * if none is specified, abort().
> + *
> + * Returns: true when a snapshot is found and @sn_info will be filled, false
> + * when error or not found. If all operation succeed but no matching one is
> + * found, @errp will NOT be set.
> + */
> +bool bdrv_snapshot_find_by_id_and_name(BlockDriverState *bs,
> +                                       const char *id,
> +                                       const char *name,
> +                                       QEMUSnapshotInfo *sn_info,
> +                                       Error **errp)
> +{
> +    QEMUSnapshotInfo *sn_tab, *sn;
> +    int nb_sns, i;
> +    bool ret = false;
> +
> +    nb_sns = bdrv_snapshot_list(bs, &sn_tab);
> +    if (nb_sns < 0) {
> +        error_setg_errno(errp, -nb_sns, "Failed to get a snapshot list");
> +        return false;
> +    } else if (nb_sns == 0) {
> +        return false;
> +    }
> +
> +    if (id && name) {
> +        for (i = 0; i < nb_sns; i++) {
> +            sn = &sn_tab[i];
> +            if (!strcmp(sn->id_str, id) && !strcmp(sn->name, name)) {
> +                *sn_info = *sn;
> +                ret = true;
> +                break;
> +            }
> +        }
> +    } else if (id) {
> +        for (i = 0; i < nb_sns; i++) {
> +            sn = &sn_tab[i];
> +            if (!strcmp(sn->id_str, id)) {
> +                *sn_info = *sn;
> +                ret = true;
> +                break;
> +            }
> +        }
> +    } else if (name) {
> +        for (i = 0; i < nb_sns; i++) {
> +            sn = &sn_tab[i];
> +            if (!strcmp(sn->name, name)) {
> +                *sn_info = *sn;
> +                ret = true;
> +                break;
> +            }
> +        }
> +    } else {
> +        /* program error */
> +        abort();
> +    }

Looks duplicated. How about:

    if (id || name) {
        for (i = 0; i < nb_sns; i++) {
            sn = &sn_tab[i];
            if ((!id || !strcmp(sn->id_str, id)) &&
                (!name || !strcmp(sn->name, name))) {
                *sn_info = *sn;
                ret = true;
                break;
            }
        }
    } else {
        abort();
    }

And why do we have to abort here? It is not completely nonsense to me to
return first snapshot with id == NULL and name == NULL.

-- 
Fam