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

[Wenchao Xia <xiawenc@linux.vnet.ibm.com>]

于 2013-6-8 15:31, Fam Zheng 写道:
> 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();
>      }
>
   Less code, but slightly slower since more "if" inside "for". I think
three "for" also show more clear about judgement logic.

> 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.
>
   Just to tip program error. An snapshot with id == NULL and name ==
NULL is not possible, isn't it?.


-- 
Best Regards

Wenchao Xia