Re: [Qemu-devel] [PATCH v2 03/12] savevm: update bdrv_snapshot_find() to find snapshot by id or name and add error parameter

[Pavel Hrdina <phrdina@redhat.com>]

On 25.4.2013 08:31, Wenchao Xia wrote:
>> Finding snapshot by a name which could also be an id isn't best way
>> how to do it. There will be rewrite of savevm, loadvm and delvm to
>> improve the behavior of these commands. The savevm and loadvm will
>> have their own patch series.
>>
>> Now bdrv_snapshot_find takes more parameters. The name parameter will
>> be matched only against the name of the snapshot and the same applies
>> to id parameter.
>>
>> There is one exception. If you set the last parameter, the name parameter
>> will be matched against the name or the id of a snapshot. This exception
>> is only for backward compatibility for other commands and it will be
>> dropped after all commands will be rewritten.
>>
>> We only need to know if that snapshot exists or not. We don't care
>> about any error message. If snapshot exists it returns TRUE otherwise
>> it returns FALSE.
>>
>> There is also new Error parameter which will containt error messeage if
>> something goes wrong.
>>
>> Signed-off-by: Pavel Hrdina <phrdina@redhat.com>
>> ---
>>    savevm.c | 93 ++++++++++++++++++++++++++++++++++++++++++++++------------------
>>    1 file changed, 67 insertions(+), 26 deletions(-)
>>
>> diff --git a/savevm.c b/savevm.c
>> index ba97c41..1622c55 100644
>> --- a/savevm.c
>> +++ b/savevm.c
>> @@ -2262,26 +2262,66 @@ out:
>>        return ret;
>>    }
>>
>> -static int bdrv_snapshot_find(BlockDriverState *bs, QEMUSnapshotInfo *sn_info,
>> -                              const char *name)
>> +static bool bdrv_snapshot_find(BlockDriverState *bs, QEMUSnapshotInfo *sn_info,
>> +                               const char *name, const char *id, Error **errp,
>> +                               bool old_match)
>    suggest directly drop old_match parameter here, or squash patch 12
> into this one, mark the change in commit message, then the logic will
> be clearer.
>    Personally hope to place parameter *id before *name.

That make sense, I'll change it.

> 
>>    {
>>        QEMUSnapshotInfo *sn_tab, *sn;
>> -    int nb_sns, i, ret;
>> +    int nb_sns, i;
>> +    bool found = false;
>> +
>> +    assert(name || id);
>>
>> -    ret = -ENOENT;
>>        nb_sns = bdrv_snapshot_list(bs, &sn_tab);
>> -    if (nb_sns < 0)
>> -        return ret;
>> -    for(i = 0; i < nb_sns; i++) {
>> +    if (nb_sns < 0) {
>> +        error_setg_errno(errp, -nb_sns, "Failed to get a snapshot list");
>> +        return found;
>> +    }
>> +
>> +    if (nb_sns == 0) {
>> +        error_setg(errp, "Device has no snapshots");
>> +        return found;
>> +    }
>      suggest not set errp here, which can be used to tip exception, but
> having not found one is a normal case.

You don't have to use the error message. It is set as the error message
but actually is more like an announcement.

> 
>> +
>> +    for (i = 0; i < nb_sns; i++) {
>>            sn = &sn_tab[i];
>> -        if (!strcmp(sn->id_str, name) || !strcmp(sn->name, name)) {
>> -            *sn_info = *sn;
>> -            ret = 0;
>> -            break;
>> +        if (name && id) {
>> +            if (!strcmp(sn->id_str, id) && !strcmp(sn->name, name)) {
>> +                *sn_info = *sn;
>> +                found = true;
>> +                break;
>> +            }
>> +        } else if (name) {
>> +            /* for compatibility for old bdrv_snapshot_find call
>> +             * will be removed */
>> +            if (old_match) {
>> +                if (!strcmp(sn->id_str, name) || !strcmp(sn->name, name)) {
>> +                    *sn_info = *sn;
>> +                    found = true;
>> +                    break;
>> +                }
>> +            } else {
>> +                if (!strcmp(sn->name, name)) {
>> +                    *sn_info = *sn;
>> +                    found = true;
>> +                    break;
>> +                }
>> +            }
>> +        } else if (id) {
>> +            if (!strcmp(sn->id_str, id)) {
>> +                *sn_info = *sn;
>> +                found = true;
>> +                break;
>> +            }
>>            }
>>        }
>    suggest change the sequence:
> 
> if (name && id) {
>      for () {
>      }
> } else if (name){
>      for () {
>      }
> } else if (id) {
>      for () {
>      }
> }
>    slightly faster, and make logic more clear.

Thanks for suggest, I'll change the logic.

> 
>> +
>> +    if (!found) {
>> +        error_setg(errp, "Failed to find snapshot '%s'", name ? name : id);
>    suggest not to set error, since it is a normal case.

The same comment as for "Device has no snapshots".

Pavel