Re: [Qemu-devel] [PATCH V2 5/5] block: make all steps in qmp_transaction() as callback

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

于 2013-4-16 21:52, Kevin Wolf 写道:
> Am 13.04.2013 um 13:11 hat Wenchao Xia geschrieben:
>>    Now qmp_transaction() can be extended with other operation,
>> external snapshot or backing chain creation, is just one case it.
>>
>> Signed-off-by: Wenchao Xia <xiawenc@linux.vnet.ibm.com>
>> ---
>>   blockdev.c |   68 +++++++++++++++++++++++++++++++++++++++++++++++++++--------
>>   1 files changed, 58 insertions(+), 10 deletions(-)
>>
>> diff --git a/blockdev.c b/blockdev.c
>> index 3e69569..9f0acfb 100644
>> --- a/blockdev.c
>> +++ b/blockdev.c
>> @@ -779,14 +779,35 @@ void qmp_blockdev_snapshot_sync(const char *device, const char *snapshot_file,
>>
>>
>>   /* New and old BlockDriverState structs for group snapshots */
>> +
>> +/* Only in prepare() it may fail, so roll back just need to take care
>> +   what is done in prepare(). */
>> +typedef struct BdrvActionOps {
>> +    /* Prepare the work, must NOT be NULL. */
>> +    int (*prepare)(BlockdevAction *action, void **p_opaque, Error **errp);
>> +    /* Commit the changes, can be NULL. */
>> +    void (*commit)(BlockdevAction *action, void *opaque);
>> +    /* Rollback the changes on fail, mut NOT be NULL. */
>
> Typo: s/mut/must/
>
>> +    void (*rollback)(BlockdevAction *action, void *opaque);
>> +    /* Clean up resource in the end, can be NULL. */
>> +    void (*clean)(BlockdevAction *action, void *opaque);
>> +} BdrvActionOps;
>
> What's the reason that commit can be NULL, but rollback can't? I can't
> imagine a case where a commit isn't needed, but one without a rollback
> action sounds possible.
>
   Commit should no be NULL, will fix it together with other comments,
thanks.

>> +
>>   typedef struct BlkTransactionStates {
>> -    BlockDriverState *old_bs;
>> -    BlockDriverState *new_bs;
>> +    BlockdevAction *action;
>> +    void *opaque;
>> +    const BdrvActionOps *ops;
>>       QSIMPLEQ_ENTRY(BlkTransactionStates) entry;
>>   } BlkTransactionStates;
>>
>> +/* external snapshot private data */
>> +typedef struct ExternalSnapshotState {
>> +    BlockDriverState *old_bs;
>> +    BlockDriverState *new_bs;
>> +} ExternalSnapshotState;
>> +
>>   static int external_snapshot_prepare(BlockdevAction *action,
>> -                                     BlkTransactionStates *states,
>> +                                     void **p_opaque,
>
> Call it just opaque.
>
>>                                        Error **errp)
>>   {
>>       BlockDriver *proto_drv;
>> @@ -797,6 +818,7 @@ static int external_snapshot_prepare(BlockdevAction *action,
>>       const char *new_image_file;
>>       const char *format = "qcow2";
>>       enum NewImageMode mode = NEW_IMAGE_MODE_ABSOLUTE_PATHS;
>> +    ExternalSnapshotState *states;
>>
>>       /* get parameters */
>>       g_assert(action->kind == BLOCKDEV_ACTION_KIND_BLOCKDEV_SNAPSHOT_SYNC);
>> @@ -817,6 +839,9 @@ static int external_snapshot_prepare(BlockdevAction *action,
>>           goto fail;
>>       }
>>
>> +    *p_opaque = g_malloc0(sizeof(ExternalSnapshotState));
>> +    states = *p_opaque;
>> +
>>       states->old_bs = bdrv_find(device);
>>       if (!states->old_bs) {
>>           error_set(errp, QERR_DEVICE_NOT_FOUND, device);
>> @@ -878,8 +903,10 @@ static int external_snapshot_prepare(BlockdevAction *action,
>>   }
>>
>>   static void external_snapshot_commit(BlockdevAction *action,
>> -                                     BlkTransactionStates *states)
>> +                                     void *opaque)
>>   {
>> +    ExternalSnapshotState *states = opaque;
>> +
>>       /* This removes our old bs from the bdrv_states, and adds the new bs */
>>       bdrv_append(states->new_bs, states->old_bs);
>>       /* We don't need (or want) to use the transactional
>> @@ -890,13 +917,27 @@ static void external_snapshot_commit(BlockdevAction *action,
>>   }
>>
>>   static void external_snapshot_rollback(BlockdevAction *action,
>> -                                       BlkTransactionStates *states)
>> +                                       void *opaque)
>>   {
>> +    ExternalSnapshotState *states = opaque;
>>       if (states->new_bs) {
>>           bdrv_delete(states->new_bs);
>>       }
>>   }
>>
>> +static void external_snapshot_clean(BlockdevAction *action,
>> +                                    void *opaque)
>
> This fits in a single line.
>
>> +{
>> +    g_free(opaque);
>> +}
>> +
>> +const BdrvActionOps external_snapshot_ops = {
>> +    .prepare = external_snapshot_prepare,
>> +    .commit = external_snapshot_commit,
>> +    .rollback = external_snapshot_rollback,
>> +    .clean = external_snapshot_clean,
>> +};
>
> Please align all = to the same column.
>
> Kevin
>


-- 
Best Regards

Wenchao Xia