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

[Kevin Wolf <kwolf@redhat.com>]

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.

> +
>  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