Re: [Qemu-devel] [PATCH v3 02/12] block: Add op blocker notifier list

[Max Reitz <mreitz@redhat.com>]

On 15.05.2015 08:04, Fam Zheng wrote:
> BDS users can register a notifier and get notified about op blocker
> changes.
>
> Signed-off-by: Fam Zheng <famz@redhat.com>
> ---
>   block.c                   | 35 +++++++++++++++++++++++++++++++++++
>   include/block/block.h     |  8 ++++++++
>   include/block/block_int.h |  3 +++
>   3 files changed, 46 insertions(+)
>
> diff --git a/block.c b/block.c
> index 7904098..178e186 100644
> --- a/block.c
> +++ b/block.c
> @@ -3375,6 +3375,19 @@ struct BdrvOpBlocker {
>       QLIST_ENTRY(BdrvOpBlocker) list;
>   };
>   
> +/* Add a notifier which will be notified when the first blocker of some type is
> + * added to bs, or when the last blocker is removed. The notifier handler
> + * should receive a BlockOpEvent data.
> + *
> + * Caller must hold bs->aio_context; the notifier handler is also called with
> + * it hold.

*held (I think)

With that fixed:

Reviewed-by: Max Reitz <mreitz@redhat.com>

(Although I'm missing a place where the notifiers are freed (on 
bdrv_delete()/bdrv_close()), but maybe that's done in a different patch)

> + */
> +void bdrv_op_blocker_add_notifier(BlockDriverState *bs,
> +                                  Notifier *notifier)
> +{
> +    notifier_list_add(&bs->op_blocker_notifiers, notifier);
> +}
> +
>   bool bdrv_op_is_blocked(BlockDriverState *bs, BlockOpType op, Error **errp)
>   {
>       BdrvOpBlocker *blocker;
> @@ -3391,26 +3404,48 @@ bool bdrv_op_is_blocked(BlockDriverState *bs, BlockOpType op, Error **errp)
>       return false;
>   }
>   
> +static void bdrv_op_blocker_notify(BlockDriverState *bs, BlockOpType op,
> +                                   Error *reason, bool blocking)
> +{
> +    BlockOpEvent event = (BlockOpEvent) {
> +        op = op,
> +        reason = reason,
> +        blocking = blocking,
> +    };
> +
> +    notifier_list_notify(&bs->op_blocker_notifiers, &event);
> +}
> +
>   void bdrv_op_block(BlockDriverState *bs, BlockOpType op, Error *reason)
>   {
> +    bool blocked;
>       BdrvOpBlocker *blocker;
>       assert((int) op >= 0 && op < BLOCK_OP_TYPE_MAX);
>   
>       blocker = g_new0(BdrvOpBlocker, 1);
>       blocker->reason = reason;
> +    blocked = !QLIST_EMPTY(&bs->op_blockers[op]);
>       QLIST_INSERT_HEAD(&bs->op_blockers[op], blocker, list);
> +    if (!blocked) {
> +        bdrv_op_blocker_notify(bs, op, reason, true);
> +    }
>   }
>   
>   void bdrv_op_unblock(BlockDriverState *bs, BlockOpType op, Error *reason)
>   {
> +    bool blocked;
>       BdrvOpBlocker *blocker, *next;
>       assert((int) op >= 0 && op < BLOCK_OP_TYPE_MAX);
> +    blocked = !QLIST_EMPTY(&bs->op_blockers[op]);
>       QLIST_FOREACH_SAFE(blocker, &bs->op_blockers[op], list, next) {
>           if (blocker->reason == reason) {
>               QLIST_REMOVE(blocker, list);
>               g_free(blocker);
>           }
>       }
> +    if (blocked && QLIST_EMPTY(&bs->op_blockers[op])) {
> +        bdrv_op_blocker_notify(bs, op, reason, false);
> +    }
>   }
>   
>   void bdrv_op_block_all(BlockDriverState *bs, Error *reason)
> diff --git a/include/block/block.h b/include/block/block.h
> index 906fb31..3420b2c 100644
> --- a/include/block/block.h
> +++ b/include/block/block.h
> @@ -163,6 +163,12 @@ typedef enum BlockOpType {
>       BLOCK_OP_TYPE_MAX,
>   } BlockOpType;
>   
> +typedef struct {
> +    BlockOpType type;
> +    Error *reason;
> +    bool blocking;
> +} BlockOpEvent;
> +
>   void bdrv_iostatus_enable(BlockDriverState *bs);
>   void bdrv_iostatus_reset(BlockDriverState *bs);
>   void bdrv_iostatus_disable(BlockDriverState *bs);
> @@ -491,6 +497,8 @@ void bdrv_disable_copy_on_read(BlockDriverState *bs);
>   void bdrv_ref(BlockDriverState *bs);
>   void bdrv_unref(BlockDriverState *bs);
>   
> +void bdrv_op_blocker_add_notifier(BlockDriverState *bs,
> +                                  Notifier *notifier);
>   bool bdrv_op_is_blocked(BlockDriverState *bs, BlockOpType op, Error **errp);
>   void bdrv_op_block(BlockDriverState *bs, BlockOpType op, Error *reason);
>   void bdrv_op_unblock(BlockDriverState *bs, BlockOpType op, Error *reason);
> diff --git a/include/block/block_int.h b/include/block/block_int.h
> index db29b74..29d1c84 100644
> --- a/include/block/block_int.h
> +++ b/include/block/block_int.h
> @@ -418,6 +418,9 @@ struct BlockDriverState {
>       /* operation blockers */
>       QLIST_HEAD(, BdrvOpBlocker) op_blockers[BLOCK_OP_TYPE_MAX];
>   
> +    /* Callback when one list in op_blockers has "empty" status change. */
> +    NotifierList op_blocker_notifiers;
> +
>       /* long-running background operation */
>       BlockJob *job;
>