Re: [PATCH 1/2] rbd: define flags field, use it for exists flag

[Dan Mick <dan.mick@inktank.com>]

Reviewed-by: Dan Mick <dan.mick@inktank.com>

On 01/14/2013 10:50 AM, Alex Elder wrote:
> Define a new rbd device flags field, manipulated using atomic bit
> operations.  Replace the use of the current "exists" flag with a
> bit in this new "flags" field.
>
> Signed-off-by: Alex Elder <elder@inktank.com>
> ---
>   drivers/block/rbd.c |   17 ++++++++++++-----
>   1 file changed, 12 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/block/rbd.c b/drivers/block/rbd.c
> index 02002b1..9eb1631 100644
> --- a/drivers/block/rbd.c
> +++ b/drivers/block/rbd.c
> @@ -232,7 +232,7 @@ struct rbd_device {
>   	spinlock_t		lock;		/* queue lock */
>
>   	struct rbd_image_header	header;
> -	atomic_t		exists;
> +	unsigned long		flags;
>   	struct rbd_spec		*spec;
>
>   	char			*header_name;
> @@ -260,6 +260,12 @@ struct rbd_device {
>   	unsigned long		open_count;
>   };
>
> +/* Flag bits for rbd_dev->flags */
> +
> +enum rbd_dev_flags {
> +	rbd_dev_flag_exists,	/* mapped snapshot has not been deleted */
> +};
> +
>   static DEFINE_MUTEX(ctl_mutex);	  /* Serialize open/close/setup/teardown */
>
>   static LIST_HEAD(rbd_dev_list);    /* devices */
> @@ -756,7 +762,8 @@ static int rbd_dev_set_mapping(struct rbd_device
> *rbd_dev)
>   			goto done;
>   		rbd_dev->mapping.read_only = true;
>   	}
> -	atomic_set(&rbd_dev->exists, 1);
> +	set_bit(rbd_dev_flag_exists, &rbd_dev->flags);
> +
>   done:
>   	return ret;
>   }
> @@ -1654,7 +1661,7 @@ static void rbd_rq_fn(struct request_queue *q)
>   			snapc = ceph_get_snap_context(rbd_dev->header.snapc);
>   			up_read(&rbd_dev->header_rwsem);
>   			rbd_assert(snapc != NULL);
> -		} else if (!atomic_read(&rbd_dev->exists)) {
> +		} else if (!test_bit(rbd_dev_flag_exists, &rbd_dev->flags)) {
>   			rbd_assert(rbd_dev->spec->snap_id != CEPH_NOSNAP);
>   			dout("request for non-existent snapshot");
>   			result = -ENXIO;
> @@ -2270,7 +2277,7 @@ struct rbd_device *rbd_dev_create(struct
> rbd_client *rbdc,
>   		return NULL;
>
>   	spin_lock_init(&rbd_dev->lock);
> -	atomic_set(&rbd_dev->exists, 0);
> +	rbd_dev->flags = 0;
>   	INIT_LIST_HEAD(&rbd_dev->node);
>   	INIT_LIST_HEAD(&rbd_dev->snaps);
>   	init_rwsem(&rbd_dev->header_rwsem);
> @@ -2902,7 +2909,7 @@ static int rbd_dev_snaps_update(struct rbd_device
> *rbd_dev)
>   			/* Existing snapshot not in the new snap context */
>
>   			if (rbd_dev->spec->snap_id == snap->id)
> -				atomic_set(&rbd_dev->exists, 0);
> +				set_bit(rbd_dev_flag_exists, &rbd_dev->flags);
>   			rbd_remove_snap_dev(snap);
>   			dout("%ssnap id %llu has been removed\n",
>   				rbd_dev->spec->snap_id == snap->id ?
>