[Sheepdog] [RFC PATCH 2/3] cluster: add blocking mechanism to notification

[Liu Yuan]

On 10/10/2011 01:46 PM, MORITA Kazutaka wrote:
> Currently Sheepdog vdi operations (create/delete/lookup/...) are
> processed in two phase multicasting:
>
>   1. multicasts a vdi request
>   2. only the master node handles the request and multicasts the
>      response
>
> During this two phase, we cannot allow any other vdi operations and
> membership changes, and this makes sheep/group.c a bit hard to read.
>
> This patch simplifies this by adding a blocking callback to the
> notification function in the cluster driver.  If the caller of
> cdrv->notify() sets 'block_cb' as an argument, block_cb() is called
> from the cluster driver before the message is notified to any node.
> All the cluster events are blocked in every nodes until the caller
> finishes the vdi operation in block_cb().
>
> With this change, the master node is no longer in charge of vdi
> operations, but this is a good change to make Sheepdog more symmetric.
>
> Signed-off-by: MORITA Kazutaka<morita.kazutaka at lab.ntt.co.jp>
> ---
>   sheep/cluster.h          |   10 ++-
>   sheep/cluster/corosync.c |  209 +++++++++++++++++++++++++++++++++++++++-------
>   sheep/group.c            |   12 ++--
>   3 files changed, 191 insertions(+), 40 deletions(-)
>
> diff --git a/sheep/cluster.h b/sheep/cluster.h
> index 43f4575..25b2d48 100644
> --- a/sheep/cluster.h
> +++ b/sheep/cluster.h
> @@ -71,11 +71,17 @@ struct cluster_driver {
>   	 *
>   	 * This function sends 'msg' to all the nodes.  The notified
>   	 * messages can be read through notify_handler() in
> -	 * cdrv_handlers.
> +	 * cdrv_handlers.  If 'block_cb' is specified, block_cb() is
> +	 * called before 'msg' is notified to all the nodes.  All the
> +	 * cluster events including this notification are blocked
> +	 * until block_cb() returns or this blocking node leaves the
> +	 * cluster.  The sheep daemon can sleep in block_cb(), so this
> +	 * callback must be called from other than the dispatch
> +	 * thread.
>   	 *
>   	 * Returns zero on success, -1 on error
>   	 */
> -	int (*notify)(void *msg, size_t msg_len);
> +	int (*notify)(void *msg, size_t msg_len, void (*block_cb)(void *arg));
>
>   	/*
>   	 * Dispatch handlers
> diff --git a/sheep/cluster/corosync.c b/sheep/cluster/corosync.c
> index e0f9a9c..022912b 100644
> --- a/sheep/cluster/corosync.c
> +++ b/sheep/cluster/corosync.c
> @@ -14,20 +14,27 @@
>   #include<corosync/cfg.h>
>
>   #include "cluster.h"
> +#include "work.h"
>
>   static cpg_handle_t cpg_handle;
>   static struct cpg_name cpg_group = { 9, "sheepdog" };
>
>   static corosync_cfg_handle_t cfg_handle;
> +static struct sheepid this_sheepid;
> +
> +static struct work_queue *corosync_block_wq;
>
>   static struct cdrv_handlers corosync_handlers;
>
>   static LIST_HEAD(corosync_event_list);
> +static LIST_HEAD(corosync_block_list);
>
>   enum corosync_event_type {
>   	COROSYNC_EVENT_TYPE_JOIN,
>   	COROSYNC_EVENT_TYPE_LEAVE,
>   	COROSYNC_EVENT_TYPE_NOTIFY,
> +	COROSYNC_EVENT_TYPE_BLOCK,
> +	COROSYNC_EVENT_TYPE_UNBLOCK,
>   };
>

how about separate block/unblock message handling from cluster message?  
More and more message handling, if any in the later dev, would make 
corosync_dispatch() more complicated  and bloated. Current unblock 
message handling in corosync_dispatch() already looks odd (tricky) to me.

>   struct corosync_event {
> @@ -42,6 +49,17 @@ struct corosync_event {
>   	void *msg;
>   	size_t msg_len;
>
> +	int blocked;
> +
> +	struct list_head list;
> +};
> +
> +struct corosync_block_msg {
> +	void *msg;
> +	size_t msg_len;
> +	void (*cb)(void *arg);
> +
> +	struct work work;
>   	struct list_head list;
>   };
>
> @@ -91,9 +109,70 @@ static void cpg_addr_to_sheepid(const struct cpg_address *cpgs,
>   	}
>   }
>
> +static int send_message(uint64_t type, void *msg, size_t msg_len)
> +{
> +	struct iovec iov[2];
> +	int ret, iov_cnt = 1;
> +
> +	iov[0].iov_base =&type;
> +	iov[0].iov_len = sizeof(type);
> +	if (msg) {
> +		iov[1].iov_base = msg;
> +		iov[1].iov_len = msg_len;
> +		iov_cnt++;
> +	}
> +retry:
> +	ret = cpg_mcast_joined(cpg_handle, CPG_TYPE_AGREED, iov, iov_cnt);
> +	switch (ret) {
> +	case CPG_OK:
> +		break;
> +	case CPG_ERR_TRY_AGAIN:
> +		dprintf("failed to send message. try again\n");
> +		sleep(1);
> +		goto retry;
> +	default:
> +		eprintf("failed to send message, %d\n", ret);
> +		return -1;
> +	}
> +	return 0;
> +}
> +
> +static void corosync_block(struct work *work, int idx)
> +{
> +	struct corosync_block_msg *bm = container_of(work, typeof(*bm), work);
> +
> +	bm->cb(bm->msg);
> +}
> +
> +static void corosync_block_done(struct work *work, int idx)
> +{
> +	struct corosync_block_msg *bm = container_of(work, typeof(*bm), work);
> +
> +	send_message(COROSYNC_EVENT_TYPE_UNBLOCK, bm->msg, bm->msg_len);
> +
> +	free(bm->msg);
> +	free(bm);
> +}
> +
> +static struct corosync_event *find_block_event(struct sheepid *sender)
> +{
> +	struct corosync_event *cevent;
> +
> +	list_for_each_entry(cevent,&corosync_event_list, list) {
> +		if (cevent->type != COROSYNC_EVENT_TYPE_BLOCK)
> +			continue;
> +
> +		if (sheepid_cmp(&cevent->sender, sender) == 0)
> +			return cevent;
> +	}
> +
> +	return NULL;
> +}
> +
>   static void __corosync_dispatch(void)
>   {
>   	struct corosync_event *cevent;
> +	struct corosync_block_msg *bm;
>
>   	while (!list_empty(&corosync_event_list)) {
>   		cevent = list_first_entry(&corosync_event_list, typeof(*cevent), list);
> @@ -114,11 +193,36 @@ static void __corosync_dispatch(void)
>   							 cevent->msg,
>   							 cevent->msg_len);
>   			break;
> +		case COROSYNC_EVENT_TYPE_BLOCK:
> +			if (sheepid_cmp(&cevent->sender,&this_sheepid) != 0)
> +				cevent->blocked = 1;
> +
> +			if (!cevent->blocked) {
> +				/* call a block callback function from a worker thread */
> +				if (list_empty(&corosync_block_list))
> +					panic("cannot call block callback\n");
> +
> +				bm = list_first_entry(&corosync_block_list, typeof(*bm), list);
> +				list_del(&bm->list);
> +
> +				bm->work.fn = corosync_block;
> +				bm->work.done = corosync_block_done;
> +				queue_work(corosync_block_wq,&bm->work);
> +				cevent->blocked = 1;
> +			}
> +

might variable *blocked* be static local one if no other ref?

Thanks,
Yuan