Re: [PATCH v4 06/10] xen/blkback: separate ring information out of struct xen_blkif

[Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>]

On Mon, Nov 02, 2015 at 12:21:42PM +0800, Bob Liu wrote:
> Split per ring information to an new structure "xen_blkif_ring", so that one vbd
> device can associate with one or more rings/hardware queues.

s/can associate/can be associated/
> 
> Introduce 'pers_gnts_lock' to protect the pool of persistent grants since we
> may have multi backend threads.
> 
> This patch is a preparation for supporting multi hardware queues/rings.
> 
> Signed-off-by: Arianna Avanzini <avanzini.arianna@gmail.com>
> Signed-off-by: Bob Liu <bob.liu@oracle.com>
> ---
>  drivers/block/xen-blkback/blkback.c | 233 ++++++++++++++++++++----------------
>  drivers/block/xen-blkback/common.h  |  64 ++++++----
>  drivers/block/xen-blkback/xenbus.c  | 107 ++++++++++-------
>  3 files changed, 234 insertions(+), 170 deletions(-)
> 
> diff --git a/drivers/block/xen-blkback/blkback.c b/drivers/block/xen-blkback/blkback.c
> index 6a685ae..eaf7ec0 100644
> --- a/drivers/block/xen-blkback/blkback.c
> +++ b/drivers/block/xen-blkback/blkback.c
> @@ -173,11 +173,11 @@ static inline void shrink_free_pagepool(struct xen_blkif *blkif, int num)
>  
>  #define vaddr(page) ((unsigned long)pfn_to_kaddr(page_to_pfn(page)))
>  
> -static int do_block_io_op(struct xen_blkif *blkif);
> -static int dispatch_rw_block_io(struct xen_blkif *blkif,
> +static int do_block_io_op(struct xen_blkif_ring *ring);
> +static int dispatch_rw_block_io(struct xen_blkif_ring *ring,
>  				struct blkif_request *req,
>  				struct pending_req *pending_req);
> -static void make_response(struct xen_blkif *blkif, u64 id,
> +static void make_response(struct xen_blkif_ring *ring, u64 id,
>  			  unsigned short op, int st);
>  
>  #define foreach_grant_safe(pos, n, rbtree, node) \
> @@ -189,14 +189,8 @@ static void make_response(struct xen_blkif *blkif, u64 id,
>  
>  
>  /*
> - * We don't need locking around the persistent grant helpers
> - * because blkback uses a single-thread for each backed, so we
> - * can be sure that this functions will never be called recursively.
> - *
> - * The only exception to that is put_persistent_grant, that can be called
> - * from interrupt context (by xen_blkbk_unmap), so we have to use atomic
> - * bit operations to modify the flags of a persistent grant and to count
> - * the number of used grants.
> + * pers_gnts_lock must be used around all the persistent grant helpers
> + * because blkback may use multi-thread/queue for each backend.
>   */

Would it make sense to have an ASSERT on the holding of the
pers_gnts_lock in this functioni (and also in get_persistent_gnt,
put_persistent_gnt, free_persistent_gnts?

>  static int add_persistent_gnt(struct xen_blkif *blkif,
>  			       struct persistent_gnt *persistent_gnt)
> @@ -322,11 +316,13 @@ void xen_blkbk_unmap_purged_grants(struct work_struct *work)
>  	int segs_to_unmap = 0;
>  	struct xen_blkif *blkif = container_of(work, typeof(*blkif), persistent_purge_work);
>  	struct gntab_unmap_queue_data unmap_data;
> +	unsigned long flags;
>  
>  	unmap_data.pages = pages;
>  	unmap_data.unmap_ops = unmap;
>  	unmap_data.kunmap_ops = NULL;
>  
> +	spin_lock_irqsave(&blkif->pers_gnts_lock, flags);
>  	while(!list_empty(&blkif->persistent_purge_list)) {
>  		persistent_gnt = list_first_entry(&blkif->persistent_purge_list,
>  		                                  struct persistent_gnt,
> @@ -348,6 +344,7 @@ void xen_blkbk_unmap_purged_grants(struct work_struct *work)
>  		}
>  		kfree(persistent_gnt);
>  	}
> +	spin_unlock_irqrestore(&blkif->pers_gnts_lock, flags);
>  	if (segs_to_unmap > 0) {
>  		unmap_data.count = segs_to_unmap;
>  		BUG_ON(gnttab_unmap_refs_sync(&unmap_data));
> @@ -362,16 +359,18 @@ static void purge_persistent_gnt(struct xen_blkif *blkif)
>  	unsigned int num_clean, total;
>  	bool scan_used = false, clean_used = false;
>  	struct rb_root *root;
> +	unsigned long flags;
>  
> +	spin_lock_irqsave(&blkif->pers_gnts_lock, flags);
>  	if (blkif->persistent_gnt_c < xen_blkif_max_pgrants ||
>  	    (blkif->persistent_gnt_c == xen_blkif_max_pgrants &&
>  	    !blkif->vbd.overflow_max_grants)) {
> -		return;
> +		goto out;
>  	}
>  
>  	if (work_busy(&blkif->persistent_purge_work)) {

Hm, looking at 'work_busy' it says that you should hold on a pool mutex.

But that is a seperate bug

>  		pr_alert_ratelimited("Scheduled work from previous purge is still busy, cannot purge list\n");
> -		return;
> +		goto out;
>  	}
>  
>  	num_clean = (xen_blkif_max_pgrants / 100) * LRU_PERCENT_CLEAN;
> @@ -379,7 +378,7 @@ static void purge_persistent_gnt(struct xen_blkif *blkif)
>  	num_clean = min(blkif->persistent_gnt_c, num_clean);
>  	if ((num_clean == 0) ||
>  	    (num_clean > (blkif->persistent_gnt_c - atomic_read(&blkif->persistent_gnt_in_use))))
> -		return;
> +		goto out;
>  
>  	/*
>  	 * At this point, we can assure that there will be no calls
> @@ -436,29 +435,35 @@ finished:
>  	}
>  
>  	blkif->persistent_gnt_c -= (total - num_clean);
> +	spin_unlock_irqrestore(&blkif->pers_gnts_lock, flags);
>  	blkif->vbd.overflow_max_grants = 0;
>  
>  	/* We can defer this work */
>  	schedule_work(&blkif->persistent_purge_work);
>  	pr_debug("Purged %u/%u\n", (total - num_clean), total);
>  	return;
> +
> +out:
> +	spin_unlock_irqrestore(&blkif->pers_gnts_lock, flags);
> +
> +	return;
>  }
>  
>  /*
>   * Retrieve from the 'pending_reqs' a free pending_req structure to be used.
>   */
> -static struct pending_req *alloc_req(struct xen_blkif *blkif)
> +static struct pending_req *alloc_req(struct xen_blkif_ring *ring)
>  {
>  	struct pending_req *req = NULL;
>  	unsigned long flags;
>  
> -	spin_lock_irqsave(&blkif->pending_free_lock, flags);
> -	if (!list_empty(&blkif->pending_free)) {
> -		req = list_entry(blkif->pending_free.next, struct pending_req,
> +	spin_lock_irqsave(&ring->pending_free_lock, flags);
> +	if (!list_empty(&ring->pending_free)) {
> +		req = list_entry(ring->pending_free.next, struct pending_req,
>  				 free_list);
>  		list_del(&req->free_list);
>  	}
> -	spin_unlock_irqrestore(&blkif->pending_free_lock, flags);
> +	spin_unlock_irqrestore(&ring->pending_free_lock, flags);
>  	return req;
>  }
>  
> @@ -466,17 +471,17 @@ static struct pending_req *alloc_req(struct xen_blkif *blkif)
>   * Return the 'pending_req' structure back to the freepool. We also
>   * wake up the thread if it was waiting for a free page.
>   */
> -static void free_req(struct xen_blkif *blkif, struct pending_req *req)
> +static void free_req(struct xen_blkif_ring *ring, struct pending_req *req)
>  {
>  	unsigned long flags;
>  	int was_empty;
>  
> -	spin_lock_irqsave(&blkif->pending_free_lock, flags);
> -	was_empty = list_empty(&blkif->pending_free);
> -	list_add(&req->free_list, &blkif->pending_free);
> -	spin_unlock_irqrestore(&blkif->pending_free_lock, flags);
> +	spin_lock_irqsave(&ring->pending_free_lock, flags);
> +	was_empty = list_empty(&ring->pending_free);
> +	list_add(&req->free_list, &ring->pending_free);
> +	spin_unlock_irqrestore(&ring->pending_free_lock, flags);
>  	if (was_empty)
> -		wake_up(&blkif->pending_free_wq);
> +		wake_up(&ring->pending_free_wq);
>  }
>  
>  /*
> @@ -556,10 +561,10 @@ abort:
>  /*
>   * Notification from the guest OS.
>   */
> -static void blkif_notify_work(struct xen_blkif *blkif)
> +static void blkif_notify_work(struct xen_blkif_ring *ring)
>  {
> -	blkif->waiting_reqs = 1;
> -	wake_up(&blkif->wq);
> +	ring->waiting_reqs = 1;
> +	wake_up(&ring->wq);
>  }
>  
>  irqreturn_t xen_blkif_be_int(int irq, void *dev_id)
> @@ -590,7 +595,8 @@ static void print_stats(struct xen_blkif *blkif)
>  
>  int xen_blkif_schedule(void *arg)
>  {
> -	struct xen_blkif *blkif = arg;
> +	struct xen_blkif_ring *ring = arg;
> +	struct xen_blkif *blkif = ring->blkif;
>  	struct xen_vbd *vbd = &blkif->vbd;
>  	unsigned long timeout;
>  	int ret;
> @@ -606,27 +612,27 @@ int xen_blkif_schedule(void *arg)
>  		timeout = msecs_to_jiffies(LRU_INTERVAL);
>  
>  		timeout = wait_event_interruptible_timeout(
> -			blkif->wq,
> -			blkif->waiting_reqs || kthread_should_stop(),
> +			ring->wq,
> +			ring->waiting_reqs || kthread_should_stop(),
>  			timeout);
>  		if (timeout == 0)
>  			goto purge_gnt_list;
>  		timeout = wait_event_interruptible_timeout(
> -			blkif->pending_free_wq,
> -			!list_empty(&blkif->pending_free) ||
> +			ring->pending_free_wq,
> +			!list_empty(&ring->pending_free) ||
>  			kthread_should_stop(),
>  			timeout);
>  		if (timeout == 0)
>  			goto purge_gnt_list;
>  
> -		blkif->waiting_reqs = 0;
> +		ring->waiting_reqs = 0;
>  		smp_mb(); /* clear flag *before* checking for work */
>  
> -		ret = do_block_io_op(blkif);
> +		ret = do_block_io_op(ring);
>  		if (ret > 0)
> -			blkif->waiting_reqs = 1;
> +			ring->waiting_reqs = 1;
>  		if (ret == -EACCES)
> -			wait_event_interruptible(blkif->shutdown_wq,
> +			wait_event_interruptible(ring->shutdown_wq,
>  						 kthread_should_stop());
>  
>  purge_gnt_list:
> @@ -649,7 +655,7 @@ purge_gnt_list:
>  	if (log_stats)
>  		print_stats(blkif);
>  
> -	blkif->xenblkd = NULL;
> +	ring->xenblkd = NULL;
>  	xen_blkif_put(blkif);
>  
>  	return 0;
> @@ -658,32 +664,40 @@ purge_gnt_list:
>  /*
>   * Remove persistent grants and empty the pool of free pages
>   */
> -void xen_blkbk_free_caches(struct xen_blkif *blkif)
> +void xen_blkbk_free_caches(struct xen_blkif_ring *ring)
>  {
> +	struct xen_blkif *blkif = ring->blkif;
> +	unsigned long flags;
> +
>  	/* Free all persistent grant pages */
> +	spin_lock_irqsave(&blkif->pers_gnts_lock, flags);
>  	if (!RB_EMPTY_ROOT(&blkif->persistent_gnts))
>  		free_persistent_gnts(blkif, &blkif->persistent_gnts,
>  			blkif->persistent_gnt_c);
>  
>  	BUG_ON(!RB_EMPTY_ROOT(&blkif->persistent_gnts));
>  	blkif->persistent_gnt_c = 0;
> +	spin_unlock_irqrestore(&blkif->pers_gnts_lock, flags);
>  
>  	/* Since we are shutting down remove all pages from the buffer */
>  	shrink_free_pagepool(blkif, 0 /* All */);
>  }
>  
>  static unsigned int xen_blkbk_unmap_prepare(
> -	struct xen_blkif *blkif,
> +	struct xen_blkif_ring *ring,
>  	struct grant_page **pages,
>  	unsigned int num,
>  	struct gnttab_unmap_grant_ref *unmap_ops,
>  	struct page **unmap_pages)
>  {
>  	unsigned int i, invcount = 0;
> +	unsigned long flags;
>  
>  	for (i = 0; i < num; i++) {
>  		if (pages[i]->persistent_gnt != NULL) {
> -			put_persistent_gnt(blkif, pages[i]->persistent_gnt);
> +			spin_lock_irqsave(&ring->blkif->pers_gnts_lock, flags);
> +			put_persistent_gnt(ring->blkif, pages[i]->persistent_gnt);
> +			spin_unlock_irqrestore(&ring->blkif->pers_gnts_lock, flags);
>  			continue;
>  		}
>  		if (pages[i]->handle == BLKBACK_INVALID_HANDLE)
> @@ -700,17 +714,18 @@ static unsigned int xen_blkbk_unmap_prepare(
>  
>  static void xen_blkbk_unmap_and_respond_callback(int result, struct gntab_unmap_queue_data *data)
>  {
> -	struct pending_req* pending_req = (struct pending_req*) (data->data);
> -	struct xen_blkif *blkif = pending_req->blkif;
> +	struct pending_req *pending_req = (struct pending_req *)(data->data);
> +	struct xen_blkif_ring *ring = pending_req->ring;
> +	struct xen_blkif *blkif = ring->blkif;
>  
>  	/* BUG_ON used to reproduce existing behaviour,
>  	   but is this the best way to deal with this? */
>  	BUG_ON(result);
>  
>  	put_free_pages(blkif, data->pages, data->count);
> -	make_response(blkif, pending_req->id,
> +	make_response(ring, pending_req->id,
>  		      pending_req->operation, pending_req->status);
> -	free_req(blkif, pending_req);
> +	free_req(ring, pending_req);
>  	/*
>  	 * Make sure the request is freed before releasing blkif,
>  	 * or there could be a race between free_req and the
> @@ -723,7 +738,7 @@ static void xen_blkbk_unmap_and_respond_callback(int result, struct gntab_unmap_
>  	 * pending_free_wq if there's a drain going on, but it has
>  	 * to be taken into account if the current model is changed.
>  	 */
> -	if (atomic_dec_and_test(&blkif->inflight) && atomic_read(&blkif->drain)) {
> +	if (atomic_dec_and_test(&ring->inflight) && atomic_read(&blkif->drain)) {
>  		complete(&blkif->drain_complete);
>  	}
>  	xen_blkif_put(blkif);
> @@ -732,11 +747,11 @@ static void xen_blkbk_unmap_and_respond_callback(int result, struct gntab_unmap_
>  static void xen_blkbk_unmap_and_respond(struct pending_req *req)
>  {
>  	struct gntab_unmap_queue_data* work = &req->gnttab_unmap_data;
> -	struct xen_blkif *blkif = req->blkif;
> +	struct xen_blkif_ring *ring = req->ring;
>  	struct grant_page **pages = req->segments;
>  	unsigned int invcount;
>  
> -	invcount = xen_blkbk_unmap_prepare(blkif, pages, req->nr_segs,
> +	invcount = xen_blkbk_unmap_prepare(ring, pages, req->nr_segs,
>  					   req->unmap, req->unmap_pages);
>  
>  	work->data = req;
> @@ -757,7 +772,7 @@ static void xen_blkbk_unmap_and_respond(struct pending_req *req)
>   * of hypercalls, but since this is only used in error paths there's
>   * no real need.
>   */
> -static void xen_blkbk_unmap(struct xen_blkif *blkif,
> +static void xen_blkbk_unmap(struct xen_blkif_ring *ring,
>                              struct grant_page *pages[],
>                              int num)
>  {
> @@ -768,20 +783,20 @@ static void xen_blkbk_unmap(struct xen_blkif *blkif,
>  
>  	while (num) {
>  		unsigned int batch = min(num, BLKIF_MAX_SEGMENTS_PER_REQUEST);
> -		
> -		invcount = xen_blkbk_unmap_prepare(blkif, pages, batch,
> +
> +		invcount = xen_blkbk_unmap_prepare(ring, pages, batch,
>  						   unmap, unmap_pages);
>  		if (invcount) {
>  			ret = gnttab_unmap_refs(unmap, NULL, unmap_pages, invcount);
>  			BUG_ON(ret);
> -			put_free_pages(blkif, unmap_pages, invcount);
> +			put_free_pages(ring->blkif, unmap_pages, invcount);
>  		}
>  		pages += batch;
>  		num -= batch;
>  	}
>  }
>  
> -static int xen_blkbk_map(struct xen_blkif *blkif,
> +static int xen_blkbk_map(struct xen_blkif_ring *ring,
>  			 struct grant_page *pages[],
>  			 int num, bool ro)
>  {
> @@ -794,6 +809,8 @@ static int xen_blkbk_map(struct xen_blkif *blkif,
>  	int ret = 0;
>  	int last_map = 0, map_until = 0;
>  	int use_persistent_gnts;
> +	struct xen_blkif *blkif = ring->blkif;
> +	unsigned long irq_flags;
>  
>  	use_persistent_gnts = (blkif->vbd.feature_gnt_persistent);
>  
> @@ -806,10 +823,13 @@ again:
>  	for (i = map_until; i < num; i++) {
>  		uint32_t flags;
>  
> -		if (use_persistent_gnts)
> +		if (use_persistent_gnts) {
> +			spin_lock_irqsave(&blkif->pers_gnts_lock, irq_flags);
>  			persistent_gnt = get_persistent_gnt(
>  				blkif,
>  				pages[i]->gref);
> +			spin_unlock_irqrestore(&blkif->pers_gnts_lock, irq_flags);
> +		}
>  
>  		if (persistent_gnt) {
>  			/*
> @@ -880,8 +900,10 @@ again:
>  			persistent_gnt->gnt = map[new_map_idx].ref;
>  			persistent_gnt->handle = map[new_map_idx].handle;
>  			persistent_gnt->page = pages[seg_idx]->page;
> +			spin_lock_irqsave(&blkif->pers_gnts_lock, irq_flags);
>  			if (add_persistent_gnt(blkif,
>  			                       persistent_gnt)) {
> +				spin_unlock_irqrestore(&blkif->pers_gnts_lock, irq_flags);
>  				kfree(persistent_gnt);
>  				persistent_gnt = NULL;
>  				goto next;
> @@ -890,6 +912,7 @@ again:
>  			pr_debug("grant %u added to the tree of persistent grants, using %u/%u\n",
>  				 persistent_gnt->gnt, blkif->persistent_gnt_c,
>  				 xen_blkif_max_pgrants);
> +			spin_unlock_irqrestore(&blkif->pers_gnts_lock, irq_flags);
>  			goto next;
>  		}
>  		if (use_persistent_gnts && !blkif->vbd.overflow_max_grants) {
> @@ -921,7 +944,7 @@ static int xen_blkbk_map_seg(struct pending_req *pending_req)
>  {
>  	int rc;
>  
> -	rc = xen_blkbk_map(pending_req->blkif, pending_req->segments,
> +	rc = xen_blkbk_map(pending_req->ring, pending_req->segments,
>  			   pending_req->nr_segs,
>  	                   (pending_req->operation != BLKIF_OP_READ));
>  
> @@ -934,7 +957,7 @@ static int xen_blkbk_parse_indirect(struct blkif_request *req,
>  				    struct phys_req *preq)
>  {
>  	struct grant_page **pages = pending_req->indirect_pages;
> -	struct xen_blkif *blkif = pending_req->blkif;
> +	struct xen_blkif_ring *ring = pending_req->ring;
>  	int indirect_grefs, rc, n, nseg, i;
>  	struct blkif_request_segment *segments = NULL;
>  
> @@ -945,7 +968,7 @@ static int xen_blkbk_parse_indirect(struct blkif_request *req,
>  	for (i = 0; i < indirect_grefs; i++)
>  		pages[i]->gref = req->u.indirect.indirect_grefs[i];
>  
> -	rc = xen_blkbk_map(blkif, pages, indirect_grefs, true);
> +	rc = xen_blkbk_map(ring, pages, indirect_grefs, true);
>  	if (rc)
>  		goto unmap;
>  
> @@ -972,15 +995,16 @@ static int xen_blkbk_parse_indirect(struct blkif_request *req,
>  unmap:
>  	if (segments)
>  		kunmap_atomic(segments);
> -	xen_blkbk_unmap(blkif, pages, indirect_grefs);
> +	xen_blkbk_unmap(ring, pages, indirect_grefs);
>  	return rc;
>  }
>  
> -static int dispatch_discard_io(struct xen_blkif *blkif,
> +static int dispatch_discard_io(struct xen_blkif_ring *ring,
>  				struct blkif_request *req)
>  {
>  	int err = 0;
>  	int status = BLKIF_RSP_OKAY;
> +	struct xen_blkif *blkif = ring->blkif;
>  	struct block_device *bdev = blkif->vbd.bdev;
>  	unsigned long secure;
>  	struct phys_req preq;
> @@ -997,7 +1021,7 @@ static int dispatch_discard_io(struct xen_blkif *blkif,
>  			preq.sector_number + preq.nr_sects, blkif->vbd.pdevice);
>  		goto fail_response;
>  	}
> -	blkif->st_ds_req++;
> +	ring->st_ds_req++;
>  
>  	secure = (blkif->vbd.discard_secure &&
>  		 (req->u.discard.flag & BLKIF_DISCARD_SECURE)) ?
> @@ -1013,26 +1037,28 @@ fail_response:
>  	} else if (err)
>  		status = BLKIF_RSP_ERROR;
>  
> -	make_response(blkif, req->u.discard.id, req->operation, status);
> +	make_response(ring, req->u.discard.id, req->operation, status);
>  	xen_blkif_put(blkif);
>  	return err;
>  }
>  
> -static int dispatch_other_io(struct xen_blkif *blkif,
> +static int dispatch_other_io(struct xen_blkif_ring *ring,
>  			     struct blkif_request *req,
>  			     struct pending_req *pending_req)
>  {
> -	free_req(blkif, pending_req);
> -	make_response(blkif, req->u.other.id, req->operation,
> +	free_req(ring, pending_req);
> +	make_response(ring, req->u.other.id, req->operation,
>  		      BLKIF_RSP_EOPNOTSUPP);
>  	return -EIO;
>  }
>  
> -static void xen_blk_drain_io(struct xen_blkif *blkif)
> +static void xen_blk_drain_io(struct xen_blkif_ring *ring)
>  {
> +	struct xen_blkif *blkif = ring->blkif;
> +
>  	atomic_set(&blkif->drain, 1);
>  	do {
> -		if (atomic_read(&blkif->inflight) == 0)
> +		if (atomic_read(&ring->inflight) == 0)
>  			break;
>  		wait_for_completion_interruptible_timeout(
>  				&blkif->drain_complete, HZ);
> @@ -1053,12 +1079,12 @@ static void __end_block_io_op(struct pending_req *pending_req, int error)
>  	if ((pending_req->operation == BLKIF_OP_FLUSH_DISKCACHE) &&
>  	    (error == -EOPNOTSUPP)) {
>  		pr_debug("flush diskcache op failed, not supported\n");
> -		xen_blkbk_flush_diskcache(XBT_NIL, pending_req->blkif->be, 0);
> +		xen_blkbk_flush_diskcache(XBT_NIL, pending_req->ring->blkif->be, 0);
>  		pending_req->status = BLKIF_RSP_EOPNOTSUPP;
>  	} else if ((pending_req->operation == BLKIF_OP_WRITE_BARRIER) &&
>  		    (error == -EOPNOTSUPP)) {
>  		pr_debug("write barrier op failed, not supported\n");
> -		xen_blkbk_barrier(XBT_NIL, pending_req->blkif->be, 0);
> +		xen_blkbk_barrier(XBT_NIL, pending_req->ring->blkif->be, 0);
>  		pending_req->status = BLKIF_RSP_EOPNOTSUPP;
>  	} else if (error) {
>  		pr_debug("Buffer not up-to-date at end of operation,"
> @@ -1092,9 +1118,9 @@ static void end_block_io_op(struct bio *bio)
>   * and transmute  it to the block API to hand it over to the proper block disk.
>   */
>  static int
> -__do_block_io_op(struct xen_blkif *blkif)
> +__do_block_io_op(struct xen_blkif_ring *ring)
>  {
> -	union blkif_back_rings *blk_rings = &blkif->blk_rings;
> +	union blkif_back_rings *blk_rings = &ring->blk_rings;
>  	struct blkif_request req;
>  	struct pending_req *pending_req;
>  	RING_IDX rc, rp;
> @@ -1107,7 +1133,7 @@ __do_block_io_op(struct xen_blkif *blkif)
>  	if (RING_REQUEST_PROD_OVERFLOW(&blk_rings->common, rp)) {
>  		rc = blk_rings->common.rsp_prod_pvt;
>  		pr_warn("Frontend provided bogus ring requests (%d - %d = %d). Halting ring processing on dev=%04x\n",
> -			rp, rc, rp - rc, blkif->vbd.pdevice);
> +			rp, rc, rp - rc, ring->blkif->vbd.pdevice);
>  		return -EACCES;
>  	}
>  	while (rc != rp) {
> @@ -1120,14 +1146,14 @@ __do_block_io_op(struct xen_blkif *blkif)
>  			break;
>  		}
>  
> -		pending_req = alloc_req(blkif);
> +		pending_req = alloc_req(ring);
>  		if (NULL == pending_req) {
> -			blkif->st_oo_req++;
> +			ring->st_oo_req++;
>  			more_to_do = 1;
>  			break;
>  		}
>  
> -		switch (blkif->blk_protocol) {
> +		switch (ring->blkif->blk_protocol) {
>  		case BLKIF_PROTOCOL_NATIVE:
>  			memcpy(&req, RING_GET_REQUEST(&blk_rings->native, rc), sizeof(req));
>  			break;
> @@ -1151,16 +1177,16 @@ __do_block_io_op(struct xen_blkif *blkif)
>  		case BLKIF_OP_WRITE_BARRIER:
>  		case BLKIF_OP_FLUSH_DISKCACHE:
>  		case BLKIF_OP_INDIRECT:
> -			if (dispatch_rw_block_io(blkif, &req, pending_req))
> +			if (dispatch_rw_block_io(ring, &req, pending_req))
>  				goto done;
>  			break;
>  		case BLKIF_OP_DISCARD:
> -			free_req(blkif, pending_req);
> -			if (dispatch_discard_io(blkif, &req))
> +			free_req(ring, pending_req);
> +			if (dispatch_discard_io(ring, &req))
>  				goto done;
>  			break;
>  		default:
> -			if (dispatch_other_io(blkif, &req, pending_req))
> +			if (dispatch_other_io(ring, &req, pending_req))
>  				goto done;
>  			break;
>  		}
> @@ -1173,13 +1199,13 @@ done:
>  }
>  
>  static int
> -do_block_io_op(struct xen_blkif *blkif)
> +do_block_io_op(struct xen_blkif_ring *ring)
>  {
> -	union blkif_back_rings *blk_rings = &blkif->blk_rings;
> +	union blkif_back_rings *blk_rings = &ring->blk_rings;
>  	int more_to_do;
>  
>  	do {
> -		more_to_do = __do_block_io_op(blkif);
> +		more_to_do = __do_block_io_op(ring);
>  		if (more_to_do)
>  			break;
>  
> @@ -1192,7 +1218,7 @@ do_block_io_op(struct xen_blkif *blkif)
>   * Transmutation of the 'struct blkif_request' to a proper 'struct bio'
>   * and call the 'submit_bio' to pass it to the underlying storage.
>   */
> -static int dispatch_rw_block_io(struct xen_blkif *blkif,
> +static int dispatch_rw_block_io(struct xen_blkif_ring *ring,
>  				struct blkif_request *req,
>  				struct pending_req *pending_req)
>  {
> @@ -1219,17 +1245,17 @@ static int dispatch_rw_block_io(struct xen_blkif *blkif,
>  
>  	switch (req_operation) {
>  	case BLKIF_OP_READ:
> -		blkif->st_rd_req++;
> +		ring->st_rd_req++;
>  		operation = READ;
>  		break;
>  	case BLKIF_OP_WRITE:
> -		blkif->st_wr_req++;
> +		ring->st_wr_req++;
>  		operation = WRITE_ODIRECT;
>  		break;
>  	case BLKIF_OP_WRITE_BARRIER:
>  		drain = true;
>  	case BLKIF_OP_FLUSH_DISKCACHE:
> -		blkif->st_f_req++;
> +		ring->st_f_req++;
>  		operation = WRITE_FLUSH;
>  		break;
>  	default:
> @@ -1254,7 +1280,7 @@ static int dispatch_rw_block_io(struct xen_blkif *blkif,
>  
>  	preq.nr_sects      = 0;
>  
> -	pending_req->blkif     = blkif;
> +	pending_req->ring     = ring;
>  	pending_req->id        = req->u.rw.id;
>  	pending_req->operation = req_operation;
>  	pending_req->status    = BLKIF_RSP_OKAY;
> @@ -1281,12 +1307,12 @@ static int dispatch_rw_block_io(struct xen_blkif *blkif,
>  			goto fail_response;
>  	}
>  
> -	if (xen_vbd_translate(&preq, blkif, operation) != 0) {
> +	if (xen_vbd_translate(&preq, ring->blkif, operation) != 0) {
>  		pr_debug("access denied: %s of [%llu,%llu] on dev=%04x\n",
>  			 operation == READ ? "read" : "write",
>  			 preq.sector_number,
>  			 preq.sector_number + preq.nr_sects,
> -			 blkif->vbd.pdevice);
> +			 ring->blkif->vbd.pdevice);
>  		goto fail_response;
>  	}
>  
> @@ -1298,7 +1324,7 @@ static int dispatch_rw_block_io(struct xen_blkif *blkif,
>  		if (((int)preq.sector_number|(int)seg[i].nsec) &
>  		    ((bdev_logical_block_size(preq.bdev) >> 9) - 1)) {
>  			pr_debug("Misaligned I/O request from domain %d\n",
> -				 blkif->domid);
> +				 ring->blkif->domid);
>  			goto fail_response;
>  		}
>  	}
> @@ -1307,7 +1333,7 @@ static int dispatch_rw_block_io(struct xen_blkif *blkif,
>  	 * issue the WRITE_FLUSH.
>  	 */
>  	if (drain)
> -		xen_blk_drain_io(pending_req->blkif);
> +		xen_blk_drain_io(pending_req->ring);
>  
>  	/*
>  	 * If we have failed at this point, we need to undo the M2P override,
> @@ -1322,8 +1348,8 @@ static int dispatch_rw_block_io(struct xen_blkif *blkif,
>  	 * This corresponding xen_blkif_put is done in __end_block_io_op, or
>  	 * below (in "!bio") if we are handling a BLKIF_OP_DISCARD.
>  	 */
> -	xen_blkif_get(blkif);
> -	atomic_inc(&blkif->inflight);
> +	xen_blkif_get(ring->blkif);
> +	atomic_inc(&ring->inflight);
>  
>  	for (i = 0; i < nseg; i++) {
>  		while ((bio == NULL) ||
> @@ -1371,19 +1397,19 @@ static int dispatch_rw_block_io(struct xen_blkif *blkif,
>  	blk_finish_plug(&plug);
>  
>  	if (operation == READ)
> -		blkif->st_rd_sect += preq.nr_sects;
> +		ring->st_rd_sect += preq.nr_sects;
>  	else if (operation & WRITE)
> -		blkif->st_wr_sect += preq.nr_sects;
> +		ring->st_wr_sect += preq.nr_sects;
>  
>  	return 0;
>  
>   fail_flush:
> -	xen_blkbk_unmap(blkif, pending_req->segments,
> +	xen_blkbk_unmap(ring, pending_req->segments,
>  	                pending_req->nr_segs);
>   fail_response:
>  	/* Haven't submitted any bio's yet. */
> -	make_response(blkif, req->u.rw.id, req_operation, BLKIF_RSP_ERROR);
> -	free_req(blkif, pending_req);
> +	make_response(ring, req->u.rw.id, req_operation, BLKIF_RSP_ERROR);
> +	free_req(ring, pending_req);
>  	msleep(1); /* back off a bit */
>  	return -EIO;
>  
> @@ -1401,21 +1427,22 @@ static int dispatch_rw_block_io(struct xen_blkif *blkif,
>  /*
>   * Put a response on the ring on how the operation fared.
>   */
> -static void make_response(struct xen_blkif *blkif, u64 id,
> +static void make_response(struct xen_blkif_ring *ring, u64 id,
>  			  unsigned short op, int st)
>  {
>  	struct blkif_response  resp;
>  	unsigned long     flags;
> -	union blkif_back_rings *blk_rings = &blkif->blk_rings;
> +	union blkif_back_rings *blk_rings;
>  	int notify;
>  
>  	resp.id        = id;
>  	resp.operation = op;
>  	resp.status    = st;
>  
> -	spin_lock_irqsave(&blkif->blk_ring_lock, flags);
> +	spin_lock_irqsave(&ring->blk_ring_lock, flags);
> +	blk_rings = &ring->blk_rings;
>  	/* Place on the response ring for the relevant domain. */
> -	switch (blkif->blk_protocol) {
> +	switch (ring->blkif->blk_protocol) {
>  	case BLKIF_PROTOCOL_NATIVE:
>  		memcpy(RING_GET_RESPONSE(&blk_rings->native, blk_rings->native.rsp_prod_pvt),
>  		       &resp, sizeof(resp));
> @@ -1433,9 +1460,9 @@ static void make_response(struct xen_blkif *blkif, u64 id,
>  	}
>  	blk_rings->common.rsp_prod_pvt++;
>  	RING_PUSH_RESPONSES_AND_CHECK_NOTIFY(&blk_rings->common, notify);
> -	spin_unlock_irqrestore(&blkif->blk_ring_lock, flags);
> +	spin_unlock_irqrestore(&ring->blk_ring_lock, flags);
>  	if (notify)
> -		notify_remote_via_irq(blkif->irq);
> +		notify_remote_via_irq(ring->irq);
>  }
>  
>  static int __init xen_blkif_init(void)
> diff --git a/drivers/block/xen-blkback/common.h b/drivers/block/xen-blkback/common.h
> index 45a044a..f0dd69a 100644
> --- a/drivers/block/xen-blkback/common.h
> +++ b/drivers/block/xen-blkback/common.h
> @@ -260,34 +260,60 @@ struct persistent_gnt {
>  	struct list_head remove_node;
>  };
>  
> +/* Per-ring information */

Missing full stop.

> +struct xen_blkif_ring {
> +	/* Physical parameters of the comms window. */
> +	unsigned int		irq;
> +	union blkif_back_rings	blk_rings;
> +	void			*blk_ring;
> +	/* Private fields. */
> +	spinlock_t		blk_ring_lock;
> +
> +	wait_queue_head_t	wq;
> +	atomic_t		inflight;
> +	/* One thread per blkif ring. */
> +	struct task_struct	*xenblkd;
> +	unsigned int		waiting_reqs;
> +
> +	/* List of all 'pending_req' available */
> +	struct list_head	pending_free;
> +	/* And its spinlock. */
> +	spinlock_t		pending_free_lock;
> +	wait_queue_head_t	pending_free_wq;
> +
> +	/* statistics */
> +	unsigned long		st_print;

This one is on the same line as the other.
> +	unsigned long long			st_rd_req;

But these are not?

Also you didn't pull these out of 'struct xen_blkif'?

Or is that meant to be done in another patch?

> +	unsigned long long			st_wr_req;
> +	unsigned long long			st_oo_req;
> +	unsigned long long			st_f_req;
> +	unsigned long long			st_ds_req;
> +	unsigned long long			st_rd_sect;
> +	unsigned long long			st_wr_sect;
> +
> +	struct work_struct	free_work;
> +	/* Thread shutdown wait queue. */
> +	wait_queue_head_t	shutdown_wq;
> +	struct xen_blkif *blkif;
> +};
> +
>  struct xen_blkif {
>  	/* Unique identifier for this interface. */
>  	domid_t			domid;
>  	unsigned int		handle;
> -	/* Physical parameters of the comms window. */
> -	unsigned int		irq;
>  	/* Comms information. */
>  	enum blkif_protocol	blk_protocol;
> -	union blkif_back_rings	blk_rings;
> -	void			*blk_ring;
>  	/* The VBD attached to this interface. */
>  	struct xen_vbd		vbd;
>  	/* Back pointer to the backend_info. */
>  	struct backend_info	*be;
> -	/* Private fields. */
> -	spinlock_t		blk_ring_lock;
>  	atomic_t		refcnt;
> -
> -	wait_queue_head_t	wq;
>  	/* for barrier (drain) requests */
>  	struct completion	drain_complete;
>  	atomic_t		drain;
> -	atomic_t		inflight;
> -	/* One thread per one blkif. */
> -	struct task_struct	*xenblkd;
> -	unsigned int		waiting_reqs;
>  
>  	/* tree to store persistent grants */
> +	spinlock_t		pers_gnts_lock;
>  	struct rb_root		persistent_gnts;
>  	unsigned int		persistent_gnt_c;
>  	atomic_t		persistent_gnt_in_use;
> @@ -302,12 +328,6 @@ struct xen_blkif {
>  	int			free_pages_num;
>  	struct list_head	free_pages;
>  
> -	/* List of all 'pending_req' available */
> -	struct list_head	pending_free;
> -	/* And its spinlock. */
> -	spinlock_t		pending_free_lock;
> -	wait_queue_head_t	pending_free_wq;
> -
>  	/* statistics */
>  	unsigned long		st_print;
>  	unsigned long long			st_rd_req;
> @@ -319,9 +339,9 @@ struct xen_blkif {
>  	unsigned long long			st_wr_sect;
>  
>  	struct work_struct	free_work;
> -	/* Thread shutdown wait queue. */
> -	wait_queue_head_t	shutdown_wq;
>  	unsigned int nr_ring_pages;
> +	/* All rings for this device */

Missing full stop.

> +	struct xen_blkif_ring ring;
>  };
>  
>  struct seg_buf {
> @@ -343,7 +363,7 @@ struct grant_page {
>   * response queued for it, with the saved 'id' passed back.
>   */
>  struct pending_req {
> -	struct xen_blkif	*blkif;
> +	struct xen_blkif_ring   *ring;
>  	u64			id;
>  	int			nr_segs;
>  	atomic_t		pendcnt;
> @@ -385,7 +405,7 @@ int xen_blkif_xenbus_init(void);
>  irqreturn_t xen_blkif_be_int(int irq, void *dev_id);
>  int xen_blkif_schedule(void *arg);
>  int xen_blkif_purge_persistent(void *arg);
> -void xen_blkbk_free_caches(struct xen_blkif *blkif);
> +void xen_blkbk_free_caches(struct xen_blkif_ring *ring);
>  
>  int xen_blkbk_flush_diskcache(struct xenbus_transaction xbt,
>  			      struct backend_info *be, int state);
> diff --git a/drivers/block/xen-blkback/xenbus.c b/drivers/block/xen-blkback/xenbus.c
> index 7676575..7bdd5fd 100644
> --- a/drivers/block/xen-blkback/xenbus.c
> +++ b/drivers/block/xen-blkback/xenbus.c
> @@ -88,7 +88,7 @@ static void xen_update_blkif_status(struct xen_blkif *blkif)
>  	char name[BLKBACK_NAME_LEN];
>  
>  	/* Not ready to connect? */
> -	if (!blkif->irq || !blkif->vbd.bdev)
> +	if (!blkif->ring.irq || !blkif->vbd.bdev)
>  		return;
>  
>  	/* Already connected? */
> @@ -113,10 +113,10 @@ static void xen_update_blkif_status(struct xen_blkif *blkif)
>  	}
>  	invalidate_inode_pages2(blkif->vbd.bdev->bd_inode->i_mapping);
>  
> -	blkif->xenblkd = kthread_run(xen_blkif_schedule, blkif, "%s", name);
> -	if (IS_ERR(blkif->xenblkd)) {
> -		err = PTR_ERR(blkif->xenblkd);
> -		blkif->xenblkd = NULL;
> +	blkif->ring.xenblkd = kthread_run(xen_blkif_schedule, &blkif->ring, "%s", name);
> +	if (IS_ERR(blkif->ring.xenblkd)) {
> +		err = PTR_ERR(blkif->ring.xenblkd);
> +		blkif->ring.xenblkd = NULL;
>  		xenbus_dev_error(blkif->be->dev, err, "start xenblkd");
>  		return;
>  	}
> @@ -125,6 +125,7 @@ static void xen_update_blkif_status(struct xen_blkif *blkif)
>  static struct xen_blkif *xen_blkif_alloc(domid_t domid)
>  {
>  	struct xen_blkif *blkif;
> +	struct xen_blkif_ring *ring;
>  
>  	BUILD_BUG_ON(MAX_INDIRECT_PAGES > BLKIF_MAX_INDIRECT_PAGES_PER_REQUEST);
>  
> @@ -133,41 +134,45 @@ static struct xen_blkif *xen_blkif_alloc(domid_t domid)
>  		return ERR_PTR(-ENOMEM);
>  
>  	blkif->domid = domid;
> -	spin_lock_init(&blkif->blk_ring_lock);
>  	atomic_set(&blkif->refcnt, 1);
> -	init_waitqueue_head(&blkif->wq);
>  	init_completion(&blkif->drain_complete);
>  	atomic_set(&blkif->drain, 0);
> -	blkif->st_print = jiffies;
> -	blkif->persistent_gnts.rb_node = NULL;
> +	INIT_WORK(&blkif->free_work, xen_blkif_deferred_free);
>  	spin_lock_init(&blkif->free_pages_lock);
>  	INIT_LIST_HEAD(&blkif->free_pages);
> -	INIT_LIST_HEAD(&blkif->persistent_purge_list);
>  	blkif->free_pages_num = 0;
> +	blkif->persistent_gnts.rb_node = NULL;
> +	INIT_LIST_HEAD(&blkif->persistent_purge_list);
>  	atomic_set(&blkif->persistent_gnt_in_use, 0);
> -	atomic_set(&blkif->inflight, 0);
>  	INIT_WORK(&blkif->persistent_purge_work, xen_blkbk_unmap_purged_grants);
>  
> -	INIT_LIST_HEAD(&blkif->pending_free);
> -	INIT_WORK(&blkif->free_work, xen_blkif_deferred_free);
> -	spin_lock_init(&blkif->pending_free_lock);
> -	init_waitqueue_head(&blkif->pending_free_wq);
> -	init_waitqueue_head(&blkif->shutdown_wq);
> +	ring = &blkif->ring;
> +	ring->blkif = blkif;
> +	spin_lock_init(&ring->blk_ring_lock);
> +	init_waitqueue_head(&ring->wq);
> +	ring->st_print = jiffies;
> +	atomic_set(&ring->inflight, 0);
> +
> +	INIT_LIST_HEAD(&ring->pending_free);
> +	spin_lock_init(&ring->pending_free_lock);
> +	init_waitqueue_head(&ring->pending_free_wq);
> +	init_waitqueue_head(&ring->shutdown_wq);
>  
>  	return blkif;
>  }
>  
> -static int xen_blkif_map(struct xen_blkif *blkif, grant_ref_t *gref,
> +static int xen_blkif_map(struct xen_blkif_ring *ring, grant_ref_t *gref,
>  			 unsigned int nr_grefs, unsigned int evtchn)
>  {
>  	int err;
> +	struct xen_blkif *blkif = ring->blkif;
>  
>  	/* Already connected through? */
> -	if (blkif->irq)
> +	if (ring->irq)
>  		return 0;
>  
>  	err = xenbus_map_ring_valloc(blkif->be->dev, gref, nr_grefs,
> -				     &blkif->blk_ring);
> +				     &ring->blk_ring);
>  	if (err < 0)
>  		return err;
>  
> @@ -175,22 +180,22 @@ static int xen_blkif_map(struct xen_blkif *blkif, grant_ref_t *gref,
>  	case BLKIF_PROTOCOL_NATIVE:
>  	{
>  		struct blkif_sring *sring;
> -		sring = (struct blkif_sring *)blkif->blk_ring;
> -		BACK_RING_INIT(&blkif->blk_rings.native, sring, PAGE_SIZE * nr_grefs);
> +		sring = (struct blkif_sring *)ring->blk_ring;
> +		BACK_RING_INIT(&ring->blk_rings.native, sring, PAGE_SIZE * nr_grefs);
>  		break;
>  	}
>  	case BLKIF_PROTOCOL_X86_32:
>  	{
>  		struct blkif_x86_32_sring *sring_x86_32;
> -		sring_x86_32 = (struct blkif_x86_32_sring *)blkif->blk_ring;
> -		BACK_RING_INIT(&blkif->blk_rings.x86_32, sring_x86_32, PAGE_SIZE * nr_grefs);
> +		sring_x86_32 = (struct blkif_x86_32_sring *)ring->blk_ring;
> +		BACK_RING_INIT(&ring->blk_rings.x86_32, sring_x86_32, PAGE_SIZE * nr_grefs);
>  		break;
>  	}
>  	case BLKIF_PROTOCOL_X86_64:
>  	{
>  		struct blkif_x86_64_sring *sring_x86_64;
> -		sring_x86_64 = (struct blkif_x86_64_sring *)blkif->blk_ring;
> -		BACK_RING_INIT(&blkif->blk_rings.x86_64, sring_x86_64, PAGE_SIZE * nr_grefs);
> +		sring_x86_64 = (struct blkif_x86_64_sring *)ring->blk_ring;
> +		BACK_RING_INIT(&ring->blk_rings.x86_64, sring_x86_64, PAGE_SIZE * nr_grefs);
>  		break;
>  	}
>  	default:
> @@ -199,13 +204,13 @@ static int xen_blkif_map(struct xen_blkif *blkif, grant_ref_t *gref,
>  
>  	err = bind_interdomain_evtchn_to_irqhandler(blkif->domid, evtchn,
>  						    xen_blkif_be_int, 0,
> -						    "blkif-backend", blkif);
> +						    "blkif-backend", ring);
>  	if (err < 0) {
> -		xenbus_unmap_ring_vfree(blkif->be->dev, blkif->blk_ring);
> -		blkif->blk_rings.common.sring = NULL;
> +		xenbus_unmap_ring_vfree(blkif->be->dev, ring->blk_ring);
> +		ring->blk_rings.common.sring = NULL;
>  		return err;
>  	}
> -	blkif->irq = err;
> +	ring->irq = err;
>  
>  	return 0;
>  }
> @@ -214,35 +219,36 @@ static int xen_blkif_disconnect(struct xen_blkif *blkif)
>  {
>  	struct pending_req *req, *n;
>  	int i = 0, j;
> +	struct xen_blkif_ring *ring = &blkif->ring;
>  
> -	if (blkif->xenblkd) {
> -		kthread_stop(blkif->xenblkd);
> -		wake_up(&blkif->shutdown_wq);
> -		blkif->xenblkd = NULL;
> +	if (ring->xenblkd) {
> +		kthread_stop(ring->xenblkd);
> +		wake_up(&ring->shutdown_wq);
> +		ring->xenblkd = NULL;
>  	}
>  
>  	/* The above kthread_stop() guarantees that at this point we
>  	 * don't have any discard_io or other_io requests. So, checking
>  	 * for inflight IO is enough.
>  	 */
> -	if (atomic_read(&blkif->inflight) > 0)
> +	if (atomic_read(&ring->inflight) > 0)
>  		return -EBUSY;
>  
> -	if (blkif->irq) {
> -		unbind_from_irqhandler(blkif->irq, blkif);
> -		blkif->irq = 0;
> +	if (ring->irq) {
> +		unbind_from_irqhandler(ring->irq, ring);
> +		ring->irq = 0;
>  	}
>  
> -	if (blkif->blk_rings.common.sring) {
> -		xenbus_unmap_ring_vfree(blkif->be->dev, blkif->blk_ring);
> -		blkif->blk_rings.common.sring = NULL;
> +	if (ring->blk_rings.common.sring) {
> +		xenbus_unmap_ring_vfree(blkif->be->dev, ring->blk_ring);
> +		ring->blk_rings.common.sring = NULL;
>  	}
>  
>  	/* Remove all persistent grants and the cache of ballooned pages. */
> -	xen_blkbk_free_caches(blkif);
> +	xen_blkbk_free_caches(ring);
>  
>  	/* Check that there is no request in use */
> -	list_for_each_entry_safe(req, n, &blkif->pending_free, free_list) {
> +	list_for_each_entry_safe(req, n, &ring->pending_free, free_list) {
>  		list_del(&req->free_list);
>  
>  		for (j = 0; j < MAX_INDIRECT_SEGMENTS; j++)
> @@ -300,6 +306,16 @@ int __init xen_blkif_interface_init(void)
>  	{								\
>  		struct xenbus_device *dev = to_xenbus_device(_dev);	\
>  		struct backend_info *be = dev_get_drvdata(&dev->dev);	\
> +		struct xen_blkif *blkif = be->blkif;			\
> +		struct xen_blkif_ring *ring = &blkif->ring;		\
> +									\
> +		blkif->st_oo_req = ring->st_oo_req;			\
> +		blkif->st_rd_req = ring->st_rd_req;			\
> +		blkif->st_wr_req = ring->st_wr_req;			\
> +		blkif->st_f_req = ring->st_f_req;			\
> +		blkif->st_ds_req = ring->st_ds_req;			\
> +		blkif->st_rd_sect = ring->st_rd_sect;			\
> +		blkif->st_wr_sect = ring->st_wr_sect;			\

If I read 'oo_req' I end up populating the 'blkif->st_oo_req'
,'blkif->st_rd_req', 'blkif->st_wr_req', and so every time.

Please rework this.

>  									\
>  		return sprintf(buf, format, ##args);			\
>  	}								\
> @@ -832,6 +848,7 @@ static int connect_ring(struct backend_info *be)
>  	char protocol[64] = "";
>  	struct pending_req *req, *n;
>  	int err, i, j;
> +	struct xen_blkif_ring *ring = &be->blkif->ring;
>  
>  	pr_debug("%s %s\n", __func__, dev->otherend);
>  
> @@ -920,7 +937,7 @@ static int connect_ring(struct backend_info *be)
>  		req = kzalloc(sizeof(*req), GFP_KERNEL);
>  		if (!req)
>  			goto fail;
> -		list_add_tail(&req->free_list, &be->blkif->pending_free);
> +		list_add_tail(&req->free_list, &ring->pending_free);
>  		for (j = 0; j < MAX_INDIRECT_SEGMENTS; j++) {
>  			req->segments[j] = kzalloc(sizeof(*req->segments[0]), GFP_KERNEL);
>  			if (!req->segments[j])
> @@ -935,7 +952,7 @@ static int connect_ring(struct backend_info *be)
>  	}
>  
>  	/* Map the shared frame, irq etc. */
> -	err = xen_blkif_map(be->blkif, ring_ref, nr_grefs, evtchn);
> +	err = xen_blkif_map(ring, ring_ref, nr_grefs, evtchn);
>  	if (err) {
>  		xenbus_dev_fatal(dev, err, "mapping ring-ref port %u", evtchn);
>  		return err;
> @@ -944,7 +961,7 @@ static int connect_ring(struct backend_info *be)
>  	return 0;
>  
>  fail:
> -	list_for_each_entry_safe(req, n, &be->blkif->pending_free, free_list) {
> +	list_for_each_entry_safe(req, n, &ring->pending_free, free_list) {
>  		list_del(&req->free_list);
>  		for (j = 0; j < MAX_INDIRECT_SEGMENTS; j++) {
>  			if (!req->segments[j])
> -- 
> 1.8.3.1
>