[PATCH 08/10] xen/blkfront: negotiate hardware queue number with backend

[Bob Liu <bob.liu@oracle.com>]

The max number of hardware queues for xen/blkfront is num_online_cpus() or set
by module parameter, while the number xen/blkback supported is notified through
xenstore("multi-queue-max-queues").
The negotiated number was the smaller one, and was written back to
xen/blkback as "multi-queue-num-queues".

Signed-off-by: Bob Liu <bob.liu@oracle.com>
---
 drivers/block/xen-blkfront.c | 71 ++++++++++++++++++++++++++++++++++++++++----
 1 file changed, 66 insertions(+), 5 deletions(-)

diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
index d551be0..32caf85 100644
--- a/drivers/block/xen-blkfront.c
+++ b/drivers/block/xen-blkfront.c
@@ -99,6 +99,10 @@ static unsigned int xen_blkif_max_segments = 32;
 module_param_named(max, xen_blkif_max_segments, int, S_IRUGO);
 MODULE_PARM_DESC(max, "Maximum amount of segments in indirect requests (default is 32)");
 
+static unsigned int xenblkif_max_queues;
+module_param_named(max_queues, xenblkif_max_queues, uint, 0644);
+MODULE_PARM_DESC(max_queues, "Maximum number of hardware queues per virtual disk");
+
 #define BLK_RING_SIZE __CONST_RING_SIZE(blkif, PAGE_SIZE)
 
 /*
@@ -677,7 +681,7 @@ static int xlvbd_init_blk_queue(struct gendisk *gd, u16 sector_size,
 
 	memset(&info->tag_set, 0, sizeof(info->tag_set));
 	info->tag_set.ops = &blkfront_mq_ops;
-	info->tag_set.nr_hw_queues = 1;
+	info->tag_set.nr_hw_queues = info->nr_rings;
 	info->tag_set.queue_depth =  BLK_RING_SIZE;
 	info->tag_set.numa_node = NUMA_NO_NODE;
 	info->tag_set.flags = BLK_MQ_F_SHOULD_MERGE | BLK_MQ_F_SG_MERGE;
@@ -1338,6 +1342,8 @@ static int talk_to_blkback(struct xenbus_device *dev,
 	struct xenbus_transaction xbt;
 	int err, i;
 	struct blkfront_ring_info *rinfo;
+	char *path;
+	size_t pathsize;
 
 	for (i = 0; i < info->nr_rings; i++) {
 		rinfo = &info->rinfo[i];
@@ -1354,6 +1360,13 @@ again:
 		goto out;
 	}
 
+	/* Write the number of queues */
+	err = xenbus_printf(xbt, dev->nodename, "multi-queue-num-queues", "%u", info->nr_rings);
+	if (err) {
+		message = "writing multi-queue-num-queues";
+		goto abort_transaction;
+	}
+
 	if (info->nr_rings == 1) {
 		rinfo = &info->rinfo[0];
 		err = xenbus_printf(xbt, dev->nodename,
@@ -1369,8 +1382,33 @@ again:
 			goto abort_transaction;
 		}
 	} else {
-		/* Not supported at this stage */
-		goto abort_transaction;
+		pathsize = strlen(dev->nodename) + 12;
+		path = kzalloc(pathsize, GFP_KERNEL);
+		if (!path) {
+			err = -ENOMEM;
+			message = "ENOMEM while writing ring references";
+			goto abort_transaction;
+		}
+		for (i = 0; i < info->nr_rings; i++) {
+			memset(path, 0, pathsize);
+			snprintf(path, pathsize, "%s/queue-%u", dev->nodename, i);
+
+			err = xenbus_printf(xbt, path,
+					"ring-ref", "%u", info->rinfo[i].ring_ref);
+			if (err) {
+				message = "writing ring-ref";
+				kfree(path);
+				goto abort_transaction;
+			}
+			err = xenbus_printf(xbt, path,
+					"event-channel", "%u", info->rinfo[i].evtchn);
+			if (err) {
+				message = "writing event-channel";
+				kfree(path);
+				goto abort_transaction;
+			}
+		}
+		kfree(path);
 	}
 	err = xenbus_printf(xbt, dev->nodename, "protocol", "%s",
 			    XEN_IO_PROTO_ABI_NATIVE);
@@ -1420,6 +1458,7 @@ static int blkfront_probe(struct xenbus_device *dev,
 	int err, vdevice, i, rindex;
 	struct blkfront_info *info;
 	struct blkfront_ring_info *rinfo;
+	unsigned int max_queues = 0;
 
 	/* FIXME: Use dynamic device id if this is not set. */
 	err = xenbus_scanf(XBT_NIL, dev->nodename,
@@ -1473,7 +1512,14 @@ static int blkfront_probe(struct xenbus_device *dev,
 	info->vdevice = vdevice;
 	info->connected = BLKIF_STATE_DISCONNECTED;
 
-	info->nr_rings = 1;
+	/* Check if backend supports multiple queues */
+	err = xenbus_scanf(XBT_NIL, info->xbdev->otherend,
+			   "multi-queue-max-queues", "%u", &max_queues);
+	if (err < 0)
+		max_queues = 1;
+
+	info->nr_rings = min(max_queues, xenblkif_max_queues);
+	printk("xen/blkfront probe info->nr_rings:%d, backend support:%d\n", info->nr_rings, max_queues);
 	info->rinfo = kzalloc(sizeof(*rinfo) * info->nr_rings, GFP_KERNEL);
 	if (!info->rinfo) {
 		xenbus_dev_fatal(dev, -ENOMEM, "allocating ring_info structure");
@@ -1654,12 +1700,24 @@ static int blkif_recover(struct blkfront_info *info)
 static int blkfront_resume(struct xenbus_device *dev)
 {
 	struct blkfront_info *info = dev_get_drvdata(&dev->dev);
-	int err;
+	int err = 0;
+	unsigned int max_queues = 0;
 
 	dev_dbg(&dev->dev, "blkfront_resume: %s\n", dev->nodename);
 
 	blkif_free(info, info->connected == BLKIF_STATE_CONNECTED);
 
+	err = xenbus_gather(XBT_NIL, info->xbdev->otherend,
+			"multi-queue-max-queues", "%u", &max_queues, NULL);
+	if (err)
+		max_queues = 1;
+
+	if (info->nr_rings != min(max_queues, xenblkif_max_queues)) {
+		/* At this stage, not support resume to a different hardware queue
+		 * number */
+		return -1;
+	}
+
 	err = talk_to_blkback(dev, info);
 
 	/*
@@ -2165,6 +2223,9 @@ static int __init xlblk_init(void)
 		return -ENODEV;
 	}
 
+	/* Allow as many queues as there are CPUs, by default */
+	xenblkif_max_queues = num_online_cpus();
+
 	ret = xenbus_register_frontend(&blkfront_driver);
 	if (ret) {
 		unregister_blkdev(XENVBD_MAJOR, DEV_NAME);
-- 
1.8.3.1