[PATCH V3,net-next, 1/3] Drivers: hv: vmbus: Add a dev_num variable based on channel offer sequence

[Haiyang Zhang <haiyangz@microsoft.com>]

This number is set to the first available number, starting from zero,
when a VMBus device’s primary channel is offered.
It will be used for stable naming when Async probing is used.

Signed-off-by: Haiyang Zhang <haiyangz@microsoft.com>
---
Changes
V3:
 Rename a local var, add code comments.

V2:
 Use nest loops in hv_set_devnum, instead of goto.
---
 drivers/hv/channel_mgmt.c | 46 ++++++++++++++++++++++++++++++++++++++++++++--
 include/linux/hyperv.h    |  6 ++++++
 2 files changed, 50 insertions(+), 2 deletions(-)

diff --git a/drivers/hv/channel_mgmt.c b/drivers/hv/channel_mgmt.c
index 8eb1675..68adfa1 100644
--- a/drivers/hv/channel_mgmt.c
+++ b/drivers/hv/channel_mgmt.c
@@ -315,6 +315,8 @@ static struct vmbus_channel *alloc_channel(void)
 	if (!channel)
 		return NULL;
 
+	channel->dev_num = HV_DEV_NUM_INVALID;
+
 	spin_lock_init(&channel->lock);
 	init_completion(&channel->rescind_event);
 
@@ -541,6 +543,44 @@ static void vmbus_add_channel_work(struct work_struct *work)
 }
 
 /*
+ * Get the first available device number of its type, then
+ * record it in the channel structure.
+ */
+static void hv_set_devnum(struct vmbus_channel *newchannel)
+{
+	struct vmbus_channel *channel;
+	int i = -1;
+	bool in_use;
+
+	BUG_ON(!mutex_is_locked(&vmbus_connection.channel_mutex));
+
+	/*
+	 * Iterate through each possible device number starting at zero.
+	 * If the device number is already in use for a device of this type,
+	 * try the next device number until finding one that is not in use.
+	 * This approach selects the smallest device number that is not in
+	 * use, and so reuses any numbers that are freed by devices that
+	 * have been removed.
+	 */
+	do {
+		i++;
+		in_use = false;
+
+		list_for_each_entry(channel, &vmbus_connection.chn_list,
+				    listentry) {
+			if (i == channel->dev_num &&
+			    guid_equal(&channel->offermsg.offer.if_type,
+				       &newchannel->offermsg.offer.if_type)) {
+				in_use = true;
+				break;
+			}
+		}
+	} while (in_use);
+
+	newchannel->dev_num = i;
+}
+
+/*
  * vmbus_process_offer - Process the offer by creating a channel/device
  * associated with this offer
  */
@@ -573,10 +613,12 @@ static void vmbus_process_offer(struct vmbus_channel *newchannel)
 		}
 	}
 
-	if (fnew)
+	if (fnew) {
+		hv_set_devnum(newchannel);
+
 		list_add_tail(&newchannel->listentry,
 			      &vmbus_connection.chn_list);
-	else {
+	} else {
 		/*
 		 * Check to see if this is a valid sub-channel.
 		 */
diff --git a/include/linux/hyperv.h b/include/linux/hyperv.h
index 26f3aee..4f110c5 100644
--- a/include/linux/hyperv.h
+++ b/include/linux/hyperv.h
@@ -718,6 +718,8 @@ struct vmbus_device {
 	bool perf_device;
 };
 
+#define HV_DEV_NUM_INVALID (-1)
+
 struct vmbus_channel {
 	struct list_head listentry;
 
@@ -849,6 +851,10 @@ struct vmbus_channel {
 	 */
 	struct vmbus_channel *primary_channel;
 	/*
+	 * Used for device naming based on channel offer sequence.
+	 */
+	int dev_num;
+	/*
 	 * Support per-channel state for use by vmbus drivers.
 	 */
 	void *per_channel_state;
-- 
1.8.3.1