dcb: Add dcb_ieee_getapp_mask() for drivers to query APP settings

With multiple APP entries per selector and protocol drivers
or stacks may want to pick a specific value or stripe traffic
across many priorities. Also if an APP entry in use is
deleted the stack/driver may want to choose from the existing
APP entries.

To facilitate this and avoid having duplicate code to walk
the APP ring provide a routine dcb_ieee_getapp_mask() to
return a u8 bitmask of all priorities set for the specified
selector and protocol. This routine and bitmask is a helper
for DCB kernel users.
Signed-off-by: John Fastabend <john.r.fastabend@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/dcbnl.h

@@ -32,6 +32,7 @@ u8 dcb_setapp(struct net_device *, struct dcb_app *);
 u8 dcb_getapp(struct net_device *, struct dcb_app *);
 int dcb_ieee_setapp(struct net_device *, struct dcb_app *);
 int dcb_ieee_delapp(struct net_device *, struct dcb_app *);
+u8 dcb_ieee_getapp_mask(struct net_device *, struct dcb_app *);
 
 int dcbnl_notify(struct net_device *dev, int event, int cmd, u32 seq, u32 pid);
 

net/dcb/dcbnl.c

@@ -1928,6 +1928,32 @@ u8 dcb_setapp(struct net_device *dev, struct dcb_app *new)
 }
 EXPORT_SYMBOL(dcb_setapp);
 
+/**
+ * dcb_ieee_getapp_mask - retrieve the IEEE DCB application priority
+ *
+ * Helper routine which on success returns a non-zero 802.1Qaz user
+ * priority bitmap otherwise returns 0 to indicate the dcb_app was
+ * not found in APP list.
+ */
+u8 dcb_ieee_getapp_mask(struct net_device *dev, struct dcb_app *app)
+{
+	struct dcb_app_type *itr;
+	u8 prio = 0;
+
+	spin_lock(&dcb_lock);
+	list_for_each_entry(itr, &dcb_app_list, list) {
+		if (itr->app.selector == app->selector &&
+		    itr->app.protocol == app->protocol &&
+		    (strncmp(itr->name, dev->name, IFNAMSIZ) == 0)) {
+			prio |= 1 << itr->app.priority;
+		}
+	}
+	spin_unlock(&dcb_lock);
+
+	return prio;
+}
+EXPORT_SYMBOL(dcb_ieee_getapp_mask);
+
 /**
  * dcb_ieee_setapp - add IEEE dcb application data to app list
  *