net: dcb: Add priority-to-DSCP map getters

On ingress, a network device such as a switch assigns to packets
priority based on various criteria. Common options include interpreting
PCP and DSCP fields according to user configuration. When a packet
egresses the switch, a reverse process may rewrite PCP and/or DSCP
values according to packet priority.

The following three functions support a) obtaining a DSCP-to-priority
map or vice versa, and b) finding default-priority entries in APP
database.

The DCB subsystem supports for APP entries a very generous M:N mapping
between priorities and protocol identifiers. Understandably,
several (say) DSCP values can map to the same priority. But this
asymmetry holds the other way around as well--one priority can map to
several DSCP values. For this reason, the following functions operate in
terms of bitmaps, with ones in positions that match some APP entry.

- dcb_ieee_getapp_dscp_prio_mask_map() to compute for a given netdevice
a map of DSCP-to-priority-mask, which gives for each DSCP value a
bitmap of priorities related to that DSCP value by APP, along the
lines of dcb_ieee_getapp_mask().

- dcb_ieee_getapp_prio_dscp_mask_map() similarly to compute for a given
netdevice a map from priorities to a bitmap of DSCPs.

- dcb_ieee_getapp_default_prio_mask() which finds all default-priority
rules for a given port in APP database, and returns a mask of
priorities allowed by these default-priority rules.

Signed-off-by: Petr Machata <[e-mail]>
Signed-off-by: Ido Schimmel <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

include/net/dcbnl.h

···
 int dcb_ieee_delapp(struct net_device *, struct dcb_app *);
 u8 dcb_ieee_getapp_mask(struct net_device *, struct dcb_app *);
 
+struct dcb_ieee_app_prio_map {
+	u64 map[IEEE_8021QAZ_MAX_TCS];
+};
+void dcb_ieee_getapp_prio_dscp_mask_map(const struct net_device *dev,
+					struct dcb_ieee_app_prio_map *p_map);
+
+struct dcb_ieee_app_dscp_map {
+	u8 map[64];
+};
+void dcb_ieee_getapp_dscp_prio_mask_map(const struct net_device *dev,
+					struct dcb_ieee_app_dscp_map *p_map);
+u8 dcb_ieee_getapp_default_prio_mask(const struct net_device *dev);
+
 int dcbnl_ieee_notify(struct net_device *dev, int event, int cmd,
 		      u32 seq, u32 pid);
 int dcbnl_cee_notify(struct net_device *dev, int event, int cmd,

net/dcb/dcbnl.c

···
 }
 EXPORT_SYMBOL(dcb_ieee_delapp);
 
+/**
+ * dcb_ieee_getapp_prio_dscp_mask_map - For a given device, find mapping from
+ * priorities to the DSCP values assigned to that priority. Initialize p_map
+ * such that each map element holds a bit mask of DSCP values configured for
+ * that priority by APP entries.
+ */
+void dcb_ieee_getapp_prio_dscp_mask_map(const struct net_device *dev,
+					struct dcb_ieee_app_prio_map *p_map)
+{
+	int ifindex = dev->ifindex;
+	struct dcb_app_type *itr;
+	u8 prio;
+
+	memset(p_map->map, 0, sizeof(p_map->map));
+
+	spin_lock_bh(&dcb_lock);
+	list_for_each_entry(itr, &dcb_app_list, list) {
+		if (itr->ifindex == ifindex &&
+		    itr->app.selector == IEEE_8021QAZ_APP_SEL_DSCP &&
+		    itr->app.protocol < 64 &&
+		    itr->app.priority < IEEE_8021QAZ_MAX_TCS) {
+			prio = itr->app.priority;
+			p_map->map[prio] |= 1ULL << itr->app.protocol;
+		}
+	}
+	spin_unlock_bh(&dcb_lock);
+}
+EXPORT_SYMBOL(dcb_ieee_getapp_prio_dscp_mask_map);
+
+/**
+ * dcb_ieee_getapp_dscp_prio_mask_map - For a given device, find mapping from
+ * DSCP values to the priorities assigned to that DSCP value. Initialize p_map
+ * such that each map element holds a bit mask of priorities configured for a
+ * given DSCP value by APP entries.
+ */
+void
+dcb_ieee_getapp_dscp_prio_mask_map(const struct net_device *dev,
+				   struct dcb_ieee_app_dscp_map *p_map)
+{
+	int ifindex = dev->ifindex;
+	struct dcb_app_type *itr;
+
+	memset(p_map->map, 0, sizeof(p_map->map));
+
+	spin_lock_bh(&dcb_lock);
+	list_for_each_entry(itr, &dcb_app_list, list) {
+		if (itr->ifindex == ifindex &&
+		    itr->app.selector == IEEE_8021QAZ_APP_SEL_DSCP &&
+		    itr->app.protocol < 64 &&
+		    itr->app.priority < IEEE_8021QAZ_MAX_TCS)
+			p_map->map[itr->app.protocol] |= 1 << itr->app.priority;
+	}
+	spin_unlock_bh(&dcb_lock);
+}
+EXPORT_SYMBOL(dcb_ieee_getapp_dscp_prio_mask_map);
+
+/**
+ * Per 802.1Q-2014, the selector value of 1 is used for matching on Ethernet
+ * type, with valid PID values >= 1536. A special meaning is then assigned to
+ * protocol value of 0: "default priority. For use when priority is not
+ * otherwise specified".
+ *
+ * dcb_ieee_getapp_default_prio_mask - For a given device, find all APP entries
+ * of the form {$PRIO, ETHERTYPE, 0} and construct a bit mask of all default
+ * priorities set by these entries.
+ */
+u8 dcb_ieee_getapp_default_prio_mask(const struct net_device *dev)
+{
+	int ifindex = dev->ifindex;
+	struct dcb_app_type *itr;
+	u8 mask = 0;
+
+	spin_lock_bh(&dcb_lock);
+	list_for_each_entry(itr, &dcb_app_list, list) {
+		if (itr->ifindex == ifindex &&
+		    itr->app.selector == IEEE_8021QAZ_APP_SEL_ETHERTYPE &&
+		    itr->app.protocol == 0 &&
+		    itr->app.priority < IEEE_8021QAZ_MAX_TCS)
+			mask |= 1 << itr->app.priority;
+	}
+	spin_unlock_bh(&dcb_lock);
+
+	return mask;
+}
+EXPORT_SYMBOL(dcb_ieee_getapp_default_prio_mask);
+
 static int __init dcbnl_init(void)
 {
 	INIT_LIST_HEAD(&dcb_app_list);