bus: add method to find device

This new method allows buses to expose their devices in a controlled
manner. A comparison function is provided by the user to discriminate
between devices, using arbitrary data as identifier.

It is possible to start an iteration from a specific point, in order to
continue a search.

Signed-off-by: Jan Blunck <jblunck@infradead.org>
Signed-off-by: Gaetan Rivet <gaetan.rivet@6wind.com>

lib/librte_eal/common/include/rte_bus.h

@@ -81,6 +81,32 @@ typedef int (*rte_bus_scan_t)(void);
  */
 typedef int (*rte_bus_probe_t)(void);
 
+/**
+ * Device iterator to find a device on a bus.
+ *
+ * This function returns an rte_device if one of those held by the bus
+ * matches the data passed as parameter.
+ *
+ * If the comparison function returns zero this function should stop iterating
+ * over any more devices. To continue a search the device of a previous search
+ * can be passed via the start parameter.
+ *
+ * @param cmp
+ *	Comparison function.
+ *
+ * @param data
+ *	Data to compare each device against.
+ *
+ * @param start
+ *	starting point for the iteration
+ *
+ * @return
+ *	The first device matching the data, NULL if none exists.
+ */
+typedef struct rte_device *
+(*rte_bus_find_device_t)(const struct rte_device *start, rte_dev_cmp_t cmp,
+			 const void *data);
+
 /**
  * A structure describing a generic bus.
  */
@@ -89,6 +115,7 @@ struct rte_bus {
 	const char *name;            /**< Name of the bus */
 	rte_bus_scan_t scan;         /**< Scan for devices attached to bus */
 	rte_bus_probe_t probe;       /**< Probe devices on bus */
+	rte_bus_find_device_t find_device; /**< Find a device on the bus */
 };
 
 /**

lib/librte_eal/common/include/rte_dev.h

@@ -191,6 +191,27 @@ int rte_eal_dev_attach(const char *name, const char *devargs);
  */
 int rte_eal_dev_detach(const char *name);
 
+/**
+ * Device comparison function.
+ *
+ * This type of function is used to compare an rte_device with arbitrary
+ * data.
+ *
+ * @param dev
+ *   Device handle.
+ *
+ * @param data
+ *   Data to compare against. The type of this parameter is determined by
+ *   the kind of comparison performed by the function.
+ *
+ * @return
+ *   0 if the device matches the data.
+ *   !0 if the device does not match.
+ *   <0 if ordering is possible and the device is lower than the data.
+ *   >0 if ordering is possible and the device is greater than the data.
+ */
+typedef int (*rte_dev_cmp_t)(const struct rte_device *dev, const void *data);
+
 #define RTE_PMD_EXPORT_NAME_ARRAY(n, idx) n##idx[]
 
 #define RTE_PMD_EXPORT_NAME(name, idx) \