Introduce "features" for the kernel backends returning kernel capabilities

src/libhydra/kernel/kernel_interface.c

@@ -137,6 +137,22 @@ struct private_kernel_interface_t {
 	bool ifaces_exclude;
 };
 
+METHOD(kernel_interface_t, get_features, kernel_feature_t,
+	private_kernel_interface_t *this)
+{
+	kernel_feature_t features = 0;
+
+	if (this->ipsec && this->ipsec->get_features)
+	{
+		features |= this->ipsec->get_features(this->ipsec);
+	}
+	if (this->net && this->net->get_features)
+	{
+		features |= this->net->get_features(this->net);
+	}
+	return features;
+}
+
 METHOD(kernel_interface_t, get_spi, status_t,
 	private_kernel_interface_t *this, host_t *src, host_t *dst,
 	u_int8_t protocol, u_int32_t reqid, u_int32_t *spi)
@@ -682,6 +698,7 @@ kernel_interface_t *kernel_interface_create()
 
 	INIT(this,
 		.public = {
+			.get_features = _get_features,
 			.get_spi = _get_spi,
 			.get_cpi = _get_cpi,
 			.add_sa = _add_sa,
@@ -757,4 +774,3 @@ kernel_interface_t *kernel_interface_create()
 
 	return &this->public;
 }
-

src/libhydra/kernel/kernel_interface.h

@@ -47,6 +47,7 @@
 #define KERNEL_INTERFACE_H_
 
 typedef struct kernel_interface_t kernel_interface_t;
+typedef enum kernel_feature_t kernel_feature_t;
 
 #include <networking/host.h>
 #include <crypto/prf_plus.h>
@@ -55,6 +56,17 @@ typedef struct kernel_interface_t kernel_interface_t;
 #include <kernel/kernel_ipsec.h>
 #include <kernel/kernel_net.h>
 
+/**
+ * Bitfield of optional features a kernel backend supports.
+ *
+ * This feature-set is for both, kernel_ipsec_t and kernel_net_t. Each
+ * backend returns a subset of these features.
+ */
+enum kernel_feature_t {
+	/** IPsec can process ESPv3 (RFC 4303) TFC padded packets */
+	KERNEL_ESP_V3_TFC = (1<<0),
+};
+
 /**
  * Constructor function for ipsec kernel interface
  */
@@ -73,6 +85,13 @@ typedef kernel_net_t* (*kernel_net_constructor_t)(void);
  */
 struct kernel_interface_t {
 
+	/**
+	 * Get the feature set supported by the net and ipsec kernel backends.
+	 *
+	 * @return				ORed feature-set of backends
+	 */
+	kernel_feature_t (*get_features)(kernel_interface_t *this);
+
 	/**
 	 * Get a SPI from the kernel.
 	 *

src/libhydra/kernel/kernel_ipsec.h

@@ -30,6 +30,7 @@ typedef struct kernel_ipsec_t kernel_ipsec_t;
 #include <ipsec/ipsec_types.h>
 #include <selectors/traffic_selector.h>
 #include <plugins/plugin.h>
+#include <kernel/kernel_interface.h>
 
 /**
  * Interface to the ipsec subsystem of the kernel.
@@ -44,6 +45,13 @@ typedef struct kernel_ipsec_t kernel_ipsec_t;
  */
 struct kernel_ipsec_t {
 
+	/**
+	 * Get the feature set supported by this kernel backend.
+	 *
+	 * @return				ORed feature-set of backend
+	 */
+	kernel_feature_t (*get_features)(kernel_ipsec_t *this);
+
 	/**
 	 * Get a SPI from the kernel.
 	 *

src/libhydra/kernel/kernel_net.h

@@ -28,6 +28,7 @@ typedef enum kernel_address_type_t kernel_address_type_t;
 #include <collections/enumerator.h>
 #include <networking/host.h>
 #include <plugins/plugin.h>
+#include <kernel/kernel_interface.h>
 
 /**
  * Type of addresses (e.g. when enumerating them)
@@ -55,6 +56,13 @@ enum kernel_address_type_t {
  */
 struct kernel_net_t {
 
+	/**
+	 * Get the feature set supported by this kernel backend.
+	 *
+	 * @return				ORed feature-set of backend
+	 */
+	kernel_feature_t (*get_features)(kernel_net_t *this);
+
 	/**
 	 * Get our outgoing source address for a destination.
 	 *