netdev: Allow recv, recv_wait, drain, send, send_wait to be null.

Suggested by partner.

diff --git a/lib/netdev-provider.h b/lib/netdev-provider.h
index 1eb1b1e..e1c18cc 100644 (file)
--- a/lib/netdev-provider.h
+++ b/lib/netdev-provider.h
@@ -175,15 +175,28 @@ struct netdev_class {
     /* Attempts to receive a packet from 'netdev' into the 'size' bytes in
      * 'buffer'.  If successful, returns the number of bytes in the received
      * packet, otherwise a negative errno value.  Returns -EAGAIN immediately
-     * if no packet is ready to be received. */
+     * if no packet is ready to be received.
+     *
+     * May return -EOPNOTSUPP if a network device does not implement packet
+     * reception through this interface.  This function may be set to null if
+     * it would always return -EOPNOTSUPP anyhow.  (This will disable the OVS
+     * integrated DHCP client and OpenFlow controller discovery, and prevent
+     * the network device from being usefully used by the netdev-based
+     * "userspace datapath".) */
     int (*recv)(struct netdev *netdev, void *buffer, size_t size);
 
     /* Registers with the poll loop to wake up from the next call to
      * poll_block() when a packet is ready to be received with netdev_recv() on
-     * 'netdev'. */
+     * 'netdev'.
+     *
+     * May be null if not needed, such as for a network device that does not
+     * implement packet reception through the 'recv' member function. */
     void (*recv_wait)(struct netdev *netdev);
 
-    /* Discards all packets waiting to be received from 'netdev'. */
+    /* Discards all packets waiting to be received from 'netdev'.
+     *
+     * May be null if not needed, such as for a network device that does not
+     * implement packet reception through the 'recv' member function. */
     int (*drain)(struct netdev *netdev);
 
     /* Sends the 'size'-byte packet in 'buffer' on 'netdev'.  Returns 0 if
@@ -196,7 +209,14 @@ struct netdev_class {
      *
      * The network device is expected to maintain a packet transmission queue,
      * so that the caller does not ordinarily have to do additional queuing of
-     * packets. */
+     * packets.
+     *
+     * May return EOPNOTSUPP if a network device does not implement packet
+     * transmission through this interface.  This function may be set to null
+     * if it would always return EOPNOTSUPP anyhow.  (This will disable the OVS
+     * integrated DHCP client and OpenFlow controller discovery, and prevent
+     * the network device from being usefully used by the netdev-based
+     * "userspace datapath".) */
     int (*send)(struct netdev *netdev, const void *buffer, size_t size);
 
     /* Registers with the poll loop to wake up from the next call to
@@ -205,7 +225,10 @@ struct netdev_class {
      *
      * The network device is expected to maintain a packet transmission queue,
      * so that the caller does not ordinarily have to do additional queuing of
-     * packets.  Thus, this function is unlikely to ever be useful. */
+     * packets.  Thus, this function is unlikely to ever be useful.
+     *
+     * May be null if not needed, such as for a network device that does not
+     * implement packet transmission through the 'send' member function. */
     void (*send_wait)(struct netdev *netdev);
 
     /* Sets 'netdev''s Ethernet address to 'mac' */

diff --git a/lib/netdev.c b/lib/netdev.c
index 2c7b260..99b5d24 100644 (file)
--- a/lib/netdev.c
+++ b/lib/netdev.c
@@ -472,17 +472,23 @@ netdev_enumerate(struct svec *svec)
  * guaranteed to contain at least ETH_TOTAL_MIN bytes.  Otherwise, returns a
  * positive errno value.  Returns EAGAIN immediately if no packet is ready to
  * be returned.
+ *
+ * Some network devices may not implement support for this function.  In such
+ * cases this function will always return EOPNOTSUPP.
  */
 int
 netdev_recv(struct netdev *netdev, struct ofpbuf *buffer)
 {
+    int (*recv)(struct netdev *, void *, size_t);
     int retval;
 
     assert(buffer->size == 0);
     assert(ofpbuf_tailroom(buffer) >= ETH_TOTAL_MIN);
 
-    retval = netdev_get_dev(netdev)->netdev_class->recv(netdev, buffer->data,
-             ofpbuf_tailroom(buffer));
+    recv = netdev_get_dev(netdev)->netdev_class->recv;
+    retval = (recv
+              ? (recv)(netdev, buffer->data, ofpbuf_tailroom(buffer))
+              : -EOPNOTSUPP);
     if (retval >= 0) {
         COVERAGE_INC(netdev_received);
         buffer->size += retval;
@@ -500,14 +506,22 @@ netdev_recv(struct netdev *netdev, struct ofpbuf *buffer)
 void
 netdev_recv_wait(struct netdev *netdev)
 {
-    netdev_get_dev(netdev)->netdev_class->recv_wait(netdev);
+    void (*recv_wait)(struct netdev *);
+
+    recv_wait = netdev_get_dev(netdev)->netdev_class->recv_wait;
+    if (recv_wait) {
+        recv_wait(netdev);
+    }
 }
 
 /* Discards all packets waiting to be received from 'netdev'. */
 int
 netdev_drain(struct netdev *netdev)
 {
-    return netdev_get_dev(netdev)->netdev_class->drain(netdev);
+    int (*drain)(struct netdev *);
+
+    drain = netdev_get_dev(netdev)->netdev_class->drain;
+    return drain ? drain(netdev) : 0;
 }
 
 /* Sends 'buffer' on 'netdev'.  Returns 0 if successful, otherwise a positive
@@ -518,12 +532,18 @@ netdev_drain(struct netdev *netdev)
  * The caller retains ownership of 'buffer' in all cases.
  *
  * The kernel maintains a packet transmission queue, so the caller is not
- * expected to do additional queuing of packets. */
+ * expected to do additional queuing of packets.
+ *
+ * Some network devices may not implement support for this function.  In such
+ * cases this function will always return EOPNOTSUPP. */
 int
 netdev_send(struct netdev *netdev, const struct ofpbuf *buffer)
 {
-    int error = netdev_get_dev(netdev)->netdev_class->send(netdev, 
-            buffer->data, buffer->size);
+    int (*send)(struct netdev *, const void *, size_t);
+    int error;
+
+    send = netdev_get_dev(netdev)->netdev_class->send;
+    error = send ? (send)(netdev, buffer->data, buffer->size) : EOPNOTSUPP;
     if (!error) {
         COVERAGE_INC(netdev_sent);
     }
@@ -540,7 +560,12 @@ netdev_send(struct netdev *netdev, const struct ofpbuf *buffer)
 void
 netdev_send_wait(struct netdev *netdev)
 {
-    return netdev_get_dev(netdev)->netdev_class->send_wait(netdev);
+    void (*send_wait)(struct netdev *);
+
+    send_wait = netdev_get_dev(netdev)->netdev_class->send_wait;
+    if (send_wait) {
+        send_wait(netdev);
+    }
 }
 
 /* Attempts to set 'netdev''s MAC address to 'mac'.  Returns 0 if successful,