event_iface: only set rcv buf size if too small

Instead of always setting the receive buffer size
to a small 8K, which causes problems when a flood of
netlink messages are received, set it to a
"minimal" value only if it is currently less
than that value.

The value used is 32 x the MAX_PAYLOAD size
of 4k, i.e. 128k.

A config value to modify this can be added if needed,
but doesn't seem warranted at this time.

Changes in V2:
* remove unneeded debugging/logging

Acked-by: Aaron Conole <aconole@redhat.com>

event_iface.c

@@ -418,18 +418,27 @@ event_iface_receive(int sock, UNUSED void *eloop_ctx, UNUSED void *sock_ctx)
 int event_iface_init()
 {
 	int fd;
-	int rcv_size = MAX_PAYLOAD;
+	int rcv_size = 0;
+	socklen_t rcv_len = sizeof(int);
 	struct sockaddr_nl snl;
 
 	fd = socket(PF_NETLINK, SOCK_RAW, NETLINK_ROUTE);
 
 	if (fd < 0)
 		return fd;
 
-	if (setsockopt(fd, SOL_SOCKET, SO_RCVBUF, &rcv_size, sizeof(int)) < 0) {
+	/* is receive buffer size too small? */
+	if (getsockopt(fd, SOL_SOCKET, SO_RCVBUF, &rcv_size, &rcv_len) < 0) {
 		close(fd);
 		return -EIO;
 	}
+	if (rcv_size < MIN_RCVBUF_SIZE) {
+		rcv_size = MIN_RCVBUF_SIZE >> 1;	/* we get back 2x what we set */
+		if (setsockopt(fd, SOL_SOCKET, SO_RCVBUF, &rcv_size, rcv_len) < 0) {
+			close(fd);
+			return -EIO;
+		}
+	}
 
 	memset((void *)&snl, 0, sizeof(struct sockaddr_nl));
 	snl.nl_family = AF_NETLINK;

include/qbg_vdpnl.h

@@ -33,6 +33,7 @@
 #include <linux/if_ether.h>
 
 #define	MAX_PAYLOAD	4096	/* Maximum Payload Size */
+#define	MIN_RCVBUF_SIZE	(MAX_PAYLOAD << 5)	/* SO_RCVBUF min */
 
 enum {
 	vdpnl_nlf1 = 1,		/* Netlink message format 1 (draft 0.2) */