examples/nf-queue: handle recv error, use larger buffer

We ask for 0xffff copy size, so we need a buffer that can
hold 0xffff, plus a few more bytes to allow for netlink attributes.

Also, turn off/handle ENOBUFS.

Signed-off-by: Florian Westphal <fw@strlen.de>

diff --git a/examples/nf-queue.c b/examples/nf-queue.c
index 7adac21..6641a24 100644 (file)
--- a/examples/nf-queue.c
+++ b/examples/nf-queue.c
@@ -1,3 +1,4 @@
+#include <errno.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <unistd.h>
@@ -82,7 +83,9 @@ static int queue_cb(const struct nlmsghdr *nlh, void *data)
 
 int main(int argc, char *argv[])
 {
-       char buf[MNL_SOCKET_BUFFER_SIZE];
+       char *buf;
+       /* largest possible packet payload, plus netlink data overhead: */
+       size_t sizeof_buf = 0xffff + (MNL_SOCKET_BUFFER_SIZE/2);
        struct nlmsghdr *nlh;
        int ret;
        unsigned int portid, queue_num;
@@ -105,6 +108,12 @@ int main(int argc, char *argv[])
        }
        portid = mnl_socket_get_portid(nl);
 
+       buf = malloc(sizeof_buf);
+       if (!buf) {
+               perror("allocate receive buffer");
+               exit(EXIT_FAILURE);
+       }
+
        nlh = nfq_hdr_put(buf, NFQNL_MSG_CONFIG, 0);
        nfq_nlmsg_cfg_put_cmd(nlh, AF_INET, NFQNL_CFG_CMD_PF_UNBIND);
 
@@ -137,23 +146,25 @@ int main(int argc, char *argv[])
                exit(EXIT_FAILURE);
        }
 
-       ret = mnl_socket_recvfrom(nl, buf, sizeof(buf));
-       if (ret == -1) {
-               perror("mnl_socket_recvfrom");
-               exit(EXIT_FAILURE);
-       }
-       while (ret > 0) {
-               ret = mnl_cb_run(buf, ret, 0, portid, queue_cb, NULL);
-               if (ret < 0){
-                       perror("mnl_cb_run");
-                       exit(EXIT_FAILURE);
-               }
+       /* ENOBUFS is signalled to userspace when packets were lost
+        * on kernel side.  In most cases, userspace isn't interested
+        * in this information, so turn it off.
+        */
+       ret = 1;
+       mnl_socket_setsockopt(nl, NETLINK_NO_ENOBUFS, &ret, sizeof(int));
 
-               ret = mnl_socket_recvfrom(nl, buf, sizeof(buf));
+       for (;;) {
+               ret = mnl_socket_recvfrom(nl, buf, sizeof_buf);
                if (ret == -1) {
                        perror("mnl_socket_recvfrom");
                        exit(EXIT_FAILURE);
                }
+
+               ret = mnl_cb_run(buf, ret, 0, portid, queue_cb, NULL);
+               if (ret < 0){
+                       perror("mnl_cb_run");
+                       exit(EXIT_FAILURE);
+               }
        }
 
        mnl_socket_close(nl);