utils: document ENOBUFS in nfqnl_test.c

This patch documents the ENOBUFS error in the example file, that
is a common problem is that question over and over again in the
mailing list.

I (Pablo) have mangled this patch with some comestic cleanups. BTW,
Mistick Levi sent a similar patch in the same timeline (amazing how
sometimes the same works can clash).

Signed-off-by: Alessandro Vesely <vesely@tana.it>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

diff --git a/utils/nfqnl_test.c b/utils/nfqnl_test.c
index 9eebd9b..a554f2d 100644 (file)
--- a/utils/nfqnl_test.c
+++ b/utils/nfqnl_test.c
@@ -5,6 +5,7 @@
 #include <netinet/in.h>
 #include <linux/types.h>
 #include <linux/netfilter.h>           /* for NF_ACCEPT */
+#include <errno.h>
 
 #include <libnetfilter_queue/libnetfilter_queue.h>
 
@@ -115,9 +116,25 @@ int main(int argc, char **argv)
 
        fd = nfq_fd(h);
 
-       while ((rv = recv(fd, buf, sizeof(buf), 0)) && rv >= 0) {
-               printf("pkt received\n");
-               nfq_handle_packet(h, buf, rv);
+       for (;;) {
+               if ((rv = recv(fd, buf, sizeof(buf), 0)) >= 0) {
+                       printf("pkt received\n");
+                       nfq_handle_packet(h, buf, rv);
+                       continue;
+               }
+               /* if your application is too slow to digest the packets that
+                * are sent from kernel-space, the socket buffer that we use
+                * to enqueue packets may fill up returning ENOBUFS. Depending
+                * on your application, this error may be ignored. Please, see
+                * the doxygen documentation of this library on how to improve
+                * this situation.
+                */
+               if (rv < 0 && errno == ENOBUFS) {
+                       printf("losing packets!\n");
+                       continue;
+               }
+               perror("recv failed");
+               break;
        }
 
        printf("unbinding from queue 0\n");