The test tool can check that the zerocopy number of completions value is
valid taking into consideration the number of datagram send calls. This can
catch the system into a state where the datagrams are still in the system
(for example in a qdisk, waiting for the network interface to return a
completion notification, etc).

This change adds a retry logic of computing the number of completions up to
a configurable (via CLI) timeout (default: 2 seconds).

Fixes: 79ebc3c26010 ("net/udpgso_bench_tx: options to exercise TX CMSG")
Signed-off-by: Andrei Gherzan <redacted>
Cc: Willem de Bruijn <willemb@google.com>
Cc: Paolo Abeni <pabeni@redhat.com>
---
 tools/testing/selftests/net/udpgso_bench_tx.c | 34 +++++++++++++++----
 1 file changed, 27 insertions(+), 7 deletions(-)

diff --git a/tools/testing/selftests/net/udpgso_bench_tx.c b/tools/testing/selftests/net/udpgso_bench_tx.c
index b47b5c32039f..ef887842522a 100644
--- a/tools/testing/selftests/net/udpgso_bench_tx.c
+++ b/tools/testing/selftests/net/udpgso_bench_tx.c

@@ -62,6 +62,7 @@ static int    cfg_payload_len = (1472 * 42);
 static int     cfg_port        = 8000;
 static int     cfg_runtime_ms  = -1;
 static bool    cfg_poll;
+static int     cfg_poll_loop_timeout_ms = 2000;
 static bool    cfg_segment;
 static bool    cfg_sendmmsg;
 static bool    cfg_tcp;

@@ -235,16 +236,17 @@ static void flush_errqueue_recv(int fd)
        }
 }

-static void flush_errqueue(int fd, const bool do_poll)
+static void flush_errqueue(int fd, const bool do_poll,
+               unsigned long poll_timeout, const bool poll_err)

 {
        if (do_poll) {
                struct pollfd fds = {0};
                int ret;

                fds.fd = fd;
-               ret = poll(&fds, 1, 500);
+               ret = poll(&fds, 1, poll_timeout);
                if (ret == 0) {
-                       if (cfg_verbose)
+                       if ((cfg_verbose) && (poll_err))
                                fprintf(stderr, "poll timeout\n");
                } else if (ret < 0) {
                        error(1, errno, "poll");

@@ -254,6 +256,20 @@ static void flush_errqueue(int fd, const bool do_poll)
        flush_errqueue_recv(fd);
 }