From c3636005831064e71b03a5f8796a21e89b2a714f Mon Sep 17 00:00:00 2001
From: Dimitri Staessens <dimitri@ouroboros.rocks>
Date: Thu, 19 Feb 2026 22:03:16 +0100
Subject: irmd: Allow direct rbuff between local processes

This allows bypassing the IPCP for local processes that share the same
packet pool, lowering latency between processes to comparable levels
as Unix sockets (RTT in the order of a microsecond).

For local processes, no IPCPs are needed:

 $ irm b prog oping n oping
 $ oping -l
 Ouroboros ping server started.
 New flow 64.
 Received 64 bytes on fd 64.

The direct IPC can be disabled with the DISABLE_DIRECT_IPC build
flag. Note that this is needed for rumba 'local' experiments to
emulate network topologies. Without this flag all processes will just
communicate directly.

Signed-off-by: Dimitri Staessens <dimitri@ouroboros.rocks>
Signed-off-by: Sander Vrijders <sander@ouroboros.rocks>
---
 src/tools/oping/oping_server.c | 68 ++++++++++++++++++++++++++++++++++++++----
 1 file changed, 62 insertions(+), 6 deletions(-)

(limited to 'src/tools/oping/oping_server.c')

diff --git a/src/tools/oping/oping_server.c b/src/tools/oping/oping_server.c
index 1670ebf3..33af28c4 100644
--- a/src/tools/oping/oping_server.c
+++ b/src/tools/oping/oping_server.c
@@ -138,7 +138,10 @@ void * accept_thread(void * o)
 
         (void) o;
 
-        printf("Ouroboros ping server started.\n");
+        printf("Ouroboros ping server started.");
+        if (server.busy)
+                printf(" [busy-poll]");
+        printf("\n");
 
         while (true) {
                 fd = flow_accept(&qs, NULL);
@@ -158,12 +161,56 @@ void * accept_thread(void * o)
                 pthread_mutex_unlock(&server.lock);
 
                 fccntl(fd, FLOWSFLAGS,
-                       FLOWFRNOBLOCK | FLOWFRDWR | FLOWFRNOPART);
+                       FLOWFRNOBLOCK | FLOWFRDWR
+                       | FLOWFRNOPART);
         }
 
         return (void *) 0;
 }
 
+void * busy_thread(void * o)
+{
+        char buf[OPING_BUF_SIZE];
+        struct oping_msg * msg = (struct oping_msg *) buf;
+        int    fd;
+        int    msg_len;
+
+        (void) o;
+
+        /* Accept a single flow. */
+        fd = flow_accept(NULL, NULL);
+        if (fd < 0) {
+                printf("Failed to accept flow.\n");
+                return (void *) -1;
+        }
+
+        printf("New flow %d (busy-poll).\n", fd);
+
+        fccntl(fd, FLOWSFLAGS,
+               FLOWFRNOBLOCK | FLOWFRDWR
+               | FLOWFRNOPART);
+
+        while (true) {
+                msg_len = flow_read(fd, buf,
+                                    OPING_BUF_SIZE);
+                if (msg_len == -EAGAIN)
+                        continue;
+                if (msg_len < 0)
+                        break;
+
+                if (ntohl(msg->type) != ECHO_REQUEST)
+                        continue;
+
+                msg->type = htonl(ECHO_REPLY);
+
+                flow_write(fd, buf, msg_len);
+        }
+
+        flow_dealloc(fd);
+
+        return (void *) 0;
+}
+
 int server_main(void)
 {
         struct sigaction sig_act;
@@ -191,12 +238,21 @@ int server_main(void)
         }
 
         pthread_create(&server.cleaner_pt, NULL, cleaner_thread, NULL);
-        pthread_create(&server.accept_pt, NULL, accept_thread, NULL);
-        pthread_create(&server.server_pt, NULL, server_thread, NULL);
 
-        pthread_join(server.accept_pt, NULL);
+        if (server.busy) {
+                pthread_create(&server.server_pt, NULL,
+                               busy_thread, NULL);
+                pthread_join(server.server_pt, NULL);
+                pthread_cancel(server.cleaner_pt);
+        } else {
+                pthread_create(&server.accept_pt, NULL,
+                               accept_thread, NULL);
+                pthread_create(&server.server_pt, NULL,
+                               server_thread, NULL);
+                pthread_join(server.accept_pt, NULL);
+                pthread_cancel(server.server_pt);
+        }
 
-        pthread_cancel(server.server_pt);
         pthread_cancel(server.cleaner_pt);
 
         fset_destroy(server.flows);
-- 
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