Convert RTP/RTCP/OSMUX I/O from osmo_fd to osmo_ioHEADmaster

Converting from osmo_fd to osmo_io allows us to switch to the new
io_uring backend and benefit from related performance benefits.

In a benchmark running 200 concurrent bi-directional voice calls with
GSM-EFR codec, I am observing:

* the code before this patch uses 40..42% of a single core on a
  Ryzen 5950X at 200 calls (=> 200 endpoints with each two connections)

* no increase in CPU utilization before/after this patch, i.e. the
  osmo_io overhead for the osmo_fd backend is insignificant compared
  to the direct osmo_fd mode before

* an almost exactly 50% reduction of CPU utilization when running the
  same osmo-mgw build with LIBOSMO_IO_BACKEND=IO_URING - top shows
  19..21% for the same workload instead of 40..42% with the OSMO_FD
  default backend.

* An increase of about 4 Megabytes in both RSS and VIRT size when
  enabling the OSMO_IO backend.  This is likely the memory-mapped rings.

No memory leakage is observed when using either of the backends.

Change-Id: I8471960d5d8088a70cf105f2f40dfa5d5458169a

7 files changed, 204 insertions, 169 deletions

diff --git a/include/osmocom/mgcp/mgcp.h b/include/osmocom/mgcp/mgcp.h
index e61ba890c..4dff4d086 100644
--- a/include/osmocom/mgcp/mgcp.h
+++ b/include/osmocom/mgcp/mgcp.h
@@ -24,6 +24,7 @@
 
 #include <osmocom/core/msgb.h>
 #include <osmocom/core/socket.h>
+#include <osmocom/core/osmo_io.h>
 #include <osmocom/core/write_queue.h>
 #include <osmocom/core/timer.h>
 #include <osmocom/core/logging.h>
@@ -205,4 +206,4 @@ int mgcp_send_reset_all(struct mgcp_config *cfg);
 
 
 int mgcp_create_bind(const char *source_addr, int port, uint8_t dscp, uint8_t prio);
-int mgcp_udp_send(int fd, const struct osmo_sockaddr *addr, const char *buf, int len);
+int mgcp_udp_send(struct osmo_io_fd *iofd, const struct osmo_sockaddr *addr, const char *buf, int len);
diff --git a/include/osmocom/mgcp/mgcp_network.h b/include/osmocom/mgcp/mgcp_network.h
index 1ec897936..8f6505c11 100644
--- a/include/osmocom/mgcp/mgcp_network.h
+++ b/include/osmocom/mgcp/mgcp_network.h
@@ -4,6 +4,7 @@
 #include <stdbool.h>
 
 #include <osmocom/core/socket.h>
+#include <osmocom/core/osmo_io.h>
 
 #include <osmocom/mgcp/mgcp.h>
 
@@ -120,8 +121,8 @@ struct mgcp_rtp_end {
 	bool rfc5993_hr_convert;
 
 	/* Each end has a separate socket for RTP and RTCP */
-	struct osmo_fd rtp;
-	struct osmo_fd rtcp;
+	struct osmo_io_fd *rtp;
+	struct osmo_io_fd *rtcp;
 
 	/* local UDP port number of the RTP socket; RTCP is +1 */
 	int local_port;
@@ -179,7 +180,7 @@ void rtpconn_rate_ctr_add(struct mgcp_conn_rtp *conn_rtp, struct mgcp_endpoint *
 				 int id, int inc);
 void rtpconn_rate_ctr_inc(struct mgcp_conn_rtp *conn_rtp, struct mgcp_endpoint *endp,
 				 int id);
-void forward_data_tap(int fd, struct mgcp_rtp_tap *tap, struct msgb *msg);
+void forward_data_tap(struct osmo_io_fd *iofd, struct mgcp_rtp_tap *tap, struct msgb *msg);
 uint32_t mgcp_get_current_ts(unsigned codec_rate);
 
 int amr_oa_bwe_convert(struct mgcp_endpoint *endp, struct msgb *msg, bool target_is_oa);
diff --git a/src/libosmo-mgcp/mgcp_conn.c b/src/libosmo-mgcp/mgcp_conn.c
index d9bc57371..5eb48971c 100644
--- a/src/libosmo-mgcp/mgcp_conn.c
+++ b/src/libosmo-mgcp/mgcp_conn.c
@@ -106,8 +106,8 @@ static int mgcp_rtp_conn_init(struct mgcp_conn_rtp *conn_rtp, struct mgcp_conn *
 	/* backpointer to the generic part of the connection */
 	conn->u.rtp.conn = conn;
 
-	end->rtp.fd = -1;
-	end->rtcp.fd = -1;
+	end->rtp = NULL;
+	end->rtcp = NULL;
 	memset(&end->addr, 0, sizeof(end->addr));
 	end->rtcp_port = 0;
 
diff --git a/src/libosmo-mgcp/mgcp_iuup.c b/src/libosmo-mgcp/mgcp_iuup.c
index 3818d3e23..7531e42ce 100644
--- a/src/libosmo-mgcp/mgcp_iuup.c
+++ b/src/libosmo-mgcp/mgcp_iuup.c
@@ -512,10 +512,9 @@ static int mgcp_send_iuup(struct mgcp_endpoint *endp, struct msgb *msg,
 		 osmo_sockaddr_port(&rtp_end->addr.u.sa), ntohs(rtp_end->rtcp_port));
 
 	/* Forward a copy of the RTP data to a debug ip/port */
-	forward_data_tap(rtp_end->rtp.fd, &conn_src->tap_out,
-		     msg);
+	forward_data_tap(rtp_end->rtp, &conn_src->tap_out, msg);
 
-	len = mgcp_udp_send(rtp_end->rtp.fd, &rtp_end->addr, (char *)hdr, buflen);
+	len = mgcp_udp_send(rtp_end->rtp, &rtp_end->addr, (char *)hdr, buflen);
 
 	if (len <= 0)
 		return len;
diff --git a/src/libosmo-mgcp/mgcp_network.c b/src/libosmo-mgcp/mgcp_network.c
index bdf516e70..1fc2c56cd 100644
--- a/src/libosmo-mgcp/mgcp_network.c
+++ b/src/libosmo-mgcp/mgcp_network.c
@@ -4,6 +4,7 @@
 /*
  * (C) 2009-2012 by Holger Hans Peter Freyther <zecke@selfish.org>
  * (C) 2009-2012 by On-Waves
+ * (C) 2013-2024 by sysmocom - s.f.m.c. GmbH
  * All Rights Reserved
  *
  * This program is free software; you can redistribute it and/or modify
@@ -794,16 +795,18 @@ static int amr_oa_check(char *data, int len)
 
 /* Forward data to a debug tap. This is debug function that is intended for
  * debugging the voice traffic with tools like gstreamer */
-void forward_data_tap(int fd, struct mgcp_rtp_tap *tap, struct msgb *msg)
+void forward_data_tap(struct osmo_io_fd *iofd, struct mgcp_rtp_tap *tap, struct msgb *msg)
 {
 	int rc;
 
 	if (!tap->enabled)
 		return;
 
-	rc = sendto(fd, msgb_data(msg), msgb_length(msg), 0, (struct sockaddr *)&tap->forward,
-		    sizeof(tap->forward));
+	struct msgb *msg2 = msgb_copy(msg, "RTP TAP Tx");
+	if (!msg2)
+		return;
 
+	rc = osmo_iofd_sendto_msgb(iofd, msg2, 0, &tap->forward);
 	if (rc < 0)
 		LOGP(DRTP, LOGL_ERROR,
 		     "Forwarding tapped (debug) voice data failed.\n");
@@ -1039,29 +1042,36 @@ static int mgcp_conn_rtp_dispatch_rtp(struct mgcp_conn_rtp *conn_dst, struct msg
 	return -1;
 }
 
-/*! send udp packet.
- *  \param[in] fd associated file descriptor.
+/*! send message buffer via udp socket.  If it succeeds, it takes ownership of the msgb and internally calls
+ *  msgb_free() after the aynchronous sendto() completes.  In case of error, the msgb is still owned by the
+ *  caller and must be free'd accordingly.
+ *  \param[in] iofd associated file descriptor.
+ *  \param[in] addr destination ip-address.
+ *  \param[in] msg message buffer that holds the data to be send.
+ *  \returns 0 in case of success (takes msgb ownership), -1 on error (doesn't take msgb ownership). */
+static int mgcp_udp_send_msg(struct osmo_io_fd *iofd, const struct osmo_sockaddr *addr, struct msgb *msg)
+{
+	LOGP(DRTP, LOGL_DEBUG, "sending %d bytes length packet to %s ...\n", msgb_length(msg),
+	     osmo_sockaddr_to_str(addr));
+
+	return osmo_iofd_sendto_msgb(iofd, msg, 0, addr);
+}
+
+/*! send udp packet from raw buffer/length.
+ *  \param[in] iofd associated file descriptor.
  *  \param[in] addr destination ip-address.
  *  \param[in] buf buffer that holds the data to be send.
  *  \param[in] len length of the data to be sent.
  *  \returns bytes sent, -1 on error. */
-int mgcp_udp_send(int fd, const struct osmo_sockaddr *addr, const char *buf, int len)
+int mgcp_udp_send(struct osmo_io_fd *iofd, const struct osmo_sockaddr *addr, const char *buf, int len)
 {
-	char ipbuf[INET6_ADDRSTRLEN];
-	size_t addr_len;
-
-	LOGP(DRTP, LOGL_DEBUG,
-	     "sending %d bytes length packet to %s:%u ...\n", len,
-	     osmo_sockaddr_ntop(&addr->u.sa, ipbuf),
-	     osmo_sockaddr_port(&addr->u.sa));
-
-	if (addr->u.sa.sa_family == AF_INET6) {
-		addr_len = sizeof(addr->u.sin6);
-	} else {
-		addr_len = sizeof(addr->u.sin);
-	}
+	struct msgb *msg = msgb_alloc_c(iofd, len, "mgcp_udp_send");
+	if (!msg)
+		return -ENOMEM;
+	memcpy(msg->tail, buf, len);
+	msgb_put(msg, len);
 
-	return sendto(fd, buf, len, 0, &addr->u.sa, addr_len);
+	return mgcp_udp_send_msg(iofd, addr, msg);
 }
 
 /*! send RTP dummy packet (to keep NAT connection open).
@@ -1089,8 +1099,7 @@ int mgcp_send_dummy(struct mgcp_endpoint *endp, struct mgcp_conn_rtp *conn)
 	if (mgcp_conn_rtp_is_iuup(conn))
 		rc = mgcp_conn_iuup_send_dummy(conn);
 	else
-		rc = mgcp_udp_send(conn->end.rtp.fd, &conn->end.addr,
-				   rtp_dummy_payload, sizeof(rtp_dummy_payload));
+		rc = mgcp_udp_send(conn->end.rtp, &conn->end.addr, rtp_dummy_payload, sizeof(rtp_dummy_payload));
 
 	if (rc == -1)
 		goto failed;
@@ -1101,7 +1110,7 @@ int mgcp_send_dummy(struct mgcp_endpoint *endp, struct mgcp_conn_rtp *conn)
 	was_rtcp = 1;
 	rtcp_addr = conn->end.addr;
 	osmo_sockaddr_set_port(&rtcp_addr.u.sa, ntohs(conn->end.rtcp_port));
-	rc = mgcp_udp_send(conn->end.rtcp.fd, &rtcp_addr,
+	rc = mgcp_udp_send(conn->end.rtcp, &rtcp_addr,
 			   rtp_dummy_payload, sizeof(rtp_dummy_payload));
 
 	if (rc >= 0)
@@ -1225,22 +1234,21 @@ int mgcp_send(struct mgcp_endpoint *endp, int is_rtp, struct osmo_sockaddr *addr
 			);
 
 		/* Forward a copy of the RTP data to a debug ip/port */
-		forward_data_tap(rtp_end->rtp.fd, &conn_src->tap_out,
-			     msg);
+		forward_data_tap(rtp_end->rtp, &conn_src->tap_out, msg);
+
+		len = msgb_length(msg);
 
-		len = mgcp_udp_send(rtp_end->rtp.fd, &rtp_end->addr,
-				    (char *)msgb_data(msg), msgb_length(msg));
-		if (len <= 0) {
+		rc = mgcp_udp_send_msg(rtp_end->rtp, &rtp_end->addr, msg);
+		if (rc < 0) {
 			msgb_free(msg);
-			return len;
+			return rc;
 		}
 
 		rtpconn_rate_ctr_inc(conn_dst, endp, RTP_PACKETS_TX_CTR);
 		rtpconn_rate_ctr_add(conn_dst, endp, RTP_OCTETS_TX_CTR, len);
 		rtp_state->alt_rtp_tx_sequence++;
 
-		msgb_free(msg);
-		return len;
+		return 0;
 	} else if (!trunk->omit_rtcp) {
 		struct osmo_sockaddr rtcp_addr = rtp_end->addr;
 		osmo_sockaddr_set_port(&rtcp_addr.u.sa, rtp_end->rtcp_port);
@@ -1251,15 +1259,19 @@ int mgcp_send(struct mgcp_endpoint *endp, int is_rtp, struct osmo_sockaddr *addr
 			 osmo_sockaddr_port(&rtcp_addr.u.sa)
 			);
 
-		len = mgcp_udp_send(rtp_end->rtcp.fd, &rtcp_addr,
-				    (char *)msgb_data(msg), msgb_length(msg));
+		len = msgb_length(msg);
+
+		rc = mgcp_udp_send_msg(rtp_end->rtcp, &rtcp_addr, msg);
+		if (rc < 0) {
+			msgb_free(msg);
+			return rc;
+		}
 
 		rtpconn_rate_ctr_inc(conn_dst, endp, RTP_PACKETS_TX_CTR);
 		rtpconn_rate_ctr_add(conn_dst, endp, RTP_OCTETS_TX_CTR, len);
 		rtp_state->alt_rtp_tx_sequence++;
 
-		msgb_free(msg);
-		return len;
+		return 0;
 	}
 
 	msgb_free(msg);
@@ -1461,7 +1473,7 @@ void mgcp_cleanup_e1_bridge_cb(struct mgcp_endpoint *endp, struct mgcp_conn *con
 }
 
 /* Handle incoming RTP data from NET */
-static int rtp_data_net(struct osmo_fd *fd, unsigned int what)
+static void rtp_recvfrom_cb(struct osmo_io_fd *iofd, int res, struct msgb *msg, const struct osmo_sockaddr *saddr)
 {
 	/* NOTE: This is a generic implementation. RTP data is received. In
 	 * case of loopback the data is just sent back to its origin. All
@@ -1472,49 +1484,34 @@ static int rtp_data_net(struct osmo_fd *fd, unsigned int what)
 
 	struct mgcp_conn_rtp *conn_src;
 	struct mgcp_endpoint *endp;
-	struct osmo_sockaddr addr;
-	socklen_t slen = sizeof(addr);
-	char ipbuf[INET6_ADDRSTRLEN];
-	int ret;
 	enum rtp_proto proto;
 	struct osmo_rtp_msg_ctx *mc;
-	struct msgb *msg;
-	int rc;
 
-	conn_src = (struct mgcp_conn_rtp *)fd->data;
+	conn_src = (struct mgcp_conn_rtp *) osmo_iofd_get_data(iofd);
 	OSMO_ASSERT(conn_src);
 	endp = conn_src->conn->endp;
 	OSMO_ASSERT(endp);
-	msg = msgb_alloc_c(endp->trunk, RTP_BUF_SIZE, "RTP-rx");
 
-	proto = (fd == &conn_src->end.rtp) ? MGCP_PROTO_RTP : MGCP_PROTO_RTCP;
+	proto = (iofd == conn_src->end.rtp) ? MGCP_PROTO_RTP : MGCP_PROTO_RTCP;
 
-	ret = recvfrom(fd->fd, msgb_data(msg), msg->data_len, 0, (struct sockaddr *)&addr.u.sa, &slen);
-
-	if (ret <= 0) {
-		LOG_CONN_RTP(conn_src, LOGL_ERROR, "recvfrom error: %s\n", strerror(errno));
-		rc = -1;
-		goto out;
+	if (res <= 0) {
+		LOG_CONN_RTP(conn_src, LOGL_ERROR, "recvfrom error: %s\n", strerror(-res));
+		goto out_free;
 	}
 
-	msgb_put(msg, ret);
-
-	LOG_CONN_RTP(conn_src, LOGL_DEBUG, "%s: rx %u bytes from %s:%u\n",
+	LOG_CONN_RTP(conn_src, LOGL_DEBUG, "%s: rx %u bytes from %s\n",
 		     proto == MGCP_PROTO_RTP ? "RTP" : "RTCP",
-		     msgb_length(msg), osmo_sockaddr_ntop(&addr.u.sa, ipbuf),
-		     osmo_sockaddr_port(&addr.u.sa));
+		     msgb_length(msg), osmo_sockaddr_to_str(saddr));
 
 	if ((proto == MGCP_PROTO_RTP && check_rtp(conn_src, msg))
 	    || (proto == MGCP_PROTO_RTCP && check_rtcp(conn_src, msg))) {
 		/* Logging happened in the two check_ functions */
-		rc = -1;
-		goto out;
+		goto out_free;
 	}
 
 	if (mgcp_is_rtp_dummy_payload(msg)) {
 		LOG_CONN_RTP(conn_src, LOGL_DEBUG, "rx dummy packet (dropped)\n");
-		rc = 0;
-		goto out;
+		goto out_free;
 	}
 
 	/* Since the msgb remains owned and freed by this function, the msg ctx data struct can just be on the stack and
@@ -1523,7 +1520,7 @@ static int rtp_data_net(struct osmo_fd *fd, unsigned int what)
 	*mc = (struct osmo_rtp_msg_ctx){
 		.proto = proto,
 		.conn_src = conn_src,
-		.from_addr = &addr,
+		.from_addr = (struct osmo_sockaddr *) saddr,
 	};
 	LOG_CONN_RTP(conn_src, LOGL_DEBUG, "msg ctx: %d %p %s\n",
 		     mc->proto, mc->conn_src,
@@ -1538,12 +1535,13 @@ static int rtp_data_net(struct osmo_fd *fd, unsigned int what)
 	/* FIXME: count RTP and RTCP separately, also count IuUP payload-less separately */
 
 	/* Forward a copy of the RTP data to a debug ip/port */
-	forward_data_tap(fd->fd, &conn_src->tap_in, msg);
+	forward_data_tap(iofd, &conn_src->tap_in, msg);
 
-	rc = rx_rtp(msg);
+	rx_rtp(msg);
+	return;
 
-out:
-	return rc;
+out_free:
+	msgb_free(msg);
 }
 
 /* Note: This function is able to handle RTP and RTCP. msgb ownership is transferred, so this function or its
@@ -1590,6 +1588,24 @@ out_free:
 	return -1;
 }
 
+static void rtp_sendto_cb(struct osmo_io_fd *iofd, int res, struct msgb *msg, const struct osmo_sockaddr *daddr)
+{
+	/* nothing; osmo_io takes care of msgb_free */
+	if (res < 0) {
+		struct mgcp_conn_rtp *conn_rtp = (struct mgcp_conn_rtp *) osmo_iofd_get_data(iofd);
+		int priv_nr = osmo_iofd_get_priv_nr(iofd);
+		char errbuf[129];
+		strerror_r(-res, errbuf, sizeof(errbuf));
+		LOG_CONN_RTP(conn_rtp, LOGL_ERROR, "%s sendto(%s) failed: %s\n", priv_nr ? "RTCP" : "RTP",
+			 osmo_sockaddr_to_str(daddr), errbuf);
+	}
+}
+
+static const struct osmo_io_ops rtp_ioops = {
+	.recvfrom_cb = rtp_recvfrom_cb,
+	.sendto_cb = rtp_sendto_cb,
+};
+
 /*! bind RTP port to osmo_fd.
  *  \param[in] source_addr source (local) address to bind on.
  *  \param[in] port to bind on.
@@ -1617,7 +1633,7 @@ int mgcp_create_bind(const char *source_addr, int port, uint8_t dscp, uint8_t pr
 static int bind_rtp(struct mgcp_config *cfg, const char *source_addr,
 		    struct mgcp_rtp_end *rtp_end, struct mgcp_endpoint *endp)
 {
-	int rc;
+	int rc, rtp_fd, rtcp_fd;
 
 	/* NOTE: The port that is used for RTCP is the RTP port incremented by one
 	 * (e.g. RTP-Port = 16000 ==> RTCP-Port = 16001) */
@@ -1629,7 +1645,7 @@ static int bind_rtp(struct mgcp_config *cfg, const char *source_addr,
 			 source_addr, rtp_end->local_port);
 		goto cleanup0;
 	}
-	rtp_end->rtp.fd = rc;
+	rtp_fd = rc;
 
 	rc = mgcp_create_bind(source_addr, rtp_end->local_port + 1, cfg->endp_dscp, cfg->endp_priority);
 	if (rc < 0) {
@@ -1638,16 +1654,16 @@ static int bind_rtp(struct mgcp_config *cfg, const char *source_addr,
 			 source_addr, rtp_end->local_port + 1);
 		goto cleanup1;
 	}
-	rtp_end->rtcp.fd = rc;
+	rtcp_fd = rc;
 
-	if (osmo_fd_register(&rtp_end->rtp) != 0) {
+	if (osmo_iofd_register(rtp_end->rtp, rtp_fd) < 0) {
 		LOGPENDP(endp, DRTP, LOGL_ERROR,
 			 "failed to register RTP port %d\n",
 			 rtp_end->local_port);
 		goto cleanup2;
 	}
 
-	if (osmo_fd_register(&rtp_end->rtcp) != 0) {
+	if (osmo_iofd_register(rtp_end->rtcp, rtcp_fd) != 0) {
 		LOGPENDP(endp, DRTP, LOGL_ERROR,
 			 "failed to register RTCP port %d\n",
 			 rtp_end->local_port + 1);
@@ -1657,13 +1673,11 @@ static int bind_rtp(struct mgcp_config *cfg, const char *source_addr,
 	return 0;
 
 cleanup3:
-	osmo_fd_unregister(&rtp_end->rtp);
+	osmo_iofd_unregister(rtp_end->rtp);
 cleanup2:
-	close(rtp_end->rtcp.fd);
-	rtp_end->rtcp.fd = -1;
+	close(rtcp_fd);
 cleanup1:
-	close(rtp_end->rtp.fd);
-	rtp_end->rtp.fd = -1;
+	close(rtp_fd);
 cleanup0:
 	return -1;
 }
@@ -1682,7 +1696,8 @@ int mgcp_bind_net_rtp_port(struct mgcp_endpoint *endp, int rtp_port,
 	snprintf(name, sizeof(name), "%s-%s", conn->conn->name, conn->conn->id);
 	end = &conn->end;
 
-	if (end->rtp.fd != -1 || end->rtcp.fd != -1) {
+	if ((end->rtp && osmo_iofd_get_fd(end->rtp) != -1) ||
+	    (end->rtcp && osmo_iofd_get_fd(end->rtcp) != -1)) {
 		LOGPENDP(endp, DRTP, LOGL_ERROR, "%u was already bound on conn:%s\n",
 			 rtp_port, mgcp_conn_dump(conn->conn));
 
@@ -1695,8 +1710,18 @@ int mgcp_bind_net_rtp_port(struct mgcp_endpoint *endp, int rtp_port,
 	}
 
 	end->local_port = rtp_port;
-	osmo_fd_setup(&end->rtp, -1, OSMO_FD_READ, rtp_data_net, conn, 0);
-	osmo_fd_setup(&end->rtcp, -1, OSMO_FD_READ, rtp_data_net, conn, 0);
+	end->rtp = osmo_iofd_setup(conn->conn, -1, name, OSMO_IO_FD_MODE_RECVFROM_SENDTO, &rtp_ioops, conn);
+	if (!end->rtp)
+		return -EIO;
+	osmo_iofd_set_alloc_info(end->rtp, RTP_BUF_SIZE, 0);
+	end->rtcp = osmo_iofd_setup(conn->conn, -1, name, OSMO_IO_FD_MODE_RECVFROM_SENDTO, &rtp_ioops, conn);
+	if (!end->rtcp) {
+		osmo_iofd_free(end->rtp);
+		end->rtp = NULL;
+		return -EIO;
+	}
+	osmo_iofd_set_alloc_info(end->rtcp, RTP_BUF_SIZE, 0);
+	osmo_iofd_set_priv_nr(end->rtcp, 1); /* we use priv_nr as identifier for RTCP */
 
 	return bind_rtp(endp->trunk->cfg, conn->end.local_addr, end, endp);
 }
@@ -1705,15 +1730,13 @@ int mgcp_bind_net_rtp_port(struct mgcp_endpoint *endp, int rtp_port,
  *  \param[in] end RTP end */
 void mgcp_free_rtp_port(struct mgcp_rtp_end *end)
 {
-	if (end->rtp.fd != -1) {
-		osmo_fd_unregister(&end->rtp);
-		close(end->rtp.fd);
-		end->rtp.fd = -1;
+	if (end->rtp) {
+		osmo_iofd_free(end->rtp);
+		end->rtp = NULL;
 	}
 
-	if (end->rtcp.fd != -1) {
-		osmo_fd_unregister(&end->rtcp);
-		close(end->rtcp.fd);
-		end->rtcp.fd = -1;
+	if (end->rtcp) {
+		osmo_iofd_free(end->rtcp);
+		end->rtcp = NULL;
 	}
 }
diff --git a/src/libosmo-mgcp/mgcp_osmux.c b/src/libosmo-mgcp/mgcp_osmux.c
index 3df99724e..df91dbc0b 100644
--- a/src/libosmo-mgcp/mgcp_osmux.c
+++ b/src/libosmo-mgcp/mgcp_osmux.c
@@ -1,6 +1,7 @@
 /*
  * (C) 2012-2013 by Pablo Neira Ayuso <pablo@gnumonks.org>
  * (C) 2012-2013 by On Waves ehf <http://www.on-waves.com>
+ * (C) 2013-2024 by sysmocom - s.f.m.c. GmbH
  * All rights not specifically granted under this license are reserved.
  *
  * This program is free software; you can redistribute it and/or modify it
@@ -13,9 +14,11 @@
 #include <string.h> /* for memcpy */
 #include <stdlib.h> /* for abs */
 #include <inttypes.h> /* for PRIu64 */
+#include <unistd.h> /* for PRIu64 */
 #include <netinet/in.h>
 #include <osmocom/core/msgb.h>
 #include <osmocom/core/socket.h>
+#include <osmocom/core/osmo_io.h>
 #include <osmocom/core/talloc.h>
 
 #include <osmocom/netif/osmux.h>
@@ -30,8 +33,8 @@
 #include <osmocom/mgcp/mgcp_endp.h>
 #include <osmocom/mgcp/mgcp_trunk.h>
 
-static struct osmo_fd osmux_fd_v4;
-static struct osmo_fd osmux_fd_v6;
+static struct osmo_io_fd *osmux_fd_v4;
+static struct osmo_io_fd *osmux_fd_v6;
 
 static LLIST_HEAD(osmux_handle_list);
 
@@ -76,34 +79,31 @@ static void rtpconn_osmux_rate_ctr_inc(struct mgcp_conn_rtp *conn_rtp, int id)
 static void osmux_deliver_cb(struct msgb *batch_msg, void *data)
 {
 	struct osmux_handle *handle = data;
-	socklen_t dest_len;
-	int rc, fd;
-	struct mgcp_trunk *trunk = (struct mgcp_trunk *)osmux_fd_v4.data;
+	int rc;
+	struct osmo_io_fd *iofd;
+	struct mgcp_trunk *trunk = (struct mgcp_trunk *) osmo_iofd_get_data(osmux_fd_v4);
 	struct rate_ctr_group *all_osmux_stats = trunk->ratectr.all_osmux_conn_stats;
 
 	switch (handle->rem_addr.u.sa.sa_family) {
 	case AF_INET6:
-		dest_len = sizeof(handle->rem_addr.u.sin6);
-		fd = osmux_fd_v6.fd;
+		iofd = osmux_fd_v6;
 		break;
 	case AF_INET:
 	default:
-		dest_len = sizeof(handle->rem_addr.u.sin);
-		fd = osmux_fd_v4.fd;
+		iofd = osmux_fd_v4;
 		break;
 	}
-	rc = sendto(fd, batch_msg->data, batch_msg->len, 0,
-		    (struct sockaddr *)&handle->rem_addr.u.sa, dest_len);
+	rc = osmo_iofd_sendto_msgb(iofd, batch_msg, 0, &handle->rem_addr);
 	if (rc < 0) {
 		char errbuf[129];
-		strerror_r(errno, errbuf, sizeof(errbuf));
+		strerror_r(-rc, errbuf, sizeof(errbuf));
 		LOGP(DOSMUX, LOGL_NOTICE, "osmux sendto(%s) failed: %s\n",
 			 osmo_sockaddr_to_str(&handle->rem_addr), errbuf);
 		rate_ctr_inc(rate_ctr_group_get_ctr(all_osmux_stats, OSMUX_DROPPED_PACKETS_CTR));
+		msgb_free(batch_msg);
 	} else {
 		rate_ctr_inc(rate_ctr_group_get_ctr(all_osmux_stats, OSMUX_PACKETS_TX_CTR));
 	}
-	msgb_free(batch_msg);
 }
 
 /* Lookup existing OSMUX handle for specified destination address. */
@@ -325,28 +325,6 @@ static void scheduled_from_osmux_tx_rtp_cb(struct msgb *msg, void *data)
 	/* dispatch_rtp_cb() has taken ownership of the msgb */
 }
 
-static struct msgb *osmux_recv(struct osmo_fd *ofd, struct osmo_sockaddr *addr)
-{
-	struct msgb *msg;
-	socklen_t slen = sizeof(addr->u.sas);
-	int ret;
-
-	msg = msgb_alloc(4096, "OSMUX");
-	if (!msg) {
-		LOGP(DOSMUX, LOGL_ERROR, "cannot allocate message\n");
-		return NULL;
-	}
-	ret = recvfrom(ofd->fd, msg->data, msg->data_len, 0, &addr->u.sa, &slen);
-	if (ret <= 0) {
-		msgb_free(msg);
-		LOGP(DOSMUX, LOGL_ERROR, "cannot receive message\n");
-		return NULL;
-	}
-	msgb_put(msg, ret);
-
-	return msg;
-}
-
 /* To be called every time some AMR data is received on a connection
  * returns: 0 if conn can process data, negative if an error ocurred and data should not be further processed */
 static int conn_osmux_event_data_received(struct mgcp_conn_rtp *conn, const struct osmo_sockaddr *rem_addr)
@@ -442,22 +420,16 @@ out:
 }
 
 #define osmux_chunk_length(msg, rem) ((rem) - (msg)->len)
-static int osmux_read_fd_cb(struct osmo_fd *ofd, unsigned int what)
+static void osmux_recvfrom_cb(struct osmo_io_fd *iofd, int res, struct msgb *msg, const struct osmo_sockaddr *rem_addr)
 {
-	struct msgb *msg;
 	struct osmux_hdr *osmuxh;
-	struct osmo_sockaddr rem_addr;
-	uint32_t rem;
-	struct mgcp_trunk *trunk = ofd->data;
+	struct mgcp_trunk *trunk = osmo_iofd_get_data(iofd);
 	struct rate_ctr_group *all_rtp_stats = trunk->ratectr.all_osmux_conn_stats;
+	uint32_t rem;
 	char addr_str[64];
 
-	msg = osmux_recv(ofd, &rem_addr);
-	if (!msg)
-		return -1;
-
 	rate_ctr_inc(rate_ctr_group_get_ctr(all_rtp_stats, OSMUX_PACKETS_RX_CTR));
-	osmo_sockaddr_to_str_buf(addr_str, sizeof(addr_str), &rem_addr);
+	osmo_sockaddr_to_str_buf(addr_str, sizeof(addr_str), rem_addr);
 
 	if (trunk->cfg->osmux.usage == OSMUX_USAGE_OFF) {
 		LOGP(DOSMUX, LOGL_ERROR,
@@ -467,14 +439,16 @@ static int osmux_read_fd_cb(struct osmo_fd *ofd, unsigned int what)
 	}
 
 	/* Catch legacy dummy message and process them separately: */
-	if (msg->len == 2 && msg->data[0] == MGCP_DUMMY_LOAD)
-		return osmux_handle_legacy_dummy(trunk, &rem_addr, msg);
+	if (msg->len == 2 && msg->data[0] == MGCP_DUMMY_LOAD) {
+		osmux_handle_legacy_dummy(trunk, rem_addr, msg);
+		return;
+	}
 
 	rem = msg->len;
 	while((osmuxh = osmux_xfrm_output_pull(msg)) != NULL) {
 		struct mgcp_conn_rtp *conn_src;
 		conn_src = osmux_conn_lookup(trunk, osmuxh->circuit_id,
-					     &rem_addr);
+					     rem_addr);
 		if (!conn_src) {
 			LOGP(DOSMUX, LOGL_DEBUG,
 			     "Cannot find a src conn for %s CID=%d\n",
@@ -482,7 +456,7 @@ static int osmux_read_fd_cb(struct osmo_fd *ofd, unsigned int what)
 			goto next;
 		}
 
-		if (conn_osmux_event_data_received(conn_src, &rem_addr) < 0)
+		if (conn_osmux_event_data_received(conn_src, rem_addr) < 0)
 			goto next;
 
 		mgcp_conn_watchdog_kick(conn_src->conn);
@@ -496,19 +470,38 @@ next:
 	}
 out:
 	msgb_free(msg);
-	return 0;
 }
 
+static void osmux_sendto_cb(struct osmo_io_fd *iofd, int res, struct msgb *msg, const struct osmo_sockaddr *rem_addr)
+{
+	/* nothing; osmo_io takes care of msgb_free */
+	if (res < 0) {
+		struct mgcp_trunk *trunk = (struct mgcp_trunk *) osmo_iofd_get_data(iofd);
+		struct rate_ctr_group *all_osmux_stats = trunk->ratectr.all_osmux_conn_stats;
+		char errbuf[129];
+		strerror_r(-res, errbuf, sizeof(errbuf));
+		LOGP(DOSMUX, LOGL_NOTICE, "osmux sendto(%s) failed: %s\n", osmo_sockaddr_to_str(rem_addr), errbuf);
+		rate_ctr_inc(rate_ctr_group_get_ctr(all_osmux_stats, OSMUX_DROPPED_PACKETS_CTR));
+	}
+}
+
+static const struct osmo_io_ops osmux_ioops = {
+	.recvfrom_cb = osmux_recvfrom_cb,
+	.sendto_cb = osmux_sendto_cb,
+};
+
 int osmux_init(struct mgcp_trunk *trunk)
 {
-	int ret;
+	int ret, fd;
 	struct mgcp_config *cfg = trunk->cfg;
 
 	/* So far we only support running on one trunk: */
 	OSMO_ASSERT(trunk == mgcp_trunk_by_num(cfg, MGCP_TRUNK_VIRTUAL, MGCP_VIRT_TRUNK_ID));
 
-	osmo_fd_setup(&osmux_fd_v4, -1, OSMO_FD_READ, osmux_read_fd_cb, trunk, 0);
-	osmo_fd_setup(&osmux_fd_v6, -1, OSMO_FD_READ, osmux_read_fd_cb, trunk, 0);
+	osmux_fd_v4 = osmo_iofd_setup(trunk, -1, "osmux_fd_v4", OSMO_IO_FD_MODE_RECVFROM_SENDTO, &osmux_ioops, trunk);
+	if (!osmux_fd_v4)
+		goto out;
+	osmo_iofd_set_alloc_info(osmux_fd_v4, 4096, 0);
 
 	if (cfg->osmux.local_addr_v4) {
 		ret = mgcp_create_bind(cfg->osmux.local_addr_v4, cfg->osmux.local_port,
@@ -516,40 +509,55 @@ int osmux_init(struct mgcp_trunk *trunk)
 		if (ret < 0) {
 			LOGP(DOSMUX, LOGL_ERROR, "Cannot bind OSMUX IPv4 socket to %s:%u\n",
 			     cfg->osmux.local_addr_v4, cfg->osmux.local_port);
-			return ret;
+			goto out_free_v4;
 		}
-		osmux_fd_v4.fd = ret;
+		fd = ret;
 
-		ret = osmo_fd_register(&osmux_fd_v4);
+		ret = osmo_iofd_register(osmux_fd_v4, fd);
 		if (ret < 0) {
-			LOGP(DOSMUX, LOGL_ERROR, "Cannot register OSMUX IPv4 socket %s\n",
-			     osmo_sock_get_name2(osmux_fd_v4.fd));
-			return ret;
+			LOGP(DOSMUX, LOGL_ERROR, "Cannot register OSMUX IPv4 socket %s\n", osmo_sock_get_name2(fd));
+			close(fd);
+			goto out_free_v4;
 		}
-		LOGP(DOSMUX, LOGL_INFO, "OSMUX IPv4 socket listening on %s\n",
-		     osmo_sock_get_name2(osmux_fd_v4.fd));
+		LOGP(DOSMUX, LOGL_INFO, "OSMUX IPv4 socket listening on %s\n", osmo_sock_get_name2(fd));
 	}
+
+	osmux_fd_v6 = osmo_iofd_setup(trunk, -1, "osmux_fd_v6", OSMO_IO_FD_MODE_RECVFROM_SENDTO, &osmux_ioops, trunk);
+	if (!osmux_fd_v6)
+		goto out_free_v4;
+	osmo_iofd_set_alloc_info(osmux_fd_v6, 4096, 0);
+
 	if (cfg->osmux.local_addr_v6) {
 		ret = mgcp_create_bind(cfg->osmux.local_addr_v6, cfg->osmux.local_port,
 					cfg->endp_dscp, cfg->endp_priority);
 		if (ret < 0) {
 			LOGP(DOSMUX, LOGL_ERROR, "Cannot bind OSMUX IPv6 socket to [%s]:%u\n",
 			     cfg->osmux.local_addr_v6, cfg->osmux.local_port);
-			return ret;
+			goto out_free_v6;
 		}
-		osmux_fd_v6.fd = ret;
+		fd = ret;
 
-		ret = osmo_fd_register(&osmux_fd_v6);
+		ret = osmo_iofd_register(osmux_fd_v6, fd);
 		if (ret < 0) {
-			LOGP(DOSMUX, LOGL_ERROR, "Cannot register OSMUX IPv6 socket %s\n",
-			     osmo_sock_get_name2(osmux_fd_v6.fd));
-			return ret;
+			LOGP(DOSMUX, LOGL_ERROR, "Cannot register OSMUX IPv6 socket %s\n", osmo_sock_get_name2(fd));
+			close(fd);
+			goto out_free_v6;
 		}
-		LOGP(DOSMUX, LOGL_INFO, "OSMUX IPv6 socket listening on %s\n",
-		     osmo_sock_get_name2(osmux_fd_v6.fd));
+		LOGP(DOSMUX, LOGL_INFO, "OSMUX IPv6 socket listening on %s\n", osmo_sock_get_name2(fd));
 	}
 	cfg->osmux.initialized = true;
 	return 0;
+
+out_free_v6:
+	/* osmo_iofd_free performs unregister + close */
+	osmo_iofd_free(osmux_fd_v6);
+	osmux_fd_v6 = NULL;
+out_free_v4:
+	/* osmo_iofd_free performs unregister + close */
+	osmo_iofd_free(osmux_fd_v4);
+	osmux_fd_v4 = NULL;
+out:
+	return -1;
 }
 
 /*! relase OSXMUX cid, that had been allocated to this connection.
@@ -715,7 +723,7 @@ int osmux_send_dummy(struct mgcp_conn_rtp *conn)
 		 osmo_sockaddr_ntop(&conn->end.addr.u.sa, ipbuf),
 		 osmo_sockaddr_port(&conn->end.addr.u.sa), conn->osmux.remote_cid);
 
-	return mgcp_udp_send(osmux_fd_v4.fd, &conn->end.addr, (char *)osmuxh, buf_len);
+	return mgcp_udp_send(osmux_fd_v4, &conn->end.addr, (char *)osmuxh, buf_len);
 }
 
 /* Keeps track of locally allocated Osmux circuit ID. +7 to round up to 8 bit boundary. */
diff --git a/tests/mgcp/mgcp_test.c b/tests/mgcp/mgcp_test.c
index c76bd9d83..ffc8a202e 100644
--- a/tests/mgcp/mgcp_test.c
+++ b/tests/mgcp/mgcp_test.c
@@ -653,12 +653,13 @@ static struct msgb *create_msg(const char *str, const char *conn_id)
 
 static int dummy_packets = 0;
 /* override and forward */
-ssize_t sendto(int sockfd, const void *buf, size_t len, int flags,
-	       const struct sockaddr *dest_addr, socklen_t addrlen)
+int osmo_iofd_sendto_msgb(struct osmo_io_fd *iofd, struct msgb *msg, int flags, const struct osmo_sockaddr *addr)
 {
 	uint32_t dest_host =
-	    htonl(((struct sockaddr_in *)dest_addr)->sin_addr.s_addr);
-	int dest_port = htons(((struct sockaddr_in *)dest_addr)->sin_port);
+	    htonl(((struct sockaddr_in *)addr)->sin_addr.s_addr);
+	int dest_port = htons(((struct sockaddr_in *)addr)->sin_port);
+	const uint8_t *buf = msgb_data(msg);
+	size_t len = msgb_length(msg);
 
 	if (len == sizeof(rtp_dummy_payload)
 	    && memcmp(buf, rtp_dummy_payload, sizeof(rtp_dummy_payload)) == 0) {
@@ -672,6 +673,8 @@ ssize_t sendto(int sockfd, const void *buf, size_t len, int flags,
 	OSMO_ASSERT(dest_host);
 	OSMO_ASSERT(dest_port);
 
+	msgb_free(msg);
+
 	return len;
 }