linux-gen: fdserver: run fd server with a separate image

Refactor existing FD server by moving the server functionality to a
separate process image and launch it with `exec()` after the current
forking step has been done. This way typical issues related to forking a
multithreaded program are avoided.

Fixes OpenDataPlane#563.

Signed-off-by: Tuomas Taipale <[email protected]>

platform/linux-generic/.gitignore

@@ -1,2 +1,3 @@
 libodp-linux.pc
+odp_fdserver_runner
 odp_libconfig_config.h

platform/linux-generic/Makefile.am

@@ -492,6 +492,17 @@ if ODP_PKTIO_PCAP
 __LIB__libodp_linux_la_LIBADD += $(PCAP_LIBS)
 endif
 
+pkglibexec_PROGRAMS = odp_fdserver_runner
+
+odp_fdserver_runner_SOURCES = odp_fdserver_runner.c
+odp_fdserver_runner_LDADD = $(LIB)/lib$(ODP_LIB_NAME).la
+
+if STATIC_APPS
+odp_fdserver_runner_LDFLAGS = -static
+endif
+
+AM_CFLAGS += -DFDSERVER_PATH='"@libexecdir@/$(PACKAGE)/odp_fdserver_runner"'
+
 CHECK_GLOBALS_REGEX = " (odp_|_odp_|_deprecated_odp_|miniz_|mz_|tdefl_|tinfl_|mp_hdlr_init_odp_pool_ops)"
 
 TESTS_ENVIRONMENT = \

platform/linux-generic/include/odp_fdserver_internal.h

@@ -1,5 +1,6 @@
 /* SPDX-License-Identifier: BSD-3-Clause
  * Copyright (c) 2016-2018 Linaro Limited
+ * Copyright (c) 2024 Nokia
  */
 
 #ifndef _FD_SERVER_INTERNAL_H
@@ -9,6 +10,26 @@
 extern "C" {
 #endif
 
+#include <odp_config_internal.h>
+
+#include <stdint.h>
+
+/* Debug level for the FD server */
+#define FD_DBG  3
+/* define the tables of file descriptors handled by this server: */
+#define FDSERVER_MAX_ENTRIES (CONFIG_SHM_BLOCKS + CONFIG_INTERNAL_SHM_BLOCKS)
+/* possible commands: */
+#define FD_REGISTER_REQ		1  /* client -> server */
+#define FD_REGISTER_ACK		2  /* server -> client */
+#define FD_REGISTER_NACK	3  /* server -> client */
+#define FD_LOOKUP_REQ		4  /* client -> server */
+#define FD_LOOKUP_ACK		5  /* server -> client */
+#define FD_LOOKUP_NACK		6  /* server -> client */
+#define FD_DEREGISTER_REQ	7  /* client -> server */
+#define FD_DEREGISTER_ACK	8  /* server -> client */
+#define FD_DEREGISTER_NACK	9  /* server -> client */
+#define FD_SERVERSTOP_REQ	10 /* client -> server (stops) */
+
 /*
  * the following enum defines the different contexts by which the
  * FD server may be used: In the FD server, the keys used to store/retrieve
@@ -25,10 +46,57 @@ typedef enum fd_server_context {
 	FD_SRV_CTX_END, /* upper enum limit */
 } fd_server_context_e;
 
+typedef struct fdentry_s {
+	fd_server_context_e context;
+	uint64_t key;
+	int  fd;
+} fdentry_t;
+
+/*
+ * define the message struct used for communication between client and server
+ * (this single message is used in both direction)
+ * The file descriptors are sent out of band as ancillary data for conversion.
+ */
+typedef struct fd_server_msg {
+	int command;
+	fd_server_context_e context;
+	uint64_t key;
+} fdserver_msg_t;
+
 int _odp_fdserver_register_fd(fd_server_context_e context, uint64_t key,
 			      int fd);
 int _odp_fdserver_deregister_fd(fd_server_context_e context, uint64_t key);
 int _odp_fdserver_lookup_fd(fd_server_context_e context, uint64_t key);
+/*
+ * Client and server function:
+ * Send a fdserver_msg, possibly including a file descriptor, on the socket
+ * This function is used both by:
+ * -the client (sending a FD_REGISTER_REQ with a file descriptor to be shared,
+ *  or FD_LOOKUP_REQ/FD_DEREGISTER_REQ without a file descriptor)
+ * -the server (sending FD_REGISTER_ACK/NACK, FD_LOOKUP_NACK,
+ *  FD_DEREGISTER_ACK/NACK... without a fd or a
+ *  FD_LOOKUP_ACK with a fd)
+ * This function make use of the ancillary data (control data) to pass and
+ * convert file descriptors over UNIX sockets
+ * Return -1 on error, 0 on success.
+ */
+int _odp_send_fdserver_msg(int sock, int command, fd_server_context_e context, uint64_t key,
+			   int fd_to_send);
+/*
+ * Client and server function
+ * Receive a fdserver_msg, possibly including a file descriptor, on the
+ * given socket.
+ * This function is used both by:
+ * -the server (receiving a FD_REGISTER_REQ with a file descriptor to be shared,
+ *  or FD_LOOKUP_REQ, FD_DEREGISTER_REQ without a file descriptor)
+ * -the client (receiving FD_REGISTER_ACK...without a fd or a FD_LOOKUP_ACK with
+ * a fd)
+ * This function make use of the ancillary data (control data) to pass and
+ * convert file descriptors over UNIX sockets.
+ * Return -1 on error, 0 on success.
+ */
+int _odp_recv_fdserver_msg(int sock, int *command, fd_server_context_e *context, uint64_t *key,
+			   int *recvd_fd);
 
 #ifdef __cplusplus
 }