From 34471d85fca14a5ec359d2d06a8d7018cb23beb2 Mon Sep 17 00:00:00 2001
From: Alexander Mohr <alexander.m.mohr@mercedes-benz.com>
Date: Wed, 5 Oct 2022 10:23:44 +0200
Subject: systemd: add support for socket activation via systemd (#401)

dlt-daemon now support activation via systemd socket.
This allows dlt-daemon to be started as soon as an application
is requesting access to the dlt socket.
This commits implements opening the socket only when
UNIX_SOCKET is used for IPC

Signed-off-by: Alexander Mohr <alexander.m.mohr@mercedes-benz.com>

Signed-off-by: Alexander Mohr <alexander.m.mohr@mercedes-benz.com>
---
 src/daemon/CMakeLists.txt           |  3 +++
 src/daemon/dlt_daemon_unix_socket.c | 50 +++++++++++++++++++++++++++++++++++++
 2 files changed, 53 insertions(+)

(limited to 'src')

diff --git a/src/daemon/CMakeLists.txt b/src/daemon/CMakeLists.txt
index e4e96bd..f7aaa26 100644
--- a/src/daemon/CMakeLists.txt
+++ b/src/daemon/CMakeLists.txt
@@ -61,6 +61,9 @@ endif(WITH_UDP_CONNECTION)
 
 add_executable(dlt-daemon ${dlt_daemon_SRCS} ${systemd_SRCS})
 target_link_libraries(dlt-daemon ${RT_LIBRARY} ${SOCKET_LIBRARY} ${CMAKE_THREAD_LIBS_INIT})
+if (WITH_SYSTEMD_SOCKET_ACTIVATION)
+    target_link_libraries(dlt-daemon systemd)
+endif()
 
 install(TARGETS dlt-daemon
         RUNTIME DESTINATION bin
diff --git a/src/daemon/dlt_daemon_unix_socket.c b/src/daemon/dlt_daemon_unix_socket.c
index ea889b0..4b9f472 100644
--- a/src/daemon/dlt_daemon_unix_socket.c
+++ b/src/daemon/dlt_daemon_unix_socket.c
@@ -38,6 +38,9 @@
 #include <sys/stat.h>
 #include <syslog.h>
 #include <errno.h>
+#if DLT_SYSTEM_SOCKET_ACTIVATION_ENABLE
+#include <systemd/sd-daemon.h>
+#endif
 
 #include "dlt-daemon.h"
 #include "dlt_common.h"
@@ -91,6 +94,48 @@ int dlt_daemon_unix_socket_open(int *sock, char *sock_path, int type, int mask)
         return -1;
     }
 
+#ifdef DLT_SYSTEM_SOCKET_ACTIVATION_ENABLE
+
+    char **names = NULL;
+    const int num_fds = sd_listen_fds_with_names(0, &names);
+    bool sd_socket_open = false;
+    int i;
+
+    if (num_fds <= 0) {
+        dlt_vlog(LOG_WARNING, "unix socket: no sockets configured via systemd, error: %s\n", strerror(errno));
+    } else {
+        for (i = 0; i < num_fds; ++i) {
+            if (strcmp(sock_path, names[i]) != 0) {
+                continue;
+            }
+
+            if (sd_is_socket_unix(i + SD_LISTEN_FDS_START, type, 1, names[i], strlen(names[i])) < 0) {
+                dlt_vlog(LOG_WARNING,
+                        "unix socket: socket with matching name is not of correct type or not in listen mode, error: %s\n",
+                        strerror(errno));
+                continue;
+            }
+
+            *sock = i + SD_LISTEN_FDS_START;
+            sd_socket_open = true;
+            dlt_vlog(LOG_INFO, "unix socket: sock_path %s found systemd socket %s\n", sock_path, names[i]);
+            break;
+        }
+
+        /*
+         * The caller [of sd_listen_fds_with_names] needs to free the array
+         * itself and each of its elements with libc's free() call after use.
+         * */
+        for (i = 0; i < num_fds; ++i) {
+            free(names[i]);
+        }
+        free(names);
+    }
+
+    if (!sd_socket_open) {
+        dlt_vlog(LOG_INFO, "unix socket: sock_path %s no systemd socket found\n", sock_path);
+#endif
+
     if ((*sock = socket(AF_UNIX, type, 0)) == -1) {
         dlt_log(LOG_WARNING, "unix socket: socket() error");
         return -1;
@@ -118,6 +163,11 @@ int dlt_daemon_unix_socket_open(int *sock, char *sock_path, int type, int mask)
     /* restore permissions */
     umask(old_mask);
 
+#ifdef DLT_SYSTEM_SOCKET_ACTIVATION_ENABLE
+    } // end of: if (!sd_socket_open) {
+#endif
+
+
     return 0;
 }
 
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