net: dhcpv4: set log backend net ip via option

Adds the option to set the log_backend_net ip via dhcpv4
option 7.

Signed-off-by: Fin Maaß <f.maass@vogl-electronic.com>

subsys/logging/backends/Kconfig.net

@@ -49,6 +49,13 @@ config LOG_BACKEND_NET_AUTOSTART
 	  started by the application later on. Otherwise the logging
 	  thread might block.
 
+config LOG_BACKEND_NET_USE_DHCPV4_OPTION
+	bool "Use DHCPv4 Log Server Option to configure syslog server"
+	depends on NET_DHCPV4
+	help
+	  When enabled the syslog server IP address is read from the DHCPv4
+	  Log Server Option (7).
+
 backend = NET
 backend-str = net
 source "subsys/logging/Kconfig.template.log_format_config"

subsys/net/lib/dhcpv4/dhcpv4.c

@@ -28,6 +28,10 @@ LOG_MODULE_REGISTER(net_dhcpv4, CONFIG_NET_DHCPV4_LOG_LEVEL);
 #include <zephyr/net/dhcpv4.h>
 #include <zephyr/net/dns_resolve.h>
 
+#include <zephyr/logging/log_backend.h>
+#include <zephyr/logging/log_backend_net.h>
+#include <zephyr/logging/log_ctrl.h>
+
 #include "dhcpv4_internal.h"
 #include "ipv4.h"
 #include "net_stats.h"
@@ -44,6 +48,11 @@ static struct k_work_delayable timeout_work;
 
 static struct net_mgmt_event_callback mgmt4_cb;
 
+#if defined(CONFIG_LOG_BACKEND_NET_USE_DHCPV4_OPTION) && \
+	defined(CONFIG_LOG_BACKEND_NET_AUTOSTART)
+extern const struct log_backend *log_backend_net_get(void);
+#endif
+
 #if defined(CONFIG_NET_DHCPV4_OPTION_CALLBACKS)
 static sys_slist_t option_callbacks;
 #endif
@@ -810,6 +819,43 @@ static bool dhcpv4_parse_options(struct net_pkt *pkt,
 			break;
 		}
 #endif
+#if defined(CONFIG_LOG_BACKEND_NET_USE_DHCPV4_OPTION)
+		case DHCPV4_OPTIONS_LOG_SERVER: {
+			struct sockaddr_in log_server = { 0 };
+
+			/* Log server option may present 1 or more
+			 * addresses. Each 4 bytes in length. Log
+			 * servers should be listed in order
+			 * of preference.  Hence we choose the first
+			 * and skip the rest.
+			 */
+			if (length % 4 != 0U) {
+				NET_ERR("options_log_server, bad length");
+				return false;
+			}
+
+			if (net_pkt_read(pkt, log_server.sin_addr.s4_addr, 4) < 0 ||
+    		    net_pkt_skip(pkt, length - 4U) < 0) {
+				NET_ERR("options_log_server, short packet");
+				return false;
+			}
+
+			log_server.sin_family = AF_INET;
+			log_backend_net_set_ip((struct sockaddr *)&log_server);
+
+#ifdef CONFIG_LOG_BACKEND_NET_AUTOSTART
+			const struct log_backend *backend = log_backend_net_get();
+
+			if (!log_backend_is_active(backend)) {
+				log_backend_activate(backend, backend->cb->ctx);
+			}
+#endif
+
+			NET_DBG("options_log_server: %s", net_sprint_ipv4_addr(&log_server));
+
+			break;
+		}
+#endif
 		case DHCPV4_OPTIONS_LEASE_TIME:
 			if (length != 4U) {
 				NET_ERR("options_lease_time, bad length");

subsys/net/lib/dhcpv4/dhcpv4_internal.h

@@ -54,6 +54,7 @@ struct dhcp_msg {
 #define DHCPV4_OPTIONS_SUBNET_MASK	1
 #define DHCPV4_OPTIONS_ROUTER		3
 #define DHCPV4_OPTIONS_DNS_SERVER	6
+#define DHCPV4_OPTIONS_LOG_SERVER	7
 #define DHCPV4_OPTIONS_HOST_NAME	12
 #define DHCPV4_OPTIONS_REQ_IPADDR	50
 #define DHCPV4_OPTIONS_LEASE_TIME	51