zero config: add disable svcname generation capability (#2410)

Setting service name can be disabled by setting `generate_service_name=false` in
the config file. In a later release service name generation will be disabled by
default.

instrumentation/Dockerfile

@@ -7,5 +7,6 @@ WORKDIR /libsplunk
 
 COPY src /libsplunk/src
 COPY testdata/instrumentation.conf /libsplunk/testdata/instrumentation.conf
+COPY testdata/instrumentation-svcname.conf /libsplunk/testdata/instrumentation-svcname.conf
 COPY install/instrumentation.conf /libsplunk/install/instrumentation.conf
 COPY Makefile /libsplunk/Makefile

instrumentation/README.md

@@ -9,7 +9,7 @@ This directory contains functionality for building a Linux .so (shared object) f
 reference to that file in
 `/etc/ld.so.preload` (provided by an installer defined elsewhere) causes processes on the host to run this .so before
 the main executable runs. If the executable that's starting is not named `java`, the .so quits silently and the
-executable starts normally. Otherwise, it attempts to set two environment variables that will cause the
+executable starts normally. Otherwise, it attempts to set environment variables that will cause the
 [Splunk OTel Java JAR](https://github.com/signalfx/splunk-otel-java) (also provided by the installer) to instrument the
 soon-to-be running Java application. In this way, all Java applications on the host will be automatically instrumented
 by the Splunk OTel Java agent.
@@ -35,6 +35,12 @@ The `java_agent_jar` parameter is set to the default location of the agent jar.
 
 The full path to the auto instrumentation JAR (provided by the installer).
 
+#### `generate_service_name` (optional)
+
+Whether to disable service name generation by the .so. If set to "true" (the default), the .so will attempt to generate
+a service name from the Java command arguments. If set to "false", it will not set the service name, leaving it to be
+generated by the Java auto-instrumentation library.
+
 #### `service_name` (optional)
 
 This is an optional override for the service name that would otherwise be generated by the shared object before Java

instrumentation/src/config.c

@@ -29,6 +29,9 @@ void load_config(logger log, struct config *cfg, char *file_name) {
     if (cfg->disable_telemetry == NULL) {
         log_debug(log, "disable_telemetry not specified in config");
     }
+    if (cfg->generate_service_name == NULL) {
+        log_debug(log, "generate_service_name not specified in config");
+    }
 }
 
 void read_config_file(logger log, struct config *cfg, char *file_name) {
@@ -63,6 +66,8 @@ void read_lines(struct config *cfg, FILE *fp) {
             cfg->resource_attributes = strdup(pair.v);
         } else if (streq(pair.k, "disable_telemetry")) {
             cfg->disable_telemetry = strdup(pair.v);
+        } else if (streq(pair.k, "generate_service_name")) {
+            cfg->generate_service_name = strdup(pair.v);
         }
     }
 }
@@ -72,10 +77,14 @@ void split_on_eq(char *string, struct kv *pair) {
     pair->v = string;
 }
 
-bool eq_true(char *v) {
+bool str_eq_true(char *v) {
     return v != NULL && !streq("false", v) && !streq("FALSE", v) && !streq("0", v);
 }
 
+bool str_eq_false(char *v) {
+    return v != NULL && (streq("false", v) || streq("FALSE", v) || streq("0", v));
+}
+
 void free_config(struct config *cfg) {
     if (cfg->java_agent_jar != NULL) {
         free(cfg->java_agent_jar);
@@ -89,4 +98,7 @@ void free_config(struct config *cfg) {
     if (cfg->disable_telemetry != NULL) {
         free(cfg->disable_telemetry);
     }
+    if (cfg->generate_service_name != NULL) {
+        free(cfg->generate_service_name);
+    }
 }

instrumentation/src/config.h

@@ -10,11 +10,14 @@ struct config {
     char *service_name;
     char *resource_attributes;
     char *disable_telemetry;
+    char *generate_service_name;
 };
 
 void load_config(logger log, struct config *cfg, char *file_name);
 
-bool eq_true(char *v);
+bool str_eq_true(char *v);
+
+bool str_eq_false(char *v);
 
 void free_config(struct config *cfg);
 

instrumentation/src/splunk.c

@@ -33,6 +33,8 @@ void set_env_var(logger log, const char *var_name, const char *value);
 
 void set_env_var_from_attr(logger log, const char *attr_name, const char *env_var_name, const char *value);
 
+void get_service_name(logger log, cmdline_reader cr, struct config *cfg, char *dest);
+
 // The entry point for all executables prior to their execution. If the executable is named "java", we
 // set the env vars JAVA_TOOL_OPTIONS to the path of the java agent jar and OTEL_SERVICE_NAME to the
 // service name based on the arguments to the java command.
@@ -85,24 +87,22 @@ void auto_instrument(
     }
 
     char service_name[MAX_CMDLINE_LEN] = "";
-    if (cfg.service_name == NULL) {
-        get_service_name_from_cmdline(log, service_name, cr);
+    if (str_eq_false(cfg.generate_service_name)) {
+        log_debug(log, "service name generation disabled");
     } else {
-        strncpy(service_name, cfg.service_name, MAX_CMDLINE_LEN);
+        get_service_name(log, cr, &cfg, service_name);
+        if (strlen(service_name) == 0) {
+            log_info(log, "service name empty, quitting");
+            return;
+        }
+        set_env_var(log, otel_service_name_var, service_name);
     }
 
-    if (strlen(service_name) == 0) {
-        log_info(log, "service name empty, quitting");
-        return;
-    }
-
-    set_env_var(log, otel_service_name_var, service_name);
-
     set_java_tool_options(log, &cfg);
 
     set_env_var_from_attr(log, "resource_attributes", resource_attributes_var, cfg.resource_attributes);
 
-    if (eq_true(cfg.disable_telemetry)) {
+    if (str_eq_true(cfg.disable_telemetry)) {
         log_info(log, "disabling telemetry as per config");
     } else {
         send_otlp_metric_func(log, service_name);
@@ -111,6 +111,14 @@ void auto_instrument(
     free_config(&cfg);
 }
 
+void get_service_name(logger log, cmdline_reader cr, struct config *cfg, char *dest) {
+    if (cfg->service_name == NULL) {
+        get_service_name_from_cmdline(log, dest, cr);
+    } else {
+        strncpy(dest, (*cfg).service_name, MAX_CMDLINE_LEN);
+    }
+}
+
 void get_service_name_from_cmdline(logger log, char *dest, cmdline_reader cr) {
     char *args[MAX_ARGS];
     int n = get_cmdline_args(args, cr, MAX_ARGS, MAX_CMDLINE_LEN, log);