generalize config file check for sentinel (#8730)

The implications of this change is just that in the past when a config file was missing,
in some cases it was exiting before printing the sever startup prints and sometimes after,
and now it'll always exit before printing them.

src/sentinel.c

@@ -549,14 +549,12 @@ void initSentinel(void) {
     server.sentinel_config = NULL;
 }
 
-/* This function gets called when the server is in Sentinel mode, started,
- * loaded the configuration, and is ready for normal operations. */
-void sentinelIsRunning(void) {
-    int j;
-
+/* This function is for checking whether sentinel config file has been set,
+ * also checking whether we have write permissions. */
+void sentinelCheckConfigFile(void) {
     if (server.configfile == NULL) {
         serverLog(LL_WARNING,
-            "Sentinel started without a config file. Exiting...");
+            "Sentinel needs config file on disk to save state. Exiting...");
         exit(1);
     } else if (access(server.configfile,W_OK) == -1) {
         serverLog(LL_WARNING,
@@ -564,6 +562,12 @@ void sentinelIsRunning(void) {
             server.configfile,strerror(errno));
         exit(1);
     }
+}
+
+/* This function gets called when the server is in Sentinel mode, started,
+ * loaded the configuration, and is ready for normal operations. */
+void sentinelIsRunning(void) {
+    int j;
 
     /* If this Sentinel has yet no ID set in the configuration file, we
      * pick a random one and persist the config on disk. From now on this

src/server.c

@@ -6247,7 +6247,6 @@ int main(int argc, char **argv) {
             server.exec_argv[1] = zstrdup(server.configfile);
             j = 2; // Skip this arg when parsing options
         }
-
         while(j < argc) {
             /* Either first or last argument - Should we read config from stdin? */
             if (argv[j][0] == '-' && argv[j][1] == '\0' && (j == 1 || j == argc-1)) {
@@ -6270,16 +6269,11 @@ int main(int argc, char **argv) {
             j++;
         }
 
-        if (server.sentinel_mode && ! server.configfile) {
-            serverLog(LL_WARNING,
-                "Sentinel needs config file on disk to save state.  Exiting...");
-            exit(1);
-        }
         loadServerConfig(server.configfile, config_from_stdin, options);
         if (server.sentinel_mode) loadSentinelConfigFromQueue();
         sdsfree(options);
     }
-
+    if (server.sentinel_mode) sentinelCheckConfigFile();
     server.supervised = redisIsSupervised(server.supervised_mode);
     int background = server.daemonize && !server.supervised;
     if (background) daemonize();

src/server.h

@@ -2404,6 +2404,7 @@ const char *sentinelHandleConfiguration(char **argv, int argc);
 void queueSentinelConfig(sds *argv, int argc, int linenum, sds line);
 void loadSentinelConfigFromQueue(void);
 void sentinelIsRunning(void);
+void sentinelCheckConfigFile(void);
 
 /* redis-check-rdb & aof */
 int redis_check_rdb(char *rdbfilename, FILE *fp);