[agroal#198] Guard PID file creation

Log FATAL when the PID file already exists.

If create_pid() fails because there is already a PID file, a log with
level FATAL is inserted before the program exits.

AUTHORS

@@ -3,4 +3,5 @@ pgagroal was created by the following authors:
 Jesper Pedersen <jesper.pedersen@redhat.com>
 David Fetter <david@fetter.org>
 Will Leinweber <will@bitfission.com>
-Junduo Dong <andj4cn@gmail.com>
+Junduo Dong <andj4cn@gmail.com>
+Luca Ferrari <fluca1978@gmail.com>

doc/CONFIGURATION.md

@@ -58,7 +58,7 @@ See a [sample](./etc/pgagroal/pgagroal.conf) configuration for running `pgagroal
 | hugepage | `try` | String | No | Huge page support (`off`, `try`, `on`) |
 | tracker | off | Bool | No | Track connection lifecycle |
 | track_prepared_statements | off | Bool | No | Track prepared statements (transaction pooling) |
-| pidfile | | String | No | Path to the PID file |
+| pidfile | | String | No | Path to the PID file. If omitted, automatically set to `unix_socket_dir`/pgagroal.`port`.pid |
 
 __Danger zone__
 

src/include/pgagroal.h

@@ -323,7 +323,7 @@ struct configuration
    int authentication_timeout;   /**< The authentication timeout in seconds */
    int disconnect_client;        /**< Disconnect client if idle for more than the specified seconds */
    bool disconnect_client_force; /**< Force a disconnect client if active for more than the specified seconds */
-   char pidfile[MISC_LENGTH];    /**< File containing the PID */
+   char pidfile[MAX_PATH];       /**< File containing the PID */
 
    char libev[MISC_LENGTH]; /**< Name of libev mode */
    int buffer_size;         /**< Socket buffer size */

src/main.c

@@ -1913,8 +1913,24 @@ create_pidfile(void)
 
    config = (struct configuration*)shmem;
 
+   if (strlen(config->pidfile) == 0)
+   {
+      // no pidfile set, use a default one
+      snprintf(config->pidfile, sizeof( config->pidfile ), "%s/pgagraol.%d.pid",
+               config->unix_socket_dir,
+               config->port);
+      pgagroal_log_debug("PID file automatically set to: [%s]", config->pidfile);
+   }
+
    if (strlen(config->pidfile) > 0)
    {
+       // check pidfile is not there
+      if (access(config->pidfile, F_OK) == 0)
+      {
+          pgagroal_log_fatal("PID file [%s] exists, is there another instance running ?", config->pidfile);
+          goto error;
+      }
+
       pid = getpid();
 
       fd = open(config->pidfile, O_WRONLY | O_CREAT | O_EXCL, 0644);
@@ -1949,7 +1965,7 @@ static void remove_pidfile(void)
 
    config = (struct configuration*)shmem;
 
-   if (strlen(config->pidfile) > 0)
+   if (strlen(config->pidfile) > 0 && access(config->pidfile, F_OK) == 0)
    {
       unlink(config->pidfile);
    }