Starting to turn relabsd into a proper daemon...

1 files changed, 126 insertions, 0 deletions

diff --git a/src/server/daemon.c b/src/server/daemon.c
new file mode 100644
index 0000000..7b8e736
--- /dev/null
+++ b/src/server/daemon.c
@@ -0,0 +1,126 @@
+/**** POSIX *******************************************************************/
+#include <sys/types.h>
+
+#include <unistd.h>
+
+/**** RELABSD *****************************************************************/
+#include <relabsd/config.h>
+#include <relabsd/debug.h>
+#include <relabsd/server.h>
+
+#include <relabsd/config/parameters.h>
+
+/******************************************************************************/
+/**** LOCAL FUNCTIONS *********************************************************/
+/******************************************************************************/
+
+/******************************************************************************/
+/**** EXPORTED FUNCTIONS ******************************************************/
+/******************************************************************************/
+/*
+ * Daemon creation function made using the instructions for old-school daemons
+ * at https://www.freedesktop.org/software/systemd/man/daemon.html
+ * Only meant to be used before things really start. This won't properly create
+ * a daemon on an already running server instance with a virtual device and so
+ * on...
+ */
+int relabsd_server_create_daemon (void)
+{
+   pid_t proc_id;
+
+   /* 1/ Close all open file descriptors ... **********************************/
+   /* None were opened at this point. */
+
+   /* 2/ Reset all signal handlers ... ****************************************/
+   /* Those were not modified at this point. */
+
+   /* 3/ Reset the signal mask using sigprocmask() ****************************/
+   /* Not modified at this point. */
+
+   /* 4/ Sanitize the environment block ... ***********************************/
+   /* What? */
+
+   /* 5/ fork() ***************************************************************/
+   errno = 0;
+   proc_id = fork();
+
+   if (proc_id == ((pid_t) -1))
+   {
+      RELABSD_FATAL
+      (
+         "Step 5 of the daemon creation process, fork(), failed: %s.",
+         strerror(errno)
+      );
+
+      return -1;
+   }
+
+   if (proc_id != ((pid_t) 0))
+   {
+      /* Awaiting step 14...*/
+      /* TODO: insert unnamed pipe */
+      /* 15/ Original process exits *******************************************/
+      exit();
+   }
+
+   /* 6/ setsid() *************************************************************/
+   errno = 0;
+
+   proc_id = setsid();
+
+   if (proc_id == ((pid_t) -1))
+   {
+      RELABSD_FATAL
+      (
+         "Step 6 of the daemon creation process, setsid(), failed: %s.",
+         strerror(errno)
+      );
+
+      return -1;
+   }
+
+   /* 7/ fork() again *********************************************************/
+   errno = 0;
+   proc_id = fork();
+
+   if (proc_id == ((pid_t) -1))
+   {
+      RELABSD_FATAL
+      (
+         "Step 5 of the daemon creation process, fork(), failed: %s.",
+         strerror(errno)
+      );
+
+      return -1;
+   }
+
+   if (proc_id != ((pid_t) 0))
+   {
+      /* 8/ First child process exits *****************************************/
+      exit();
+   }
+
+   /* 9/ /dev/null for standard input/outputs *********************************/
+
+   /* 10/ reset umask to 0 ****************************************************/
+
+   /* 11/ Set current directory to / ******************************************/
+   errno = 0;
+
+   if (chdir("/") == -1)
+   {
+      // Can't print an error message at that point though...
+      return -1;
+   }
+
+   /* 12/ lock file using PID to assert single instance ***********************/
+   /* Don't want to limit to a single instance. */
+
+   /* 13/ Drop privileges *****************************************************/
+
+   /* 14/ Signal completion ***************************************************/
+
+   /* Step 15 is done on the very first process. */
+
+   return 0;
+}