core: reuse the same /tmp, /var/tmp and inaccessible dir

All Execs within the service, will get mounted the same
/tmp and /var/tmp directories, if service is configured with
PrivateTmp=yes. Temporary directories are cleaned up by service
itself in addition to systemd-tmpfiles. Directory which is mounted
as inaccessible is created at runtime in /run/systemd.

src/core/execute.h

@@ -36,6 +36,8 @@ typedef struct ExecContext ExecContext;
 struct CGroupBonding;
 struct CGroupAttribute;
 
+typedef struct Unit Unit;
+
 #include "list.h"
 #include "util.h"
 
@@ -141,6 +143,8 @@ struct ExecContext {
         bool non_blocking;
         bool private_tmp;
         bool private_network;
+        char *tmp_dir;
+        char *var_tmp_dir;
 
         bool no_new_privileges;
 
@@ -164,7 +168,7 @@ struct ExecContext {
 
 int exec_spawn(ExecCommand *command,
                char **argv,
-               const ExecContext *context,
+               ExecContext *context,
                int fds[], unsigned n_fds,
                char **environment,
                bool apply_permissions,
@@ -192,13 +196,15 @@ void exec_command_append_list(ExecCommand **l, ExecCommand *e);
 int exec_command_set(ExecCommand *c, const char *path, ...);
 
 void exec_context_init(ExecContext *c);
-void exec_context_done(ExecContext *c);
+void exec_context_done(ExecContext *c, bool reloading_or_reexecuting);
+void exec_context_tmp_dirs_done(ExecContext *c);
 void exec_context_dump(ExecContext *c, FILE* f, const char *prefix);
 void exec_context_tty_reset(const ExecContext *context);
 
 int exec_context_load_environment(const ExecContext *c, char ***l);
 
 bool exec_context_may_touch_console(ExecContext *c);
+void exec_context_serialize(const ExecContext *c, Unit *u, FILE *f);
 
 void exec_status_start(ExecStatus *s, pid_t pid);
 void exec_status_exit(ExecStatus *s, ExecContext *context, pid_t pid, int code, int status);