Better heuristic to get FUSE options

lib/Fuse_main.c

@@ -19,6 +19,19 @@
   02111-1307  USA
 
   Alessandro Strada
+
+  Warning: this main() contains a hack that's requested for compatibility
+  with OCaml version 5 and later. The new Multicore runtime prohibits
+  calling a fork() from C after caml_main() is called. So, I'm calling
+  fuse_daemonize() before caml_main(), and I try to detect any option that
+  keeps the process in foreground. But there are a couple of problems with this
+  hack: First, if the foreground option is injected by caml_main(), I will miss
+  it. Also, fuse_daemonize() redirects stdout and stderr to /dev/null, so it
+  gobbles up any error message produced by caml_main().
+
+  See
+  https://discuss.ocaml.org/t/multicore-and-fork-called-from-c-bindings/13993/2
+  for further details.
 */
 
 #include <caml/version.h>
@@ -41,17 +54,34 @@
 char **insert_foreground_option(int argc, char **argv);
 void free_fuse_argv(int n, char **fuse_argv);
 void start_program(int argc, char **argv, char *mountpoint, int foreground);
-void parse_fuse_args(int argc, char **argv, struct fuse_args *args);
-bool is_fuse_arg(char *arg, char *prev);
+void parse_fuse_args(int argc, char **argv, struct fuse_args *args,
+                     bool *debug);
+bool is_fuse_arg(char *arg, char *prev, bool is_last);
+bool is_debug(char *arg);
+int main_ocaml5(int argc, char **argv);
+int main_ocaml4(int argc, char **argv);
 
 /* https://v2.ocaml.org/releases/5.1/htmlman/intfc.html#ss:main-c */
 int main(int argc, char **argv) {
+#if OCAML_VERSION < 50000
+  main_ocaml4(argc, argv);
+#else
+  main_ocaml5(argc, argv);
+#endif
+}
+
+/* https://v2.ocaml.org/releases/5.1/htmlman/intfc.html#ss:main-c */
+int main_ocaml5(int argc, char **argv) {
   struct fuse_args args = FUSE_ARGS_INIT(0, NULL);
   char *mountpoint;
   int foreground;
+  bool debug;
 
-  parse_fuse_args(argc, argv, &args);
+  parse_fuse_args(argc, argv, &args, &debug);
   if (fuse_parse_cmdline(&args, &mountpoint, NULL, &foreground) != -1) {
+    if (debug) {
+      foreground = 1;
+    }
     start_program(argc, argv, mountpoint, foreground);
 
     fuse_opt_free_args(&args);
@@ -62,19 +92,25 @@ int main(int argc, char **argv) {
   return 1;
 }
 
-void parse_fuse_args(int argc, char **argv, struct fuse_args *args) {
+int main_ocaml4(int argc, char **argv) { caml_main(argv); }
+
+void parse_fuse_args(int argc, char **argv, struct fuse_args *args,
+                     bool *debug) {
   int i = 1;
 
   fuse_opt_add_arg(args, argv[0]);
   while (i < argc) {
-    if (is_fuse_arg(argv[i], argv[i - 1])) {
+    if (is_fuse_arg(argv[i], argv[i - 1], i == argc - 1)) {
       fuse_opt_add_arg(args, argv[i]);
     }
+    if (is_debug(argv[i])) {
+      *debug = true;
+    }
     ++i;
   }
 }
 
-bool is_fuse_arg(char *arg, char *prev) {
+bool is_fuse_arg(char *arg, char *prev, bool is_last) {
   if (strcmp(arg, "--help") == 0) {
     return true;
   }
@@ -95,19 +131,29 @@ bool is_fuse_arg(char *arg, char *prev) {
     if (prev != NULL && strcmp(prev, "-o") == 0) {
       return true;
     } else {
-      if (access(arg, F_OK) == 0) {
+      if (is_last && access(arg, F_OK) == 0) {
         return true;
       }
     }
   }
   return false;
 }
 
+bool is_debug(char *arg) {
+  if (strcmp(arg, "--debug") == 0) {
+    return true;
+  }
+  if (strcmp(arg, "-debug") == 0) {
+    return true;
+  }
+  return false;
+}
+
 void start_program(int argc, char **argv, char *mountpoint, int foreground) {
   char **fuse_argv = argv;
 
   if (mountpoint != NULL) {
-    /* https://github.com/libfuse/libfuse/blob/d04687923194d906fe5ad82dcd546c9807bf15b6/include/fuse_common.h#L246
+    /* https://github.com/libfuse/libfuse/blob/fuse-2.9.9/include/fuse_common.h#L246
      */
     if (fuse_daemonize(foreground) == -1) {
       perror("fuse_daemonize");