fs: implement FD_CLOEXEC flag

Author: d4ilyrun

include/kernel/file.h

@@ -33,6 +33,7 @@ enum file_flags {
     FD_WRITE = _FWRITE,
     FD_RW = FD_READ | FD_WRITE,
     FD_APPEND = _FAPPEND,
+    FD_NOINHERIT = _FNOINHERIT, /* FD_CLOEXEC is already defined by fcntl(). */
 };
 
 /** Opened file description.

kernel/fs/vfs.c

@@ -342,8 +342,7 @@ static inline error_t file_compute_flags(int oflags, int *flags)
 {
     *flags = 0;
 
-    if (oflags & (O_TRUNC | O_SYNC | O_NONBLOCK | O_NOCTTY) ||
-        oflags & (O_CLOEXEC | O_NOFOLLOW))
+    if (oflags & (O_TRUNC | O_SYNC | O_NONBLOCK | O_NOCTTY | O_NOFOLLOW))
         return -E_INVAL;
 
     if (O_READABLE(oflags))
@@ -353,6 +352,8 @@ static inline error_t file_compute_flags(int oflags, int *flags)
 
     if (oflags & O_APPEND)
         *flags |= FD_APPEND;
+    if (oflags & O_CLOEXEC)
+        *flags |= FD_NOINHERIT;
 
     return E_SUCCESS;
 }

kernel/misc/exec.c

@@ -60,6 +60,20 @@ static NO_RETURN void execfmt_execute_executable(struct executable *executable,
                                                  void *stack_pointer,
                                                  void *base_pointer)
 {
+    struct process *process = current->process;
+
+    /*
+     * Close all files marked as CLOEXEC.
+     */
+    locked_scope(&current->process->files_lock) {
+        for (size_t i = 0; i < PROCESS_FD_COUNT; ++i) {
+            if (process->files[i] && process->files[i]->flags & FD_NOINHERIT) {
+                file_put(process->files[i]);
+                process->files[i] = NULL;
+            }
+        }
+    }
+
     thread_jump_to_userland(stack_pointer, base_pointer, executable->entrypoint,
                             NULL);
 }