fd: dup2() and dup3() now close newfd in case it was open

fdset(fd, fp) now installs fp on fd and closes a previousely opened file
if there was any, this makes dup2() and dup3() behave as expected.

fs/vfs/kern_descrip.c

@@ -69,7 +69,7 @@ int fdclose(int fd)
 }
 
 /*
- * Try to set assign a file pointer to a specific file descriptor.
+ * Assigns a file pointer to a specific file descriptor.
  * Grabs a reference to the file pointer if successful.
  */
 int fdset(int fd, struct file *fp)
@@ -80,16 +80,14 @@ int fdset(int fd, struct file *fp)
 	        return EBADF;
 
 	fhold(fp);
-	mutex_lock(&gfdt_lock);
 
-	/* Make sure that no file pointer is currently installed on fd */
+	mutex_lock(&gfdt_lock);
 	orig = gfdt[fd];
 	if (orig != NULL) {
-		mutex_unlock(&gfdt_lock);
-		fdrop(fp);
-		return EBADF;
+		fdrop(orig);
 	}
 
+	/* Install new file structure in place */
 	gfdt[fd] = fp;
 	mutex_unlock(&gfdt_lock);
 

fs/vfs/main.c

@@ -782,7 +782,7 @@ out_errno:
  */
 int dup3(int oldfd, int newfd, int flags)
 {
-	struct file *fp, *org = NULL;
+	struct file *fp;
 	int error;
 
 	/*
@@ -803,10 +803,6 @@ int dup3(int oldfd, int newfd, int flags)
 	if (error)
 		goto out_errno;
 
-	/* FIXME: Should atomically close newfd or report error */
-	error = fget(newfd, &org);
-	assert(error == 0);
-
 	error = fdset(newfd, fp);
 	if (error) {
 		fdrop(fp);