Implemented disconnecting file descriptors: this will be used by the

force unmounting code.


git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@15949 a95241bf-73f2-0310-859d-f6bbb57e9c96

headers/private/kernel/fs/fd.h

@@ -1,5 +1,5 @@
 /* 
- * Copyright 2002-2005, Axel Dörfler, [email protected].
+ * Copyright 2002-2006, Axel Dörfler, [email protected].
  * Distributed under the terms of the MIT License.
  */
 #ifndef _FD_H
@@ -61,6 +61,8 @@ enum fd_types {
 	FDTYPE_SOCKET
 };
 
+// additional open mode - kernel special
+#define O_DISCONNECTED 0x80000000
 
 /* Prototypes */
 
@@ -70,8 +72,11 @@ extern int new_fd(struct io_context *, struct file_descriptor *);
 extern struct file_descriptor *get_fd(struct io_context *, int);
 extern void close_fd(struct file_descriptor *descriptor);
 extern void put_fd(struct file_descriptor *descriptor);
-extern status_t select_fd(int fd, uint8 event, uint32 ref, struct select_sync *sync, bool kernel);
+extern void disconnect_fd(struct file_descriptor *descriptor);
-extern status_t deselect_fd(int fd, uint8 event, struct select_sync *sync, bool kernel);
+extern status_t select_fd(int fd, uint8 event, uint32 ref,
+					struct select_sync *sync, bool kernel);
+extern status_t deselect_fd(int fd, uint8 event, struct select_sync *sync,
+					bool kernel);
 extern bool fd_is_valid(int fd, bool kernel);
 extern struct vnode *fd_vnode(struct file_descriptor *descriptor);
 

src/system/kernel/fs/fd.c

@@ -1,6 +1,6 @@
 /* Operations on file descriptors
  *
- * Copyright 2002-2005, Axel Dörfler, [email protected].
+ * Copyright 2002-2006, Axel Dörfler, [email protected].
  * Distributed under the terms of the MIT License.
  */
 
@@ -126,15 +126,36 @@ new_fd(struct io_context *context, struct file_descriptor *descriptor)
 void
 put_fd(struct file_descriptor *descriptor)
 {
-	TRACE(("put_fd(descriptor = %p [ref = %ld, cookie = %p])\n", descriptor, descriptor->ref_count, descriptor->cookie));
+	int32 previous = atomic_add(&descriptor->ref_count, -1);
+
+	TRACE(("put_fd(descriptor = %p [ref = %ld, cookie = %p])\n",
+		descriptor, descriptor->ref_count, descriptor->cookie));
 
 	// free the descriptor if we don't need it anymore
-	if (atomic_add(&descriptor->ref_count, -1) == 1) {
+	if (previous == 1) {
 		// free the underlying object
 		if (descriptor->ops->fd_free)
 			descriptor->ops->fd_free(descriptor);
 
 		free(descriptor);
+	} else if ((descriptor->open_mode & O_DISCONNECTED) != 0
+		&& previous == descriptor->open_count) {
+		// the descriptor has been disconnected - it cannot
+		// be accessed anymore, let's close it (no one is
+		// currently accessing this descriptor)
+
+		if (descriptor->ops->fd_close)
+			descriptor->ops->fd_close(descriptor);
+		if (descriptor->ops->fd_free)
+			descriptor->ops->fd_free(descriptor);
+
+		// prevent this descriptor from being closed/freed again
+		descriptor->open_count = -1;
+		descriptor->ref_count = -1;
+		descriptor->u.vnode = NULL;
+
+		// the file descriptor is kept intact, so that it's not
+		// reused until someone explicetly closes it
 	}
 }
 
@@ -153,6 +174,20 @@ close_fd(struct file_descriptor *descriptor)
 }
 
 
+/**	This descriptor's underlying object will be closed and freed
+ *	as soon as possible (in one of the next calls to put_fd() -
+ *	get_fd() will no longer succeed on this descriptor).
+ *	This is useful if the underlying object is gone, for instance
+ *	when a (mounted) volume got removed unexpectedly.
+ */
+
+void
+disconnect_fd(struct file_descriptor *descriptor)
+{
+	descriptor->open_mode |= O_DISCONNECTED;
+}
+
+
 struct file_descriptor *
 get_fd(struct io_context *context, int fd)
 {
@@ -166,6 +201,10 @@ get_fd(struct io_context *context, int fd)
 	if ((uint32)fd < context->table_size)
 		descriptor = context->fds[fd];
 
+	// Disconnected descriptors cannot be accessed anymore
+	if (descriptor->open_mode & O_DISCONNECTED)
+		descriptor = NULL;
+
 	if (descriptor != NULL) // fd is valid
 		atomic_add(&descriptor->ref_count, 1);