VFS FIFO: Enlarge FIFO buffer sizes

* Increase FIFO buffer capacity from 32 to 64 KiB and the FIFO atomic
  write size ({BUF_SIZE}) from 512 bytes to 4 KiB (both like Linux).
* Fix *pathconf(..., _PC_PIPE_BUF). It was returning 4 KiB although the
  implemented atomic write size was 512 bytes only. Now both *pathconf()
  and the FIFO implementation refer to the same constant.

headers/private/system/vfs_defs.h

@@ -1,6 +1,7 @@
 /*
- * Copyright 2002-2008, Axel Dörfler, [email protected]. All rights reserved.
- * Distributed under the terms of the MIT License.
+ * Copyright 2002-2008, Axel Dörfler, [email protected].
+ * Copyright 2013, Ingo Weinhold, [email protected]e.
+ * All rights reserved. Distributed under the terms of the MIT License.
  *
  * Copyright 2001-2002, Travis Geiselbrecht. All rights reserved.
  * Distributed under the terms of the NewOS License.
@@ -8,6 +9,8 @@
 #ifndef _SYSTEM_VFS_DEFS_H
 #define _SYSTEM_VFS_DEFS_H
 
+
+#include <limits.h>
 #include <sys/stat.h>
 
 #include <SupportDefs.h>
@@ -20,4 +23,18 @@ struct fd_info {
 	ino_t	node;
 };
 
+
+/* maximum write size to a pipe/FIFO that is guaranteed not to be interleaved
+   with other writes (aka {PIPE_BUF}; must be >= _POSIX_PIPE_BUF) */
+#define VFS_FIFO_ATOMIC_WRITE_SIZE	(4 * 1024)
+
+/* pipe/FIFO buffer capacity */
+#define VFS_FIFO_BUFFER_CAPACITY	(64 * 1024)
+
+// make sure the constant values are sane
+#if VFS_FIFO_ATOMIC_WRITE_SIZE < _POSIX_PIPE_BUF
+#	error VFS_FIFO_ATOMIC_WRITE_SIZE < _POSIX_PIPE_BUF!
+#endif
+
+
 #endif	/* _SYSTEM_VFS_DEFS_H */