limits.h: define PIPE_BUF.

headers/posix/limits.h

@@ -40,6 +40,7 @@
 #define OPEN_MAX				(128)
 #define PAGESIZE				(4096)
 #define PATH_MAX				(1024)
+#define PIPE_BUF				(4 * 1024)
 #define PIPE_MAX				(512)
 #define PTHREAD_KEYS_MAX		256
 #define PTHREAD_STACK_MIN		(2 * PAGESIZE)

headers/private/system/vfs_defs.h

@@ -26,7 +26,7 @@ struct fd_info {
 
 /* 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)
+#define VFS_FIFO_ATOMIC_WRITE_SIZE	PIPE_BUF
 
 /* pipe/FIFO buffer capacity */
 #define VFS_FIFO_BUFFER_CAPACITY	(64 * 1024)