--- orig/libguile/fports.c
+++ mod/libguile/fports.c
@@ -90,10 +90,10 @@
 /* default buffer size, used if the O/S won't supply a value.  */
 static const size_t default_buffer_size = 1024;
 
-/* create FPORT buffer with specified sizes (or -1 to use default size or
-   0 for no buffer.  */
+/* Create FPORT buffer with specified sizes (or -1 to use default size or
+   0 for no buffer).  */
 static void
-scm_fport_buffer_add (SCM port, long read_size, int write_size)
+scm_fport_buffer_add (SCM port, long read_size, long write_size)
 #define FUNC_NAME "scm_fport_buffer_add"
 {
   scm_t_port *pt = SCM_PTAB_ENTRY (port);
@@ -217,6 +217,115 @@
 }
 #undef FUNC_NAME
 
+SCM_DEFINE (scm_set_port_input_buffer_size_x, "set-port-input-buffer-size!",
+	    2, 0, 0,
+	    (SCM port, SCM size),
+	    "Use a @var{size}-octet input buffer for @var{port}, which "
+	    "must be a file or socket port.  The current input buffer "
+	    "of @var{port} must contain less than @var{size} octets.")
+#define FUNC_NAME s_scm_set_port_input_buffer_size_x
+{
+  scm_t_port *pt;
+  size_t c_size;
+
+  SCM_VALIDATE_FPORT (1, port);
+  c_size = scm_to_uint (size);
+
+  pt = SCM_PTAB_ENTRY (port);
+
+  if (pt->read_buf_size != c_size)
+    {
+      size_t c_offset, c_end;
+      unsigned char *new_buf;
+
+      c_end = pt->read_end - pt->read_buf;
+      c_offset = pt->read_pos - pt->read_buf;
+
+      if (c_offset > c_size)
+	scm_wrong_type_arg_msg (FUNC_NAME, 1, port,
+				"Input buffer must be flushed before it "
+				"can be shrunk");
+
+      if (c_size == 0)
+	new_buf = &pt->shortbuf, c_size = 1;
+      else
+	{
+	  if (pt->read_buf != &pt->shortbuf)
+	    new_buf = scm_gc_realloc (pt->read_buf,
+				      pt->read_buf_size, c_size,
+				      "port buffer");
+	  else
+	    new_buf = scm_gc_malloc (c_size, "port buffer");
+	}
+
+      pt->read_buf = new_buf;
+      pt->read_end = new_buf + c_end;
+      pt->read_pos = new_buf + c_offset;
+      pt->read_buf_size = c_size;
+
+      if ((pt->read_buf_size == 0) && (pt->write_buf_size == 0))
+	SCM_SET_CELL_WORD_0 (port, SCM_CELL_WORD_0 (port) | SCM_BUF0);
+    }
+
+  return SCM_UNSPECIFIED;
+}
+#undef FUNC_NAME
+
+SCM_DEFINE (scm_set_port_output_buffer_size_x, "set-port-output-buffer-size!",
+	    2, 0, 0,
+	    (SCM port, SCM size),
+	    "Use a @var{size}-octet output buffer for @var{port}, which "
+	    "must be a file or socket port.  The current output buffer of "
+	    "@var{port} must contain less than @var{size} octets.")
+#define FUNC_NAME s_scm_set_port_output_buffer_size_x
+{
+  scm_t_port *pt;
+  size_t c_size;
+
+  SCM_VALIDATE_FPORT (1, port);
+  c_size = scm_to_uint (size);
+
+  pt = SCM_PTAB_ENTRY (port);
+
+  if (pt->write_buf_size != c_size)
+    {
+      size_t c_offset, c_end;
+      unsigned char *new_buf;
+
+      c_end = pt->write_end - pt->write_buf;
+      c_offset = pt->write_pos - pt->write_buf;
+
+      if (c_offset > c_size)
+	scm_wrong_type_arg_msg (FUNC_NAME, 1, port,
+				"Output buffer must be flushed before it "
+				"can be shrunk");
+
+      if (c_size == 0)
+	new_buf = &pt->shortbuf, c_size = 1;
+      else
+	{
+	  if (pt->write_buf != &pt->shortbuf)
+	    new_buf = scm_gc_realloc (pt->write_buf,
+				      pt->write_buf_size, c_size,
+				      "port buffer");
+	  else
+	    new_buf = scm_gc_malloc (c_size, "port buffer");
+	}
+
+      pt->write_buf = new_buf;
+      pt->write_end = new_buf + c_end;
+      pt->write_pos = new_buf + c_offset;
+      pt->write_buf_size = c_size;
+
+      if ((pt->read_buf_size == 0) && (pt->write_buf_size == 0))
+	SCM_SET_CELL_WORD_0 (port, SCM_CELL_WORD_0 (port) | SCM_BUF0);
+    }
+
+  return SCM_UNSPECIFIED;
+}
+#undef FUNC_NAME
+
+
 /* Move ports with the specified file descriptor to new descriptors,
  * resetting the revealed count to 0.
  */


--- orig/libguile/fports.h
+++ mod/libguile/fports.h
@@ -49,6 +49,8 @@
 
 SCM_API SCM scm_setbuf0 (SCM port);
 SCM_API SCM scm_setvbuf (SCM port, SCM mode, SCM size);
+SCM_API SCM scm_set_port_input_buffer_size_x (SCM port, SCM size);
+SCM_API SCM scm_set_port_output_buffer_size_x (SCM port, SCM size);
 SCM_API void scm_evict_ports (int fd);
 SCM_API SCM scm_open_file (SCM filename, SCM modes);
 SCM_API SCM scm_fdes_to_port (int fdes, char *mode, SCM name);