Cygwin: cfsetspeed: allow speed to be a numerical baud rate

The Linux man page for cfsetspeed(3) specifies that the speed argument
must be one of the constants Bnnn (e.g., B9600) defined in termios.h.
But Linux in fact allows the speed to be the numerical baud rate
(e.g., 9600).  For consistency with Linux, we now do the same.

Addresses: https://cygwin.com/pipermail/cygwin/2021-July/248887.html

winsup/cygwin/release/3.2.1

@@ -5,6 +5,10 @@ What's new:
 What changed:
 -------------
 
+- The speed argument to cfsetspeed(3) can now be a numerical baud rate
+  rather than a Bnnn constant, as on Linux.
+  Addresses: https://cygwin.com/pipermail/cygwin/2021-July/248887.html
+
 
 Bug Fixes
 ---------

winsup/cygwin/termios.cc

@@ -325,12 +325,71 @@ cfsetispeed (struct termios *in_tp, speed_t speed)
   return res;
 }
 
+struct speed_struct
+{
+  speed_t value;
+  speed_t internal;
+};
+
+static const struct speed_struct speeds[] =
+  {
+    { 0, B0 },
+    { 50, B50 },
+    { 75, B75 },
+    { 110, B110 },
+    { 134, B134 },
+    { 150, B150 },
+    { 200, B200 },
+    { 300, B300 },
+    { 600, B600 },
+    { 1200, B1200 },
+    { 1800, B1800 },
+    { 2400, B2400 },
+    { 4800, B4800 },
+    { 9600, B9600 },
+    { 19200, B19200 },
+    { 38400, B38400 },
+    { 57600, B57600 },
+    { 115200, B115200 },
+    { 128000, B128000 },
+    { 230400, B230400 },
+    { 256000, B256000 },
+    { 460800, B460800 },
+    { 500000, B500000 },
+    { 576000, B576000 },
+    { 921600, B921600 },
+    { 1000000, B1000000 },
+    { 1152000, B1152000 },
+    { 1500000, B1500000 },
+    { 2000000, B2000000 },
+    { 2500000, B2500000 },
+    { 3000000, B3000000 },
+  };
+
+/* Given a numerical baud rate (e.g., 9600), convert it to a Bnnn
+   constant (e.g., B9600). */
+static speed_t
+convert_speed (speed_t speed)
+{
+  for (size_t i = 0; i < sizeof speeds / sizeof speeds[0]; i++)
+    {
+      if (speed == speeds[i].internal)
+	return speed;
+      else if (speed == speeds[i].value)
+	return speeds[i].internal;
+    }
+  return speed;
+}
+
 /* cfsetspeed: 4.4BSD */
+/* Following Linux (undocumented), allow speed to be a numerical baud rate. */
 extern "C" int
 cfsetspeed (struct termios *in_tp, speed_t speed)
 {
   struct termios *tp = __tonew_termios (in_tp);
   int res;
+
+  speed = convert_speed (speed);
   /* errors come only from unsupported baud rates, so setspeed() would return
      identical results in both calls */
   if ((res = setspeed (tp->c_ospeed, speed)) == 0)

winsup/doc/new-features.xml

@@ -71,11 +71,16 @@ facl(2) now fails with EBADF on a file opened with O_PATH.
 </para></listitem>
 
 <listitem><para>
-- Allow to start Windows Store executables via their "app execution
+Allow to start Windows Store executables via their "app execution
 aliases".  Handle these aliases (which are special reparse points)
 as symlinks to the actual executables.
 </para></listitem>
 
+<listitem><para>
+The speed argument to cfsetspeed(3) can now be a numerical baud rate
+rather than a Bnnn constant, as on Linux.
+</para></listitem>
+
 </itemizedlist>
 
 </sect2>