While investigating an emacs bug
(https://debbugs.gnu.org/cgi/bugreport.cgi?bug=49524), I noticed a difference in
the behavior of cfsetspeed(3) on Cygwin and Linux. I'm not sure we should "fix"
this, because Cygwin's behavior is consistent with the Linux man page, and
Linux's behavior is not. But I thought I should point it out for the sake of
discussion, because Cygwin generally tries to emulate Linux. Here are the details:
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). Test case:
$ cat cfsetspeed_test.c
#include <termios.h>
#include <stdio.h>
int
main ()
{
struct termios tp;
printf ("Calling cfsetspeed with speed B9600\n");
if (cfsetspeed (&tp, B9600) < 0)
perror ("cfsetspeed");
else
printf ("cfgetispeed reports speed %u\n", cfgetispeed (&tp));
printf ("Calling cfsetspeed with speed 9600\n");
if (cfsetspeed (&tp, 9600) < 0)
perror ("cfsetspeed");
else
printf ("cfgetispeed reports speed %u\n", cfgetispeed (&tp));
}
$ gcc cfsetspeed_test.c
$ ./a.out
Calling cfsetspeed with speed B9600
cfgetispeed reports speed 13
Calling cfsetspeed with speed 9600
cfgetispeed reports speed 13
On Cygwin, however, the output of the same program is:
$ ./a
Calling cfsetspeed with speed B9600
cfgetispeed reports speed 13
Calling cfsetspeed with speed 9600
cfsetspeed: Invalid argument
If we decide that Cygwin should emulate Linux here, it would be a simple matter
to copy the glibc code, which checks whether the speed is a numerical baud rate
and, if so, converts it to a Bnnn constant.
Ken
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