On 4/27/2022 11:53 AM, Eli Zaretskii wrote:
>> Date: Wed, 27 Apr 2022 11:16:46 -0400
>> From: Ken Brown <kbrown@cornell.edu>
>>
>> +# ifdef CYGWIN
>> +  /* ttname */
>> +  strcpy (procfn_end, "/ctty");
>> +  fd = emacs_open (fn, O_RDONLY, 0);
>> +  if (fd < 0)
>> +    nread = 0;
>> +  else
>> +    {
>> +      record_unwind_protect_int (close_file_unwind, fd);
>> +      nread = emacs_read_quit (fd, procbuf, sizeof procbuf);
>> +    }
>> +  /* /proc/<pid>/ctty should always end in newline. */
>> +  if (0 < nread && procbuf[nread - 1] == '\n')
>> +    procbuf[nread - 1] = '\0';
>> +  else
>> +    procbuf[0] = '\0';
>> +  attrs = Fcons (Fcons (Qttname, build_string (procbuf)), attrs);
> 
> Is what you read from /proc/<pid>/ctty guaranteed to be pure-ASCII
> string?

Yes.  It's typically something like "/dev/pty0".

> P.S. Doesn't this warrant a NEWS entry?

Revised patch attached, with a NEWS entry.

Ken