From:	pfitz AT pratique DOT fr (Tony FITZPATRICK)
Subject:	RE: "info.exe" finally working on W95
13 Mar 1997 18:04:21 -0800 :
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Original-To:	Sergey Okhapkin <sos AT prospect DOT com DOT ru>
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At 11:56 13/03/97 +0300, you wrote:
>>
>> #include <sys/fcntl.h>
>> #define O_NDELAY	_FNDELAY
>> extern int ndelay_set;
>>
>
>It's better to use c_cc[VMIN] and c_cc[VTIME] fields of termios structure 
>for this. Would You like to correct Your patch according to this note?
>
Thanks for the response and I agree with you that "fhandler.cc" should also
take into account the case were VMIN and VTIME are both zero as it has the
same effect as O_NDELAY. However, if I understand you correctly, I still
have a problem with O_NDELAY. I could interpret O_NELAY in "fcntl" and set
VMIN and VTIME to zero for "fhandler" to interpret later but I would have to
save the current values of VMIN and VTIME to restore them the next time
"fcntl" is called without the O_NDELAY flag and it is this that worries me.
"info.exe" is an example of a program which uses both VMIN/VTIME and
O_NDELAY in the same program. It appears to use O_NDELAY to temporarily
override the VMIN/VTIME settings. Using VMIN/VTIME to implement O_NDELAY
would work in this case but it would not in the opposite case.

VMIN=a VTIME=b

fcntl (tty, F_SETFL, (flags | O_NDELAY));
...
  ttybuff.c_cc[VMIN] = 1;
  ttybuff.c_cc[VTIME] = 0;
  tcsetattr (tty, TCSANOW, &ttybuff);
...
fcntl (tty, F_SETFL, flags);

VMIN=a VTIME=b and not VMIN=1 VTIME=0 as they should be!

I accept that this kind of programming is improbable but anything is
possible. I haven't found any documentation that says O_NDELAY takes
priority over VMIN/VTIME either. O_NDELAY and VMIN/VTIME work on entirely
different structures and creating this kind of interaction between them does
not seem to me to be a good idea, it is also not necessary.

I have to admit however that I don't understand the difference between the
attributes of a "file descriptor", a "console" and a "terminal" and why
there are two ways to do the same thing, still, nobodys perfect.


                                        Tony

  






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