Date: Tue, 2 Mar 2004 22:56:57 +0100 From: Erik Trulsson <ertr1013@student.uu.se> To: "Jordan K. Hubbard" <jkh@queasyweasel.com> Cc: freebsd-arch@freebsd.org Subject: Re: Another conformance question... This time fputs(). Message-ID: <20040302215657.GA88174@falcon.midgard.homeip.net> In-Reply-To: <E7470FE8-6C82-11D8-9000-000393BB9222@queasyweasel.com> References: <1060DC2A-6C31-11D8-9000-000393BB9222@queasyweasel.com> <20040302213412.X1223@gamplex.bde.org> <E7470FE8-6C82-11D8-9000-000393BB9222@queasyweasel.com>
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On Tue, Mar 02, 2004 at 11:50:48AM -0800, Jordan K. Hubbard wrote:
> Thanks to everyone (not just bde) for reviewing the fix. Linux was
> right, I was wrong, EBADF it is!
>
> On Mar 2, 2004, at 4:03 AM, Bruce Evans wrote:
>
> >Should be EBADF, as in Linux.
> >
> >> return (EOF);
> >>+ }
> >
> >Otherwise, I agree with this change except for its style bugs
> >(unsorting
> >of the #includes and tab lossage).
>
> Change committed with #includes sorted and proper use of tabs (change
> is consistent with the rest of the file's style).
>
> It's also not clear to me why ENODEV is being returned, though I'm not
> as inclined to blame isatty() since it appears to do the right thing:
>
> #include <stdio.h>
> #include <fcntl.h>
> #include <errno.h>
>
> main() {
> int fd, ret;
>
> fd = open("/dev/null", O_RDONLY);
> ret = isatty(fd);
> printf("ret = %d, errno = %d\n", ret, errno);
> close(fd);
> }
>
> Prints: ret = 0, errno = 25
>
> All isatty() does is call tcgetattr(), it doesn't do an
> ioctl(...TIOCGETA...).
But tcgetattr does call ioctl(..TIOCGETA...).
In particular isatty is implemented as
[...]
retval = (tcgetattr(fd, &t) != -1);
[...]
return retval;
[...]
so if isatty returns 0, then tcgetattr returned -1.
If tcgetattr returns -1 it means some error occured and errno is set to
indicate the type of error.
errno==25 is ENOTTY which is exactly what tcgetattr(3) is documented to
return if the file descriptor does not refer to a terminal (which it
does not do in this example.)
In short: The code above seems to behave absolutely correctly and as
one would expect.
Unless a function actually returns an error, (and the documentation
says it sets errno) errno should be assumed to contain garbage.
>From the intro(2) manpage:
When a system call detects an error, it returns an integer value
indicating failure (usually -1) and sets the variable errno
accordingly. <This allows interpretation of the failure on receiving
a -1 and to take action accordingly.> Successful calls never set
errno; once set, it remains until another error occurs. It should
only be examined after an error. Note that a number of system calls
overload the meanings of these error numbers, and that the meanings
must be interpreted according to the type and circumstances of the
call.
--
<Insert your favourite quote here.>
Erik Trulsson
ertr1013@student.uu.se
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