[Bug 10056] False error on serial port read

http://bugs.winehq.org/show_bug.cgi?id=10056

Wolfgang Walter  changed:

What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |wolfgang.walter@studentenwer
                   |                            |k.mhn.de

--- Comment #3 from Wolfgang Walter   2008-01-07 13:35:19 ---
Posix does not define whether VMIN/VTIME mechanism or O_NONBLOCK has preference
in "Non-canonical Mode Input Processing":

See

http://www.opengroup.org/onlinepubs/007908799/xbd/termios.html

"In non-canonical mode input processing, input bytes are not assembled into
lines, and erase and kill processing does not occur. The values of the MIN and
TIME members of the c_cc array are used to determine how to process the bytes
received. The ISO POSIX-1 standard does not specify whether the setting of
O_NONBLOCK takes precedence over MIN or TIME settings. Therefor, if O_NONBLOCK
is set, read() may return immediately, regardless of the setting of MIN or
TIME. Also, if no data is available, read() may either return 0, or return -1
with errno set to [EAGAIN]."

I think that i.e. Linux returns with 0 instead of -1, errno=EAGAIN in this case
whereas Solarix always returns with -1, errno=EAGAIN.

Setting VMIN=1 probably does not solve the problem as then read may block on
some OS even for non-blocking handles. (Though for linux it should work).

The last patch of Adrian Cox isn't a perfect solution, either. With VMIN=0 EOF
is not detected any more for serial devices. This is a regression for systems
where O_NONBLOCK has priority over VMIN/VTIME (On the other hand this patch
makes serial devices work at all on those systems where VMIN,VTIME semantics
win).

Another workaround is to check for serial fds if there is actually something to
read:

for (;;)
{
    int n = 0;
    if (type != FD_TYPE_SERIAL || (ioctl(unix_handle, FIONREAD, &n) != -1 &&
n>0))
    {
        if ((result = read( unix_handle, (char *)buffer + total, length - total
)) >= 0)
        {
            total += result;
            .....
        }
        else
        {
            .....
        }
    }
    if (!(options & (FILE_SYNCHRONOUS_IO_ALERT |
FILE_SYNCHRONOUS_IO_NONALERT)))
.....
.....
}