Re: dialog --pause not timing out on serial console (dialog 1.2)

[Rich Coe]

Hi Stefan,

    I looked at the linux tty driver, and I was partially correct.
    TCSETSW is going to wait for the output to drain before setting the
    new termios attributes. 

    So no carrier or blocked output is going to hang the TCSETSW until
    the output drains.

    Since this hangs without a terminal attached, the problem is probably
    some output written to the terminal line before anyone can set CLOCAL.
    And that's going to prevent any changes to the tty driver until a 
    device is connected.

    What you'll probably need is 'terminator' to wrap DTR to DCD to make
    the driver think a terminal is attached when there is none.

Rich

On Thu, 15 Jul 2021 08:14:39 -0500
Rich Coe <rich.coe@elucidbio.com> wrote:
> Hi Stefan,
> 
> I seem to recall that a serial tty would block setting line attributes
> in some cases if there was no carrier (CD) present on the line.
> I also think there might be a line setting to ignore the CD value.
> 
> I'll have to do some research to refresh my memory.
> 
> Rich
> 
> On Wed, 14 Jul 2021 16:21:56 +0300
> Stefan Puiu <stefan.puiu@gmail.com> wrote:
> > Hi Thomas,
> > 
> > Sorry for resurrecting an old thread, but I dug a bit deeper into this
> > and was wondering if the new info rings any bells.
> > 
> > On Thu, Jan 28, 2021 at 9:59 PM Thomas Dickey <dickey@his.com> wrote:
> > >
> > [...]
> > > > > > We have dialog 1.2 (release 4.20130902.fc20) and ncurses 5.9 
> > > > > > (release
> > > > > > 12.20130511.fc20), I know, ancient stuff.
> > > > >
> > > > > yes, that's known and supposed to have been fixed.
> > > > > This appears to be relevant:
> > > > >
> > > > > https://invisible-island.net/dialog/CHANGES.html#t20030818
> > > > >         + better solution for initializing curses when "--stdout" 
> > > > > option is
> > > > >           used, e.g., use stderr for the output if it is a tty.  Also 
> > > > > correct
> > > > >           the error handling, so dialog exits with an error if it 
> > > > > cannot
> > > > >           find a way to do output (Debian #205509).
> > > >
> > > > Thanks for the pointer. I think that change is a bit old, though, the
> > > > Fedora package seems to be from 2013, and from the look of the release
> > > > tag (and the RPM changelog), I think it's based on
> > > > dialog-1.2.20130902.
> > >
> > > agreed - I mentioned it because I didn't notice further change notes
> > > for this issue (though I seem to recall some followup).
> > 
> > Somebody managed to reproduce this again, and this time I debugged
> > dialog a bit with gdb, and it seems to be stuck inside a tcsetattr
> > call:
> > 
> > (gdb) bt
> > #0  0x0000003b96aeb5cc in __GI_tcsetattr (fd=1,
> > optional_actions=optional_actions@entry=1,
> >     termios_p=termios_p@entry=0x7fff17feba40) at
> > ../sysdeps/unix/sysv/linux/tcsetattr.c:83
> > #1  0x0000003b98e1677a in _nc_set_tty_mode
> > (buf=buf@entry=0x7fff17feba40) at
> > ../../ncurses/tinfo/lib_ttyflags.c:108
> > #2  0x0000003b98e10d8c in cbreak () at ../../ncurses/tinfo/lib_raw.c:155
> > #3  0x0000003b97214f33 in _nc_initscr () at 
> > ../../ncurses/base/lib_newterm.c:79
> > #4  newterm (name=<optimized out>, ofp=<optimized out>, ifp=<optimized
> > out>) at ../../ncurses/base/lib_newterm.c:332
> > #5  0x0000003b97211343 in initscr () at ../../ncurses/base/lib_initscr.c:87
> > #6  0x0000003e24225f5d in init_dialog (input=<optimized out>,
> > output=0x3b96db81c0 <_IO_2_1_stderr_>) at util.c:385
> > #7  0x0000000000402351 in main (argc=12, argv=0x7fff17fec638) at 
> > dialog.c:1844
> > 
> > (gdb) info locals
> > resultvar = 18446744073709551104
> > k_termios = {c_iflag = 21504, c_oflag = 5, c_cflag = 7346, c_lflag =
> > 2105, c_line = 0 '\000',
> >   c_cc = 
> > "\003\034\177\025\004\000\001\000\021\023\032\000\022\017\027\026\000\000"}
> > cmd = <optimized out>
> > retval = <optimized out>
> > 
> > 
> > As far as I can tell, it's trying to call ioctl 0x5043 (TCSETSW) on fd
> > 1 (stdout), and that call blocks. Maybe the serial driver in the
> > kernel is getting blocked on something? Any ideas?
> > 
> > Thanks in advance,
> > Stefan.
> > 
> 
> 
> -- 
> Rich Coe <rich.coe@elucidbio.com>
> 


-- 
Rich Coe <rich.coe@elucidbio.com>