Re: Why doesn't ncurses use my Terminfo file's `cols` and `lines`?

[Thomas Dickey]

On Thu, Jun 22, 2023 at 10:11:09AM -0400, Stefan Monnier wrote:
> > It's in the manpage - setupterm:
> 
> Thanks.
> 
> >        The  terminfo  variables lines and columns are initialized by 
> > setupterm
> >        as follows:
> >
> >        •   If use_env(FALSE) has been called, values  for  lines  and  
> > columns
> >            specified in terminfo are used.
> >
> >        •   Otherwise,  if  the  environment variables LINES and COLUMNS 
> > exist,
> >            their values are used.  If these environment variables do not 
> > exist
> >            and  the program is running in a window, the current window size 
> > is
> >            used.  Otherwise, if the environment variables do  not  exist,  
> > the
> >            values for lines and columns specified in the terminfo database 
> > are
> >            used.
> 
> The program is running in a real terminal started from getty started
> from systemd.
> 
> > Also, use_tioctl and use_env.  But aside from adding use_tioctl in 2012
> 
> Aha!  Last time I used that terminal was around year 2000.
> 
> >     https://invisible-island.net/ncurses/NEWS.html#t20120714
> >
> > the rules for initialization haven't changed for a long time (barring bugs
> > of course).  That "current window size" refers to information from a
> > TIOCGWINSZ ioctl.
> 
> In the `strace tput lines` I see that the right terminfo file is read
> and it ends with:
> 
>     ioctl(0, TCGETS, {c_iflag=ICRNL|IXON|IXOFF|IUTF8, 
> c_oflag=NL0|CR0|TAB0|BS0|VT0|FF0|OPOST|ONLCR, 
> c_cflag=B19200|CS8|CREAD|HUPCL|CLOCAL, 
> c_lflag=ISIG|ICANON|ECHO|ECHOE|ECHOK|ECHOCTL|ECHOKE, ...}) = 0
>     ioctl(0, TIOCGWINSZ, {ws_row=24, ws_col=80, ws_xpixel=0, ws_ypixel=0}) = 0
>     statx(1, "", AT_STATX_SYNC_AS_STAT|AT_NO_AUTOMOUNT|AT_EMPTY_PATH, 
> STATX_BASIC_STATS, {stx_mask=STATX_BASIC_STATS|STATX_MNT_ID, 
> stx_attributes=0, stx_mode=S_IFREG|0644, stx_size=6357, ...}) = 0
>     write(1, "24\n", 324
>     )                     = 3
>     exit_group(0)                           = ?
>     +++ exited with 0 +++
> 
> So, IIUC this line:
> 
>     ioctl(0, TIOCGWINSZ, {ws_row=24, ws_col=80, ws_xpixel=0, ws_ypixel=0}) = 0
> 
> says that `tput` queried the kernel about TIOCGWINSZ and the kernel
> replied with 80x24.  So, IIUC this is a kernel bug?

no - it's a default value, and nothing comes along to improve it.

Actually, given the description

        Human Designed Systems HDS3200 model 20; VT220 7bits; 50x132; 
auto-wrap=no

I'd expect that you could use "resize" to get the window size updated.
 
> I see that's what `stty cols NN rows MM` can override this, so, I should
> figure out how to get systemd/getty to do that setup to work around
> the problem.
> 
> > In a quick check, if I disable the TIOCGWINSZ call in ncurses, and test
> > your terminfo, ncurses does set lines/cols as you expect.  If your terminal
> > is connected directly to a serial port, I would not expect stty to give a
> > size -- but if it's through some intermediate application (even something
> > such as ssh, which "should" not helpfully provide a size), then that could
> > be providing a size.
> 
> Indeed, it's weird that the kernel returns 80x24 for a real terminal
> connected via a USB<->RS232 adapter.  Then again, I guess such setups
> are getting extremely rare.
> 
> Thanks,
> 
> 
>         Stefan
> 

-- 
Thomas E. Dickey <dickey@invisible-island.net>
https://invisible-island.net

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