[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
bug#37564: [PATCH] don't export LINES and COLUMNS env vars in term to fi
From: |
Matthew Leach |
Subject: |
bug#37564: [PATCH] don't export LINES and COLUMNS env vars in term to fix ncurses applications |
Date: |
Tue, 01 Oct 2019 20:24:14 +0100 |
User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/26.3 (gnu/linux) |
Eli Zaretskii <eliz@gnu.org> writes:
>> From: Matthew Leach <matthew@mattleach.net>
>> Cc: 37564@debbugs.gnu.org
>> Date: Tue, 01 Oct 2019 19:33:39 +0100
>>
>> >> I'm curious as to which programs you are referring? AFAIK, if a program
>> >> tries to read the LINES and COLUMNS environment variables, using
>> >> `getenv()', they don't exist.
>> >
>> > What makes you say that?
>>
>> If I run the C program in my previous post in an xterm and resize I get:
>>
>> getenv: (null) (null)
>> ioctl: 24 80
>> getenv: (null) (null)
>> ioctl: 42 169
>>
>> You can see that doing getenv() on LINES and COLUMNS returns a null
>> pointer. I've tested this same behaviour on gnome-terminal and numerous
>> other terminal emulators.
>
> I simply tried "env | fgrep LINES" and I do see the variable, although
> it wasn't there before I launched Emacs.
I would expect the variable to be there when inside Emacs as it has
exported it. You should find that it won't exist if ran outside Emacs,
for example in xterm.
> 'env' is just another program accessing the environment, right? I have
> no idea why your test program doesn't see that, but then I'm far from
> being an expert on these issues.
Indeed, it does see the variables if I run inside Emacs. If I run it
outside then they are not there, on my machine anyway.
>> > Emacs exports these variables into the environment that is passed to
>> > child subprocesses, so those subprocesses will definitely see them
>> > using getenv.
>>
>> I'm no expert on how these things work but it doesn't appear to be the
>> way that it's done, on my machine anyway. Perhaps there are programs
>> that uses these variables on MacOS or Windows?
>
> I tried the above on a Trisquel GNU/Windows machine, FWIW.
I'm running on Arch GNU/Linux this end.
>> I'm testing this on the latest Emacs Git version. I can see that
>> window-adjust-process-window-size-function is used in term.el however,
>> this doesn't appear to update the environment variables exported to the
>> terminal process.
>
> AFAIR, it's supposed to send the corresponding ioctl command, in
> addition to setting LINES and COLUMNS.
>
>> If I run the same program with term on Emacs git and
>> resize I get:
>>
>> getenv: 31 80
>> ioctl: 30 89
>> getenv: 31 80
>> ioctl: 30 90
>> getenv: 31 80
>> ioctl: 30 91
>> getenv: 31 80
>> ioctl: 31 92
>> getenv: 31 80
>> ioctl: 31 93
>> getenv: 31 80
>> ioctl: 31 94
>> ...
>>
>> Notice that the values returned by getenv don't change.
>
> Again, the "env | fgrep LINES" method does show the change when I
> resize the window on the machine I tried this, so I'm unsure why you
> don't see it.
Ah, indeed if I try and resize and print the variable it has updated:
matthew@hopton ~ $ env | grep -i lines
LINES=30
matthew@hopton ~ $ env | grep -i lines
LINES=12
I think the issue is that the environment can't be while a process is
running; the environment variables are fixed when the program has
started. For a ncurses application this presents a problem as LINES and
COLUMNS can't be updated when the window size is changed and the program
handles a SIGWINCH. You can see that on the output above.
>> Given that this functionality is broken, I'm suggesting that we don't
>> export the variables.
>
> I don't agree that it's broken; it isn't for me. I think someone who
> understands more than I do about this stuff should chime in and
> explain why we see such different results.
I think the above explains what's going on. Perhaps that's why terminal
emulators don't export LINES and COLUMNS to programs so an ioctl() is used
instead?
--
Matt
- bug#37564: [PATCH] don't export LINES and COLUMNS env vars in term to fix ncurses applications, Eli Zaretskii, 2019/10/01
- bug#37564: [PATCH] don't export LINES and COLUMNS env vars in term to fix ncurses applications, Matthew Leach, 2019/10/01
- bug#37564: [PATCH] don't export LINES and COLUMNS env vars in term to fix ncurses applications, Eli Zaretskii, 2019/10/01
- bug#37564: [PATCH] don't export LINES and COLUMNS env vars in term to fix ncurses applications, Matthew Leach, 2019/10/01
- bug#37564: [PATCH] don't export LINES and COLUMNS env vars in term to fix ncurses applications, Eli Zaretskii, 2019/10/01
- bug#37564: [PATCH] don't export LINES and COLUMNS env vars in term to fix ncurses applications, Eli Zaretskii, 2019/10/01
- bug#37564: [PATCH] don't export LINES and COLUMNS env vars in term to fix ncurses applications,
Matthew Leach <=
- bug#37564: [PATCH] don't export LINES and COLUMNS env vars in term to fix ncurses applications, Eli Zaretskii, 2019/10/01
- bug#37564: [PATCH] don't export LINES and COLUMNS env vars in term to fix ncurses applications, Glenn Morris, 2019/10/03
- bug#37564: [PATCH] don't export LINES and COLUMNS env vars in term to fix ncurses applications, Matthew Leach, 2019/10/04
- bug#37564: [PATCH] don't export LINES and COLUMNS env vars in term to fix ncurses applications, Matthew Leach, 2019/10/04
- bug#37564: [PATCH] don't export LINES and COLUMNS env vars in term to fix ncurses applications, Lars Ingebrigtsen, 2019/10/07
- bug#37564: [PATCH] don't export LINES and COLUMNS env vars in term to fix ncurses applications, Andreas Schwab, 2019/10/07
- bug#37564: [PATCH] don't export LINES and COLUMNS env vars in term to fix ncurses applications, Lars Ingebrigtsen, 2019/10/08