[screen-devel] [bug #48339] Default settings of termios parameters (VKILL, etc.) are ugly

[Valentin Nechayev]

URL:
  <http://savannah.gnu.org/bugs/?48339>

                 Summary: Default settings of termios parameters (VKILL, etc.)
are ugly
                 Project: GNU Screen
            Submitted by: netch
            Submitted on: Wed 29 Jun 2016 09:06:13 AM GMT
                Category: Program Logic
                Severity: 3 - Normal
                Priority: 5 - Normal
                  Status: None
                 Privacy: Public
             Assigned to: None
             Open/Closed: Open
         Discussion Lock: Any
                 Release: Cur Dev Sources
           Fixed Release: None
         Planned Release: None
           Work Required: None

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Details:

There are three issues in the same code chunk so I prefer to note them
together.

I. InitTTY() in tty.c currently has (in master branch):

#if defined(VKILL)
#if (VKILL < MAXCC)
        m->tio.c_cc[VKILL] = Ctrl('H');
#endif

All other settings look reasonable but Ctrl+H for VKILL is strongly weird
because the default for the thorough Unix life is Ctrl+U.

This value is copied from pre-Git times, reasoning isn't known, so I suggest
this is typo going from times of battle between two Backspace styles.

This affects terminals created in initially detached mode, with command like
"screen -c $config -dm" and config lines like

screen -t proxy 0
stuff "~/utils/gasket proxy\n"

the created terminal is badly controllable.

Fix is trivial:

diff --git a/src/tty.c b/src/tty.c
index 585e0f50..d50486f7 100644
--- a/src/tty.c
+++ b/src/tty.c
@@ -272,7 +272,7 @@ void InitTTY(struct mode *m, int ttyflag)
 #endif                         /* VERASE */
 #if defined(VKILL)
 #if (VKILL < MAXCC)
-       m->tio.c_cc[VKILL] = Ctrl('H');
+       m->tio.c_cc[VKILL] = Ctrl('U');
 #endif
 #endif                         /* VKILL */
 #if defined(VEOF)

II. Also, such terminals get VMIN=0, despite tty.c code sets TTYVMIN to 1 and
then sets VMIN to TTYVMIN.

III. For some parameters, it sets values to 0 in context where they supposed
to be disabled:

#if defined(VEOL)
#if (VEOL < MAXCC)
        m->tio.c_cc[VEOL] = 0000;
#endif

the same for VEOL2, VSWTCH. But, 0 is "disable" at Linux and some other
flavors, but not BSD group.

Suggested fix:

diff --git a/src/tty.c b/src/tty.c
index 585e0f50..48af30a6 100644
--- a/src/tty.c
+++ b/src/tty.c
@@ -47,6 +47,10 @@
 #include "telnet.h"
 #include "tty.h"
 
+#ifndef _POSIX_VDISABLE
+#define _POSIX_VDISABLE 0000
+#endif
+
 static void consredir_readev_fn(Event *, void *);
 
 bool separate_sids = true;
@@ -282,17 +286,17 @@ void InitTTY(struct mode *m, int ttyflag)
 #endif                         /* VEOF */
 #if defined(VEOL)
 #if (VEOL < MAXCC)
-       m->tio.c_cc[VEOL] = 0000;
+       m->tio.c_cc[VEOL] = _POSIX_VDISABLE;
 #endif
 #endif                         /* VEOL */
 #if defined(VEOL2)
 #if (VEOL2 < MAXCC)
-       m->tio.c_cc[VEOL2] = 0000;
+       m->tio.c_cc[VEOL2] = _POSIX_VDISABLE;
 #endif
 #endif                         /* VEOL2 */
 #if defined(VSWTCH)
 #if (VSWTCH < MAXCC)
-       m->tio.c_cc[VSWTCH] = 0000;
+       m->tio.c_cc[VSWTCH] = _POSIX_VDISABLE;
 #endif
 #endif                         /* VSWTCH */
 #if defined(VSTART)





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