exec-invoke: move terminal initialization a bit

It's a bit confusing, but we actually initialize the terminal twice for
each service, potentially. One earlier time, where we might end up
firing vhangup() and vt_disallocate(), which is a pretty brutal way to
reset things, by disconnecting and possibly invalidating the tty
completely. When we do this we do not keep any fd open afterwards, since
it quite likely points to a dead connection of a tty.

The 2nd time we initialize things when we actually want to use it.

The first initialization is hence "destructive" (killing any left-overs
from previous uses) the 2nd one "constructive" (preparing things for our
new use), if you so will.

Let's document this distinction in comments, and let's also move both
initializations to exec_invoke(), so that they are easier to see in their
symmetric behaviour. Moreover, let's run the tty initialization after we
opened both input and output, since we need both for doing the fancy
dimension auto init stuff now.

Oh, and of course, one thing to mention: we nowadays initialize
terminals both with ioctl() and with ansi sequences. But the latter
means we need an fd that is open for *write* (since we are *writing*
those ansi sequences to the tty). Hence, resetting via the input fd is
conceptually wrong, it worked only so far if we had O_RDWR open mode
selected)

1 files changed, 5 insertions, 0 deletions

diff --git a/src/core/execute.c b/src/core/execute.c
index 8982af10aa..dc418fd14c 100644
--- a/src/core/execute.c
+++ b/src/core/execute.c
@@ -149,6 +149,11 @@ void exec_context_tty_reset(const ExecContext *context, const ExecParameters *p)
 
         assert(context);
 
+        /* Note that this is potentially a "destructive" reset of a TTY device. It's about getting rid of the
+         * remains of previous uses of the TTY. It's *not* about getting things set up for coming uses. We'll
+         * potentially invalidate the TTY here through hangups or VT disallocations, and hence do not keep a
+         * continous fd open. */
+
         const char *path = exec_context_tty_path(context);
 
         if (p && p->stdout_fd >= 0 && isatty_safe(p->stdout_fd))