bug#2148: In shell mode, comint-send-input seems to cut off at 254 characters

[Richard M Stallman]

    The obvious fix is to not add this ^D.  At least I could never
    understand what it was supposed to do ("force it though"?  what does
    that mean?).

The problem is that the subprogram is reading from its tty with line
editing, so it won't receive any input until Emacs "types" one of the
few characters that says "give the input to the program".  Until that
occurs, theoretically Emacs could get rid of the pending input by
typing DEL or Backspace or C-u or C-w.

If the system's line-editing buffer gets full, everything hangs.  The
subprogram waits for a complete input line, but Emacs can't finish the
line because it's waiting for space to appear in that buffer (and
anyway the buffer has no room for more).

At least this is what was happening at the time I implemented that code.

If emacs_set_tty turns off the line editing, or turns off the
characters that could cancel input, it would be proper for the kernel
to give the characters to the subprogram right away.  Then the buffer
would never get full.  We could suggest this change in Linux.