RE: [PATCH] tty: n_gsm: fix missing assignment of gsm->receive() in gsmld_attach_gsm()

[Starke, Daniel]

> Fix this by setting the gsm->receive() function when the line 
> discipline is being attached to the terminal device, inside 
> gsmld_attach_gsm(). This will guarantee that the function is assigned 
> and a call to TIOCSTI, which calls gsmld_receive_buf(), will not
> reference a null pointer.

In my opinion there are only two possible ways to fix this:
a) Move the gsm->receive initialization from gsm_activate_mux() to
gsmld_attach_gsm().
b) Avoid calling gsm->receive in gsmld_receive_buf() if not initialized.

The current code might assume that gsm->receive is only called after MUX
activation. Therefore, variant a) may break the code in other places.
I see no need to initialize gsm->receive in gsm_activate_mux() and
gsmld_attach_gsm().

Best regards,
Daniel Starke