RE: [PATCH 3/3] tty: n_gsm: add TIOCMIWAIT support

Starke, Daniel
2023-02-01T09:30:35Z

> > Add support for the TIOCMIWAIT ioctl on the virtual ttys. This enables the
> > user to wait for virtual modem signals like RING.
> >
> > Signed-off-by: Daniel Starke <daniel.starke@siemens.com>
> > ---
> > drivers/tty/n_gsm.c | 32 ++++++++++++++++++++++++++++++++
> > 1 file changed, 32 insertions(+)
> >
> > diff --git a/drivers/tty/n_gsm.c b/drivers/tty/n_gsm.c
> > index 118511c1fa37..48fb7dad44cd 100644
> > --- a/drivers/tty/n_gsm.c
> > +++ b/drivers/tty/n_gsm.c
> > @@ -1542,6 +1542,7 @@ static void gsm_process_modem(struct tty_struct *tty, struct gsm_dlci *dlci,
> > if (brk & 0x01)
> > tty_insert_flip_char(&dlci->port, 0, TTY_BREAK);
> > dlci->modem_rx = mlines;
> > + wake_up_interruptible(&dlci->gsm->event);
> > }
> >
> > /**
> > @@ -3848,6 +3849,35 @@ static int gsm_modem_update(struct gsm_dlci *dlci, u8 brk)
> > return -EPROTONOSUPPORT;
> > }
> >
> > +/**
> > + * gsm_wait_modem_change - wait for modem status line change
>
> No need for tabs.
>
> Or for kernel doc for static functions, but that's not a big deal.

All other functions follow the same style here. Nevertheless, I will
replace the tabs with spaces. Originally, I had planned a code clean-up
after committing all the changes from my original RFC.

> > + * @dlci: channel
> > + * @mask: modem status line bits
> > + */
> > +
>
> No blank line please, didn't checkpatch warn about that?

No, checkpatch did not warn about this and all other functions follow the
same style. I will remove the blank line.

> > +static int gsm_wait_modem_change(struct gsm_dlci *dlci, u32 mask)
> > +{
> > + struct gsm_mux *gsm = dlci->gsm;
> > + u32 old = dlci->modem_rx & mask;
> > + int ret;
> > +
> > + if (gsm->dead)
> > + return -ENODEV;
> > +
> > + do {
> > + ret = wait_event_interruptible(gsm->event, gsm->dead
> > + || old ^ (dlci->modem_rx & mask));
> > + if (ret)
> > + return ret;
> > + if (dlci->state != DLCI_OPEN)
> > + return -EL2NSYNC;
> > + if (gsm->dead)
> > + return -ENODEV;
> > + } while ((old ^ (dlci->modem_rx & mask)) == 0);
>
> No way to break out of the loop if it goes for forever?

I assume that this is the expected behavior for TIOCMIWAIT. The functions
returns if:
- the requested modem signal changed
- the wait function got interrupted (e.g. by a signal)
- the underlying DLCI was closed
- the underlying ldisc device was removed

I can add that the function returns immediate if a mask has been passed
which matches no modem signal if this is preferred?

Best regards,
Daniel Starke