netdev - Re: small design problem with hso driver

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Date:	Thu, 09 Oct 2008 11:56:38 +0200
From:	Denis Joseph Barrow <D.Barow@...ion.com>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Filip Aben <F.Aben@...ion.com>,
	Andrew Bird <ajb@...eresystems.co.uk>,
	Paul Hardwick <P.Hardwick@...ion.com>
CC:	Greg KH <greg@...ah.com>,
	Linux USB kernel mailing list <linux-usb@...r.kernel.org>,
	Linux netdev Mailing list <netdev@...r.kernel.org>
Subject: Re: small design problem with hso driver

Hi Alan,
No they are not.
Have a look at.
/drivers/char/nozomi.c
admittedly it's written by some of the same guys.
/* Called when the userspace process opens the tty, /dev/noz*.  */
static int ntty_open(struct tty_struct *tty, struct file *file)
{
	struct port *port = get_port_by_tty(tty);
	struct nozomi *dc = get_dc_by_tty(tty);
	unsigned long flags;

	if (!port || !dc || dc->state != NOZOMI_STATE_READY)
		return -ENODEV;

	if (mutex_lock_interruptible(&port->tty_sem))
		return -ERESTARTSYS;

	port->tty_open_count++;
	dc->open_ttys++;

	/* Enable interrupt downlink for channel */
	if (port->tty_open_count == 1) {
		tty->low_latency = 1;
		tty->driver_data = port;
		port->tty = tty;
		DBG1("open: %d", port->token_dl);
		spin_lock_irqsave(&dc->spin_mutex, flags);
		dc->last_ier = dc->last_ier | port->token_dl;
		writew(dc->last_ier, dc->reg_ier);
		spin_unlock_irqrestore(&dc->spin_mutex, flags);
	}

	mutex_unlock(&port->tty_sem);

	return 0;
}

/* Called when the userspace process close the tty, /dev/noz*. */
static void ntty_close(struct tty_struct *tty, struct file *file)
{
	struct nozomi *dc = get_dc_by_tty(tty);
	struct port *port = tty->driver_data;
	unsigned long flags;

	if (!dc || !port)
		return;

	if (mutex_lock_interruptible(&port->tty_sem))
		return;

	if (!port->tty_open_count)
		goto exit;

	dc->open_ttys--;
	port->tty_open_count--;

	if (port->tty_open_count == 0) {
		DBG1("close: %d", port->token_dl);
		spin_lock_irqsave(&dc->spin_mutex, flags);
		dc->last_ier &= ~(port->token_dl);
		writew(dc->last_ier, dc->reg_ier);
		spin_unlock_irqrestore(&dc->spin_mutex, flags);
	}

exit:
	mutex_unlock(&port->tty_sem);
}


Alan Cox wrote:
>> Surely if the driver returns an error code on hso_serial_open
>> hso_serial_close shouldn't be called
>> or have I a complete misunderstanding
>> of char driver semantics.
> 
> Generally yes that would be sane. The tty layer has always called the
> close method of drivers on a failed open and the drivers are all written
> assuming that.
> 
> It would be nice to change but there are far bigger fish to fry.
> 
> Alan


-- 
best regards,
D.J. Barrow
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