staging: Add dgrp driver for Digi Realport devices

config DGRP

       tristate "Digi Realport driver"

       default n

       depends on SYSFS

       ---help---

       Support for Digi Realport devices.  These devices allow you to

       access remote serial ports as if they are local tty devices.  This

       will build the kernel driver, you will still need the userspace

       component to make your Realport device work.

obj-$(CONFIG_DGRP) += dgrp.o

dgrp-y := 			\

	dgrp_common.o 		\

	dgrp_dpa_ops.o 		\

	dgrp_driver.o 		\

	dgrp_mon_ops.o 	 	\

	dgrp_net_ops.o 		\

	dgrp_ports_ops.o 	\

	dgrp_specproc.o 	\

	dgrp_tty.o 		\

	dgrp_sysfs.o

The user space code to work with this driver is located at

https://github.com/wfp5p/dgrp-utils

- Use configfs for config stuff.  This will require changes to the

  user space code.

- Check the calls to tty_register_device.  In particular, check to see

  if there should be some handling for IS_ERR(classp).

- dgrp_send() and dgrp_receive() could use some refactoring

/*

 *

 * Copyright 1999 Digi International (www.digi.com)

 *     James Puzzo <jamesp at digi dot com>

 *

 * This program is free software; you can redistribute it and/or modify

 * it under the terms of the GNU General Public License as published by

 * the Free Software Foundation; either version 2, or (at your option)

 * any later version.

 *

 * This program is distributed in the hope that it will be useful,

 * but WITHOUT ANY WARRANTY, EXPRESS OR IMPLIED; without even the

 * implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR

 * PURPOSE.  See the GNU General Public License for more details.

 *

 */

/*

 *

 *  Filename:

 *

 *     dgrp_common.c

 *

 *  Description:

 *

 *     Definitions of global variables and functions which are either

 *     shared by the tty, mon, and net drivers; or which cross them

 *     functionally (like the poller).

 *

 *  Author:

 *

 *     James A. Puzzo

 *

 */

#include <linux/errno.h>

#include <linux/tty.h>

#include <linux/sched.h>

#include <linux/cred.h>

#include "dgrp_common.h"

/**

 * dgrp_carrier -- check for carrier change state and act

 * @ch: struct ch_struct *

 */

void dgrp_carrier(struct ch_struct *ch)

{

	struct nd_struct *nd;

	int virt_carrier = 0;

	int phys_carrier = 0;

	/* fix case when the tty has already closed. */

	if (!ch)

		return;

	nd  = ch->ch_nd;

	if (!nd)

		return;

	/*

	 *  If we are currently waiting to determine the status of the port,

	 *  we don't yet know the state of the modem lines.  As a result,

	 *  we ignore state changes when we are waiting for the modem lines

	 *  to be established.  We know, as a result of code in dgrp_net_ops,

	 *  that we will be called again immediately following the reception

	 *  of the status message with the true modem status flags in it.

	 */

	if (ch->ch_expect & RR_STATUS)

		return;

	/*

	 * If CH_HANGUP is set, we gotta keep trying to get all the processes

	 * that have the port open to close the port.

	 * So lets just keep sending a hangup every time we get here.

	 */

	if ((ch->ch_flag & CH_HANGUP) &&

	    (ch->ch_tun.un_open_count > 0))

		tty_hangup(ch->ch_tun.un_tty);

	/*

	 *  Compute the effective state of both the physical and virtual

	 *  senses of carrier.

	 */

	if (ch->ch_s_mlast & DM_CD)

		phys_carrier = 1;

	if ((ch->ch_s_mlast & DM_CD) ||

	    (ch->ch_digi.digi_flags & DIGI_FORCEDCD) ||

	    (ch->ch_flag & CH_CLOCAL))

		virt_carrier = 1;

	/*

	 *  Test for a VIRTUAL carrier transition to HIGH.

	 *

	 *  The CH_HANGUP condition is intended to prevent any action

	 *  except for close.  As a result, we ignore positive carrier

	 *  transitions during CH_HANGUP.

	 */

	if (((ch->ch_flag & CH_HANGUP)  == 0) &&

	    ((ch->ch_flag & CH_VIRT_CD) == 0) &&

	    (virt_carrier == 1)) {

		/*

		 * When carrier rises, wake any threads waiting

		 * for carrier in the open routine.

		 */

		nd->nd_tx_work = 1;

		if (waitqueue_active(&ch->ch_flag_wait))

			wake_up_interruptible(&ch->ch_flag_wait);

	}

	/*

	 *  Test for a PHYSICAL transition to low, so long as we aren't

	 *  currently ignoring physical transitions (which is what "virtual

	 *  carrier" indicates).

	 *

	 *  The transition of the virtual carrier to low really doesn't

	 *  matter... it really only means "ignore carrier state", not

	 *  "make pretend that carrier is there".

	 */

	if ((virt_carrier == 0) &&

	    ((ch->ch_flag & CH_PHYS_CD) != 0) &&

	    (phys_carrier == 0)) {

		/*

		 * When carrier drops:

		 *

		 *   Do a Hard Hangup if that is called for.

		 *

		 *   Drop carrier on all open units.

		 *

		 *   Flush queues, waking up any task waiting in the

		 *   line discipline.

		 *

		 *   Send a hangup to the control terminal.

		 *

		 *   Enable all select calls.

		 */

		nd->nd_tx_work = 1;

		ch->ch_flag &= ~(CH_LOW | CH_EMPTY | CH_DRAIN | CH_INPUT);

		if (waitqueue_active(&ch->ch_flag_wait))

			wake_up_interruptible(&ch->ch_flag_wait);

		if (ch->ch_tun.un_open_count > 0)

			tty_hangup(ch->ch_tun.un_tty);

		if (ch->ch_pun.un_open_count > 0)

			tty_hangup(ch->ch_pun.un_tty);

	}

	/*

	 *  Make sure that our cached values reflect the current reality.

	 */

	if (virt_carrier == 1)

		ch->ch_flag |= CH_VIRT_CD;

	else

		ch->ch_flag &= ~CH_VIRT_CD;

	if (phys_carrier == 1)

		ch->ch_flag |= CH_PHYS_CD;

	else

		ch->ch_flag &= ~CH_PHYS_CD;

}

/**

 * dgrp_chk_perm() -- check permissions for net device

 * @inode: pointer to inode structure for the net communication device

 * @op: operation to be tested

 *

 * The file permissions and ownerships are tested to determine whether

 * the operation "op" is permitted on the file pointed to by the inode.

 * Returns 0 if the operation is permitted, -EACCESS otherwise

 */

int dgrp_chk_perm(int mode, int op)

{

	if (!current_euid())

		mode >>= 6;

	else if (in_egroup_p(0))

		mode >>= 3;

	if ((mode & op & 0007) == op)

		return 0;

	if (capable(CAP_SYS_ADMIN))

		return 0;

	return -EACCES;

}

/* dgrp_chk_perm wrapper for permission call in struct inode_operations */

int dgrp_inode_permission(struct inode *inode, int op)

{

	return dgrp_chk_perm(inode->i_mode, op);

}