/* sane - Scanner Access Now Easy.

   Copyright (C) 2009-12 Stéphane Voltz <stef.dev@free.fr>

   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 of the
   License, or (at your option) any later version.

   This program is distributed in the hope that it will be useful, but
   WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program.  If not, see <https://www.gnu.org/licenses/>.
*/
/*   --------------------------------------------------------------------------

*/

/* ------------------------------------------------------------------------- */
/*! \mainpage Primax PagePartner Parallel Port scanner Index Page
 *
 * \section intro_sec Introduction
 *
 * This backend provides support for the Prima PagePartner sheet fed parallel
 * port scanner.
 *
 * \section sane_api SANE API
 *
 * \subsection sane_flow sane flow
   SANE FLOW
   - sane_init() : initialize backend, attach scanners.
   	- sane_get_devices() : query list of scanner devices, backend must
                           	probe for new devices.
   	- sane_open() : open a particular scanner device, adding a handle
   		     	to the opened device
		- sane_set_io_mode() : set blocking mode
		- sane_get_select_fd() : get scanner fd
		- sane_get_option_descriptor() : get option information
		- sane_control_option() : change option values
		- sane_start() : start image acquisition
			- sane_get_parameters() : returns actual scan parameters for the ongoing scan
			- sane_read() : read image data
		- sane_cancel() : cancel operation, end scan
   	- sane_close() : close opened scanner device, freeing scanner handle
   - sane_exit() : terminate use of backend, freeing all resources for attached
   		   devices when last frontend quits
 */

/**
 * the build number allow to know which version of the backend is running.
 */
#define BUILD 2301

#include "p5.h"

/**
 * Import directly the low level part needed to
 * operate scanner. The alternative is to prefix all public functions
 * with sanei_p5_ ,and have all the functions prototyped in
 * p5_device.h .
 */
#include "p5_device.c"

/**
 * number of time the backend has been loaded by sane_init.
 */
static int init_count = 0;

/**
 * NULL terminated list of opened frontend sessions. Sessions are
 * inserted here on sane_open() and removed on sane_close().
 */
static P5_Session *sessions = NULL;

/**
 * NULL terminated list of detected physical devices.
 * The same device may be opened several time by different sessions.
 * Entry are inserted here by the attach() function.
 * */
static P5_Device *devices = NULL;

/**
 * NULL terminated list of devices needed by sane_get_devices(), since
 * the result returned must stay consistent until next call.
 */
static const SANE_Device **devlist = 0;

/**
 * list of possible color modes
 */
static SANE_String_Const mode_list[] = {
  SANE_I18N (COLOR_MODE),
  SANE_I18N (GRAY_MODE),
  /* SANE_I18N (LINEART_MODE), not supported yet */
  0
};

static SANE_Range x_range = {
  SANE_FIX (0.0),		/* minimum */
  SANE_FIX (216.0),		/* maximum */
  SANE_FIX (0.0)		/* quantization */
};

static SANE_Range y_range = {
  SANE_FIX (0.0),		/* minimum */
  SANE_FIX (299.0),		/* maximum */
  SANE_FIX (0.0)		/* no quantization */
};

/**
 * finds the maximum string length in a string array.
 */
static size_t
max_string_size (const SANE_String_Const strings[])
{
  size_t size, max_size = 0;
  SANE_Int i;

  for (i = 0; strings[i]; ++i)
    {
      size = strlen (strings[i]) + 1;
      if (size > max_size)
	max_size = size;
    }
  return max_size;
}

/**> placeholders for decoded configuration values */
static P5_Config p5cfg;


/* ------------------------------------------------------------------------- */

/*
 * SANE Interface
 */


/**
 * Called by SANE initially.
 *
 * From the SANE spec:
 * This function must be called before any other SANE function can be
 * called. The behavior of a SANE backend is undefined if this
 * function is not called first. The version code of the backend is
 * returned in the value pointed to by version_code. If that pointer
 * is NULL, no version code is returned. Argument authorize is either
 * a pointer to a function that is invoked when the backend requires
 * authentication for a specific resource or NULL if the frontend does
 * not support authentication.
 */
SANE_Status
sane_init (SANE_Int * version_code, SANE_Auth_Callback authorize)
{
  SANE_Status status;

  authorize = authorize;	/* get rid of compiler warning */

  init_count++;

  /* init backend debug */
  DBG_INIT ();
  DBG (DBG_info, "SANE P5 backend version %d.%d-%d\n",
       SANE_CURRENT_MAJOR, SANE_CURRENT_MINOR, BUILD);
  DBG (DBG_proc, "sane_init: start\n");
  DBG (DBG_trace, "sane_init: init_count=%d\n", init_count);

  if (version_code)
    *version_code = SANE_VERSION_CODE (SANE_CURRENT_MAJOR, SANE_CURRENT_MINOR, BUILD);

  /* cold-plugging case : probe for already plugged devices */
  status = probe_p5_devices ();

  DBG (DBG_proc, "sane_init: exit\n");
  return status;
}


/**
 * Called by SANE to find out about supported devices.
 *
 * From the SANE spec:
 * This function can be used to query the list of devices that are
 * available. If the function executes successfully, it stores a
 * pointer to a NULL terminated array of pointers to SANE_Device
 * structures in *device_list. The returned list is guaranteed to
 * remain unchanged and valid until (a) another call to this function
 * is performed or (b) a call to sane_exit() is performed. This
 * function can be called repeatedly to detect when new devices become
 * available. If argument local_only is true, only local devices are
 * returned (devices directly attached to the machine that SANE is
 * running on). If it is false, the device list includes all remote
 * devices that are accessible to the SANE library.
 *
 * SANE does not require that this function is called before a
 * sane_open() call is performed. A device name may be specified
 * explicitly by a user which would make it unnecessary and
 * undesirable to call this function first.
 * @param device_list pointer where to store the device list
 * @param local_only SANE_TRUE if only local devices are required.
 * @return SANE_STATUS_GOOD when successful
 */
SANE_Status
sane_get_devices (const SANE_Device *** device_list, SANE_Bool local_only)
{
  int dev_num, devnr;
  struct P5_Device *device;
  SANE_Device *sane_device;
  int i;

  DBG (DBG_proc, "sane_get_devices: start: local_only = %s\n",
       local_only == SANE_TRUE ? "true" : "false");

  /* free existing devlist first */
  if (devlist)
    {
      for (i = 0; devlist[i] != NULL; i++)
	free ((void *)devlist[i]);
      free (devlist);
      devlist = NULL;
    }

  /**
   * Since sane_get_devices() may be called repeatedly to detect new devices,
   * the device detection must be run at each call. We are handling
   * hot-plugging : we probe for devices plugged since sane_init() was called.
   */
  probe_p5_devices ();

  /* if no devices detected, just return an empty list */
  if (devices == NULL)
    {
      devlist = malloc (sizeof (devlist[0]));
      if (!devlist)
	return SANE_STATUS_NO_MEM;
      devlist[0] = NULL;
      *device_list = devlist;
      DBG (DBG_proc, "sane_get_devices: exit with no device\n");
      return SANE_STATUS_GOOD;
    }

  /* count physical devices */
  devnr = 1;
  device = devices;
  while (device->next)
    {
      devnr++;
      device = device->next;
    }

  /* allocate room for the list, plus 1 for the NULL terminator */
  devlist = malloc ((devnr + 1) * sizeof (devlist[0]));
  if (!devlist)
    return SANE_STATUS_NO_MEM;

  *device_list = devlist;

  dev_num = 0;
  device = devices;

  /* we build a list of SANE_Device from the list of attached devices */
  for (i = 0; i < devnr; i++)
    {
      /* add device according to local only flag */
      if ((local_only == SANE_TRUE && device->local == SANE_TRUE)
	  || local_only == SANE_FALSE)
	{
	  /* allocate memory to add the device */
	  sane_device = malloc (sizeof (*sane_device));
	  if (!sane_device)
	    {
	      return SANE_STATUS_NO_MEM;
	    }

	  /* copy data */
	  sane_device->name = device->name;
	  sane_device->vendor = device->model->vendor;
	  sane_device->model = device->model->product;
	  sane_device->type = device->model->type;
	  devlist[dev_num] = sane_device;

	  /* increment device counter */
	  dev_num++;
	}

      /* go to next detected device */
      device = device->next;
    }
  devlist[dev_num] = 0;

  *device_list = devlist;

  DBG (DBG_proc, "sane_get_devices: exit\n");

  return SANE_STATUS_GOOD;
}


/**
 * Called to establish connection with the session. This function will
 * also establish meaningful defaults and initialize the options.
 *
 * From the SANE spec:
 * This function is used to establish a connection to a particular
 * device. The name of the device to be opened is passed in argument
 * name. If the call completes successfully, a handle for the device
 * is returned in *h. As a special case, specifying a zero-length
 * string as the device requests opening the first available device
 * (if there is such a device). Another special case is to only give
 * the name of the backend as the device name, in this case the first
 * available device will also be used.
 * @param name name of the device to open
 * @param handle opaque pointer where to store the pointer of
 *        the opened P5_Session
 * @return SANE_STATUS_GOOD on success
 */
SANE_Status
sane_open (SANE_String_Const name, SANE_Handle * handle)
{
  struct P5_Session *session = NULL;
  struct P5_Device *device = NULL;

  DBG (DBG_proc, "sane_open: start (devicename=%s)\n", name);

  /* check there is at least a device */
  if (devices == NULL)
    {
      DBG (DBG_proc, "sane_open: exit, no device to open!\n");
      return SANE_STATUS_INVAL;
    }

  if (name[0] == 0 || strncmp (name, "p5", strlen ("p5")) == 0)
    {
      DBG (DBG_info,
	   "sane_open: no specific device requested, using default\n");
      if (devices)
	{
	  device = devices;
	  DBG (DBG_info, "sane_open: device %s used as default device\n",
	       device->name);
	}
    }
  else
    {
      DBG (DBG_info, "sane_open: device %s requested\n", name);
      /* walk the device list until we find a matching name */
      device = devices;
      while (device && strcmp (device->name, name) != 0)
	{
	  DBG (DBG_trace, "sane_open: device %s doesn't match\n",
	       device->name);
	  device = device->next;
	}
    }

  /* check whether we have found a match or reach the end of the device list */
  if (!device)
    {
      DBG (DBG_info, "sane_open: no device found\n");
      return SANE_STATUS_INVAL;
    }

  /* now we have a device, duplicate it and return it in handle */
  DBG (DBG_info, "sane_open: device %s found\n", name);

  /* device initialization */
  if (device->initialized == SANE_FALSE)
    {
      /**
       * call to hardware initialization function here.
       */
      device->fd = open_pp (device->name);
      if (device->fd < 0)
	{
	  DBG (DBG_error, "sane_open: failed to open '%s' device!\n",
	       device->name);
	  return SANE_STATUS_INVAL;
	}

      /* now try to connect to scanner */
      if (connect (device->fd) != SANE_TRUE)
	{
	  DBG (DBG_error, "sane_open: failed to connect!\n");
	  close_pp (device->fd);
	  return SANE_STATUS_INVAL;
	}

      /* load calibration data */
      restore_calibration (device);

      /* device link is OK now */
      device->initialized = SANE_TRUE;
    }
  device->buffer = NULL;
  device->gain = NULL;
  device->offset = NULL;

  /* prepare handle to return */
  session = (P5_Session *) malloc (sizeof (P5_Session));
  if (session == NULL)
    {
      DBG (DBG_proc, "sane_open: exit OOM\n");
      return SANE_STATUS_NO_MEM;
    }

  /* initialize session */
  session->dev = device;
  session->scanning = SANE_FALSE;
  session->non_blocking = SANE_FALSE;

  /* initialize SANE options for this session */
  init_options (session);

  /* add the handle to the linked list of sessions */
  session->next = sessions;
  sessions = session;

  /* store result */
  *handle = session;

  /* exit success */
  DBG (DBG_proc, "sane_open: exit\n");
  return SANE_STATUS_GOOD;
}


/**
 * Set non blocking mode. In this mode, read return immediately when
 * no data is available within sane_read(), instead of polling the scanner.
 */
SANE_Status
sane_set_io_mode (SANE_Handle handle, SANE_Bool non_blocking)
{
  P5_Session *session = (P5_Session *) handle;

  DBG (DBG_proc, "sane_set_io_mode: start\n");
  if (session->scanning != SANE_TRUE)
    {
      DBG (DBG_error, "sane_set_io_mode: called out of a scan\n");
      return SANE_STATUS_INVAL;
    }
  session->non_blocking = non_blocking;
  DBG (DBG_info, "sane_set_io_mode: I/O mode set to %sblocking.\n",
       non_blocking ? "non " : " ");
  DBG (DBG_proc, "sane_set_io_mode: exit\n");
  return SANE_STATUS_GOOD;
}


/**
 * An advanced method we don't support but have to define. At SANE API
 * level this function is meant to provide a file descriptor on which the
 * frontend can do select()/poll() to wait for data.
 */
SANE_Status
sane_get_select_fd (SANE_Handle handle, SANE_Int * fdp)
{
  /* make compiler happy ... */
  handle = handle;
  fdp = fdp;

  DBG (DBG_proc, "sane_get_select_fd: start\n");
  DBG (DBG_warn, "sane_get_select_fd: unsupported ...\n");
  DBG (DBG_proc, "sane_get_select_fd: exit\n");
  return SANE_STATUS_UNSUPPORTED;
}


/**
 * Returns the options we know.
 *
 * From the SANE spec:
 * This function is used to access option descriptors. The function
 * returns the option descriptor for option number n of the device
 * represented by handle h. Option number 0 is guaranteed to be a
 * valid option. Its value is an integer that specifies the number of
 * options that are available for device handle h (the count includes
 * option 0). If n is not a valid option index, the function returns
 * NULL. The returned option descriptor is guaranteed to remain valid
 * (and at the returned address) until the device is closed.
 */
const SANE_Option_Descriptor *
sane_get_option_descriptor (SANE_Handle handle, SANE_Int option)
{
  struct P5_Session *session = handle;

  DBG (DBG_proc, "sane_get_option_descriptor: start\n");

  if ((unsigned) option >= NUM_OPTIONS)
    return NULL;

  DBG (DBG_info, "sane_get_option_descriptor: \"%s\"\n",
       session->options[option].descriptor.name);

  DBG (DBG_proc, "sane_get_option_descriptor: exit\n");
  return &(session->options[option].descriptor);
}

/**
 * sets automatic value for an option , called by sane_control_option after
 * all checks have been done */
static SANE_Status
set_automatic_value (P5_Session * s, int option, SANE_Int * myinfo)
{
  SANE_Status status = SANE_STATUS_GOOD;
  SANE_Int i, min;
  SANE_Word *dpi_list;

  switch (option)
    {
    case OPT_TL_X:
      s->options[OPT_TL_X].value.w = x_range.min;
      *myinfo |= SANE_INFO_RELOAD_PARAMS;
      break;
    case OPT_TL_Y:
      s->options[OPT_TL_Y].value.w = y_range.min;
      *myinfo |= SANE_INFO_RELOAD_PARAMS;
      break;
    case OPT_BR_X:
      s->options[OPT_BR_X].value.w = x_range.max;
      *myinfo |= SANE_INFO_RELOAD_PARAMS;
      break;
    case OPT_BR_Y:
      s->options[OPT_BR_Y].value.w = y_range.max;
      *myinfo |= SANE_INFO_RELOAD_PARAMS;
      break;
    case OPT_RESOLUTION:
      /* we set up to the lowest available dpi value */
      dpi_list =
	(SANE_Word *) s->options[OPT_RESOLUTION].descriptor.constraint.
	word_list;
      min = 65536;
      for (i = 1; i < dpi_list[0]; i++)
	{
	  if (dpi_list[i] < min)
	    min = dpi_list[i];
	}
      s->options[OPT_RESOLUTION].value.w = min;
      *myinfo |= SANE_INFO_RELOAD_PARAMS;
      break;
    case OPT_PREVIEW:
      s->options[OPT_PREVIEW].value.w = SANE_FALSE;
      *myinfo |= SANE_INFO_RELOAD_PARAMS;
      break;
    case OPT_MODE:
      if (s->options[OPT_MODE].value.s)
	free (s->options[OPT_MODE].value.s);
      s->options[OPT_MODE].value.s = strdup (mode_list[0]);
      *myinfo |= SANE_INFO_RELOAD_OPTIONS;
      *myinfo |= SANE_INFO_RELOAD_PARAMS;
      break;
    default:
      DBG (DBG_warn, "set_automatic_value: can't set unknown option %d\n",
	   option);
    }

  return status;
}

/**
 * sets an option , called by sane_control_option after all
 * checks have been done */
static SANE_Status
set_option_value (P5_Session * s, int option, void *val, SANE_Int * myinfo)
{
  SANE_Status status = SANE_STATUS_GOOD;
  SANE_Word tmpw;

  switch (option)
    {
    case OPT_TL_X:
    case OPT_BR_X:
    case OPT_TL_Y:
    case OPT_BR_Y:
      s->options[option].value.w = *(SANE_Word *) val;
      /* we ensure geometry is coherent */
      /* this happens when user drags TL corner right or below the BR point */
      if (s->options[OPT_BR_Y].value.w < s->options[OPT_TL_Y].value.w)
	{
	  tmpw = s->options[OPT_BR_Y].value.w;
	  s->options[OPT_BR_Y].value.w = s->options[OPT_TL_Y].value.w;
	  s->options[OPT_TL_Y].value.w = tmpw;
	}
      if (s->options[OPT_BR_X].value.w < s->options[OPT_TL_X].value.w)
	{
	  tmpw = s->options[OPT_BR_X].value.w;
	  s->options[OPT_BR_X].value.w = s->options[OPT_TL_X].value.w;
	  s->options[OPT_TL_X].value.w = tmpw;
	}

      *myinfo |= SANE_INFO_RELOAD_PARAMS;
      break;

    case OPT_RESOLUTION:
    case OPT_PREVIEW:
      s->options[option].value.w = *(SANE_Word *) val;
      *myinfo |= SANE_INFO_RELOAD_PARAMS;
      break;

    case OPT_MODE:
      if (s->options[option].value.s)
	free (s->options[option].value.s);
      s->options[option].value.s = strdup (val);
      *myinfo |= SANE_INFO_RELOAD_PARAMS | SANE_INFO_RELOAD_OPTIONS;
      break;

    case OPT_CALIBRATE:
      status = sheetfed_calibration (s->dev);
      *myinfo |= SANE_INFO_RELOAD_OPTIONS;
      break;

    case OPT_CLEAR_CALIBRATION:
      cleanup_calibration (s->dev);
      *myinfo |= SANE_INFO_RELOAD_OPTIONS;
      break;

    default:
      DBG (DBG_warn, "set_option_value: can't set unknown option %d\n",
	   option);
    }
  return status;
}

/**
 * gets an option , called by sane_control_option after all checks
 * have been done */
static SANE_Status
get_option_value (P5_Session * s, int option, void *val)
{
  SANE_Status status;

  switch (option)
    {
      /* word or word equivalent options: */
    case OPT_NUM_OPTS:
    case OPT_RESOLUTION:
    case OPT_PREVIEW:
    case OPT_TL_X:
    case OPT_TL_Y:
    case OPT_BR_X:
    case OPT_BR_Y:
      *(SANE_Word *) val = s->options[option].value.w;
      break;

      /* string options: */
    case OPT_MODE:
      strcpy (val, s->options[option].value.s);
      break;

      /* sensor options */
    case OPT_PAGE_LOADED_SW:
      status = test_document (s->dev->fd);
      if (status == SANE_STATUS_GOOD)
	s->options[option].value.b = SANE_TRUE;
      else
	s->options[option].value.b = SANE_FALSE;
      *(SANE_Bool *) val = s->options[option].value.b;
      break;

    case OPT_NEED_CALIBRATION_SW:
      *(SANE_Bool *) val = !s->dev->calibrated;
      break;


      /* unhandled options */
    default:
      DBG (DBG_warn, "get_option_value: can't get unknown option %d\n",
	   option);
    }

  return SANE_STATUS_GOOD;
}

/**
 * Gets or sets an option value.
 *
 * From the SANE spec:
 * This function is used to set or inquire the current value of option
 * number n of the device represented by handle h. The manner in which
 * the option is controlled is specified by parameter action. The
 * possible values of this parameter are described in more detail
 * below.  The value of the option is passed through argument val. It
 * is a pointer to the memory that holds the option value. The memory
 * area pointed to by v must be big enough to hold the entire option
 * value (determined by member size in the corresponding option
 * descriptor).
 *
 * The only exception to this rule is that when setting the value of a
 * string option, the string pointed to by argument v may be shorter
 * since the backend will stop reading the option value upon
 * encountering the first NUL terminator in the string. If argument i
 * is not NULL, the value of *i will be set to provide details on how
 * well the request has been met.
 * action is SANE_ACTION_GET_VALUE, SANE_ACTION_SET_VALUE or SANE_ACTION_SET_AUTO
 */
SANE_Status
sane_control_option (SANE_Handle handle, SANE_Int option,
		     SANE_Action action, void *val, SANE_Int * info)
{
  P5_Session *s = handle;
  SANE_Status status;
  SANE_Word cap;
  SANE_Int myinfo = 0;

  DBG (DBG_io2,
       "sane_control_option: start: action = %s, option = %s (%d)\n",
       (action == SANE_ACTION_GET_VALUE) ? "get" : (action ==
						    SANE_ACTION_SET_VALUE) ?
       "set" : (action == SANE_ACTION_SET_AUTO) ? "set_auto" : "unknown",
       s->options[option].descriptor.name, option);

  if (info)
    *info = 0;

  /* do checks before trying to apply action */

  if (s->scanning)
    {
      DBG (DBG_warn, "sane_control_option: don't call this function while "
	   "scanning (option = %s (%d))\n",
	   s->options[option].descriptor.name, option);
      return SANE_STATUS_DEVICE_BUSY;
    }

  /* option must be within existing range */
  if (option >= NUM_OPTIONS || option < 0)
    {
      DBG (DBG_warn,
	   "sane_control_option: option %d >= NUM_OPTIONS || option < 0\n",
	   option);
      return SANE_STATUS_INVAL;
    }

  /* don't access an inactive option */
  cap = s->options[option].descriptor.cap;
  if (!SANE_OPTION_IS_ACTIVE (cap))
    {
      DBG (DBG_warn, "sane_control_option: option %d is inactive\n", option);
      return SANE_STATUS_INVAL;
    }

  /* now checks have been done, apply action */
  switch (action)
    {
    case SANE_ACTION_GET_VALUE:
      status = get_option_value (s, option, val);
      break;

    case SANE_ACTION_SET_VALUE:
      if (!SANE_OPTION_IS_SETTABLE (cap))
	{
	  DBG (DBG_warn, "sane_control_option: option %d is not settable\n",
	       option);
	  return SANE_STATUS_INVAL;
	}

      status =
	sanei_constrain_value (&s->options[option].descriptor, val, &myinfo);
      if (status != SANE_STATUS_GOOD)
	{
	  DBG (DBG_warn,
	       "sane_control_option: sanei_constrain_value returned %s\n",
	       sane_strstatus (status));
	  return status;
	}

      /* return immediately if no change */
      if (s->options[option].descriptor.type == SANE_TYPE_INT
	  && *(SANE_Word *) val == s->options[option].value.w)
	{
	  status = SANE_STATUS_GOOD;
	}
      else
	{			/* apply change */
	  status = set_option_value (s, option, val, &myinfo);
	}
      break;

    case SANE_ACTION_SET_AUTO:
      /* sets automatic values */
      if (!(cap & SANE_CAP_AUTOMATIC))
	{
	  DBG (DBG_warn,
	       "sane_control_option: option %d is not autosettable\n",
	       option);
	  return SANE_STATUS_INVAL;
	}

      status = set_automatic_value (s, option, &myinfo);
      break;

    default:
      DBG (DBG_error, "sane_control_option: invalid action %d\n", action);
      status = SANE_STATUS_INVAL;
      break;
    }

  if (info)
    *info = myinfo;

  DBG (DBG_io2, "sane_control_option: exit\n");
  return status;
}

/**
 * Called by SANE when a page acquisition operation is to be started.
 * @param handle opaque handle to a frontend session
 * @return SANE_STATUS_GOOD on success, SANE_STATUS_BUSY if the device is
 * in use by another session or SANE_STATUS_WARMING_UP if the device is
 * warming up. In this case the fronted as to call sane_start again until
 * warming up is done. Any other values returned are error status.
 */
SANE_Status
sane_start (SANE_Handle handle)
{
  struct P5_Session *session = handle;
  int status = SANE_STATUS_GOOD;
  P5_Device *dev = session->dev;

  DBG (DBG_proc, "sane_start: start\n");

  /* if already scanning, tell we're busy */
  if (session->scanning == SANE_TRUE)
    {
      DBG (DBG_info, "sane_start: device is already scanning\n");
      return SANE_STATUS_DEVICE_BUSY;
    }

  /* check that the device has been initialized */
  if (dev->initialized == SANE_FALSE)
    {
      DBG (DBG_error, "sane_start: device is not initialized\n");
      return SANE_STATUS_INVAL;
    }

  /* check if there is a document */
  status = test_document (dev->fd);
  if (status != SANE_STATUS_GOOD)
    {
      DBG (DBG_error, "sane_start: device is already scanning\n");
      return status;
    }

  /* we compute all the scan parameters so that */
  /* we will be able to set up the registers correctly */
  compute_parameters (session);

  /* move to scan area if needed */
  if (dev->ystart > 0)
    {
      status = move (dev);
      if (status != SANE_STATUS_GOOD)
	{
	  DBG (DBG_error, "sane_start: failed to move to scan area\n");
	  return SANE_STATUS_INVAL;
	}
    }

  /* send scan command */
  status = start_scan (dev, dev->mode, dev->ydpi, dev->xstart, dev->pixels);
  if (status != SANE_STATUS_GOOD)
    {
      DBG (DBG_error, "sane_start: failed to start scan\n");
      return SANE_STATUS_INVAL;
    }

  /* allocates work buffer */
  if (dev->buffer != NULL)
    {
      free (dev->buffer);
    }

  dev->position = 0;
  dev->top = 0;
  /* compute amount of lines needed for lds correction */
  dev->bottom = dev->bytes_per_line * 2 * dev->lds;
  /* computes buffer size, 66 color lines plus eventual amount needed for lds */
  dev->size = dev->pixels * 3 * 66 + dev->bottom;
  dev->buffer = (uint8_t *) malloc (dev->size);
  if (dev->buffer == NULL)
    {
      DBG (DBG_error, "sane_start: failed to allocate %lu bytes\n", (unsigned long)dev->size);
      sane_cancel (handle);
      return SANE_STATUS_NO_MEM;
    }

  /* return now the scan has been initiated */
  session->scanning = SANE_TRUE;
  session->sent = 0;

  DBG (DBG_io, "sane_start: to_send=%d\n", session->to_send);
  DBG (DBG_io, "sane_start: size=%lu\n", (unsigned long)dev->size);
  DBG (DBG_io, "sane_start: top=%lu\n", (unsigned long)dev->top);
  DBG (DBG_io, "sane_start: bottom=%lu\n", (unsigned long)dev->bottom);
  DBG (DBG_io, "sane_start: position=%lu\n", (unsigned long)dev->position);

  DBG (DBG_proc, "sane_start: exit\n");
  return status;
}

/** @brief compute scan parameters
 * This function computes two set of parameters. The one for the SANE's standard
 * and the other for the hardware. Among these parameters are the bit depth, total
 * number of lines, total number of columns, extra line to read for data reordering...
 * @param session fronted session to compute final scan parameters
 * @return SANE_STATUS_GOOD on success
 */
static SANE_Status
compute_parameters (P5_Session * session)
{
  P5_Device *dev = session->dev;
  SANE_Int dpi;			/* dpi for scan */
  SANE_String mode;
  SANE_Status status = SANE_STATUS_GOOD;

  int tl_x, tl_y, br_x, br_y;

  mode = session->options[OPT_MODE].value.s;
  dpi = session->options[OPT_RESOLUTION].value.w;

  /* scan coordinates */
  tl_x = SANE_UNFIX (session->options[OPT_TL_X].value.w);
  tl_y = SANE_UNFIX (session->options[OPT_TL_Y].value.w);
  br_x = SANE_UNFIX (session->options[OPT_BR_X].value.w);
  br_y = SANE_UNFIX (session->options[OPT_BR_Y].value.w);

  /* only single pass scanning supported */
  session->params.last_frame = SANE_TRUE;

  /* gray modes */
  if (strcmp (mode, GRAY_MODE) == 0)
    {
      session->params.format = SANE_FRAME_GRAY;
      dev->mode = MODE_GRAY;
      dev->lds = 0;
    }
  else if (strcmp (mode, LINEART_MODE) == 0)
    {
      session->params.format = SANE_FRAME_GRAY;
      dev->mode = MODE_LINEART;
      dev->lds = 0;
    }
  else
    {
      /* Color */
      session->params.format = SANE_FRAME_RGB;
      dev->mode = MODE_COLOR;
      dev->lds = (dev->model->lds * dpi) / dev->model->max_ydpi;
    }

  /* SANE level values */
  session->params.lines = ((br_y - tl_y) * dpi) / MM_PER_INCH;
  if (session->params.lines == 0)
    session->params.lines = 1;
  session->params.pixels_per_line = ((br_x - tl_x) * dpi) / MM_PER_INCH;
  if (session->params.pixels_per_line == 0)
    session->params.pixels_per_line = 1;

  DBG (DBG_data, "compute_parameters: pixels_per_line   =%d\n",
       session->params.pixels_per_line);

  if (strcmp (mode, LINEART_MODE) == 0)
    {
      session->params.depth = 1;
      /* in lineart, having pixels multiple of 8 avoids a costly test */
      /* at each bit to see we must go to the next byte               */
      /* TODO : implement this requirement in sane_control_option */
      session->params.pixels_per_line =
	((session->params.pixels_per_line + 7) / 8) * 8;
    }
  else
    session->params.depth = 8;

  /* width needs to be even */
  if (session->params.pixels_per_line & 1)
    session->params.pixels_per_line++;

  /* Hardware settings : they can differ from the ones at SANE level */
  /* for instance the effective DPI used by a sensor may be higher   */
  /* than the one needed for the SANE scan parameters                */
  dev->lines = session->params.lines;
  dev->pixels = session->params.pixels_per_line;

  /* motor and sensor DPI */
  dev->xdpi = dpi;
  dev->ydpi = dpi;

  /* handle bounds of motor's dpi range */
  if (dev->ydpi > dev->model->max_ydpi)
    {
      dev->ydpi = dev->model->max_ydpi;
      dev->lines = (dev->lines * dev->model->max_ydpi) / dpi;
      if (dev->lines == 0)
	dev->lines = 1;

      /* round number of lines */
      session->params.lines =
	(session->params.lines / dev->lines) * dev->lines;
      if (session->params.lines == 0)
	session->params.lines = 1;
    }
  if (dev->ydpi < dev->model->min_ydpi)
    {
      dev->ydpi = dev->model->min_ydpi;
      dev->lines = (dev->lines * dev->model->min_ydpi) / dpi;
    }

  /* hardware values */
  dev->xstart =
    ((SANE_UNFIX (dev->model->x_offset) + tl_x) * dpi) / MM_PER_INCH;
  dev->ystart =
    ((SANE_UNFIX (dev->model->y_offset) + tl_y) * dev->ydpi) / MM_PER_INCH;

  /* take lds correction into account when moving to scan area */
  if (dev->ystart > 2 * dev->lds)
    dev->ystart -= 2 * dev->lds;


  /* computes bytes per line */
  session->params.bytes_per_line = session->params.pixels_per_line;
  dev->bytes_per_line = dev->pixels;
  if (session->params.format == SANE_FRAME_RGB)
    {
      dev->bytes_per_line *= 3;
    }

  /* in lineart mode we adjust bytes_per_line needed by frontend */
  /* we do that here because we needed sent/to_send to be as if  */
  /* there was no lineart                                        */
  if (session->params.depth == 1)
    {
      session->params.bytes_per_line =
	(session->params.bytes_per_line + 7) / 8;
    }

  session->params.bytes_per_line = dev->bytes_per_line;
  session->to_send = session->params.bytes_per_line * session->params.lines;
  session->params.bytes_per_line = dev->bytes_per_line;

  DBG (DBG_data, "compute_parameters: bytes_per_line    =%d\n",
       session->params.bytes_per_line);
  DBG (DBG_data, "compute_parameters: depth             =%d\n",
       session->params.depth);
  DBG (DBG_data, "compute_parameters: lines             =%d\n",
       session->params.lines);
  DBG (DBG_data, "compute_parameters: image size        =%d\n",
       session->to_send);

  DBG (DBG_data, "compute_parameters: xstart            =%d\n", dev->xstart);
  DBG (DBG_data, "compute_parameters: ystart            =%d\n", dev->ystart);
  DBG (DBG_data, "compute_parameters: dev lines         =%d\n", dev->lines);
  DBG (DBG_data, "compute_parameters: dev bytes per line=%d\n",
       dev->bytes_per_line);
  DBG (DBG_data, "compute_parameters: dev pixels        =%d\n", dev->pixels);
  DBG (DBG_data, "compute_parameters: lds               =%d\n", dev->lds);

  return status;
}


/**
 * Called by SANE to retrieve information about the type of data
 * that the current scan will return.
 *
 * From the SANE spec:
 * This function is used to obtain the current scan parameters. The
 * returned parameters are guaranteed to be accurate between the time
 * a scan has been started (sane_start() has been called) and the
 * completion of that request. Outside of that window, the returned
 * values are best-effort estimates of what the parameters will be
 * when sane_start() gets invoked.
 *
 * Calling this function before a scan has actually started allows,
 * for example, to get an estimate of how big the scanned image will
 * be. The parameters passed to this function are the handle of the
 * device for which the parameters should be obtained and a pointer
 * to a parameter structure.
 */
SANE_Status
sane_get_parameters (SANE_Handle handle, SANE_Parameters * params)
{
  SANE_Status status;
  struct P5_Session *session = (struct P5_Session *) handle;

  DBG (DBG_proc, "sane_get_parameters: start\n");

  /* call parameters computing function */
  status = compute_parameters (session);
  if (status == SANE_STATUS_GOOD && params)
    *params = session->params;

  DBG (DBG_proc, "sane_get_parameters: exit\n");
  return status;
}


/**
 * Called by SANE to read data.
 *
 * From the SANE spec:
 * This function is used to read image data from the device
 * represented by handle h.  Argument buf is a pointer to a memory
 * area that is at least maxlen bytes long.  The number of bytes
 * returned is stored in *len. A backend must set this to zero when
 * the call fails (i.e., when a status other than SANE_STATUS_GOOD is
 * returned).
 *
 * When the call succeeds, the number of bytes returned can be
 * anywhere in the range from 0 to maxlen bytes.
 *
 * Returned data is read from working buffer.
 */
SANE_Status
sane_read (SANE_Handle handle, SANE_Byte * buf,
	   SANE_Int max_len, SANE_Int * len)
{
  struct P5_Session *session = (struct P5_Session *) handle;
  struct P5_Device *dev = session->dev;
  SANE_Status status = SANE_STATUS_GOOD;
  int count;
  int size, lines;
  SANE_Bool x2;
  SANE_Int i;

  DBG (DBG_proc, "sane_read: start\n");
  DBG (DBG_io, "sane_read: up to %d bytes required by frontend\n", max_len);

  /* some sanity checks first to protect from would be buggy frontends */
  if (!session)
    {
      DBG (DBG_error, "sane_read: handle is null!\n");
      return SANE_STATUS_INVAL;
    }

  if (!buf)
    {
      DBG (DBG_error, "sane_read: buf is null!\n");
      return SANE_STATUS_INVAL;
    }

  if (!len)
    {
      DBG (DBG_error, "sane_read: len is null!\n");
      return SANE_STATUS_INVAL;
    }

  /* no data read yet */
  *len = 0;

  /* check if session is scanning */
  if (!session->scanning)
    {
      DBG (DBG_warn,
	   "sane_read: scan was cancelled, is over or has not been initiated yet\n");
      return SANE_STATUS_CANCELLED;
    }

  /* check for EOF, must be done before any physical read */
  if (session->sent >= session->to_send)
    {
      DBG (DBG_io, "sane_read: end of scan reached\n");
      return SANE_STATUS_EOF;
    }

  /* if working buffer is empty, we do a physical data read */
  if (dev->top <= dev->bottom)
    {
      DBG (DBG_io, "sane_read: physical data read\n");
      /* check is there is data available. In case of non-blocking mode we return
       * as soon it is detected there is no data yet. Reads must by done line by
       * line, so we read only when count is bigger than bytes per line
       * */
      count = available_bytes (dev->fd);
      DBG (DBG_io, "sane_read: count=%d bytes\n", count);
      if (count < dev->bytes_per_line && session->non_blocking == SANE_TRUE)
	{
	  DBG (DBG_io, "sane_read: scanner hasn't enough data available\n");
	  DBG (DBG_proc, "sane_read: exit\n");
	  return SANE_STATUS_GOOD;
	}

      /* now we can wait for data here */
      while (count < dev->bytes_per_line)
	{
	  /* test if document left the feeder, so we have to terminate the scan */
	  status = test_document (dev->fd);
	  if (status == SANE_STATUS_NO_DOCS)
	    {
	      session->to_send = session->sent;
	      return SANE_STATUS_EOF;
	    }

	  /* don't call scanner too often */
	  usleep (10000);
	  count = available_bytes (dev->fd);
	}

      /** compute size of physical data to read
       * on first read, position will be 0, while it will be 'bottom'
       * for the subsequent reads.
       * We try to read a complete buffer */
      size = dev->size - dev->position;

      if (session->to_send - session->sent < size)
	{
	  /* not enough data left, so read remainder of scan */
	  size = session->to_send - session->sent;
	}

      /* 600 dpi is 300x600 physical, and 400 is 200x400 */
      if (dev->ydpi > dev->model->max_xdpi)
	{
	  x2 = SANE_TRUE;
	}
      else
	{
	  x2 = SANE_FALSE;
	}
      lines = read_line (dev,
			 dev->buffer + dev->position,
			 dev->bytes_per_line,
			 size / dev->bytes_per_line,
			 SANE_TRUE, x2, dev->mode, dev->calibrated);

      /* handle document end detection TODO try to recover the partial
       * buffer already read before EOD */
      if (lines == -1)
	{
	  DBG (DBG_io, "sane_read: error reading line\n");
	  return SANE_STATUS_IO_ERROR;
	}

      /* gather lines until we have more than needed for lds */
      dev->position += lines * dev->bytes_per_line;
      dev->top = dev->position;
      if (dev->position > dev->bottom)
	{
	  dev->position = dev->bottom;
	}
      DBG (DBG_io, "sane_read: size    =%lu\n", (unsigned long)dev->size);
      DBG (DBG_io, "sane_read: bottom  =%lu\n", (unsigned long)dev->bottom);
      DBG (DBG_io, "sane_read: position=%lu\n", (unsigned long)dev->position);
      DBG (DBG_io, "sane_read: top     =%lu\n", (unsigned long)dev->top);
    }				/* end of physical data reading */

  /* logical data reading */
  /* check if there data available in working buffer */
  if (dev->position < dev->top && dev->position >= dev->bottom)
    {
      DBG (DBG_io, "sane_read: logical data read\n");
      /* we have more data in internal buffer than asked ,
       * then send only max data */
      size = dev->top - dev->position;
      if (max_len < size)
	{
	  *len = max_len;
	}
      else
	/* if we don't have enough, send all what we have */
	{
	  *len = dev->top - dev->position;
	}

      /* data copy */
      if (dev->lds == 0)
	{
	  memcpy (buf, dev->buffer + dev->position, *len);
	}
      else
	{
	  /* compute count of bytes for lds */
	  count = dev->lds * dev->bytes_per_line;

	  /* adjust for lds as we copy data to frontend */
	  for (i = 0; i < *len; i++)
	    {
	      switch ((dev->position + i) % 3)
		{
		  /* red */
		case 0:
		  buf[i] = dev->buffer[dev->position + i - 2 * count];
		  break;
		  /* green */
		case 1:
		  buf[i] = dev->buffer[dev->position + i - count];
		  break;
		  /* blue */
		default:
		  buf[i] = dev->buffer[dev->position + i];
		  break;
		}
	    }
	}
      dev->position += *len;

      /* update byte accounting */
      session->sent += *len;
      DBG (DBG_io, "sane_read: sent %d bytes from buffer to frontend\n",
	   *len);
      return SANE_STATUS_GOOD;
    }

  /* check if we exhausted working buffer */
  if (dev->position >= dev->top && dev->position >= dev->bottom)
    {
      /* copy extra lines needed for lds in next buffer */
      if (dev->position > dev->bottom && dev->lds > 0)
	{
	  memcpy (dev->buffer,
		  dev->buffer + dev->position - dev->bottom, dev->bottom);
	}

      /* restart buffer */
      dev->position = dev->bottom;
      dev->top = 0;
    }

  DBG (DBG_io, "sane_read: size    =%lu\n", (unsigned long)dev->size);
  DBG (DBG_io, "sane_read: bottom  =%lu\n", (unsigned long)dev->bottom);
  DBG (DBG_io, "sane_read: position=%lu\n", (unsigned long)dev->position);
  DBG (DBG_io, "sane_read: top     =%lu\n", (unsigned long)dev->top);

  DBG (DBG_proc, "sane_read: exit\n");
  return status;
}


/**
 * Cancels a scan.
 *
 * From the SANE spec:
 * This function is used to immediately or as quickly as possible
 * cancel the currently pending operation of the device represented by
 * handle h.  This function can be called at any time (as long as
 * handle h is a valid handle) but usually affects long-running
 * operations only (such as image is acquisition). It is safe to call
 * this function asynchronously (e.g., from within a signal handler).
 * It is important to note that completion of this operation does not
 * imply that the currently pending operation has been cancelled. It
 * only guarantees that cancellation has been initiated. Cancellation
 * completes only when the cancelled call returns (typically with a
 * status value of SANE_STATUS_CANCELLED).  Since the SANE API does
 * not require any other operations to be re-entrant, this implies
 * that a frontend must not call any other operation until the
 * cancelled operation has returned.
 */
void
sane_cancel (SANE_Handle handle)
{
  P5_Session *session = handle;

  DBG (DBG_proc, "sane_cancel: start\n");

  /* if scanning, abort and park head */
  if (session->scanning == SANE_TRUE)
    {
      /* detects if we are called after the scan is finished,
       * or if the scan is aborted */
      if (session->sent < session->to_send)
	{
	  DBG (DBG_info, "sane_cancel: aborting scan.\n");
	  /* device hasn't finished scan, we are aborting it
	   * and we may have to do something specific for it here */
	}
      else
	{
	  DBG (DBG_info, "sane_cancel: cleaning up after scan.\n");
	}
      session->scanning = SANE_FALSE;
    }
  eject (session->dev->fd);

  DBG (DBG_proc, "sane_cancel: exit\n");
}


/**
 * Ends use of the session.
 *
 * From the SANE spec:
 * This function terminates the association between the device handle
 * passed in argument h and the device it represents. If the device is
 * presently active, a call to sane_cancel() is performed first. After
 * this function returns, handle h must not be used anymore.
 *
 * Handle resources are free'd before disposing the handle. But devices
 * resources must not be mdofied, since it could be used or reused until
 * sane_exit() is called.
 */
void
sane_close (SANE_Handle handle)
{
  P5_Session *prev, *session;

  DBG (DBG_proc, "sane_close: start\n");

  /* remove handle from list of open handles: */
  prev = NULL;
  for (session = sessions; session; session = session->next)
    {
      if (session == handle)
	break;
      prev = session;
    }
  if (!session)
    {
      DBG (DBG_error0, "close: invalid handle %p\n", handle);
      return;			/* oops, not a handle we know about */
    }

  /* cancel any active scan */
  if (session->scanning == SANE_TRUE)
    {
      sane_cancel (handle);
    }

  if (prev)
    prev->next = session->next;
  else
    sessions = session->next;

  /* close low level device */
  if (session->dev->initialized == SANE_TRUE)
    {
      if (session->dev->calibrated == SANE_TRUE)
	{
	  save_calibration (session->dev);
	}
      disconnect (session->dev->fd);
      close_pp (session->dev->fd);
      session->dev->fd = -1;
      session->dev->initialized = SANE_FALSE;

      /* free device data */
      if (session->dev->buffer != NULL)
	{
	  free (session->dev->buffer);
	}
      if (session->dev->buffer != NULL)
	{
	  free (session->dev->gain);
	  free (session->dev->offset);
	}
      if (session->dev->calibrated == SANE_TRUE)
	{
	  cleanup_calibration (session->dev);
	}
    }

  /* free per session data */
  free (session->options[OPT_MODE].value.s);
  free ((void *)session->options[OPT_RESOLUTION].descriptor.constraint.word_list);

  free (session);

  DBG (DBG_proc, "sane_close: exit\n");
}


/**
 * Terminates the backend.
 *
 * From the SANE spec:
 * This function must be called to terminate use of a backend. The
 * function will first close all device handles that still might be
 * open (it is recommended to close device handles explicitly through
 * a call to sane_close(), but backends are required to release all
 * resources upon a call to this function). After this function
 * returns, no function other than sane_init() may be called
 * (regardless of the status value returned by sane_exit(). Neglecting
 * to call this function may result in some resources not being
 * released properly.
 */
void
sane_exit (void)
{
  struct P5_Session *session, *next;
  struct P5_Device *dev, *nextdev;
  int i;

  DBG (DBG_proc, "sane_exit: start\n");
  init_count--;

  if (init_count > 0)
    {
      DBG (DBG_info,
	   "sane_exit: still %d fronteds to leave before effective exit.\n",
	   init_count);
      return;
    }

  /* free session structs */
  for (session = sessions; session; session = next)
    {
      next = session->next;
      sane_close ((SANE_Handle *) session);
      free (session);
    }
  sessions = NULL;

  /* free devices structs */
  for (dev = devices; dev; dev = nextdev)
    {
      nextdev = dev->next;
      free (dev->name);
      free (dev);
    }
  devices = NULL;

  /* now list of devices */
  if (devlist)
    {
      i = 0;
      while ((SANE_Device *) devlist[i])
	{
	  free ((SANE_Device *) devlist[i]);
	  i++;
	}
      free (devlist);
      devlist = NULL;
    }

  DBG (DBG_proc, "sane_exit: exit\n");
}


/** @brief probe for all supported devices
 * This functions tries to probe if any of the supported devices of
 * the backend is present. Each detected device will be added to the
 * 'devices' list
 */
static SANE_Status
probe_p5_devices (void)
{
  /**> configuration structure used during attach */
  SANEI_Config config;
  /**> list of configuration options */
  SANE_Option_Descriptor *cfg_options[NUM_CFG_OPTIONS];
  /**> placeholders pointers for option values */
  void *values[NUM_CFG_OPTIONS];
  int i;
  SANE_Status status;

  DBG (DBG_proc, "probe_p5_devices: start\n");

  /* initialize configuration options */
  cfg_options[CFG_MODEL_NAME] =
    (SANE_Option_Descriptor *) malloc (sizeof (SANE_Option_Descriptor));
  cfg_options[CFG_MODEL_NAME]->name = "modelname";
  cfg_options[CFG_MODEL_NAME]->desc = "user provided scanner's model name";
  cfg_options[CFG_MODEL_NAME]->type = SANE_TYPE_INT;
  cfg_options[CFG_MODEL_NAME]->unit = SANE_UNIT_NONE;
  cfg_options[CFG_MODEL_NAME]->size = sizeof (SANE_Word);
  cfg_options[CFG_MODEL_NAME]->cap = SANE_CAP_SOFT_SELECT;
  cfg_options[CFG_MODEL_NAME]->constraint_type = SANE_CONSTRAINT_NONE;
  values[CFG_MODEL_NAME] = &p5cfg.modelname;

  /* set configuration options structure */
  config.descriptors = cfg_options;
  config.values = values;
  config.count = NUM_CFG_OPTIONS;

  /* generic configure and attach function */
  status = sanei_configure_attach (P5_CONFIG_FILE, &config,
                                   config_attach, NULL);
  /* free allocated options */
  for (i = 0; i < NUM_CFG_OPTIONS; i++)
    {
      free (cfg_options[i]);
    }

  DBG (DBG_proc, "probe_p5_devices: end\n");
  return status;
}

/** This function is called by sanei_configure_attach to try
 * to attach the backend to a device specified by the configuration file.
 *
 * @param config configuration structure filled with values read
 * 	         from configuration file
 * @param devname name of the device to try to attach to, it is
 * 	          the unprocessed line of the configuration file
 *
 * @return status SANE_STATUS_GOOD if no errors (even if no matching
 * 	    devices found)
 * 	   SANE_STATUS_INVAL in case of error
 */
static SANE_Status
config_attach (SANEI_Config __sane_unused__ * config, const char *devname,
               void __sane_unused__ *data)
{
  /* currently, the config is a global variable so config is useless here */
  /* the correct thing would be to have a generic sanei_attach_matching_devices
   * using an attach function with a config parameter */
  config = config;

  /* the devname has been processed and is ready to be used
   * directly. The config struct contains all the configuration data for
   * the corresponding device. Since there is no resources common to each
   * backends regarding parallel port, we can directly call the attach
   * function. */
  attach_p5 (devname, config);

  return SANE_STATUS_GOOD;
}

/** @brief try to attach to a device by its name
 * The attach tries to open the given device and match it
 * with devices handled by the backend. The configuration parameter
 * contains the values of the already parsed configuration options
 * from the conf file.
 * @param config configuration structure filled with values read
 * 	         from configuration file
 * @param devicename name of the device to try to attach to, it is
 * 	          the unprocessed line of the configuration file
 *
 * @return status SANE_STATUS_GOOD if no errors (even if no matching
 * 	    devices found)
 * 	   SANE_STATUS_NOM_MEM if there isn't enough memory to allocate the
 * 	   			device structure
 * 	   SANE_STATUS_UNSUPPORTED if the device if unknown by the backend
 * 	   SANE_STATUS_INVAL in case of other error
 */
static SANE_Status
attach_p5 (const char *devicename, SANEI_Config * config)
{
  struct P5_Device *device;
  struct P5_Model *model;

  DBG (DBG_proc, "attach(%s): start\n", devicename);
  if(config==NULL)
    {
      DBG (DBG_warn, "attach: config is NULL\n");
    }

  /* search if we already have it attached */
  for (device = devices; device; device = device->next)
    {
      if (strcmp (device->name, devicename) == 0)
	{
	  DBG (DBG_info, "attach: device already attached\n");
	  DBG (DBG_proc, "attach: exit\n");
	  return SANE_STATUS_GOOD;
	}
    }

  /**
   * do physical probe of the device here. In case the device is recognized,
   * we allocate a device struct and give it options and model.
   * Else we return SANE_STATUS_UNSUPPORTED.
   */
  model = probe (devicename);
  if (model == NULL)
    {
      DBG (DBG_info,
	   "attach: device %s is not managed by the backend\n", devicename);
      DBG (DBG_proc, "attach: exit\n");
      return SANE_STATUS_UNSUPPORTED;
    }

  /* allocate device struct */
  device = malloc (sizeof (*device));
  if (device == NULL)
    {
      return SANE_STATUS_NO_MEM;
      DBG (DBG_proc, "attach: exit\n");
    }
  memset (device, 0, sizeof (*device));
  device->model = model;

  /* name of the device */
  device->name = strdup (devicename);

  DBG (DBG_info, "attach: found %s %s %s at %s\n",
       device->model->vendor, device->model->product, device->model->type,
       device->name);

  /* we insert new device at start of the chained list */
  /* head of the list becomes the next, and start is replaced */
  /* with the new session struct */
  device->next = devices;
  devices = device;

  /* initialization is done at sane_open */
  device->initialized = SANE_FALSE;
  device->calibrated = SANE_FALSE;

  DBG (DBG_proc, "attach: exit\n");
  return SANE_STATUS_GOOD;
}


/** @brief set initial value for the scanning options
 * for each sessions, control options are initialized based on the capability
 * of the model of the physical device.
 * @param session scanner session to initialize options
 * @return SANE_STATUS_GOOD on success
 */
static SANE_Status
init_options (struct P5_Session *session)
{
  SANE_Int option, i, min, idx;
  SANE_Word *dpi_list;
  P5_Model *model = session->dev->model;

  DBG (DBG_proc, "init_options: start\n");

  /* we first initialize each options with a default value */
  memset (session->options, 0, sizeof (session->options[OPT_NUM_OPTS]));
  for (option = 0; option < NUM_OPTIONS; option++)
    {
      session->options[option].descriptor.size = sizeof (SANE_Word);
      session->options[option].descriptor.cap =
	SANE_CAP_SOFT_SELECT | SANE_CAP_SOFT_DETECT;
    }

  /* we set up all the options listed in the P5_Option enum */

  /* last option / end of list marker */
  session->options[OPT_NUM_OPTS].descriptor.name = SANE_NAME_NUM_OPTIONS;
  session->options[OPT_NUM_OPTS].descriptor.title = SANE_TITLE_NUM_OPTIONS;
  session->options[OPT_NUM_OPTS].descriptor.desc = SANE_DESC_NUM_OPTIONS;
  session->options[OPT_NUM_OPTS].descriptor.type = SANE_TYPE_INT;
  session->options[OPT_NUM_OPTS].descriptor.cap = SANE_CAP_SOFT_DETECT;
  session->options[OPT_NUM_OPTS].value.w = NUM_OPTIONS;

  /* "Standard" group: */
  session->options[OPT_STANDARD_GROUP].descriptor.title = SANE_TITLE_STANDARD;
  session->options[OPT_STANDARD_GROUP].descriptor.name = SANE_NAME_STANDARD;
  session->options[OPT_STANDARD_GROUP].descriptor.desc = SANE_DESC_STANDARD;
  session->options[OPT_STANDARD_GROUP].descriptor.type = SANE_TYPE_GROUP;
  session->options[OPT_STANDARD_GROUP].descriptor.size = 0;
  session->options[OPT_STANDARD_GROUP].descriptor.cap = 0;
  session->options[OPT_STANDARD_GROUP].descriptor.constraint_type =
    SANE_CONSTRAINT_NONE;

  /* scan mode */
  session->options[OPT_MODE].descriptor.name = SANE_NAME_SCAN_MODE;
  session->options[OPT_MODE].descriptor.title = SANE_TITLE_SCAN_MODE;
  session->options[OPT_MODE].descriptor.desc = SANE_DESC_SCAN_MODE;
  session->options[OPT_MODE].descriptor.type = SANE_TYPE_STRING;
  session->options[OPT_MODE].descriptor.cap |= SANE_CAP_AUTOMATIC;
  session->options[OPT_MODE].descriptor.constraint_type =
    SANE_CONSTRAINT_STRING_LIST;
  session->options[OPT_MODE].descriptor.size = max_string_size (mode_list);
  session->options[OPT_MODE].descriptor.constraint.string_list = mode_list;
  session->options[OPT_MODE].value.s = strdup (mode_list[0]);

  /* preview */
  session->options[OPT_PREVIEW].descriptor.name = SANE_NAME_PREVIEW;
  session->options[OPT_PREVIEW].descriptor.title = SANE_TITLE_PREVIEW;
  session->options[OPT_PREVIEW].descriptor.desc = SANE_DESC_PREVIEW;
  session->options[OPT_PREVIEW].descriptor.type = SANE_TYPE_BOOL;
  session->options[OPT_PREVIEW].descriptor.cap |= SANE_CAP_AUTOMATIC;
  session->options[OPT_PREVIEW].descriptor.unit = SANE_UNIT_NONE;
  session->options[OPT_PREVIEW].descriptor.constraint_type =
    SANE_CONSTRAINT_NONE;
  session->options[OPT_PREVIEW].value.w = SANE_FALSE;

  /** @brief build resolution list
   * We merge xdpi and ydpi list to provide only one resolution option control.
   * This is the most common case for backends and fronteds and give 'square'
   * pixels. The SANE API allow to control x and y dpi independently, but this is
   * rarely done and may confuse both frontends and users. In case a dpi value exists
   * for one but not for the other, the backend will have to crop data so that the
   * frontend is unaffected. A common case is that motor resolution (ydpi) is higher
   * than sensor resolution (xdpi), so scan lines must be scaled up to keep square
   * pixel when doing sane_read().
   * TODO this deserves a dedicated function and some unit testing
   */

  /* find minimum first */
  min = 65535;
  for (i = 0; i < MAX_RESOLUTIONS && model->xdpi_values[i] > 0; i++)
    {
      if (model->xdpi_values[i] < min)
	min = model->xdpi_values[i];
    }
  for (i = 0; i < MAX_RESOLUTIONS && model->ydpi_values[i] > 0; i++)
    {
      if (model->ydpi_values[i] < min)
	min = model->ydpi_values[i];
    }

  dpi_list = malloc ((MAX_RESOLUTIONS * 2 + 1) * sizeof (SANE_Word));
  if (!dpi_list)
    return SANE_STATUS_NO_MEM;
  dpi_list[1] = min;
  idx = 2;

  /* find any value greater than the last used min and
   * less than the max value
   */
  do
    {
      min = 65535;
      for (i = 0; i < MAX_RESOLUTIONS && model->xdpi_values[i] > 0; i++)
	{
	  if (model->xdpi_values[i] < min
	      && model->xdpi_values[i] > dpi_list[idx - 1])
	    min = model->xdpi_values[i];
	}
      for (i = 0; i < MAX_RESOLUTIONS && model->ydpi_values[i] > 0; i++)
	{
	  if (model->ydpi_values[i] < min
	      && model->ydpi_values[i] > dpi_list[idx - 1])
	    min = model->ydpi_values[i];
	}
      if (min < 65535)
	{
	  dpi_list[idx] = min;
	  idx++;
	}
    }
  while (min != 65535);
  dpi_list[idx] = 0;
  /* the count of different resolution is put at the beginning */
  dpi_list[0] = idx - 1;

  session->options[OPT_RESOLUTION].descriptor.name =
    SANE_NAME_SCAN_RESOLUTION;
  session->options[OPT_RESOLUTION].descriptor.title =
    SANE_TITLE_SCAN_RESOLUTION;
  session->options[OPT_RESOLUTION].descriptor.desc =
    SANE_DESC_SCAN_RESOLUTION;
  session->options[OPT_RESOLUTION].descriptor.type = SANE_TYPE_INT;
  session->options[OPT_RESOLUTION].descriptor.cap |= SANE_CAP_AUTOMATIC;
  session->options[OPT_RESOLUTION].descriptor.unit = SANE_UNIT_DPI;
  session->options[OPT_RESOLUTION].descriptor.constraint_type =
    SANE_CONSTRAINT_WORD_LIST;
  session->options[OPT_RESOLUTION].descriptor.constraint.word_list = dpi_list;

  /* initial value is lowest available dpi */
  session->options[OPT_RESOLUTION].value.w = min;

  /* "Geometry" group: */
  session->options[OPT_GEOMETRY_GROUP].descriptor.title = SANE_TITLE_GEOMETRY;
  session->options[OPT_GEOMETRY_GROUP].descriptor.name = SANE_NAME_GEOMETRY;
  session->options[OPT_GEOMETRY_GROUP].descriptor.desc = SANE_DESC_GEOMETRY;
  session->options[OPT_GEOMETRY_GROUP].descriptor.type = SANE_TYPE_GROUP;
  session->options[OPT_GEOMETRY_GROUP].descriptor.cap = SANE_CAP_ADVANCED;
  session->options[OPT_GEOMETRY_GROUP].descriptor.size = 0;
  session->options[OPT_GEOMETRY_GROUP].descriptor.constraint_type =
    SANE_CONSTRAINT_NONE;

  /* adapt the constraint range to the detected model */
  x_range.max = model->x_size;
  y_range.max = model->y_size;

  /* top-left x */
  session->options[OPT_TL_X].descriptor.name = SANE_NAME_SCAN_TL_X;
  session->options[OPT_TL_X].descriptor.title = SANE_TITLE_SCAN_TL_X;
  session->options[OPT_TL_X].descriptor.desc = SANE_DESC_SCAN_TL_X;
  session->options[OPT_TL_X].descriptor.type = SANE_TYPE_FIXED;
  session->options[OPT_TL_X].descriptor.cap |= SANE_CAP_AUTOMATIC;
  session->options[OPT_TL_X].descriptor.unit = SANE_UNIT_MM;
  session->options[OPT_TL_X].descriptor.constraint_type =
    SANE_CONSTRAINT_RANGE;
  session->options[OPT_TL_X].descriptor.constraint.range = &x_range;
  session->options[OPT_TL_X].value.w = 0;

  /* top-left y */
  session->options[OPT_TL_Y].descriptor.name = SANE_NAME_SCAN_TL_Y;
  session->options[OPT_TL_Y].descriptor.title = SANE_TITLE_SCAN_TL_Y;
  session->options[OPT_TL_Y].descriptor.desc = SANE_DESC_SCAN_TL_Y;
  session->options[OPT_TL_Y].descriptor.type = SANE_TYPE_FIXED;
  session->options[OPT_TL_Y].descriptor.cap |= SANE_CAP_AUTOMATIC;
  session->options[OPT_TL_Y].descriptor.unit = SANE_UNIT_MM;
  session->options[OPT_TL_Y].descriptor.constraint_type =
    SANE_CONSTRAINT_RANGE;
  session->options[OPT_TL_Y].descriptor.constraint.range = &y_range;
  session->options[OPT_TL_Y].value.w = 0;

  /* bottom-right x */
  session->options[OPT_BR_X].descriptor.name = SANE_NAME_SCAN_BR_X;
  session->options[OPT_BR_X].descriptor.title = SANE_TITLE_SCAN_BR_X;
  session->options[OPT_BR_X].descriptor.desc = SANE_DESC_SCAN_BR_X;
  session->options[OPT_BR_X].descriptor.type = SANE_TYPE_FIXED;
  session->options[OPT_BR_X].descriptor.cap |= SANE_CAP_AUTOMATIC;
  session->options[OPT_BR_X].descriptor.unit = SANE_UNIT_MM;
  session->options[OPT_BR_X].descriptor.constraint_type =
    SANE_CONSTRAINT_RANGE;
  session->options[OPT_BR_X].descriptor.constraint.range = &x_range;
  session->options[OPT_BR_X].value.w = x_range.max;

  /* bottom-right y */
  session->options[OPT_BR_Y].descriptor.name = SANE_NAME_SCAN_BR_Y;
  session->options[OPT_BR_Y].descriptor.title = SANE_TITLE_SCAN_BR_Y;
  session->options[OPT_BR_Y].descriptor.desc = SANE_DESC_SCAN_BR_Y;
  session->options[OPT_BR_Y].descriptor.type = SANE_TYPE_FIXED;
  session->options[OPT_BR_Y].descriptor.cap |= SANE_CAP_AUTOMATIC;
  session->options[OPT_BR_Y].descriptor.unit = SANE_UNIT_MM;
  session->options[OPT_BR_Y].descriptor.constraint_type =
    SANE_CONSTRAINT_RANGE;
  session->options[OPT_BR_Y].descriptor.constraint.range = &y_range;
  session->options[OPT_BR_Y].value.w = y_range.max;

  /* sensor group */
  session->options[OPT_SENSOR_GROUP].descriptor.name = SANE_NAME_SENSORS;
  session->options[OPT_SENSOR_GROUP].descriptor.title = SANE_TITLE_SENSORS;
  session->options[OPT_SENSOR_GROUP].descriptor.desc = SANE_DESC_SENSORS;
  session->options[OPT_SENSOR_GROUP].descriptor.type = SANE_TYPE_GROUP;
  session->options[OPT_SENSOR_GROUP].descriptor.constraint_type =
    SANE_CONSTRAINT_NONE;

  /* page loaded sensor */
  session->options[OPT_PAGE_LOADED_SW].descriptor.name =
    SANE_NAME_PAGE_LOADED;
  session->options[OPT_PAGE_LOADED_SW].descriptor.title =
    SANE_TITLE_PAGE_LOADED;
  session->options[OPT_PAGE_LOADED_SW].descriptor.desc =
    SANE_DESC_PAGE_LOADED;
  session->options[OPT_PAGE_LOADED_SW].descriptor.type = SANE_TYPE_BOOL;
  session->options[OPT_PAGE_LOADED_SW].descriptor.unit = SANE_UNIT_NONE;
  session->options[OPT_PAGE_LOADED_SW].descriptor.cap =
    SANE_CAP_SOFT_DETECT | SANE_CAP_HARD_SELECT | SANE_CAP_ADVANCED;
  session->options[OPT_PAGE_LOADED_SW].value.b = 0;

  /* calibration needed */
  session->options[OPT_NEED_CALIBRATION_SW].descriptor.name =
    "need-calibration";
  session->options[OPT_NEED_CALIBRATION_SW].descriptor.title =
    SANE_I18N ("Need calibration");
  session->options[OPT_NEED_CALIBRATION_SW].descriptor.desc =
    SANE_I18N ("The scanner needs calibration for the current settings");
  session->options[OPT_NEED_CALIBRATION_SW].descriptor.type = SANE_TYPE_BOOL;
  session->options[OPT_NEED_CALIBRATION_SW].descriptor.unit = SANE_UNIT_NONE;
  session->options[OPT_NEED_CALIBRATION_SW].descriptor.cap =
    SANE_CAP_SOFT_DETECT | SANE_CAP_HARD_SELECT | SANE_CAP_ADVANCED;
  session->options[OPT_NEED_CALIBRATION_SW].value.b = 0;

  /* button group */
  session->options[OPT_BUTTON_GROUP].descriptor.name = "Buttons";
  session->options[OPT_BUTTON_GROUP].descriptor.title = SANE_I18N ("Buttons");
  session->options[OPT_BUTTON_GROUP].descriptor.desc = SANE_I18N ("Buttons");
  session->options[OPT_BUTTON_GROUP].descriptor.type = SANE_TYPE_GROUP;
  session->options[OPT_BUTTON_GROUP].descriptor.constraint_type =
    SANE_CONSTRAINT_NONE;

  /* calibrate button */
  session->options[OPT_CALIBRATE].descriptor.name = "calibrate";
  session->options[OPT_CALIBRATE].descriptor.title = SANE_I18N ("Calibrate");
  session->options[OPT_CALIBRATE].descriptor.desc =
    SANE_I18N ("Start calibration using special sheet");
  session->options[OPT_CALIBRATE].descriptor.type = SANE_TYPE_BUTTON;
  session->options[OPT_CALIBRATE].descriptor.unit = SANE_UNIT_NONE;
  session->options[OPT_CALIBRATE].descriptor.cap =
    SANE_CAP_SOFT_DETECT | SANE_CAP_SOFT_SELECT | SANE_CAP_ADVANCED |
    SANE_CAP_AUTOMATIC;
  session->options[OPT_CALIBRATE].value.b = 0;

  /* clear calibration cache button */
  session->options[OPT_CLEAR_CALIBRATION].descriptor.name = "clear";
  session->options[OPT_CLEAR_CALIBRATION].descriptor.title =
    SANE_I18N ("Clear calibration");
  session->options[OPT_CLEAR_CALIBRATION].descriptor.desc =
    SANE_I18N ("Clear calibration cache");
  session->options[OPT_CLEAR_CALIBRATION].descriptor.type = SANE_TYPE_BUTTON;
  session->options[OPT_CLEAR_CALIBRATION].descriptor.unit = SANE_UNIT_NONE;
  session->options[OPT_CLEAR_CALIBRATION].descriptor.cap =
    SANE_CAP_SOFT_DETECT | SANE_CAP_SOFT_SELECT | SANE_CAP_ADVANCED |
    SANE_CAP_AUTOMATIC;
  session->options[OPT_CLEAR_CALIBRATION].value.b = 0;

  /* until work on calibration isfinished */
  DISABLE (OPT_CALIBRATE);
  DISABLE (OPT_CLEAR_CALIBRATION);

  DBG (DBG_proc, "init_options: exit\n");
  return SANE_STATUS_GOOD;
}

/** @brief physical probe of a device
 * This function probes for a scanning device using the given name. If the
 * device is managed, a model structure describing the device will be returned.
 * @param devicename low level device to access to probe hardware
 * @return NULL is the device is unsupported, or a model struct describing the
 * device.
 */
P5_Model *
probe (const char *devicename)
{
  int fd;

  /* open parallel port device */
  fd = open_pp (devicename);
  if (fd < 0)
    {
      DBG (DBG_error, "probe: failed to open '%s' device!\n", devicename);
      return NULL;
    }

  /* now try to connect to scanner */
  if (connect (fd) != SANE_TRUE)
    {
      DBG (DBG_error, "probe: failed to connect!\n");
      close_pp (fd);
      return NULL;
    }

  /* set up for memory test */
  write_reg (fd, REG1, 0x00);
  write_reg (fd, REG7, 0x00);
  write_reg (fd, REG0, 0x00);
  write_reg (fd, REG1, 0x00);
  write_reg (fd, REGF, 0x80);
  if (memtest (fd, 0x0100) != SANE_TRUE)
    {
      disconnect (fd);
      close_pp (fd);
      DBG (DBG_error, "probe: memory test failed!\n");
      return NULL;
    }
  else
    {
      DBG (DBG_info, "memtest() OK...\n");
    }
  write_reg (fd, REG7, 0x00);

  /* check for document presence 0xC6: present, 0xC3 no document */
  test_document (fd);

  /* release device and parport for next uses */
  disconnect (fd);
  close_pp (fd);

  /* for there is only one supported model, so we use hardcoded values */
  DBG (DBG_proc, "probe: exit\n");
  return &pagepartner_model;
}


/* vim: set sw=2 cino=>2se-1sn-1s{s^-1st0(0u0 smarttab expandtab: */
