drivers/s390/char/sclp_rw.c - linux/torvalds/linux - Git at Google

 // SPDX-License-Identifier: GPL-2.0
 /*
  * driver: reading from and writing to system console on S/390 via SCLP
  *
  * Copyright IBM Corp. 1999, 2009
  *
  * Author(s): Martin Peschke <mpeschke@de.ibm.com>
  *	      Martin Schwidefsky <schwidefsky@de.ibm.com>
  */

 #include <linux/kmod.h>
 #include <linux/types.h>
 #include <linux/err.h>
 #include <linux/string.h>
 #include <linux/spinlock.h>
 #include <linux/ctype.h>
 #include <linux/uaccess.h>

 #include "sclp.h"
 #include "sclp_rw.h"

 /*
  * The room for the SCCB (only for writing) is not equal to a pages size
  * (as it is specified as the maximum size in the SCLP documentation)
  * because of the additional data structure described above.
  */
 #define MAX_SCCB_ROOM (PAGE_SIZE - sizeof(struct sclp_buffer))

 static void sclp_rw_pm_event(struct sclp_register *reg,
 			     enum sclp_pm_event sclp_pm_event)
 {
 	sclp_console_pm_event(sclp_pm_event);
 }

 /* Event type structure for write message and write priority message */
 static struct sclp_register sclp_rw_event = {
 	.send_mask = EVTYP_MSG_MASK,
 	.pm_event_fn = sclp_rw_pm_event,
 };

 /*
  * Setup a sclp write buffer. Gets a page as input (4K) and returns
  * a pointer to a struct sclp_buffer structure that is located at the
  * end of the input page. This reduces the buffer space by a few
  * bytes but simplifies things.
  */
 struct sclp_buffer *
 sclp_make_buffer(void *page, unsigned short columns, unsigned short htab)
 {
 	struct sclp_buffer *buffer;
 	struct sccb_header *sccb;

 	sccb = (struct sccb_header *) page;
 	/*
 	 * We keep the struct sclp_buffer structure at the end
 	 * of the sccb page.
 	 */
 	buffer = ((struct sclp_buffer *) ((addr_t) sccb + PAGE_SIZE)) - 1;
 	buffer->sccb = sccb;
 	buffer->retry_count = 0;
 	buffer->messages = 0;
 	buffer->char_sum = 0;
 	buffer->current_line = NULL;
 	buffer->current_length = 0;
 	buffer->columns = columns;
 	buffer->htab = htab;

 	/* initialize sccb */
 	memset(sccb, 0, sizeof(struct sccb_header));
 	sccb->length = sizeof(struct sccb_header);

 	return buffer;
 }

 /*
  * Return a pointer to the original page that has been used to create
  * the buffer.
  */
 void *
 sclp_unmake_buffer(struct sclp_buffer *buffer)
 {
 	return buffer->sccb;
 }

 /*
  * Initialize a new message the end of the provided buffer with
  * enough room for max_len characters. Return 0 on success.
  */
 static int
 sclp_initialize_mto(struct sclp_buffer *buffer, int max_len)
 {
 	struct sccb_header *sccb;
 	struct msg_buf *msg;
 	struct mdb *mdb;
 	struct go *go;
 	struct mto *mto;
 	int msg_size;

 	/* max size of new message including message text  */
 	msg_size = sizeof(struct msg_buf) + max_len;

 	/* check if current buffer sccb can contain the mto */
 	sccb = buffer->sccb;
 	if ((MAX_SCCB_ROOM - sccb->length) < msg_size)
 		return -ENOMEM;

 	msg = (struct msg_buf *)((addr_t) sccb + sccb->length);
 	memset(msg, 0, sizeof(struct msg_buf));
 	msg->header.length = sizeof(struct msg_buf);
 	msg->header.type = EVTYP_MSG;

 	mdb = &msg->mdb;
 	mdb->header.length = sizeof(struct mdb);
 	mdb->header.type = 1;
 	mdb->header.tag = 0xD4C4C240;	/* ebcdic "MDB " */
 	mdb->header.revision_code = 1;

 	go = &mdb->go;
 	go->length = sizeof(struct go);
 	go->type = 1;

 	mto = &mdb->mto;
 	mto->length = sizeof(struct mto);
 	mto->type = 4;	/* message text object */
 	mto->line_type_flags = LNTPFLGS_ENDTEXT; /* end text */

 	/* set pointer to first byte after struct mto. */
 	buffer->current_msg = msg;
 	buffer->current_line = (char *) (mto + 1);
 	buffer->current_length = 0;

 	return 0;
 }

 /*
  * Finalize message initialized by sclp_initialize_mto(),
  * updating the sizes of MTO, enclosing MDB, event buffer and SCCB.
  */
 static void
 sclp_finalize_mto(struct sclp_buffer *buffer)
 {
 	struct sccb_header *sccb;
 	struct msg_buf *msg;

 	/*
 	 * update values of sizes
 	 * (SCCB, Event(Message) Buffer, Message Data Block)
 	 */
 	sccb = buffer->sccb;
 	msg = buffer->current_msg;
 	msg->header.length += buffer->current_length;
 	msg->mdb.header.length += buffer->current_length;
 	msg->mdb.mto.length += buffer->current_length;
 	sccb->length += msg->header.length;

 	/*
 	 * count number of buffered messages (= number of Message Text
 	 * Objects) and number of buffered characters
 	 * for the SCCB currently used for buffering and at all
 	 */
 	buffer->messages++;
 	buffer->char_sum += buffer->current_length;

 	buffer->current_line = NULL;
 	buffer->current_length = 0;
 	buffer->current_msg = NULL;
 }

 /*
  * processing of a message including escape characters,
  * returns number of characters written to the output sccb
  * ("processed" means that is not guaranteed that the character have already
  *  been sent to the SCLP but that it will be done at least next time the SCLP
  *  is not busy)
  */
 int
 sclp_write(struct sclp_buffer *buffer, const unsigned char *msg, int count)
 {
 	int spaces, i_msg;
 	int rc;

 	/*
 	 * parse msg for escape sequences (\t,\v ...) and put formated
 	 * msg into an mto (created by sclp_initialize_mto).
 	 *
 	 * We have to do this work ourselfs because there is no support for
 	 * these characters on the native machine and only partial support
 	 * under VM (Why does VM interpret \n but the native machine doesn't ?)
 	 *
 	 * Depending on i/o-control setting the message is always written
 	 * immediately or we wait for a final new line maybe coming with the
 	 * next message. Besides we avoid a buffer overrun by writing its
 	 * content.
 	 *
 	 * RESTRICTIONS:
 	 *
 	 * \r and \b work within one line because we are not able to modify
 	 * previous output that have already been accepted by the SCLP.
 	 *
 	 * \t combined with following \r is not correctly represented because
 	 * \t is expanded to some spaces but \r does not know about a
 	 * previous \t and decreases the current position by one column.
 	 * This is in order to a slim and quick implementation.
 	 */
 	for (i_msg = 0; i_msg < count; i_msg++) {
 		switch (msg[i_msg]) {
 		case '\n':	/* new line, line feed (ASCII)	*/
 			/* check if new mto needs to be created */
 			if (buffer->current_line == NULL) {
 				rc = sclp_initialize_mto(buffer, 0);
 				if (rc)
 					return i_msg;
 			}
 			sclp_finalize_mto(buffer);
 			break;
 		case '\a':	/* bell, one for several times	*/
 			/* set SCLP sound alarm bit in General Object */
 			if (buffer->current_line == NULL) {
 				rc = sclp_initialize_mto(buffer,
 							 buffer->columns);
 				if (rc)
 					return i_msg;
 			}
 			buffer->current_msg->mdb.go.general_msg_flags |=
 				GNRLMSGFLGS_SNDALRM;
 			break;
 		case '\t':	/* horizontal tabulator	 */
 			/* check if new mto needs to be created */
 			if (buffer->current_line == NULL) {
 				rc = sclp_initialize_mto(buffer,
 							 buffer->columns);
 				if (rc)
 					return i_msg;
 			}
 			/* "go to (next htab-boundary + 1, same line)" */
 			do {
 				if (buffer->current_length >= buffer->columns)
 					break;
 				/* ok, add a blank */
 				*buffer->current_line++ = 0x40;
 				buffer->current_length++;
 			} while (buffer->current_length % buffer->htab);
 			break;
 		case '\f':	/* form feed  */
 		case '\v':	/* vertical tabulator  */
 			/* "go to (actual column, actual line + 1)" */
 			/* = new line, leading spaces */
 			if (buffer->current_line != NULL) {
 				spaces = buffer->current_length;
 				sclp_finalize_mto(buffer);
 				rc = sclp_initialize_mto(buffer,
 							 buffer->columns);
 				if (rc)
 					return i_msg;
 				memset(buffer->current_line, 0x40, spaces);
 				buffer->current_line += spaces;
 				buffer->current_length = spaces;
 			} else {
 				/* one an empty line this is the same as \n */
 				rc = sclp_initialize_mto(buffer,
 							 buffer->columns);
 				if (rc)
 					return i_msg;
 				sclp_finalize_mto(buffer);
 			}
 			break;
 		case '\b':	/* backspace  */
 			/* "go to (actual column - 1, actual line)" */
 			/* decrement counter indicating position, */
 			/* do not remove last character */
 			if (buffer->current_line != NULL &&
 			    buffer->current_length > 0) {
 				buffer->current_length--;
 				buffer->current_line--;
 			}
 			break;
 		case 0x00:	/* end of string  */
 			/* transfer current line to SCCB */
 			if (buffer->current_line != NULL)
 				sclp_finalize_mto(buffer);
 			/* skip the rest of the message including the 0 byte */
 			i_msg = count - 1;
 			break;
 		default:	/* no escape character	*/
 			/* do not output unprintable characters */
 			if (!isprint(msg[i_msg]))
 				break;
 			/* check if new mto needs to be created */
 			if (buffer->current_line == NULL) {
 				rc = sclp_initialize_mto(buffer,
 							 buffer->columns);
 				if (rc)
 					return i_msg;
 			}
 			*buffer->current_line++ = sclp_ascebc(msg[i_msg]);
 			buffer->current_length++;
 			break;
 		}
 		/* check if current mto is full */
 		if (buffer->current_line != NULL &&
 		    buffer->current_length >= buffer->columns)
 			sclp_finalize_mto(buffer);
 	}

 	/* return number of processed characters */
 	return i_msg;
 }

 /*
  * Return the number of free bytes in the sccb
  */
 int
 sclp_buffer_space(struct sclp_buffer *buffer)
 {
 	struct sccb_header *sccb;
 	int count;

 	sccb = buffer->sccb;
 	count = MAX_SCCB_ROOM - sccb->length;
 	if (buffer->current_line != NULL)
 		count -= sizeof(struct msg_buf) + buffer->current_length;
 	return count;
 }

 /*
  * Return number of characters in buffer
  */
 int
 sclp_chars_in_buffer(struct sclp_buffer *buffer)
 {
 	int count;

 	count = buffer->char_sum;
 	if (buffer->current_line != NULL)
 		count += buffer->current_length;
 	return count;
 }

 /*
  * sets or provides some values that influence the drivers behaviour
  */
 void
 sclp_set_columns(struct sclp_buffer *buffer, unsigned short columns)
 {
 	buffer->columns = columns;
 	if (buffer->current_line != NULL &&
 	    buffer->current_length > buffer->columns)
 		sclp_finalize_mto(buffer);
 }

 void
 sclp_set_htab(struct sclp_buffer *buffer, unsigned short htab)
 {
 	buffer->htab = htab;
 }

 /*
  * called by sclp_console_init and/or sclp_tty_init
  */
 int
 sclp_rw_init(void)
 {
 	static int init_done = 0;
 	int rc;

 	if (init_done)
 		return 0;

 	rc = sclp_register(&sclp_rw_event);
 	if (rc == 0)
 		init_done = 1;
 	return rc;
 }

 #define SCLP_BUFFER_MAX_RETRY		1

 /*
  * second half of Write Event Data-function that has to be done after
  * interruption indicating completion of Service Call.
  */
 static void
 sclp_writedata_callback(struct sclp_req *request, void *data)
 {
 	int rc;
 	struct sclp_buffer *buffer;
 	struct sccb_header *sccb;

 	buffer = (struct sclp_buffer *) data;
 	sccb = buffer->sccb;

 	if (request->status == SCLP_REQ_FAILED) {
 		if (buffer->callback != NULL)
 			buffer->callback(buffer, -EIO);
 		return;
 	}
 	/* check SCLP response code and choose suitable action	*/
 	switch (sccb->response_code) {
 	case 0x0020 :
 		/* Normal completion, buffer processed, message(s) sent */
 		rc = 0;
 		break;

 	case 0x0340: /* Contained SCLP equipment check */
 		if (++buffer->retry_count > SCLP_BUFFER_MAX_RETRY) {
 			rc = -EIO;
 			break;
 		}
 		/* remove processed buffers and requeue rest */
 		if (sclp_remove_processed((struct sccb_header *) sccb) > 0) {
 			/* not all buffers were processed */
 			sccb->response_code = 0x0000;
 			buffer->request.status = SCLP_REQ_FILLED;
 			rc = sclp_add_request(request);
 			if (rc == 0)
 				return;
 		} else
 			rc = 0;
 		break;

 	case 0x0040: /* SCLP equipment check */
 	case 0x05f0: /* Target resource in improper state */
 		if (++buffer->retry_count > SCLP_BUFFER_MAX_RETRY) {
 			rc = -EIO;
 			break;
 		}
 		/* retry request */
 		sccb->response_code = 0x0000;
 		buffer->request.status = SCLP_REQ_FILLED;
 		rc = sclp_add_request(request);
 		if (rc == 0)
 			return;
 		break;
 	default:
 		if (sccb->response_code == 0x71f0)
 			rc = -ENOMEM;
 		else
 			rc = -EINVAL;
 		break;
 	}
 	if (buffer->callback != NULL)
 		buffer->callback(buffer, rc);
 }

 /*
  * Setup the request structure in the struct sclp_buffer to do SCLP Write
  * Event Data and pass the request to the core SCLP loop. Return zero on
  * success, non-zero otherwise.
  */
 int
 sclp_emit_buffer(struct sclp_buffer *buffer,
 		 void (*callback)(struct sclp_buffer *, int))
 {
 	/* add current line if there is one */
 	if (buffer->current_line != NULL)
 		sclp_finalize_mto(buffer);

 	/* Are there messages in the output buffer ? */
 	if (buffer->messages == 0)
 		return -EIO;

 	buffer->request.command = SCLP_CMDW_WRITE_EVENT_DATA;
 	buffer->request.status = SCLP_REQ_FILLED;
 	buffer->request.callback = sclp_writedata_callback;
 	buffer->request.callback_data = buffer;
 	buffer->request.sccb = buffer->sccb;
 	buffer->callback = callback;
 	return sclp_add_request(&buffer->request);
 }
	// SPDX-License-Identifier: GPL-2.0
	/*
	* driver: reading from and writing to system console on S/390 via SCLP
	*
	* Copyright IBM Corp. 1999, 2009
	*
	* Author(s): Martin Peschke <mpeschke@de.ibm.com>
	* Martin Schwidefsky <schwidefsky@de.ibm.com>
	*/

	#include <linux/kmod.h>
	#include <linux/types.h>
	#include <linux/err.h>
	#include <linux/string.h>
	#include <linux/spinlock.h>
	#include <linux/ctype.h>
	#include <linux/uaccess.h>

	#include "sclp.h"
	#include "sclp_rw.h"

	/*
	* The room for the SCCB (only for writing) is not equal to a pages size
	* (as it is specified as the maximum size in the SCLP documentation)
	* because of the additional data structure described above.
	*/
	#define MAX_SCCB_ROOM (PAGE_SIZE - sizeof(struct sclp_buffer))

	static void sclp_rw_pm_event(struct sclp_register *reg,
	enum sclp_pm_event sclp_pm_event)
	{
	sclp_console_pm_event(sclp_pm_event);
	}

	/* Event type structure for write message and write priority message */
	static struct sclp_register sclp_rw_event = {
	.send_mask = EVTYP_MSG_MASK,
	.pm_event_fn = sclp_rw_pm_event,
	};

	/*
	* Setup a sclp write buffer. Gets a page as input (4K) and returns
	* a pointer to a struct sclp_buffer structure that is located at the
	* end of the input page. This reduces the buffer space by a few
	* bytes but simplifies things.
	*/
	struct sclp_buffer *
	sclp_make_buffer(void *page, unsigned short columns, unsigned short htab)
	{
	struct sclp_buffer *buffer;
	struct sccb_header *sccb;

	sccb = (struct sccb_header *) page;
	/*
	* We keep the struct sclp_buffer structure at the end
	* of the sccb page.
	*/
	buffer = ((struct sclp_buffer *) ((addr_t) sccb + PAGE_SIZE)) - 1;
	buffer->sccb = sccb;
	buffer->retry_count = 0;
	buffer->messages = 0;
	buffer->char_sum = 0;
	buffer->current_line = NULL;
	buffer->current_length = 0;
	buffer->columns = columns;
	buffer->htab = htab;

	/* initialize sccb */
	memset(sccb, 0, sizeof(struct sccb_header));
	sccb->length = sizeof(struct sccb_header);

	return buffer;
	}

	/*
	* Return a pointer to the original page that has been used to create
	* the buffer.
	*/
	void *
	sclp_unmake_buffer(struct sclp_buffer *buffer)
	{
	return buffer->sccb;
	}

	/*
	* Initialize a new message the end of the provided buffer with
	* enough room for max_len characters. Return 0 on success.
	*/
	static int
	sclp_initialize_mto(struct sclp_buffer *buffer, int max_len)
	{
	struct sccb_header *sccb;
	struct msg_buf *msg;
	struct mdb *mdb;
	struct go *go;
	struct mto *mto;
	int msg_size;

	/* max size of new message including message text */
	msg_size = sizeof(struct msg_buf) + max_len;

	/* check if current buffer sccb can contain the mto */
	sccb = buffer->sccb;
	if ((MAX_SCCB_ROOM - sccb->length) < msg_size)
	return -ENOMEM;

	msg = (struct msg_buf *)((addr_t) sccb + sccb->length);
	memset(msg, 0, sizeof(struct msg_buf));
	msg->header.length = sizeof(struct msg_buf);
	msg->header.type = EVTYP_MSG;

	mdb = &msg->mdb;
	mdb->header.length = sizeof(struct mdb);
	mdb->header.type = 1;
	mdb->header.tag = 0xD4C4C240; /* ebcdic "MDB " */
	mdb->header.revision_code = 1;

	go = &mdb->go;
	go->length = sizeof(struct go);
	go->type = 1;

	mto = &mdb->mto;
	mto->length = sizeof(struct mto);
	mto->type = 4; /* message text object */
	mto->line_type_flags = LNTPFLGS_ENDTEXT; /* end text */

	/* set pointer to first byte after struct mto. */
	buffer->current_msg = msg;
	buffer->current_line = (char *) (mto + 1);
	buffer->current_length = 0;

	return 0;
	}

	/*
	* Finalize message initialized by sclp_initialize_mto(),
	* updating the sizes of MTO, enclosing MDB, event buffer and SCCB.
	*/
	static void
	sclp_finalize_mto(struct sclp_buffer *buffer)
	{
	struct sccb_header *sccb;
	struct msg_buf *msg;

	/*
	* update values of sizes
	* (SCCB, Event(Message) Buffer, Message Data Block)
	*/
	sccb = buffer->sccb;
	msg = buffer->current_msg;
	msg->header.length += buffer->current_length;
	msg->mdb.header.length += buffer->current_length;
	msg->mdb.mto.length += buffer->current_length;
	sccb->length += msg->header.length;

	/*
	* count number of buffered messages (= number of Message Text
	* Objects) and number of buffered characters
	* for the SCCB currently used for buffering and at all
	*/
	buffer->messages++;
	buffer->char_sum += buffer->current_length;

	buffer->current_line = NULL;
	buffer->current_length = 0;
	buffer->current_msg = NULL;
	}

	/*
	* processing of a message including escape characters,
	* returns number of characters written to the output sccb
	* ("processed" means that is not guaranteed that the character have already
	* been sent to the SCLP but that it will be done at least next time the SCLP
	* is not busy)
	*/
	int
	sclp_write(struct sclp_buffer buffer, const unsigned char msg, int count)
	{
	int spaces, i_msg;
	int rc;

	/*
	* parse msg for escape sequences (\t,\v ...) and put formated
	* msg into an mto (created by sclp_initialize_mto).
	*
	* We have to do this work ourselfs because there is no support for
	* these characters on the native machine and only partial support
	* under VM (Why does VM interpret \n but the native machine doesn't ?)
	*
	* Depending on i/o-control setting the message is always written
	* immediately or we wait for a final new line maybe coming with the
	* next message. Besides we avoid a buffer overrun by writing its
	* content.
	*
	* RESTRICTIONS:
	*
	* \r and \b work within one line because we are not able to modify
	* previous output that have already been accepted by the SCLP.
	*
	* \t combined with following \r is not correctly represented because
	* \t is expanded to some spaces but \r does not know about a
	* previous \t and decreases the current position by one column.
	* This is in order to a slim and quick implementation.
	*/
	for (i_msg = 0; i_msg < count; i_msg++) {
	switch (msg[i_msg]) {
	case '\n': /* new line, line feed (ASCII) */
	/* check if new mto needs to be created */
	if (buffer->current_line == NULL) {
	rc = sclp_initialize_mto(buffer, 0);
	if (rc)
	return i_msg;
	}
	sclp_finalize_mto(buffer);
	break;
	case '\a': /* bell, one for several times */
	/* set SCLP sound alarm bit in General Object */
	if (buffer->current_line == NULL) {
	rc = sclp_initialize_mto(buffer,
	buffer->columns);
	if (rc)
	return i_msg;
	}
	buffer->current_msg->mdb.go.general_msg_flags \|=
	GNRLMSGFLGS_SNDALRM;
	break;
	case '\t': /* horizontal tabulator */
	/* check if new mto needs to be created */
	if (buffer->current_line == NULL) {
	rc = sclp_initialize_mto(buffer,
	buffer->columns);
	if (rc)
	return i_msg;
	}
	/* "go to (next htab-boundary + 1, same line)" */
	do {
	if (buffer->current_length >= buffer->columns)
	break;
	/* ok, add a blank */
	*buffer->current_line++ = 0x40;
	buffer->current_length++;
	} while (buffer->current_length % buffer->htab);
	break;
	case '\f': /* form feed */
	case '\v': /* vertical tabulator */
	/* "go to (actual column, actual line + 1)" */
	/* = new line, leading spaces */
	if (buffer->current_line != NULL) {
	spaces = buffer->current_length;
	sclp_finalize_mto(buffer);
	rc = sclp_initialize_mto(buffer,
	buffer->columns);
	if (rc)
	return i_msg;
	memset(buffer->current_line, 0x40, spaces);
	buffer->current_line += spaces;
	buffer->current_length = spaces;
	} else {
	/* one an empty line this is the same as \n */
	rc = sclp_initialize_mto(buffer,
	buffer->columns);
	if (rc)
	return i_msg;
	sclp_finalize_mto(buffer);
	}
	break;
	case '\b': /* backspace */
	/* "go to (actual column - 1, actual line)" */
	/* decrement counter indicating position, */
	/* do not remove last character */
	if (buffer->current_line != NULL &&
	buffer->current_length > 0) {
	buffer->current_length--;
	buffer->current_line--;
	}
	break;
	case 0x00: /* end of string */
	/* transfer current line to SCCB */
	if (buffer->current_line != NULL)
	sclp_finalize_mto(buffer);
	/* skip the rest of the message including the 0 byte */
	i_msg = count - 1;
	break;
	default: /* no escape character */
	/* do not output unprintable characters */
	if (!isprint(msg[i_msg]))
	break;
	/* check if new mto needs to be created */
	if (buffer->current_line == NULL) {
	rc = sclp_initialize_mto(buffer,
	buffer->columns);
	if (rc)
	return i_msg;
	}
	*buffer->current_line++ = sclp_ascebc(msg[i_msg]);
	buffer->current_length++;
	break;
	}
	/* check if current mto is full */
	if (buffer->current_line != NULL &&
	buffer->current_length >= buffer->columns)
	sclp_finalize_mto(buffer);
	}

	/* return number of processed characters */
	return i_msg;
	}

	/*
	* Return the number of free bytes in the sccb
	*/
	int
	sclp_buffer_space(struct sclp_buffer *buffer)
	{
	struct sccb_header *sccb;
	int count;

	sccb = buffer->sccb;
	count = MAX_SCCB_ROOM - sccb->length;
	if (buffer->current_line != NULL)
	count -= sizeof(struct msg_buf) + buffer->current_length;
	return count;
	}

	/*
	* Return number of characters in buffer
	*/
	int
	sclp_chars_in_buffer(struct sclp_buffer *buffer)
	{
	int count;

	count = buffer->char_sum;
	if (buffer->current_line != NULL)
	count += buffer->current_length;
	return count;
	}

	/*
	* sets or provides some values that influence the drivers behaviour
	*/
	void
	sclp_set_columns(struct sclp_buffer *buffer, unsigned short columns)
	{
	buffer->columns = columns;
	if (buffer->current_line != NULL &&
	buffer->current_length > buffer->columns)
	sclp_finalize_mto(buffer);
	}

	void
	sclp_set_htab(struct sclp_buffer *buffer, unsigned short htab)
	{
	buffer->htab = htab;
	}

	/*
	* called by sclp_console_init and/or sclp_tty_init
	*/
	int
	sclp_rw_init(void)
	{
	static int init_done = 0;
	int rc;

	if (init_done)
	return 0;

	rc = sclp_register(&sclp_rw_event);
	if (rc == 0)
	init_done = 1;
	return rc;
	}

	#define SCLP_BUFFER_MAX_RETRY 1

	/*
	* second half of Write Event Data-function that has to be done after
	* interruption indicating completion of Service Call.
	*/
	static void
	sclp_writedata_callback(struct sclp_req request, void data)
	{
	int rc;
	struct sclp_buffer *buffer;
	struct sccb_header *sccb;

	buffer = (struct sclp_buffer *) data;
	sccb = buffer->sccb;

	if (request->status == SCLP_REQ_FAILED) {
	if (buffer->callback != NULL)
	buffer->callback(buffer, -EIO);
	return;
	}
	/* check SCLP response code and choose suitable action */
	switch (sccb->response_code) {
	case 0x0020 :
	/* Normal completion, buffer processed, message(s) sent */
	rc = 0;
	break;

	case 0x0340: /* Contained SCLP equipment check */
	if (++buffer->retry_count > SCLP_BUFFER_MAX_RETRY) {
	rc = -EIO;
	break;
	}
	/* remove processed buffers and requeue rest */
	if (sclp_remove_processed((struct sccb_header *) sccb) > 0) {
	/* not all buffers were processed */
	sccb->response_code = 0x0000;
	buffer->request.status = SCLP_REQ_FILLED;
	rc = sclp_add_request(request);
	if (rc == 0)
	return;
	} else
	rc = 0;
	break;

	case 0x0040: /* SCLP equipment check */
	case 0x05f0: /* Target resource in improper state */
	if (++buffer->retry_count > SCLP_BUFFER_MAX_RETRY) {
	rc = -EIO;
	break;
	}
	/* retry request */
	sccb->response_code = 0x0000;
	buffer->request.status = SCLP_REQ_FILLED;
	rc = sclp_add_request(request);
	if (rc == 0)
	return;
	break;
	default:
	if (sccb->response_code == 0x71f0)
	rc = -ENOMEM;
	else
	rc = -EINVAL;
	break;
	}
	if (buffer->callback != NULL)
	buffer->callback(buffer, rc);
	}

	/*
	* Setup the request structure in the struct sclp_buffer to do SCLP Write
	* Event Data and pass the request to the core SCLP loop. Return zero on
	* success, non-zero otherwise.
	*/
	int
	sclp_emit_buffer(struct sclp_buffer *buffer,
	void (callback)(struct sclp_buffer , int))
	{
	/* add current line if there is one */
	if (buffer->current_line != NULL)
	sclp_finalize_mto(buffer);

	/* Are there messages in the output buffer ? */
	if (buffer->messages == 0)
	return -EIO;

	buffer->request.command = SCLP_CMDW_WRITE_EVENT_DATA;
	buffer->request.status = SCLP_REQ_FILLED;
	buffer->request.callback = sclp_writedata_callback;
	buffer->request.callback_data = buffer;
	buffer->request.sccb = buffer->sccb;
	buffer->callback = callback;
	return sclp_add_request(&buffer->request);
	}