path: root/drivers/s390/block/dasd_eer.c

/*
 *	character device driver for extended error reporting
 *
 *
 *	Copyright (C) 2005 IBM Corporation
 *	extended error reporting for DASD ECKD devices
 *	Author(s): Stefan Weinhuber <wein@de.ibm.com>
 *
 */

#include <linux/init.h>
#include <linux/fs.h>
#include <linux/kernel.h>
#include <linux/miscdevice.h>
#include <linux/module.h>
#include <linux/moduleparam.h>
#include <linux/device.h>
#include <linux/workqueue.h>
#include <linux/poll.h>
#include <linux/notifier.h>

#include <asm/uaccess.h>
#include <asm/semaphore.h>
#include <asm/atomic.h>
#include <asm/ebcdic.h>

#include "dasd_int.h"
#include "dasd_eckd.h"


MODULE_LICENSE("GPL");

MODULE_AUTHOR("Stefan Weinhuber <wein@de.ibm.com>");
MODULE_DESCRIPTION("DASD extended error reporting module");


#ifdef PRINTK_HEADER
#undef PRINTK_HEADER
#endif				/* PRINTK_HEADER */
#define PRINTK_HEADER "dasd(eer):"





/*****************************************************************************/
/*      the internal buffer                                                  */
/*****************************************************************************/

/*
 * The internal buffer is meant to store obaque blobs of data, so it doesn't
 * know of higher level concepts like triggers.
 * It consists of a number of pages that are used as a ringbuffer. Each data
 * blob is stored in a simple record that consists of an integer, which
 * contains the size of the following data, and the data bytes themselfes.
 *
 * To allow for multiple independent readers we create one internal buffer
 * each time the device is opened and destroy the buffer when the file is
 * closed again.
 *
 * One record can be written to a buffer by using the functions
 * - dasd_eer_start_record (one time per record to write the size to the buffer
 *                          and reserve the space for the data)
 * - dasd_eer_write_buffer (one or more times per record to write the data)
 * The data can be written in several steps but you will have to compute
 * the total size up front for the invocation of dasd_eer_start_record.
 * If the ringbuffer is full, dasd_eer_start_record will remove the required
 * number of old records.
 *
 * A record is typically read in two steps, first read the integer that
 * specifies the size of the following data, then read the data.
 * Both can be done by
 * - dasd_eer_read_buffer
 *
 * For all mentioned functions you need to get the bufferlock first and keep it
 * until a complete record is written or read.
 */


/*
 * Alle information necessary to keep track of an internal buffer is kept in
 * a struct eerbuffer. The buffer specific to a file pointer is strored in
 * the private_data field of that file. To be able to write data to all
 * existing buffers, each buffer is also added to the bufferlist.
 * If the user doesn't want to read a complete record in one go, we have to
 * keep track of the rest of the record. residual stores the number of bytes
 * that are still to deliver. If the rest of the record is invalidated between
 * two reads then residual will be set to -1 so that the next read will fail.
 * All entries in the eerbuffer structure are protected with the bufferlock.
 * To avoid races between writing to a buffer on the one side and creating
 * and destroying buffers on the other side, the bufferlock must also be used
 * to protect the bufferlist.
 */

struct eerbuffer {
	struct list_head list;
	char **buffer;
	int buffersize;
	int buffer_page_count;
	int head;
        int tail;
	int residual;
};

LIST_HEAD(bufferlist);

static spinlock_t bufferlock = SPIN_LOCK_UNLOCKED;

DECLARE_WAIT_QUEUE_HEAD(dasd_eer_read_wait_queue);

/*
 * How many free bytes are available on the buffer.
 * needs to be called with bufferlock held
 */
static int
dasd_eer_get_free_bytes(struct eerbuffer *eerb)
{
	if (eerb->head < eerb->tail) {
		return eerb->tail - eerb->head - 1;
	} else
		return eerb->buffersize - eerb->head + eerb->tail -1;
}

/*
 * How many bytes of buffer space are used.
 * needs to be called with bufferlock held
 */
static int
dasd_eer_get_filled_bytes(struct eerbuffer *eerb)
{

	if (eerb->head >= eerb->tail) {
		return eerb->head - eerb->tail;
	} else
		return eerb->buffersize - eerb->tail + eerb->head;
}

/*
 * The dasd_eer_write_buffer function just copies count bytes of data
 * to the buffer. Make sure to call dasd_eer_start_record first, to
 * make sure that enough free space is available.
 * needs to be called with bufferlock held
 */
static void
dasd_eer_write_buffer(struct eerbuffer *eerb, int count, char *data)
{

	unsigned long headindex,localhead;
	unsigned long rest, len;
	char *nextdata;

	nextdata = data;
	rest = count;
	while (rest > 0) {
 		headindex = eerb->head / PAGE_SIZE;
 		localhead = eerb->head % PAGE_SIZE;
		len = min(rest, (PAGE_SIZE - localhead));
		memcpy(eerb->buffer[headindex]+localhead, nextdata, len);
		nextdata += len;
		rest -= len;
		eerb->head += len;
		if ( eerb->head == eerb->buffersize )
			eerb->head = 0; /* wrap around */
		if (eerb->head > eerb->buffersize) {
			MESSAGE(KERN_ERR, "%s", "runaway buffer head.");
			BUG();
		}
	}
}

/*
 * needs to be called with bufferlock held
 */
static int
dasd_eer_read_buffer(struct eerbuffer *eerb, int count, char *data)
{

	unsigned long tailindex,localtail;
	unsigned long rest, len, finalcount;
	char *nextdata