dasd_eer.c

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/*
 *  Character device driver for extended error reporting.
 *
 *  Copyright (C) 2005 IBM Corporation
 *  extended error reporting for DASD ECKD devices
 *  Author(s): Stefan Weinhuber <[e-mail]>
 */

#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/poll.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"

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

/*
 * SECTION: the internal buffer
 */

/*
 * The internal buffer is meant to store obaque blobs of data, so it does
 * not 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. The number of pages used for this buffer is determined by
 * the module parmeter eer_pages.
 *
 * 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.
 *
 * All 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 does not 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.
 */

static int eer_pages = 5;
module_param(eer_pages, int, S_IRUGO|S_IWUSR);

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

static LIST_HEAD(bufferlist);
static spinlock_t bufferlock = SPIN_LOCK_UNLOCKED;
static 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;
	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;
	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,
				  char *data, int count)
{

	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 */
		BUG_ON(eerb->head > eerb->buffersize);
	}
}

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

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

	finalcount = min(count, dasd_eer_get_filled_bytes(eerb));
	nextdata = data;
	rest = finalcount;
	while (rest > 0) {
 		tailindex = eerb->tail / PAGE_SIZE;
 		localtail = eerb->tail % PAGE_SIZE;
		len = min(rest, PAGE_SIZE - localtail);
		memcpy(nextdata, eerb->buffer[tailindex] + localtail, len);
		nextdata += len;
		rest -= len;
		eerb->tail += len;
		if (eerb->tail == eerb->buffersize)
			eerb->tail = 0; /* wrap around */
		BUG_ON(eerb->tail > eerb->buffersize);
	}
	return finalcount;
}

/*
 * Whenever you want to write a blob of data to the internal buffer you
 * have to start by using this function first. It will write the number
 * of bytes that will be written to the buffer. If necessary it will remove
 * old records to make room for the new one.
 * Needs to be called with bufferlock held.
 */
static int dasd_eer_start_record(struct eerbuffer *eerb, int count)
{
	int tailcount;

	if (count + sizeof(count) > eerb->buffersize)
		return -ENOMEM;
	while (dasd_eer_get_free_bytes(eerb) < count + sizeof(count)) {
		if (eerb->residual > 0) {
			eerb->tail += eerb->residual;
			if (eerb->tail >= eerb->buffersize)
				eerb->tail -= eerb->buffersize;
			eerb->residual = -1;
		}
		dasd_eer_read_buffer(eerb, (char *) &tailcount,
				     sizeof(tailcount));
		eerb->tail += tailcount;
		if (eerb->tail >= eerb->buffersize)
			eerb->tail -= eerb->buffersize;
	}
	dasd_eer_write_buffer(eerb, (char*) &count, sizeof(count));

	return 0;
};

/*
 * Release pages that are not used anymore.
 */
static void dasd_eer_free_buffer_pages(char **buf, int no_pages)
{
	int i;

	for (i = 0; i < no_pages; i++)
		free_page((unsigned long) buf[i]);
}

/*
 * Allocate a new set of memory pages.
 */
static int dasd_eer_allocate_buffer_pages(char **buf, int no_pages)
{
	int i;

	for (i = 0; i < no_pages; i++) {
		buf[i] = (char *) get_zeroed_page(GFP_KERNEL);
		if (!buf[i]) {
			dasd_eer_free_buffer_pages(buf, i);
			return -ENOMEM;
		}
	}
	return 0;
}

/*
 * SECTION: The extended error reporting functionality
 */

/*
 * When a DASD device driver wants to report an error, it calls the
 * function dasd_eer_write and gives the respective trigger ID as
 * parameter. Currently there are four kinds of triggers:
 *
 * DASD_EER_FATALERROR:  all kinds of unrecoverable I/O problems
 * DASD_EER_PPRCSUSPEND: PPRC was suspended
 * DASD_EER_NOPATH:      There is no path to the device left.
 * DASD_EER_STATECHANGE: The state of the device has changed.
 *
 * For the first three triggers all required information can be supplied by
 * the caller. For these triggers a record is written by the function
 * dasd_eer_write_standard_trigger.
 *
 * The DASD_EER_STATECHANGE trigger is special since a sense subsystem
 * status ccw need to be executed to gather the necessary sense data first.
 * The dasd_eer_snss function will queue the SNSS request and the request
 * callback will then call dasd_eer_write with the DASD_EER_STATCHANGE
 * trigger.
 *
 * To avoid memory allocations at runtime, the necessary memory is allocated
 * when the extended error reporting is enabled for a device (by
 * dasd_eer_probe). There is one sense subsystem status request for each
 * eer enabled DASD device. The presence of the cqr in device->eer_cqr
 * indicates that eer is enable for the device. The use of the snss request
 * is protected by the DASD_FLAG_EER_IN_USE bit. When this flag indicates
 * that the cqr is currently in use, dasd_eer_snss cannot start a second
 * request but sets the DASD_FLAG_EER_SNSS flag instead. The callback of
 * the SNSS request will check the bit and call dasd_eer_snss again.
 */

#define SNSS_DATA_SIZE 44

#define DASD_EER_BUSID_SIZE 10
struct dasd_eer_header {
	__u32 total_size;
	__u32 trigger;
	__u64 tv_sec;
	__u64 tv_usec;
	char busid[DASD_EER_BUSID_SIZE];
};

/*
 * The following function can be used for those triggers that have
 * all necessary data available when the function is called.
 * If the parameter cqr is not NULL, the chain of requests will be searched
 * for valid sense data, and all valid sense data sets will be added to
 * the triggers data.
 */
static void dasd_eer_write_standard_trigger(struct dasd_device *device,
					    struct dasd_ccw_req *cqr,
					    int trigger)
{
	struct dasd_ccw_req *temp_cqr;
	int data_size;
	struct timeval tv;
	struct dasd_eer_header header;
	unsigned long flags;
	struct eerbuffer *eerb;

	/* go through cqr chain and count the valid sense data sets */
	data_size = 0;
	for (temp_cqr = cqr; temp_cqr; temp_cqr = temp_cqr->refers)
		if (temp_cqr->irb.esw.esw0.erw.cons)
			data_size += 32;

	header.total_size = sizeof(header) + data_size + 4; /* "EOR" */
	header.trigger = trigger;
	do_gettimeofday(&tv);
	header.tv_sec = tv.tv_sec;
	header.tv_usec = tv.tv_usec;
	strncpy(header.busid, device->cdev->dev.bus_id, DASD_EER_BUSID_SIZE);

	spin_lock_irqsave(&bufferlock, flags);
	list_for_each_entry(eerb, &bufferlist, list) {
		dasd_eer_start_record(eerb, header.total_size);
		dasd_eer_write_buffer(eerb, (char *) &header, sizeof(header));
		for (temp_cqr = cqr; temp_cqr; temp_cqr = temp_cqr->refers)
			if (temp_cqr->irb.esw.esw0.erw.cons)
				dasd_eer_write_buffer(eerb, cqr->irb.ecw, 32);
		dasd_eer_write_buffer(eerb, "EOR", 4);
	}
	spin_unlock_irqrestore(&bufferlock, flags);
	wake_up_interruptible(&dasd_eer_read_wait_queue);
}

/*
 * This function writes a DASD_EER_STATECHANGE trigger.
 */
static void dasd_eer_write_snss_trigger(struct dasd_device *device,
					struct dasd_ccw_req *cqr,
					int trigger)
{
	int data_size;
	int snss_rc;
	struct timeval tv;
	struct dasd_eer_header header;
	unsigned long flags;
	struct eerbuffer *eerb;

	snss_rc = (cqr->status == DASD_CQR_FAILED) ? -EIO : 0;
	if (snss_rc)
		data_size = 0;
	else