drivers/s390/block/dasd_eer.c

   1 /*
   2  *  Character device driver for extended error reporting.
   3  *
   4  *  Copyright (C) 2005 IBM Corporation
   5  *  extended error reporting for DASD ECKD devices
   6  *  Author(s): Stefan Weinhuber <wein@de.ibm.com>
   7  */
   8
   9 #define KMSG_COMPONENT "dasd"
  10
  11 #include <linux/init.h>
  12 #include <linux/fs.h>
  13 #include <linux/kernel.h>
  14 #include <linux/miscdevice.h>
  15 #include <linux/module.h>
  16 #include <linux/moduleparam.h>
  17 #include <linux/device.h>
  18 #include <linux/poll.h>
  19 #include <linux/mutex.h>
  20 #include <linux/smp_lock.h>
  21 #include <linux/err.h>
  22
  23 #include <asm/uaccess.h>
  24 #include <asm/atomic.h>
  25 #include <asm/ebcdic.h>
  26
  27 #include "dasd_int.h"
  28 #include "dasd_eckd.h"
  29
  30 #ifdef PRINTK_HEADER
  31 #undef PRINTK_HEADER
  32 #endif                          /* PRINTK_HEADER */
  33 #define PRINTK_HEADER "dasd(eer):"
  34
  35 /*
  36  * SECTION: the internal buffer
  37  */
  38
  39 /*
  40  * The internal buffer is meant to store obaque blobs of data, so it does
  41  * not know of higher level concepts like triggers.
  42  * It consists of a number of pages that are used as a ringbuffer. Each data
  43  * blob is stored in a simple record that consists of an integer, which
  44  * contains the size of the following data, and the data bytes themselfes.
  45  *
  46  * To allow for multiple independent readers we create one internal buffer
  47  * each time the device is opened and destroy the buffer when the file is
  48  * closed again. The number of pages used for this buffer is determined by
  49  * the module parmeter eer_pages.
  50  *
  51  * One record can be written to a buffer by using the functions
  52  * - dasd_eer_start_record (one time per record to write the size to the
  53  *                          buffer and reserve the space for the data)
  54  * - dasd_eer_write_buffer (one or more times per record to write the data)
  55  * The data can be written in several steps but you will have to compute
  56  * the total size up front for the invocation of dasd_eer_start_record.
  57  * If the ringbuffer is full, dasd_eer_start_record will remove the required
  58  * number of old records.
  59  *
  60  * A record is typically read in two steps, first read the integer that
  61  * specifies the size of the following data, then read the data.
  62  * Both can be done by
  63  * - dasd_eer_read_buffer
  64  *
  65  * For all mentioned functions you need to get the bufferlock first and keep
  66  * it until a complete record is written or read.
  67  *
  68  * All information necessary to keep track of an internal buffer is kept in
  69  * a struct eerbuffer. The buffer specific to a file pointer is strored in
  70  * the private_data field of that file. To be able to write data to all
  71  * existing buffers, each buffer is also added to the bufferlist.
  72  * If the user does not want to read a complete record in one go, we have to
  73  * keep track of the rest of the record. residual stores the number of bytes
  74  * that are still to deliver. If the rest of the record is invalidated between
  75  * two reads then residual will be set to -1 so that the next read will fail.
  76  * All entries in the eerbuffer structure are protected with the bufferlock.
  77  * To avoid races between writing to a buffer on the one side and creating
  78  * and destroying buffers on the other side, the bufferlock must also be used
  79  * to protect the bufferlist.
  80  */
  81
  82 static int eer_pages = 5;
  83 module_param(eer_pages, int, S_IRUGO|S_IWUSR);
  84
  85 struct eerbuffer {
  86         struct list_head list;
  87         char **buffer;
  88         int buffersize;
  89         int buffer_page_count;
  90         int head;
  91         int tail;
  92         int residual;
  93 };
  94
  95 static LIST_HEAD(bufferlist);
  96 static DEFINE_SPINLOCK(bufferlock);
  97 static DECLARE_WAIT_QUEUE_HEAD(dasd_eer_read_wait_queue);
  98
  99 /*
 100  * How many free bytes are available on the buffer.
 101  * Needs to be called with bufferlock held.
 102  */
 103 static int dasd_eer_get_free_bytes(struct eerbuffer *eerb)
 104 {
 105         if (eerb->head < eerb->tail)
 106                 return eerb->tail - eerb->head - 1;
 107         return eerb->buffersize - eerb->head + eerb->tail -1;
 108 }
 109
 110 /*
 111  * How many bytes of buffer space are used.
 112  * Needs to be called with bufferlock held.
 113  */
 114 static int dasd_eer_get_filled_bytes(struct eerbuffer *eerb)
 115 {
 116
 117         if (eerb->head >= eerb->tail)
 118                 return eerb->head - eerb->tail;
 119         return eerb->buffersize - eerb->tail + eerb->head;
 120 }
 121
 122 /*
 123  * The dasd_eer_write_buffer function just copies count bytes of data
 124  * to the buffer. Make sure to call dasd_eer_start_record first, to
 125  * make sure that enough free space is available.
 126  * Needs to be called with bufferlock held.
 127  */
 128 static void dasd_eer_write_buffer(struct eerbuffer *eerb,
 129                                   char *data, int count)
 130 {
 131
 132         unsigned long headindex,localhead;
 133         unsigned long rest, len;
 134         char *nextdata;
 135
 136         nextdata = data;
 137         rest = count;
 138         while (rest > 0) {
 139                 headindex = eerb->head / PAGE_SIZE;
 140                 localhead = eerb->head % PAGE_SIZE;
 141                 len = min(rest, PAGE_SIZE - localhead);
 142                 memcpy(eerb->buffer[headindex]+localhead, nextdata, len);
 143                 nextdata += len;
 144                 rest -= len;
 145                 eerb->head += len;
 146                 if (eerb->head == eerb->buffersize)
 147                         eerb->head = 0; /* wrap around */
 148                 BUG_ON(eerb->head > eerb->buffersize);
 149         }
 150 }
 151
 152 /*
 153  * Needs to be called with bufferlock held.
 154  */
 155 static int dasd_eer_read_buffer(struct eerbuffer *eerb, char *data, int count)
 156 {
 157
 158         unsigned long tailindex,localtail;
 159         unsigned long rest, len, finalcount;
 160         char *nextdata;
 161
 162         finalcount = min(count, dasd_eer_get_filled_bytes(eerb));
 163         nextdata = data;
 164         rest = finalcount;
 165         while (rest > 0) {
 166                 tailindex = eerb->tail / PAGE_SIZE;
 167                 localtail = eerb->tail % PAGE_SIZE;
 168                 len = min(rest, PAGE_SIZE - localtail);
 169                 memcpy(nextdata, eerb->buffer[tailindex] + localtail, len);
 170                 nextdata += len;
 171                 rest -= len;
 172                 eerb->tail += len;
 173                 if (eerb->tail == eerb->buffersize)
 174                         eerb->tail = 0; /* wrap around */
 175                 BUG_ON(eerb->tail > eerb->buffersize);
 176         }
 177         return finalcount;
 178 }
 179
 180 /*
 181  * Whenever you want to write a blob of data to the internal buffer you
 182  * have to start by using this function first. It will write the number
 183  * of bytes that will be written to the buffer. If necessary it will remove
 184  * old records to make room for the new one.
 185  * Needs to be called with bufferlock held.
 186  */
 187 static int dasd_eer_start_record(struct eerbuffer *eerb, int count)
 188 {
 189         int tailcount;
 190
 191         if (count + sizeof(count) > eerb->buffersize)
 192                 return -ENOMEM;
 193         while (dasd_eer_get_free_bytes(eerb) < count + sizeof(count)) {
 194                 if (eerb->residual > 0) {
 195                         eerb->tail += eerb->residual;
 196                         if (eerb->tail >= eerb->buffersize)
 197                                 eerb->tail -= eerb->buffersize;
 198                         eerb->residual = -1;
 199                 }
 200                 dasd_eer_read_buffer(eerb, (char *) &tailcount,
 201                                      sizeof(tailcount));
 202                 eerb->tail += tailcount;
 203                 if (eerb->tail >= eerb->buffersize)
 204                         eerb->tail -= eerb->buffersize;
 205         }
 206         dasd_eer_write_buffer(eerb, (char*) &count, sizeof(count));
 207
 208         return 0;
 209 };
 210
 211 /*
 212  * Release pages that are not used anymore.
 213  */
 214 static void dasd_eer_free_buffer_pages(char **buf, int no_pages)
 215 {
 216         int i;
 217
 218         for (i = 0; i < no_pages; i++)
 219                 free_page((unsigned long) buf[i]);
 220 }
 221
 222 /*
 223  * Allocate a new set of memory pages.
 224  */
 225 static int dasd_eer_allocate_buffer_pages(char **buf, int no_pages)
 226 {
 227         int i;
 228
 229         for (i = 0; i < no_pages; i++) {
 230                 buf[i] = (char *) get_zeroed_page(GFP_KERNEL);
 231                 if (!buf[i]) {
 232                         dasd_eer_free_buffer_pages(buf, i);
 233                         return -ENOMEM;
 234                 }
 235         }
 236         return 0;
 237 }
 238
 239 /*
 240  * SECTION: The extended error reporting functionality
 241  */
 242
 243 /*
 244  * When a DASD device driver wants to report an error, it calls the
 245  * function dasd_eer_write and gives the respective trigger ID as
 246  * parameter. Currently there are four kinds of triggers:
 247  *
 248  * DASD_EER_FATALERROR:  all kinds of unrecoverable I/O problems
 249  * DASD_EER_PPRCSUSPEND: PPRC was suspended
 250  * DASD_EER_NOPATH:      There is no path to the device left.
 251  * DASD_EER_STATECHANGE: The state of the device has changed.
 252  *
 253  * For the first three triggers all required information can be supplied by
 254  * the caller. For these triggers a record is written by the function
 255  * dasd_eer_write_standard_trigger.
 256  *
 257  * The DASD_EER_STATECHANGE trigger is special since a sense subsystem
 258  * status ccw need to be executed to gather the necessary sense data first.
 259  * The dasd_eer_snss function will queue the SNSS request and the request
 260  * callback will then call dasd_eer_write with the DASD_EER_STATCHANGE
 261  * trigger.
 262  *
 263  * To avoid memory allocations at runtime, the necessary memory is allocated
 264  * when the extended error reporting is enabled for a device (by
 265  * dasd_eer_probe). There is one sense subsystem status request for each
 266  * eer enabled DASD device. The presence of the cqr in device->eer_cqr
 267  * indicates that eer is enable for the device. The use of the snss request
 268  * is protected by the DASD_FLAG_EER_IN_USE bit. When this flag indicates
 269  * that the cqr is currently in use, dasd_eer_snss cannot start a second
 270  * request but sets the DASD_FLAG_EER_SNSS flag instead. The callback of
 271  * the SNSS request will check the bit and call dasd_eer_snss again.
 272  */
 273
 274 #define SNSS_DATA_SIZE 44
 275
 276 #define DASD_EER_BUSID_SIZE 10
 277 struct dasd_eer_header {
 278         __u32 total_size;
 279         __u32 trigger;
 280         __u64 tv_sec;
 281         __u64 tv_usec;
 282         char busid[DASD_EER_BUSID_SIZE];
 283 } __attribute__ ((packed));
 284
 285 /*
 286  * The following function can be used for those triggers that have
 287  * all necessary data available when the function is called.
 288  * If the parameter cqr is not NULL, the chain of requests will be searched
 289  * for valid sense data, and all valid sense data sets will be added to
 290  * the triggers data.
 291  */
 292 static void dasd_eer_write_standard_trigger(struct dasd_device *device,
 293                                             struct dasd_ccw_req *cqr,
 294                                             int trigger)
 295 {
 296         struct dasd_ccw_req *temp_cqr;
 297         int data_size;
 298         struct timeval tv;
 299         struct dasd_eer_header header;
 300         unsigned long flags;
 301         struct eerbuffer *eerb;
 302         char *sense;
 303
 304         /* go through cqr chain and count the valid sense data sets */
 305         data_size = 0;
 306         for (temp_cqr = cqr; temp_cqr; temp_cqr = temp_cqr->refers)
 307                 if (dasd_get_sense(&temp_cqr->irb))
 308                         data_size += 32;
 309
 310         header.total_size = sizeof(header) + data_size + 4; /* "EOR" */
 311         header.trigger = trigger;
 312         do_gettimeofday(&tv);
 313         header.tv_sec = tv.tv_sec;
 314         header.tv_usec = tv.tv_usec;
 315         strncpy(header.busid, dev_name(&device->cdev->dev),
 316                 DASD_EER_BUSID_SIZE);
 317
 318         spin_lock_irqsave(&bufferlock, flags);
 319         list_for_each_entry(eerb, &bufferlist, list) {
 320                 dasd_eer_start_record(eerb, header.total_size);
 321                 dasd_eer_write_buffer(eerb, (char *) &header, sizeof(header));
 322                 for (temp_cqr = cqr; temp_cqr; temp_cqr = temp_cqr->refers) {
 323                         sense = dasd_get_sense(&temp_cqr->irb);
 324                         if (sense)
 325                                 dasd_eer_write_buffer(eerb, sense, 32);
 326                 }
 327                 dasd_eer_write_buffer(eerb, "EOR", 4);
 328         }
 329         spin_unlock_irqrestore(&bufferlock, flags);
 330         wake_up_interruptible(&dasd_eer_read_wait_queue);
 331 }
 332
 333 /*
 334  * This function writes a DASD_EER_STATECHANGE trigger.
 335  */
 336 static void dasd_eer_write_snss_trigger(struct dasd_device *device,
 337                                         struct dasd_ccw_req *cqr,
 338                                         int trigger)
 339 {
 340         int data_size;
 341         int snss_rc;
 342         struct timeval tv;
 343         struct dasd_eer_header header;
 344         unsigned long flags;
 345         struct eerbuffer *eerb;
 346
 347         snss_rc = (cqr->status == DASD_CQR_DONE) ? 0 : -EIO;
 348         if (snss_rc)
 349                 data_size = 0;
 350         else
 351                 data_size = SNSS_DATA_SIZE;
 352
 353         header.total_size = sizeof(header) + data_size + 4; /* "EOR" */
 354         header.trigger = DASD_EER_STATECHANGE;
 355         do_gettimeofday(&tv);
 356         header.tv_sec = tv.tv_sec;
 357         header.tv_usec = tv.tv_usec;
 358         strncpy(header.busid, dev_name(&device->cdev->dev),
 359                 DASD_EER_BUSID_SIZE);
 360
 361         spin_lock_irqsave(&bufferlock, flags);
 362         list_for_each_entry(eerb, &bufferlist, list) {
 363                 dasd_eer_start_record(eerb, header.total_size);
 364                 dasd_eer_write_buffer(eerb, (char *) &header , sizeof(header));
 365                 if (!snss_rc)
 366                         dasd_eer_write_buffer(eerb, cqr->data, SNSS_DATA_SIZE);
 367                 dasd_eer_write_buffer(eerb, "EOR", 4);
 368         }
 369         spin_unlock_irqrestore(&bufferlock, flags);
 370         wake_up_interruptible(&dasd_eer_read_wait_queue);
 371 }
 372
 373 /*
 374  * This function is called for all triggers. It calls the appropriate
 375  * function that writes the actual trigger records.
 376  */
 377 void dasd_eer_write(struct dasd_device *device, struct dasd_ccw_req *cqr,
 378                     unsigned int id)
 379 {
 380         if (!device->eer_cqr)
 381                 return;
 382         switch (id) {
 383         case DASD_EER_FATALERROR:
 384         case DASD_EER_PPRCSUSPEND:
 385                 dasd_eer_write_standard_trigger(device, cqr, id);
 386                 break;
 387         case DASD_EER_NOPATH:
 388                 dasd_eer_write_standard_trigger(device, NULL, id);
 389                 break;
 390         case DASD_EER_STATECHANGE:
 391                 dasd_eer_write_snss_trigger(device, cqr, id);
 392                 break;
 393         default: /* unknown trigger, so we write it without any sense data */
 394                 dasd_eer_write_standard_trigger(device, NULL, id);
 395                 break;
 396         }
 397 }
 398 EXPORT_SYMBOL(dasd_eer_write);
 399
 400 /*
 401  * Start a sense subsystem status request.
 402  * Needs to be called with the device held.
 403  */
 404 void dasd_eer_snss(struct dasd_device *device)
 405 {
 406         struct dasd_ccw_req *cqr;
 407
 408         cqr = device->eer_cqr;
 409         if (!cqr)       /* Device not eer enabled. */
 410                 return;
 411         if (test_and_set_bit(DASD_FLAG_EER_IN_USE, &device->flags)) {
 412                 /* Sense subsystem status request in use. */
 413                 set_bit(DASD_FLAG_EER_SNSS, &device->flags);
 414                 return;
 415         }
 416         /* cdev is already locked, can't use dasd_add_request_head */
 417         clear_bit(DASD_FLAG_EER_SNSS, &device->flags);
 418         cqr->status = DASD_CQR_QUEUED;
 419         list_add(&cqr->devlist, &device->ccw_queue);
 420         dasd_schedule_device_bh(device);
 421 }
 422
 423 /*
 424  * Callback function for use with sense subsystem status request.
 425  */
 426 static void dasd_eer_snss_cb(struct dasd_ccw_req *cqr, void *data)
 427 {
 428         struct dasd_device *device = cqr->startdev;
 429         unsigned long flags;
 430
 431         dasd_eer_write(device, cqr, DASD_EER_STATECHANGE);
 432         spin_lock_irqsave(get_ccwdev_lock(device->cdev), flags);
 433         if (device->eer_cqr == cqr) {
 434                 clear_bit(DASD_FLAG_EER_IN_USE, &device->flags);
 435                 if (test_bit(DASD_FLAG_EER_SNSS, &device->flags))
 436                         /* Another SNSS has been requested in the meantime. */
 437                         dasd_eer_snss(device);
 438                 cqr = NULL;
 439         }
 440         spin_unlock_irqrestore(get_ccwdev_lock(device->cdev), flags);
 441         if (cqr)
 442                 /*
 443                  * Extended error recovery has been switched off while
 444                  * the SNSS request was running. It could even have
 445                  * been switched off and on again in which case there
 446                  * is a new ccw in device->eer_cqr. Free the "old"
 447                  * snss request now.
 448                  */
 449                 dasd_kfree_request(cqr, device);
 450 }
 451
 452 /*
 453  * Enable error reporting on a given device.
 454  */
 455 int dasd_eer_enable(struct dasd_device *device)
 456 {
 457         struct dasd_ccw_req *cqr;
 458         unsigned long flags;
 459         struct ccw1 *ccw;
 460
 461         if (device->eer_cqr)
 462                 return 0;
 463
 464         if (!device->discipline || strcmp(device->discipline->name, "ECKD"))
 465                 return -EPERM;  /* FIXME: -EMEDIUMTYPE ? */
 466
 467         cqr = dasd_kmalloc_request("ECKD", 1 /* SNSS */,
 468                                    SNSS_DATA_SIZE, device);
 469         if (IS_ERR(cqr))
 470                 return -ENOMEM;
 471
 472         cqr->startdev = device;
 473         cqr->retries = 255;
 474         cqr->expires = 10 * HZ;
 475         clear_bit(DASD_CQR_FLAGS_USE_ERP, &cqr->flags);
 476
 477         ccw = cqr->cpaddr;
 478         ccw->cmd_code = DASD_ECKD_CCW_SNSS;
 479         ccw->count = SNSS_DATA_SIZE;
 480         ccw->flags = 0;
 481         ccw->cda = (__u32)(addr_t) cqr->data;
 482
 483         cqr->buildclk = get_clock();
 484         cqr->status = DASD_CQR_FILLED;
 485         cqr->callback = dasd_eer_snss_cb;
 486
 487         spin_lock_irqsave(get_ccwdev_lock(device->cdev), flags);
 488         if (!device->eer_cqr) {
 489                 device->eer_cqr = cqr;
 490                 cqr = NULL;
 491         }
 492         spin_unlock_irqrestore(get_ccwdev_lock(device->cdev), flags);
 493         if (cqr)
 494                 dasd_kfree_request(cqr, device);
 495         return 0;
 496 }
 497
 498 /*
 499  * Disable error reporting on a given device.
 500  */
 501 void dasd_eer_disable(struct dasd_device *device)
 502 {
 503         struct dasd_ccw_req *cqr;
 504         unsigned long flags;
 505         int in_use;
 506
 507         if (!device->eer_cqr)
 508                 return;
 509         spin_lock_irqsave(get_ccwdev_lock(device->cdev), flags);
 510         cqr = device->eer_cqr;
 511         device->eer_cqr = NULL;
 512         clear_bit(DASD_FLAG_EER_SNSS, &device->flags);
 513         in_use = test_and_clear_bit(DASD_FLAG_EER_IN_USE, &device->flags);
 514         spin_unlock_irqrestore(get_ccwdev_lock(device->cdev), flags);
 515         if (cqr && !in_use)
 516                 dasd_kfree_request(cqr, device);
 517 }
 518
 519 /*
 520  * SECTION: the device operations
 521  */
 522
 523 /*
 524  * On the one side we need a lock to access our internal buffer, on the
 525  * other side a copy_to_user can sleep. So we need to copy the data we have
 526  * to transfer in a readbuffer, which is protected by the readbuffer_mutex.
 527  */
 528 static char readbuffer[PAGE_SIZE];
 529 static DEFINE_MUTEX(readbuffer_mutex);
 530
 531 static int dasd_eer_open(struct inode *inp, struct file *filp)
 532 {
 533         struct eerbuffer *eerb;
 534         unsigned long flags;
 535
 536         eerb = kzalloc(sizeof(struct eerbuffer), GFP_KERNEL);
 537         if (!eerb)
 538                 return -ENOMEM;
 539         lock_kernel();
 540         eerb->buffer_page_count = eer_pages;
 541         if (eerb->buffer_page_count < 1 ||
 542             eerb->buffer_page_count > INT_MAX / PAGE_SIZE) {
 543                 kfree(eerb);
 544                 DBF_EVENT(DBF_WARNING, "can't open device since module "
 545                         "parameter eer_pages is smaller than 1 or"
 546                         " bigger than %d", (int)(INT_MAX / PAGE_SIZE));
 547                 unlock_kernel();
 548                 return -EINVAL;
 549         }
 550         eerb->buffersize = eerb->buffer_page_count * PAGE_SIZE;
 551         eerb->buffer = kmalloc(eerb->buffer_page_count * sizeof(char *),
 552                                GFP_KERNEL);
 553         if (!eerb->buffer) {
 554                 kfree(eerb);
 555                 unlock_kernel();
 556                 return -ENOMEM;
 557         }
 558         if (dasd_eer_allocate_buffer_pages(eerb->buffer,
 559                                            eerb->buffer_page_count)) {
 560                 kfree(eerb->buffer);
 561                 kfree(eerb);
 562                 unlock_kernel();
 563                 return -ENOMEM;
 564         }
 565         filp->private_data = eerb;
 566         spin_lock_irqsave(&bufferlock, flags);
 567         list_add(&eerb->list, &bufferlist);
 568         spin_unlock_irqrestore(&bufferlock, flags);
 569
 570         unlock_kernel();
 571         return nonseekable_open(inp,filp);
 572 }
 573
 574 static int dasd_eer_close(struct inode *inp, struct file *filp)
 575 {
 576         struct eerbuffer *eerb;
 577         unsigned long flags;
 578
 579         eerb = (struct eerbuffer *) filp->private_data;
 580         spin_lock_irqsave(&bufferlock, flags);
 581         list_del(&eerb->list);
 582         spin_unlock_irqrestore(&bufferlock, flags);
 583         dasd_eer_free_buffer_pages(eerb->buffer, eerb->buffer_page_count);
 584         kfree(eerb->buffer);
 585         kfree(eerb);
 586
 587         return 0;
 588 }
 589
 590 static ssize_t dasd_eer_read(struct file *filp, char __user *buf,
 591                              size_t count, loff_t *ppos)
 592 {
 593         int tc,rc;
 594         int tailcount,effective_count;
 595         unsigned long flags;
 596         struct eerbuffer *eerb;
 597
 598         eerb = (struct eerbuffer *) filp->private_data;
 599         if (mutex_lock_interruptible(&readbuffer_mutex))
 600                 return -ERESTARTSYS;
 601
 602         spin_lock_irqsave(&bufferlock, flags);
 603
 604         if (eerb->residual < 0) { /* the remainder of this record */
 605                                   /* has been deleted             */
 606                 eerb->residual = 0;
 607                 spin_unlock_irqrestore(&bufferlock, flags);
 608                 mutex_unlock(&readbuffer_mutex);
 609                 return -EIO;
 610         } else if (eerb->residual > 0) {
 611                 /* OK we still have a second half of a record to deliver */
 612                 effective_count = min(eerb->residual, (int) count);
 613                 eerb->residual -= effective_count;
 614         } else {
 615                 tc = 0;
 616                 while (!tc) {
 617                         tc = dasd_eer_read_buffer(eerb, (char *) &tailcount,
 618                                                   sizeof(tailcount));
 619                         if (!tc) {
 620                                 /* no data available */
 621                                 spin_unlock_irqrestore(&bufferlock, flags);
 622                                 mutex_unlock(&readbuffer_mutex);
 623                                 if (filp->f_flags & O_NONBLOCK)
 624                                         return -EAGAIN;
 625                                 rc = wait_event_interruptible(
 626                                         dasd_eer_read_wait_queue,
 627                                         eerb->head != eerb->tail);
 628                                 if (rc)
 629                                         return rc;
 630                                 if (mutex_lock_interruptible(&readbuffer_mutex))
 631                                         return -ERESTARTSYS;
 632                                 spin_lock_irqsave(&bufferlock, flags);
 633                         }
 634                 }
 635                 WARN_ON(tc != sizeof(tailcount));
 636                 effective_count = min(tailcount,(int)count);
 637                 eerb->residual = tailcount - effective_count;
 638         }
 639
 640         tc = dasd_eer_read_buffer(eerb, readbuffer, effective_count);
 641         WARN_ON(tc != effective_count);
 642
 643         spin_unlock_irqrestore(&bufferlock, flags);
 644
 645         if (copy_to_user(buf, readbuffer, effective_count)) {
 646                 mutex_unlock(&readbuffer_mutex);
 647                 return -EFAULT;
 648         }
 649
 650         mutex_unlock(&readbuffer_mutex);
 651         return effective_count;
 652 }
 653
 654 static unsigned int dasd_eer_poll(struct file *filp, poll_table *ptable)
 655 {
 656         unsigned int mask;
 657         unsigned long flags;
 658         struct eerbuffer *eerb;
 659
 660         eerb = (struct eerbuffer *) filp->private_data;
 661         poll_wait(filp, &dasd_eer_read_wait_queue, ptable);
 662         spin_lock_irqsave(&bufferlock, flags);
 663         if (eerb->head != eerb->tail)
 664                 mask = POLLIN | POLLRDNORM ;
 665         else
 666                 mask = 0;
 667         spin_unlock_irqrestore(&bufferlock, flags);
 668         return mask;
 669 }
 670
 671 static const struct file_operations dasd_eer_fops = {
 672         .open           = &dasd_eer_open,
 673         .release        = &dasd_eer_close,
 674         .read           = &dasd_eer_read,
 675         .poll           = &dasd_eer_poll,
 676         .owner          = THIS_MODULE,
 677 };
 678
 679 static struct miscdevice *dasd_eer_dev = NULL;
 680
 681 int __init dasd_eer_init(void)
 682 {
 683         int rc;
 684
 685         dasd_eer_dev = kzalloc(sizeof(*dasd_eer_dev), GFP_KERNEL);
 686         if (!dasd_eer_dev)
 687                 return -ENOMEM;
 688
 689         dasd_eer_dev->minor = MISC_DYNAMIC_MINOR;
 690         dasd_eer_dev->name  = "dasd_eer";
 691         dasd_eer_dev->fops  = &dasd_eer_fops;
 692
 693         rc = misc_register(dasd_eer_dev);
 694         if (rc) {
 695                 kfree(dasd_eer_dev);
 696                 dasd_eer_dev = NULL;
 697                 DBF_EVENT(DBF_ERR, "%s", "dasd_eer_init could not "
 698                        "register misc device");
 699                 return rc;
 700         }
 701
 702         return 0;
 703 }
 704
 705 void dasd_eer_exit(void)
 706 {
 707         if (dasd_eer_dev) {
 708                 WARN_ON(misc_deregister(dasd_eer_dev) != 0);
 709                 kfree(dasd_eer_dev);
 710                 dasd_eer_dev = NULL;
 711         }
 712 }