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 #include <linux/init.h>
  10 #include <linux/fs.h>
  11 #include <linux/kernel.h>
  12 #include <linux/miscdevice.h>
  13 #include <linux/module.h>
  14 #include <linux/moduleparam.h>
  15 #include <linux/device.h>
  16 #include <linux/poll.h>
  17 #include <linux/mutex.h>
  18
  19 #include <asm/uaccess.h>
  20 #include <asm/atomic.h>
  21 #include <asm/ebcdic.h>
  22
  23 #include "dasd_int.h"
  24 #include "dasd_eckd.h"
  25
  26 #ifdef PRINTK_HEADER
  27 #undef PRINTK_HEADER
  28 #endif                          /* PRINTK_HEADER */
  29 #define PRINTK_HEADER "dasd(eer):"
  30
  31 /*
  32  * SECTION: the internal buffer
  33  */
  34
  35 /*
  36  * The internal buffer is meant to store obaque blobs of data, so it does
  37  * not know of higher level concepts like triggers.
  38  * It consists of a number of pages that are used as a ringbuffer. Each data
  39  * blob is stored in a simple record that consists of an integer, which
  40  * contains the size of the following data, and the data bytes themselfes.
  41  *
  42  * To allow for multiple independent readers we create one internal buffer
  43  * each time the device is opened and destroy the buffer when the file is
  44  * closed again. The number of pages used for this buffer is determined by
  45  * the module parmeter eer_pages.
  46  *
  47  * One record can be written to a buffer by using the functions
  48  * - dasd_eer_start_record (one time per record to write the size to the
  49  *                          buffer and reserve the space for the data)
  50  * - dasd_eer_write_buffer (one or more times per record to write the data)
  51  * The data can be written in several steps but you will have to compute
  52  * the total size up front for the invocation of dasd_eer_start_record.
  53  * If the ringbuffer is full, dasd_eer_start_record will remove the required
  54  * number of old records.
  55  *
  56  * A record is typically read in two steps, first read the integer that
  57  * specifies the size of the following data, then read the data.
  58  * Both can be done by
  59  * - dasd_eer_read_buffer
  60  *
  61  * For all mentioned functions you need to get the bufferlock first and keep
  62  * it until a complete record is written or read.
  63  *
  64  * All information necessary to keep track of an internal buffer is kept in
  65  * a struct eerbuffer. The buffer specific to a file pointer is strored in
  66  * the private_data field of that file. To be able to write data to all
  67  * existing buffers, each buffer is also added to the bufferlist.
  68  * If the user does not want to read a complete record in one go, we have to
  69  * keep track of the rest of the record. residual stores the number of bytes
  70  * that are still to deliver. If the rest of the record is invalidated between
  71  * two reads then residual will be set to -1 so that the next read will fail.
  72  * All entries in the eerbuffer structure are protected with the bufferlock.
  73  * To avoid races between writing to a buffer on the one side and creating
  74  * and destroying buffers on the other side, the bufferlock must also be used
  75  * to protect the bufferlist.
  76  */
  77
  78 static int eer_pages = 5;
  79 module_param(eer_pages, int, S_IRUGO|S_IWUSR);
  80
  81 struct eerbuffer {
  82         struct list_head list;
  83         char **buffer;
  84         int buffersize;
  85         int buffer_page_count;
  86         int head;
  87         int tail;
  88         int residual;
  89 };
  90
  91 static LIST_HEAD(bufferlist);
  92 static DEFINE_SPINLOCK(bufferlock);
  93 static DECLARE_WAIT_QUEUE_HEAD(dasd_eer_read_wait_queue);
  94
  95 /*
  96  * How many free bytes are available on the buffer.
  97  * Needs to be called with bufferlock held.
  98  */
  99 static int dasd_eer_get_free_bytes(struct eerbuffer *eerb)
 100 {
 101         if (eerb->head < eerb->tail)
 102                 return eerb->tail - eerb->head - 1;
 103         return eerb->buffersize - eerb->head + eerb->tail -1;
 104 }
 105
 106 /*
 107  * How many bytes of buffer space are used.
 108  * Needs to be called with bufferlock held.
 109  */
 110 static int dasd_eer_get_filled_bytes(struct eerbuffer *eerb)
 111 {
 112
 113         if (eerb->head >= eerb->tail)
 114                 return eerb->head - eerb->tail;
 115         return eerb->buffersize - eerb->tail + eerb->head;
 116 }
 117
 118 /*
 119  * The dasd_eer_write_buffer function just copies count bytes of data
 120  * to the buffer. Make sure to call dasd_eer_start_record first, to
 121  * make sure that enough free space is available.
 122  * Needs to be called with bufferlock held.
 123  */
 124 static void dasd_eer_write_buffer(struct eerbuffer *eerb,
 125                                   char *data, int count)
 126 {
 127
 128         unsigned long headindex,localhead;
 129         unsigned long rest, len;
 130         char *nextdata;
 131
 132         nextdata = data;
 133         rest = count;
 134         while (rest > 0) {
 135                 headindex = eerb->head / PAGE_SIZE;
 136                 localhead = eerb->head % PAGE_SIZE;
 137                 len = min(rest, PAGE_SIZE - localhead);
 138                 memcpy(eerb->buffer[headindex]+localhead, nextdata, len);
 139                 nextdata += len;
 140                 rest -= len;
 141                 eerb->head += len;
 142                 if (eerb->head == eerb->buffersize)
 143                         eerb->head = 0; /* wrap around */
 144                 BUG_ON(eerb->head > eerb->buffersize);
 145         }
 146 }
 147
 148 /*
 149  * Needs to be called with bufferlock held.
 150  */
 151 static int dasd_eer_read_buffer(struct eerbuffer *eerb, char *data, int count)
 152 {
 153
 154         unsigned long tailindex,localtail;
 155         unsigned long rest, len, finalcount;
 156         char *nextdata;
 157
 158         finalcount = min(count, dasd_eer_get_filled_bytes(eerb));
 159         nextdata = data;
 160         rest = finalcount;
 161         while (rest > 0) {
 162                 tailindex = eerb->tail / PAGE_SIZE;
 163                 localtail = eerb->tail % PAGE_SIZE;
 164                 len = min(rest, PAGE_SIZE - localtail);
 165                 memcpy(nextdata, eerb->buffer[tailindex] + localtail, len);
 166                 nextdata += len;
 167                 rest -= len;
 168                 eerb->tail += len;
 169                 if (eerb->tail == eerb->buffersize)
 170                         eerb->tail = 0; /* wrap around */
 171                 BUG_ON(eerb->tail > eerb->buffersize);
 172         }
 173         return finalcount;
 174 }
 175
 176 /*
 177  * Whenever you want to write a blob of data to the internal buffer you
 178  * have to start by using this function first. It will write the number
 179  * of bytes that will be written to the buffer. If necessary it will remove
 180  * old records to make room for the new one.
 181  * Needs to be called with bufferlock held.
 182  */
 183 static int dasd_eer_start_record(struct eerbuffer *eerb, int count)
 184 {
 185         int tailcount;
 186
 187         if (count + sizeof(count) > eerb->buffersize)
 188                 return -ENOMEM;
 189         while (dasd_eer_get_free_bytes(eerb) < count + sizeof(count)) {
 190                 if (eerb->residual > 0) {
 191                         eerb->tail += eerb->residual;
 192                         if (eerb->tail >= eerb->buffersize)
 193                                 eerb->tail -= eerb->buffersize;
 194                         eerb->residual = -1;
 195                 }
 196                 dasd_eer_read_buffer(eerb, (char *) &tailcount,
 197                                      sizeof(tailcount));
 198                 eerb->tail += tailcount;
 199                 if (eerb->tail >= eerb->buffersize)
 200                         eerb->tail -= eerb->buffersize;
 201         }
 202         dasd_eer_write_buffer(eerb, (char*) &count, sizeof(count));
 203
 204         return 0;
 205 };
 206
 207 /*
 208  * Release pages that are not used anymore.
 209  */
 210 static void dasd_eer_free_buffer_pages(char **buf, int no_pages)
 211 {
 212         int i;
 213
 214         for (i = 0; i < no_pages; i++)
 215                 free_page((unsigned long) buf[i]);
 216 }
 217
 218 /*
 219  * Allocate a new set of memory pages.
 220  */
 221 static int dasd_eer_allocate_buffer_pages(char **buf, int no_pages)
 222 {
 223         int i;
 224
 225         for (i = 0; i < no_pages; i++) {
 226                 buf[i] = (char *) get_zeroed_page(GFP_KERNEL);
 227                 if (!buf[i]) {
 228                         dasd_eer_free_buffer_pages(buf, i);
 229                         return -ENOMEM;
 230                 }
 231         }
 232         return 0;
 233 }
 234
 235 /*
 236  * SECTION: The extended error reporting functionality
 237  */
 238
 239 /*
 240  * When a DASD device driver wants to report an error, it calls the
 241  * function dasd_eer_write and gives the respective trigger ID as
 242  * parameter. Currently there are four kinds of triggers:
 243  *
 244  * DASD_EER_FATALERROR:  all kinds of unrecoverable I/O problems
 245  * DASD_EER_PPRCSUSPEND: PPRC was suspended
 246  * DASD_EER_NOPATH:      There is no path to the device left.
 247  * DASD_EER_STATECHANGE: The state of the device has changed.
 248  *
 249  * For the first three triggers all required information can be supplied by
 250  * the caller. For these triggers a record is written by the function
 251  * dasd_eer_write_standard_trigger.
 252  *
 253  * The DASD_EER_STATECHANGE trigger is special since a sense subsystem
 254  * status ccw need to be executed to gather the necessary sense data first.
 255  * The dasd_eer_snss function will queue the SNSS request and the request
 256  * callback will then call dasd_eer_write with the DASD_EER_STATCHANGE
 257  * trigger.
 258  *
 259  * To avoid memory allocations at runtime, the necessary memory is allocated
 260  * when the extended error reporting is enabled for a device (by
 261  * dasd_eer_probe). There is one sense subsystem status request for each
 262  * eer enabled DASD device. The presence of the cqr in device->eer_cqr
 263  * indicates that eer is enable for the device. The use of the snss request
 264  * is protected by the DASD_FLAG_EER_IN_USE bit. When this flag indicates
 265  * that the cqr is currently in use, dasd_eer_snss cannot start a second
 266  * request but sets the DASD_FLAG_EER_SNSS flag instead. The callback of
 267  * the SNSS request will check the bit and call dasd_eer_snss again.
 268  */
 269
 270 #define SNSS_DATA_SIZE 44
 271
 272 #define DASD_EER_BUSID_SIZE 10
 273 struct dasd_eer_header {
 274         __u32 total_size;
 275         __u32 trigger;
 276         __u64 tv_sec;
 277         __u64 tv_usec;
 278         char busid[DASD_EER_BUSID_SIZE];
 279 } __attribute__ ((packed));
 280
 281 /*
 282  * The following function can be used for those triggers that have
 283  * all necessary data available when the function is called.
 284  * If the parameter cqr is not NULL, the chain of requests will be searched
 285  * for valid sense data, and all valid sense data sets will be added to
 286  * the triggers data.
 287  */
 288 static void dasd_eer_write_standard_trigger(struct dasd_device *device,
 289                                             struct dasd_ccw_req *cqr,
 290                                             int trigger)
 291 {
 292         struct dasd_ccw_req *temp_cqr;
 293         int data_size;
 294         struct timeval tv;
 295         struct dasd_eer_header header;
 296         unsigned long flags;
 297         struct eerbuffer *eerb;
 298
 299         /* go through cqr chain and count the valid sense data sets */
 300         data_size = 0;
 301         for (temp_cqr = cqr; temp_cqr; temp_cqr = temp_cqr->refers)
 302                 if (temp_cqr->irb.esw.esw0.erw.cons)
 303                         data_size += 32;
 304
 305         header.total_size = sizeof(header) + data_size + 4; /* "EOR" */
 306         header.trigger = trigger;
 307         do_gettimeofday(&tv);
 308         header.tv_sec = tv.tv_sec;
 309         header.tv_usec = tv.tv_usec;
 310         strncpy(header.busid, device->cdev->dev.bus_id, DASD_EER_BUSID_SIZE);
 311
 312         spin_lock_irqsave(&bufferlock, flags);
 313         list_for_each_entry(eerb, &bufferlist, list) {
 314                 dasd_eer_start_record(eerb, header.total_size);
 315                 dasd_eer_write_buffer(eerb, (char *) &header, sizeof(header));
 316                 for (temp_cqr = cqr; temp_cqr; temp_cqr = temp_cqr->refers)
 317                         if (temp_cqr->irb.esw.esw0.erw.cons)
 318                                 dasd_eer_write_buffer(eerb, cqr->irb.ecw, 32);
 319                 dasd_eer_write_buffer(eerb, "EOR", 4);
 320         }
 321         spin_unlock_irqrestore(&bufferlock, flags);
 322         wake_up_interruptible(&dasd_eer_read_wait_queue);
 323 }
 324
 325 /*
 326  * This function writes a DASD_EER_STATECHANGE trigger.
 327  */
 328 static void dasd_eer_write_snss_trigger(struct dasd_device *device,
 329                                         struct dasd_ccw_req *cqr,
 330                                         int trigger)
 331 {
 332         int data_size;
 333         int snss_rc;
 334         struct timeval tv;
 335         struct dasd_eer_header header;
 336         unsigned long flags;
 337         struct eerbuffer *eerb;
 338
 339         snss_rc = (cqr->status == DASD_CQR_FAILED) ? -EIO : 0;
 340         if (snss_rc)
 341                 data_size = 0;
 342         else
 343                 data_size = SNSS_DATA_SIZE;
 344
 345         header.total_size = sizeof(header) + data_size + 4; /* "EOR" */
 346         header.trigger = DASD_EER_STATECHANGE;
 347         do_gettimeofday(&tv);
 348         header.tv_sec = tv.tv_sec;
 349         header.tv_usec = tv.tv_usec;
 350         strncpy(header.busid, device->cdev->dev.bus_id, DASD_EER_BUSID_SIZE);
 351
 352         spin_lock_irqsave(&bufferlock, flags);
 353         list_for_each_entry(eerb, &bufferlist, list) {
 354                 dasd_eer_start_record(eerb, header.total_size);
 355                 dasd_eer_write_buffer(eerb, (char *) &header , sizeof(header));
 356                 if (!snss_rc)
 357                         dasd_eer_write_buffer(eerb, cqr->data, SNSS_DATA_SIZE);
 358                 dasd_eer_write_buffer(eerb, "EOR", 4);
 359         }
 360         spin_unlock_irqrestore(&bufferlock, flags);
 361         wake_up_interruptible(&dasd_eer_read_wait_queue);
 362 }
 363
 364 /*
 365  * This function is called for all triggers. It calls the appropriate
 366  * function that writes the actual trigger records.
 367  */
 368 void dasd_eer_write(struct dasd_device *device, struct dasd_ccw_req *cqr,
 369                     unsigned int id)
 370 {
 371         if (!device->eer_cqr)
 372                 return;
 373         switch (id) {
 374         case DASD_EER_FATALERROR:
 375         case DASD_EER_PPRCSUSPEND:
 376                 dasd_eer_write_standard_trigger(device, cqr, id);
 377                 break;
 378         case DASD_EER_NOPATH:
 379                 dasd_eer_write_standard_trigger(device, NULL, id);
 380                 break;
 381         case DASD_EER_STATECHANGE:
 382                 dasd_eer_write_snss_trigger(device, cqr, id);
 383                 break;
 384         default: /* unknown trigger, so we write it without any sense data */
 385                 dasd_eer_write_standard_trigger(device, NULL, id);
 386                 break;
 387         }
 388 }
 389 EXPORT_SYMBOL(dasd_eer_write);
 390
 391 /*
 392  * Start a sense subsystem status request.
 393  * Needs to be called with the device held.
 394  */
 395 void dasd_eer_snss(struct dasd_device *device)
 396 {
 397         struct dasd_ccw_req *cqr;
 398
 399         cqr = device->eer_cqr;
 400         if (!cqr)       /* Device not eer enabled. */
 401                 return;
 402         if (test_and_set_bit(DASD_FLAG_EER_IN_USE, &device->flags)) {
 403                 /* Sense subsystem status request in use. */
 404                 set_bit(DASD_FLAG_EER_SNSS, &device->flags);
 405                 return;
 406         }
 407         clear_bit(DASD_FLAG_EER_SNSS, &device->flags);
 408         cqr->status = DASD_CQR_QUEUED;
 409         list_add(&cqr->list, &device->ccw_queue);
 410         dasd_schedule_bh(device);
 411 }
 412
 413 /*
 414  * Callback function for use with sense subsystem status request.
 415  */
 416 static void dasd_eer_snss_cb(struct dasd_ccw_req *cqr, void *data)
 417 {
 418         struct dasd_device *device = cqr->device;
 419         unsigned long flags;
 420
 421         dasd_eer_write(device, cqr, DASD_EER_STATECHANGE);
 422         spin_lock_irqsave(get_ccwdev_lock(device->cdev), flags);
 423         if (device->eer_cqr == cqr) {
 424                 clear_bit(DASD_FLAG_EER_IN_USE, &device->flags);
 425                 if (test_bit(DASD_FLAG_EER_SNSS, &device->flags))
 426                         /* Another SNSS has been requested in the meantime. */
 427                         dasd_eer_snss(device);
 428                 cqr = NULL;
 429         }
 430         spin_unlock_irqrestore(get_ccwdev_lock(device->cdev), flags);
 431         if (cqr)
 432                 /*
 433                  * Extended error recovery has been switched off while
 434                  * the SNSS request was running. It could even have
 435                  * been switched off and on again in which case there
 436                  * is a new ccw in device->eer_cqr. Free the "old"
 437                  * snss request now.
 438                  */
 439                 dasd_kfree_request(cqr, device);
 440 }
 441
 442 /*
 443  * Enable error reporting on a given device.
 444  */
 445 int dasd_eer_enable(struct dasd_device *device)
 446 {
 447         struct dasd_ccw_req *cqr;
 448         unsigned long flags;
 449
 450         if (device->eer_cqr)
 451                 return 0;
 452
 453         if (!device->discipline || strcmp(device->discipline->name, "ECKD"))
 454                 return -EPERM;  /* FIXME: -EMEDIUMTYPE ? */
 455
 456         cqr = dasd_kmalloc_request("ECKD", 1 /* SNSS */,
 457                                    SNSS_DATA_SIZE, device);
 458         if (!cqr)
 459                 return -ENOMEM;
 460
 461         cqr->device = device;
 462         cqr->retries = 255;
 463         cqr->expires = 10 * HZ;
 464         clear_bit(DASD_CQR_FLAGS_USE_ERP, &cqr->flags);
 465
 466         cqr->cpaddr->cmd_code = DASD_ECKD_CCW_SNSS;
 467         cqr->cpaddr->count = SNSS_DATA_SIZE;
 468         cqr->cpaddr->flags = 0;
 469         cqr->cpaddr->cda = (__u32)(addr_t) cqr->data;
 470
 471         cqr->buildclk = get_clock();
 472         cqr->status = DASD_CQR_FILLED;
 473         cqr->callback = dasd_eer_snss_cb;
 474
 475         spin_lock_irqsave(get_ccwdev_lock(device->cdev), flags);
 476         if (!device->eer_cqr) {
 477                 device->eer_cqr = cqr;
 478                 cqr = NULL;
 479         }
 480         spin_unlock_irqrestore(get_ccwdev_lock(device->cdev), flags);
 481         if (cqr)
 482                 dasd_kfree_request(cqr, device);
 483         return 0;
 484 }
 485
 486 /*
 487  * Disable error reporting on a given device.
 488  */
 489 void dasd_eer_disable(struct dasd_device *device)
 490 {
 491         struct dasd_ccw_req *cqr;
 492         unsigned long flags;
 493         int in_use;
 494
 495         if (!device->eer_cqr)
 496                 return;
 497         spin_lock_irqsave(get_ccwdev_lock(device->cdev), flags);
 498         cqr = device->eer_cqr;
 499         device->eer_cqr = NULL;
 500         clear_bit(DASD_FLAG_EER_SNSS, &device->flags);
 501         in_use = test_and_clear_bit(DASD_FLAG_EER_IN_USE, &device->flags);
 502         spin_unlock_irqrestore(get_ccwdev_lock(device->cdev), flags);
 503         if (cqr && !in_use)
 504                 dasd_kfree_request(cqr, device);
 505 }
 506
 507 /*
 508  * SECTION: the device operations
 509  */
 510
 511 /*
 512  * On the one side we need a lock to access our internal buffer, on the
 513  * other side a copy_to_user can sleep. So we need to copy the data we have
 514  * to transfer in a readbuffer, which is protected by the readbuffer_mutex.
 515  */
 516 static char readbuffer[PAGE_SIZE];
 517 static DEFINE_MUTEX(readbuffer_mutex);
 518
 519 static int dasd_eer_open(struct inode *inp, struct file *filp)
 520 {
 521         struct eerbuffer *eerb;
 522         unsigned long flags;
 523
 524         eerb = kzalloc(sizeof(struct eerbuffer), GFP_KERNEL);
 525         if (!eerb)
 526                 return -ENOMEM;
 527         eerb->buffer_page_count = eer_pages;
 528         if (eerb->buffer_page_count < 1 ||
 529             eerb->buffer_page_count > INT_MAX / PAGE_SIZE) {
 530                 kfree(eerb);
 531                 MESSAGE(KERN_WARNING, "can't open device since module "
 532                         "parameter eer_pages is smaller then 1 or"
 533                         " bigger then %d", (int)(INT_MAX / PAGE_SIZE));
 534                 return -EINVAL;
 535         }
 536         eerb->buffersize = eerb->buffer_page_count * PAGE_SIZE;
 537         eerb->buffer = kmalloc(eerb->buffer_page_count * sizeof(char *),
 538                                GFP_KERNEL);
 539         if (!eerb->buffer) {
 540                 kfree(eerb);
 541                 return -ENOMEM;
 542         }
 543         if (dasd_eer_allocate_buffer_pages(eerb->buffer,
 544                                            eerb->buffer_page_count)) {
 545                 kfree(eerb->buffer);
 546                 kfree(eerb);
 547                 return -ENOMEM;
 548         }
 549         filp->private_data = eerb;
 550         spin_lock_irqsave(&bufferlock, flags);
 551         list_add(&eerb->list, &bufferlist);
 552         spin_unlock_irqrestore(&bufferlock, flags);
 553
 554         return nonseekable_open(inp,filp);
 555 }
 556
 557 static int dasd_eer_close(struct inode *inp, struct file *filp)
 558 {
 559         struct eerbuffer *eerb;
 560         unsigned long flags;
 561
 562         eerb = (struct eerbuffer *) filp->private_data;
 563         spin_lock_irqsave(&bufferlock, flags);
 564         list_del(&eerb->list);
 565         spin_unlock_irqrestore(&bufferlock, flags);
 566         dasd_eer_free_buffer_pages(eerb->buffer, eerb->buffer_page_count);
 567         kfree(eerb->buffer);
 568         kfree(eerb);
 569
 570         return 0;
 571 }
 572
 573 static ssize_t dasd_eer_read(struct file *filp, char __user *buf,
 574                              size_t count, loff_t *ppos)
 575 {
 576         int tc,rc;
 577         int tailcount,effective_count;
 578         unsigned long flags;
 579         struct eerbuffer *eerb;
 580
 581         eerb = (struct eerbuffer *) filp->private_data;
 582         if (mutex_lock_interruptible(&readbuffer_mutex))
 583                 return -ERESTARTSYS;
 584
 585         spin_lock_irqsave(&bufferlock, flags);
 586
 587         if (eerb->residual < 0) { /* the remainder of this record */
 588                                   /* has been deleted             */
 589                 eerb->residual = 0;
 590                 spin_unlock_irqrestore(&bufferlock, flags);
 591                 mutex_unlock(&readbuffer_mutex);
 592                 return -EIO;
 593         } else if (eerb->residual > 0) {
 594                 /* OK we still have a second half of a record to deliver */
 595                 effective_count = min(eerb->residual, (int) count);
 596                 eerb->residual -= effective_count;
 597         } else {
 598                 tc = 0;
 599                 while (!tc) {
 600                         tc = dasd_eer_read_buffer(eerb, (char *) &tailcount,
 601                                                   sizeof(tailcount));
 602                         if (!tc) {
 603                                 /* no data available */
 604                                 spin_unlock_irqrestore(&bufferlock, flags);
 605                                 mutex_unlock(&readbuffer_mutex);
 606                                 if (filp->f_flags & O_NONBLOCK)
 607                                         return -EAGAIN;
 608                                 rc = wait_event_interruptible(
 609                                         dasd_eer_read_wait_queue,
 610                                         eerb->head != eerb->tail);
 611                                 if (rc)
 612                                         return rc;
 613                                 if (mutex_lock_interruptible(&readbuffer_mutex))
 614                                         return -ERESTARTSYS;
 615                                 spin_lock_irqsave(&bufferlock, flags);
 616                         }
 617                 }
 618                 WARN_ON(tc != sizeof(tailcount));
 619                 effective_count = min(tailcount,(int)count);
 620                 eerb->residual = tailcount - effective_count;
 621         }
 622
 623         tc = dasd_eer_read_buffer(eerb, readbuffer, effective_count);
 624         WARN_ON(tc != effective_count);
 625
 626         spin_unlock_irqrestore(&bufferlock, flags);
 627
 628         if (copy_to_user(buf, readbuffer, effective_count)) {
 629                 mutex_unlock(&readbuffer_mutex);
 630                 return -EFAULT;
 631         }
 632
 633         mutex_unlock(&readbuffer_mutex);
 634         return effective_count;
 635 }
 636
 637 static unsigned int dasd_eer_poll(struct file *filp, poll_table *ptable)
 638 {
 639         unsigned int mask;
 640         unsigned long flags;
 641         struct eerbuffer *eerb;
 642
 643         eerb = (struct eerbuffer *) filp->private_data;
 644         poll_wait(filp, &dasd_eer_read_wait_queue, ptable);
 645         spin_lock_irqsave(&bufferlock, flags);
 646         if (eerb->head != eerb->tail)
 647                 mask = POLLIN | POLLRDNORM ;
 648         else
 649                 mask = 0;
 650         spin_unlock_irqrestore(&bufferlock, flags);
 651         return mask;
 652 }
 653
 654 static const struct file_operations dasd_eer_fops = {
 655         .open           = &dasd_eer_open,
 656         .release        = &dasd_eer_close,
 657         .read           = &dasd_eer_read,
 658         .poll           = &dasd_eer_poll,
 659         .owner          = THIS_MODULE,
 660 };
 661
 662 static struct miscdevice *dasd_eer_dev = NULL;
 663
 664 int __init dasd_eer_init(void)
 665 {
 666         int rc;
 667
 668         dasd_eer_dev = kzalloc(sizeof(*dasd_eer_dev), GFP_KERNEL);
 669         if (!dasd_eer_dev)
 670                 return -ENOMEM;
 671
 672         dasd_eer_dev->minor = MISC_DYNAMIC_MINOR;
 673         dasd_eer_dev->name  = "dasd_eer";
 674         dasd_eer_dev->fops  = &dasd_eer_fops;
 675
 676         rc = misc_register(dasd_eer_dev);
 677         if (rc) {
 678                 kfree(dasd_eer_dev);
 679                 dasd_eer_dev = NULL;
 680                 MESSAGE(KERN_ERR, "%s", "dasd_eer_init could not "
 681                        "register misc device");
 682                 return rc;
 683         }
 684
 685         return 0;
 686 }
 687
 688 void dasd_eer_exit(void)
 689 {
 690         if (dasd_eer_dev) {
 691                 WARN_ON(misc_deregister(dasd_eer_dev) != 0);
 692                 kfree(dasd_eer_dev);
 693                 dasd_eer_dev = NULL;
 694         }
 695 }