release/src-rt-6.x.4708/linux/linux-2.6.36/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-eckd"
  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 #include <linux/slab.h>
  23
  24 #include <asm/uaccess.h>
  25 #include <asm/atomic.h>
  26 #include <asm/ebcdic.h>
  27
  28 #include "dasd_int.h"
  29 #include "dasd_eckd.h"
  30
  31 #ifdef PRINTK_HEADER
  32 #undef PRINTK_HEADER
  33 #endif                          /* PRINTK_HEADER */
  34 #define PRINTK_HEADER "dasd(eer):"
  35
  36 /*
  37  * SECTION: the internal buffer
  38  */
  39
  40 /*
  41  * The internal buffer is meant to store obaque blobs of data, so it does
  42  * not know of higher level concepts like triggers.
  43  * It consists of a number of pages that are used as a ringbuffer. Each data
  44  * blob is stored in a simple record that consists of an integer, which
  45  * contains the size of the following data, and the data bytes themselfes.
  46  *
  47  * To allow for multiple independent readers we create one internal buffer
  48  * each time the device is opened and destroy the buffer when the file is
  49  * closed again. The number of pages used for this buffer is determined by
  50  * the module parmeter eer_pages.
  51  *
  52  * One record can be written to a buffer by using the functions
  53  * - dasd_eer_start_record (one time per record to write the size to the
  54  *                          buffer and reserve the space for the data)
  55  * - dasd_eer_write_buffer (one or more times per record to write the data)
  56  * The data can be written in several steps but you will have to compute
  57  * the total size up front for the invocation of dasd_eer_start_record.
  58  * If the ringbuffer is full, dasd_eer_start_record will remove the required
  59  * number of old records.
  60  *
  61  * A record is typically read in two steps, first read the integer that
  62  * specifies the size of the following data, then read the data.
  63  * Both can be done by
  64  * - dasd_eer_read_buffer
  65  *
  66  * For all mentioned functions you need to get the bufferlock first and keep
  67  * it until a complete record is written or read.
  68  *
  69  * All information necessary to keep track of an internal buffer is kept in
  70  * a struct eerbuffer. The buffer specific to a file pointer is strored in
  71  * the private_data field of that file. To be able to write data to all
  72  * existing buffers, each buffer is also added to the bufferlist.
  73  * If the user does not want to read a complete record in one go, we have to
  74  * keep track of the rest of the record. residual stores the number of bytes
  75  * that are still to deliver. If the rest of the record is invalidated between
  76  * two reads then residual will be set to -1 so that the next read will fail.
  77  * All entries in the eerbuffer structure are protected with the bufferlock.
  78  * To avoid races between writing to a buffer on the one side and creating
  79  * and destroying buffers on the other side, the bufferlock must also be used
  80  * to protect the bufferlist.
  81  */
  82
  83 static int eer_pages = 5;
  84 module_param(eer_pages, int, S_IRUGO|S_IWUSR);
  85
  86 struct eerbuffer {
  87         struct list_head list;
  88         char **buffer;
  89         int buffersize;
  90         int buffer_page_count;
  91         int head;
  92         int tail;
  93         int residual;
  94 };
  95
  96 static LIST_HEAD(bufferlist);
  97 static DEFINE_SPINLOCK(bufferlock);
  98 static DECLARE_WAIT_QUEUE_HEAD(dasd_eer_read_wait_queue);
  99
 100 /*
 101  * How many free bytes are available on the buffer.
 102  * Needs to be called with bufferlock held.
 103  */
 104 static int dasd_eer_get_free_bytes(struct eerbuffer *eerb)
 105 {
 106         if (eerb->head < eerb->tail)
 107                 return eerb->tail - eerb->head - 1;
 108         return eerb->buffersize - eerb->head + eerb->tail -1;
 109 }
 110
 111 /*
 112  * How many bytes of buffer space are used.
 113  * Needs to be called with bufferlock held.
 114  */
 115 static int dasd_eer_get_filled_bytes(struct eerbuffer *eerb)
 116 {
 117
 118         if (eerb->head >= eerb->tail)
 119                 return eerb->head - eerb->tail;
 120         return eerb->buffersize - eerb->tail + eerb->head;
 121 }
 122
 123 /*
 124  * The dasd_eer_write_buffer function just copies count bytes of data
 125  * to the buffer. Make sure to call dasd_eer_start_record first, to
 126  * make sure that enough free space is available.
 127  * Needs to be called with bufferlock held.
 128  */
 129 static void dasd_eer_write_buffer(struct eerbuffer *eerb,
 130                                   char *data, int count)
 131 {
 132
 133         unsigned long headindex,localhead;
 134         unsigned long rest, len;
 135         char *nextdata;
 136
 137         nextdata = data;
 138         rest = count;
 139         while (rest > 0) {
 140                 headindex = eerb->head / PAGE_SIZE;
 141                 localhead = eerb->head % PAGE_SIZE;
 142                 len = min(rest, PAGE_SIZE - localhead);
 143                 memcpy(eerb->buffer[headindex]+localhead, nextdata, len);
 144                 nextdata += len;
 145                 rest -= len;
 146                 eerb->head += len;
 147                 if (eerb->head == eerb->buffersize)
 148                         eerb->head = 0; /* wrap around */
 149                 BUG_ON(eerb->head > eerb->buffersize);
 150         }
 151 }
 152
 153 /*
 154  * Needs to be called with bufferlock held.
 155  */
 156 static int dasd_eer_read_buffer(struct eerbuffer *eerb, char *data, int count)
 157 {
 158
 159         unsigned long tailindex,localtail;
 160         unsigned long rest, len, finalcount;
 161         char *nextdata;
 162
 163         finalcount = min(count, dasd_eer_get_filled_bytes(eerb));
 164         nextdata = data;
 165         rest = finalcount;
 166         while (rest > 0) {
 167                 tailindex = eerb->tail / PAGE_SIZE;
 168                 localtail = eerb->tail % PAGE_SIZE;
 169                 len = min(rest, PAGE_SIZE - localtail);
 170                 memcpy(nextdata, eerb->buffer[tailindex] + localtail, len);
 171                 nextdata += len;
 172                 rest -= len;
 173                 eerb->tail += len;
 174                 if (eerb->tail == eerb->buffersize)
 175                         eerb->tail = 0; /* wrap around */
 176                 BUG_ON(eerb->tail > eerb->buffersize);
 177         }
 178         return finalcount;
 179 }
 180
 181 /*
 182  * Whenever you want to write a blob of data to the internal buffer you
 183  * have to start by using this function first. It will write the number
 184  * of bytes that will be written to the buffer. If necessary it will remove
 185  * old records to make room for the new one.
 186  * Needs to be called with bufferlock held.
 187  */
 188 static int dasd_eer_start_record(struct eerbuffer *eerb, int count)
 189 {
 190         int tailcount;
 191
 192         if (count + sizeof(count) > eerb->buffersize)
 193                 return -ENOMEM;
 194         while (dasd_eer_get_free_bytes(eerb) < count + sizeof(count)) {
 195                 if (eerb->residual > 0) {
 196                         eerb->tail += eerb->residual;
 197                         if (eerb->tail >= eerb->buffersize)
 198                                 eerb->tail -= eerb->buffersize;
 199                         eerb->residual = -1;
 200                 }
 201                 dasd_eer_read_buffer(eerb, (char *) &tailcount,
 202                                      sizeof(tailcount));
 203                 eerb->tail += tailcount;
 204                 if (eerb->tail >= eerb->buffersize)
 205                         eerb->tail -= eerb->buffersize;
 206         }
 207         dasd_eer_write_buffer(eerb, (char*) &count, sizeof(count));
 208
 209         return 0;
 210 };
 211
 212 /*
 213  * Release pages that are not used anymore.
 214  */
 215 static void dasd_eer_free_buffer_pages(char **buf, int no_pages)
 216 {
 217         int i;
 218
 219         for (i = 0; i < no_pages; i++)
 220                 free_page((unsigned long) buf[i]);
 221 }
 222
 223 /*
 224  * Allocate a new set of memory pages.
 225  */
 226 static int dasd_eer_allocate_buffer_pages(char **buf, int no_pages)
 227 {
 228         int i;
 229
 230         for (i = 0; i < no_pages; i++) {
 231                 buf[i] = (char *) get_zeroed_page(GFP_KERNEL);
 232                 if (!buf[i]) {
 233                         dasd_eer_free_buffer_pages(buf, i);
 234                         return -ENOMEM;
 235                 }
 236         }
 237         return 0;
 238 }
 239
 240 /*
 241  * SECTION: The extended error reporting functionality
 242  */
 243
 244 /*
 245  * When a DASD device driver wants to report an error, it calls the
 246  * function dasd_eer_write and gives the respective trigger ID as
 247  * parameter. Currently there are four kinds of triggers:
 248  *
 249  * DASD_EER_FATALERROR:  all kinds of unrecoverable I/O problems
 250  * DASD_EER_PPRCSUSPEND: PPRC was suspended
 251  * DASD_EER_NOPATH:      There is no path to the device left.
 252  * DASD_EER_STATECHANGE: The state of the device has changed.
 253  *
 254  * For the first three triggers all required information can be supplied by
 255  * the caller. For these triggers a record is written by the function
 256  * dasd_eer_write_standard_trigger.
 257  *
 258  * The DASD_EER_STATECHANGE trigger is special since a sense subsystem
 259  * status ccw need to be executed to gather the necessary sense data first.
 260  * The dasd_eer_snss function will queue the SNSS request and the request
 261  * callback will then call dasd_eer_write with the DASD_EER_STATCHANGE
 262  * trigger.
 263  *
 264  * To avoid memory allocations at runtime, the necessary memory is allocated
 265  * when the extended error reporting is enabled for a device (by
 266  * dasd_eer_probe). There is one sense subsystem status request for each
 267  * eer enabled DASD device. The presence of the cqr in device->eer_cqr
 268  * indicates that eer is enable for the device. The use of the snss request
 269  * is protected by the DASD_FLAG_EER_IN_USE bit. When this flag indicates
 270  * that the cqr is currently in use, dasd_eer_snss cannot start a second
 271  * request but sets the DASD_FLAG_EER_SNSS flag instead. The callback of
 272  * the SNSS request will check the bit and call dasd_eer_snss again.
 273  */
 274
 275 #define SNSS_DATA_SIZE 44
 276
 277 #define DASD_EER_BUSID_SIZE 10
 278 struct dasd_eer_header {
 279         __u32 total_size;
 280         __u32 trigger;
 281         __u64 tv_sec;
 282         __u64 tv_usec;
 283         char busid[DASD_EER_BUSID_SIZE];
 284 } __attribute__ ((packed));
 285
 286 /*
 287  * The following function can be used for those triggers that have
 288  * all necessary data available when the function is called.
 289  * If the parameter cqr is not NULL, the chain of requests will be searched
 290  * for valid sense data, and all valid sense data sets will be added to
 291  * the triggers data.
 292  */
 293 static void dasd_eer_write_standard_trigger(struct dasd_device *device,
 294                                             struct dasd_ccw_req *cqr,
 295                                             int trigger)
 296 {
 297         struct dasd_ccw_req *temp_cqr;
 298         int data_size;
 299         struct timeval tv;
 300         struct dasd_eer_header header;
 301         unsigned long flags;
 302         struct eerbuffer *eerb;
 303         char *sense;
 304
 305         /* go through cqr chain and count the valid sense data sets */
 306         data_size = 0;
 307         for (temp_cqr = cqr; temp_cqr; temp_cqr = temp_cqr->refers)
 308                 if (dasd_get_sense(&temp_cqr->irb))
 309                         data_size += 32;
 310
 311         header.total_size = sizeof(header) + data_size + 4; /* "EOR" */
 312         header.trigger = trigger;
 313         do_gettimeofday(&tv);
 314         header.tv_sec = tv.tv_sec;
 315         header.tv_usec = tv.tv_usec;
 316         strncpy(header.busid, dev_name(&device->cdev->dev),
 317                 DASD_EER_BUSID_SIZE);
 318
 319         spin_lock_irqsave(&bufferlock, flags);
 320         list_for_each_entry(eerb, &bufferlist, list) {
 321                 dasd_eer_start_record(eerb, header.total_size);
 322                 dasd_eer_write_buffer(eerb, (char *) &header, sizeof(header));
 323                 for (temp_cqr = cqr; temp_cqr; temp_cqr = temp_cqr->refers) {
 324                         sense = dasd_get_sense(&temp_cqr->irb);
 325                         if (sense)
 326                                 dasd_eer_write_buffer(eerb, sense, 32);
 327                 }
 328                 dasd_eer_write_buffer(eerb, "EOR", 4);
 329         }
 330         spin_unlock_irqrestore(&bufferlock, flags);
 331         wake_up_interruptible(&dasd_eer_read_wait_queue);
 332 }
 333
 334 /*
 335  * This function writes a DASD_EER_STATECHANGE trigger.
 336  */
 337 static void dasd_eer_write_snss_trigger(struct dasd_device *device,
 338                                         struct dasd_ccw_req *cqr,
 339                                         int trigger)
 340 {
 341         int data_size;
 342         int snss_rc;
 343         struct timeval tv;
 344         struct dasd_eer_header header;
 345         unsigned long flags;
 346         struct eerbuffer *eerb;
 347
 348         snss_rc = (cqr->status == DASD_CQR_DONE) ? 0 : -EIO;
 349         if (snss_rc)
 350                 data_size = 0;
 351         else
 352                 data_size = SNSS_DATA_SIZE;
 353
 354         header.total_size = sizeof(header) + data_size + 4; /* "EOR" */
 355         header.trigger = DASD_EER_STATECHANGE;
 356         do_gettimeofday(&tv);
 357         header.tv_sec = tv.tv_sec;
 358         header.tv_usec = tv.tv_usec;
 359         strncpy(header.busid, dev_name(&device->cdev->dev),
 360                 DASD_EER_BUSID_SIZE);
 361
 362         spin_lock_irqsave(&bufferlock, flags);
 363         list_for_each_entry(eerb, &bufferlist, list) {
 364                 dasd_eer_start_record(eerb, header.total_size);
 365                 dasd_eer_write_buffer(eerb, (char *) &header , sizeof(header));
 366                 if (!snss_rc)
 367                         dasd_eer_write_buffer(eerb, cqr->data, SNSS_DATA_SIZE);
 368                 dasd_eer_write_buffer(eerb, "EOR", 4);
 369         }
 370         spin_unlock_irqrestore(&bufferlock, flags);
 371         wake_up_interruptible(&dasd_eer_read_wait_queue);
 372 }
 373
 374 /*
 375  * This function is called for all triggers. It calls the appropriate
 376  * function that writes the actual trigger records.
 377  */
 378 void dasd_eer_write(struct dasd_device *device, struct dasd_ccw_req *cqr,
 379                     unsigned int id)
 380 {
 381         if (!device->eer_cqr)
 382                 return;
 383         switch (id) {
 384         case DASD_EER_FATALERROR:
 385         case DASD_EER_PPRCSUSPEND:
 386                 dasd_eer_write_standard_trigger(device, cqr, id);
 387                 break;
 388         case DASD_EER_NOPATH:
 389                 dasd_eer_write_standard_trigger(device, NULL, id);
 390                 break;
 391         case DASD_EER_STATECHANGE:
 392                 dasd_eer_write_snss_trigger(device, cqr, id);
 393                 break;
 394         default: /* unknown trigger, so we write it without any sense data */
 395                 dasd_eer_write_standard_trigger(device, NULL, id);
 396                 break;
 397         }
 398 }
 399 EXPORT_SYMBOL(dasd_eer_write);
 400
 401 /*
 402  * Start a sense subsystem status request.
 403  * Needs to be called with the device held.
 404  */
 405 void dasd_eer_snss(struct dasd_device *device)
 406 {
 407         struct dasd_ccw_req *cqr;
 408
 409         cqr = device->eer_cqr;
 410         if (!cqr)       /* Device not eer enabled. */
 411                 return;
 412         if (test_and_set_bit(DASD_FLAG_EER_IN_USE, &device->flags)) {
 413                 /* Sense subsystem status request in use. */
 414                 set_bit(DASD_FLAG_EER_SNSS, &device->flags);
 415                 return;
 416         }
 417         /* cdev is already locked, can't use dasd_add_request_head */
 418         clear_bit(DASD_FLAG_EER_SNSS, &device->flags);
 419         cqr->status = DASD_CQR_QUEUED;
 420         list_add(&cqr->devlist, &device->ccw_queue);
 421         dasd_schedule_device_bh(device);
 422 }
 423
 424 /*
 425  * Callback function for use with sense subsystem status request.
 426  */
 427 static void dasd_eer_snss_cb(struct dasd_ccw_req *cqr, void *data)
 428 {
 429         struct dasd_device *device = cqr->startdev;
 430         unsigned long flags;
 431
 432         dasd_eer_write(device, cqr, DASD_EER_STATECHANGE);
 433         spin_lock_irqsave(get_ccwdev_lock(device->cdev), flags);
 434         if (device->eer_cqr == cqr) {
 435                 clear_bit(DASD_FLAG_EER_IN_USE, &device->flags);
 436                 if (test_bit(DASD_FLAG_EER_SNSS, &device->flags))
 437                         /* Another SNSS has been requested in the meantime. */
 438                         dasd_eer_snss(device);
 439                 cqr = NULL;
 440         }
 441         spin_unlock_irqrestore(get_ccwdev_lock(device->cdev), flags);
 442         if (cqr)
 443                 /*
 444                  * Extended error recovery has been switched off while
 445                  * the SNSS request was running. It could even have
 446                  * been switched off and on again in which case there
 447                  * is a new ccw in device->eer_cqr. Free the "old"
 448                  * snss request now.
 449                  */
 450                 dasd_kfree_request(cqr, device);
 451 }
 452
 453 /*
 454  * Enable error reporting on a given device.
 455  */
 456 int dasd_eer_enable(struct dasd_device *device)
 457 {
 458         struct dasd_ccw_req *cqr;
 459         unsigned long flags;
 460         struct ccw1 *ccw;
 461
 462         if (device->eer_cqr)
 463                 return 0;
 464
 465         if (!device->discipline || strcmp(device->discipline->name, "ECKD"))
 466                 return -EPERM;
 467
 468         cqr = dasd_kmalloc_request(DASD_ECKD_MAGIC, 1 /* SNSS */,
 469                                    SNSS_DATA_SIZE, device);
 470         if (IS_ERR(cqr))
 471                 return -ENOMEM;
 472
 473         cqr->startdev = device;
 474         cqr->retries = 255;
 475         cqr->expires = 10 * HZ;
 476         clear_bit(DASD_CQR_FLAGS_USE_ERP, &cqr->flags);
 477
 478         ccw = cqr->cpaddr;
 479         ccw->cmd_code = DASD_ECKD_CCW_SNSS;
 480         ccw->count = SNSS_DATA_SIZE;
 481         ccw->flags = 0;
 482         ccw->cda = (__u32)(addr_t) cqr->data;
 483
 484         cqr->buildclk = get_clock();
 485         cqr->status = DASD_CQR_FILLED;
 486         cqr->callback = dasd_eer_snss_cb;
 487
 488         spin_lock_irqsave(get_ccwdev_lock(device->cdev), flags);
 489         if (!device->eer_cqr) {
 490                 device->eer_cqr = cqr;
 491                 cqr = NULL;
 492         }
 493         spin_unlock_irqrestore(get_ccwdev_lock(device->cdev), flags);
 494         if (cqr)
 495                 dasd_kfree_request(cqr, device);
 496         return 0;
 497 }
 498
 499 /*
 500  * Disable error reporting on a given device.
 501  */
 502 void dasd_eer_disable(struct dasd_device *device)
 503 {
 504         struct dasd_ccw_req *cqr;
 505         unsigned long flags;
 506         int in_use;
 507
 508         if (!device->eer_cqr)
 509                 return;
 510         spin_lock_irqsave(get_ccwdev_lock(device->cdev), flags);
 511         cqr = device->eer_cqr;
 512         device->eer_cqr = NULL;
 513         clear_bit(DASD_FLAG_EER_SNSS, &device->flags);
 514         in_use = test_and_clear_bit(DASD_FLAG_EER_IN_USE, &device->flags);
 515         spin_unlock_irqrestore(get_ccwdev_lock(device->cdev), flags);
 516         if (cqr && !in_use)
 517                 dasd_kfree_request(cqr, device);
 518 }
 519
 520 /*
 521  * SECTION: the device operations
 522  */
 523
 524 /*
 525  * On the one side we need a lock to access our internal buffer, on the
 526  * other side a copy_to_user can sleep. So we need to copy the data we have
 527  * to transfer in a readbuffer, which is protected by the readbuffer_mutex.
 528  */
 529 static char readbuffer[PAGE_SIZE];
 530 static DEFINE_MUTEX(readbuffer_mutex);
 531
 532 static int dasd_eer_open(struct inode *inp, struct file *filp)
 533 {
 534         struct eerbuffer *eerb;
 535         unsigned long flags;
 536
 537         eerb = kzalloc(sizeof(struct eerbuffer), GFP_KERNEL);
 538         if (!eerb)
 539                 return -ENOMEM;
 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                 return -EINVAL;
 548         }
 549         eerb->buffersize = eerb->buffer_page_count * PAGE_SIZE;
 550         eerb->buffer = kmalloc(eerb->buffer_page_count * sizeof(char *),
 551                                GFP_KERNEL);
 552         if (!eerb->buffer) {
 553                 kfree(eerb);
 554                 return -ENOMEM;
 555         }
 556         if (dasd_eer_allocate_buffer_pages(eerb->buffer,
 557                                            eerb->buffer_page_count)) {
 558                 kfree(eerb->buffer);
 559                 kfree(eerb);
 560                 return -ENOMEM;
 561         }
 562         filp->private_data = eerb;
 563         spin_lock_irqsave(&bufferlock, flags);
 564         list_add(&eerb->list, &bufferlist);
 565         spin_unlock_irqrestore(&bufferlock, flags);
 566
 567         return nonseekable_open(inp,filp);
 568 }
 569
 570 static int dasd_eer_close(struct inode *inp, struct file *filp)
 571 {
 572         struct eerbuffer *eerb;
 573         unsigned long flags;
 574
 575         eerb = (struct eerbuffer *) filp->private_data;
 576         spin_lock_irqsave(&bufferlock, flags);
 577         list_del(&eerb->list);
 578         spin_unlock_irqrestore(&bufferlock, flags);
 579         dasd_eer_free_buffer_pages(eerb->buffer, eerb->buffer_page_count);
 580         kfree(eerb->buffer);
 581         kfree(eerb);
 582
 583         return 0;
 584 }
 585
 586 static ssize_t dasd_eer_read(struct file *filp, char __user *buf,
 587                              size_t count, loff_t *ppos)
 588 {
 589         int tc,rc;
 590         int tailcount,effective_count;
 591         unsigned long flags;
 592         struct eerbuffer *eerb;
 593
 594         eerb = (struct eerbuffer *) filp->private_data;
 595         if (mutex_lock_interruptible(&readbuffer_mutex))
 596                 return -ERESTARTSYS;
 597
 598         spin_lock_irqsave(&bufferlock, flags);
 599
 600         if (eerb->residual < 0) { /* the remainder of this record */
 601                                   /* has been deleted             */
 602                 eerb->residual = 0;
 603                 spin_unlock_irqrestore(&bufferlock, flags);
 604                 mutex_unlock(&readbuffer_mutex);
 605                 return -EIO;
 606         } else if (eerb->residual > 0) {
 607                 /* OK we still have a second half of a record to deliver */
 608                 effective_count = min(eerb->residual, (int) count);
 609                 eerb->residual -= effective_count;
 610         } else {
 611                 tc = 0;
 612                 while (!tc) {
 613                         tc = dasd_eer_read_buffer(eerb, (char *) &tailcount,
 614                                                   sizeof(tailcount));
 615                         if (!tc) {
 616                                 /* no data available */
 617                                 spin_unlock_irqrestore(&bufferlock, flags);
 618                                 mutex_unlock(&readbuffer_mutex);
 619                                 if (filp->f_flags & O_NONBLOCK)
 620                                         return -EAGAIN;
 621                                 rc = wait_event_interruptible(
 622                                         dasd_eer_read_wait_queue,
 623                                         eerb->head != eerb->tail);
 624                                 if (rc)
 625                                         return rc;
 626                                 if (mutex_lock_interruptible(&readbuffer_mutex))
 627                                         return -ERESTARTSYS;
 628                                 spin_lock_irqsave(&bufferlock, flags);
 629                         }
 630                 }
 631                 WARN_ON(tc != sizeof(tailcount));
 632                 effective_count = min(tailcount,(int)count);
 633                 eerb->residual = tailcount - effective_count;
 634         }
 635
 636         tc = dasd_eer_read_buffer(eerb, readbuffer, effective_count);
 637         WARN_ON(tc != effective_count);
 638
 639         spin_unlock_irqrestore(&bufferlock, flags);
 640
 641         if (copy_to_user(buf, readbuffer, effective_count)) {
 642                 mutex_unlock(&readbuffer_mutex);
 643                 return -EFAULT;
 644         }
 645
 646         mutex_unlock(&readbuffer_mutex);
 647         return effective_count;
 648 }
 649
 650 static unsigned int dasd_eer_poll(struct file *filp, poll_table *ptable)
 651 {
 652         unsigned int mask;
 653         unsigned long flags;
 654         struct eerbuffer *eerb;
 655
 656         eerb = (struct eerbuffer *) filp->private_data;
 657         poll_wait(filp, &dasd_eer_read_wait_queue, ptable);
 658         spin_lock_irqsave(&bufferlock, flags);
 659         if (eerb->head != eerb->tail)
 660                 mask = POLLIN | POLLRDNORM ;
 661         else
 662                 mask = 0;
 663         spin_unlock_irqrestore(&bufferlock, flags);
 664         return mask;
 665 }
 666
 667 static const struct file_operations dasd_eer_fops = {
 668         .open           = &dasd_eer_open,
 669         .release        = &dasd_eer_close,
 670         .read           = &dasd_eer_read,
 671         .poll           = &dasd_eer_poll,
 672         .owner          = THIS_MODULE,
 673 };
 674
 675 static struct miscdevice *dasd_eer_dev = NULL;
 676
 677 int __init dasd_eer_init(void)
 678 {
 679         int rc;
 680
 681         dasd_eer_dev = kzalloc(sizeof(*dasd_eer_dev), GFP_KERNEL);
 682         if (!dasd_eer_dev)
 683                 return -ENOMEM;
 684
 685         dasd_eer_dev->minor = MISC_DYNAMIC_MINOR;
 686         dasd_eer_dev->name  = "dasd_eer";
 687         dasd_eer_dev->fops  = &dasd_eer_fops;
 688
 689         rc = misc_register(dasd_eer_dev);
 690         if (rc) {
 691                 kfree(dasd_eer_dev);
 692                 dasd_eer_dev = NULL;
 693                 DBF_EVENT(DBF_ERR, "%s", "dasd_eer_init could not "
 694                        "register misc device");
 695                 return rc;
 696         }
 697
 698         return 0;
 699 }
 700
 701 void dasd_eer_exit(void)
 702 {
 703         if (dasd_eer_dev) {
 704                 misc_deregister(dasd_eer_dev);
 705                 kfree(dasd_eer_dev);
 706                 dasd_eer_dev = NULL;
 707         }
 708 }