drivers/s390/block/dasd_eer.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  *  Character device driver for extended error reporting.
   4  *
   5  *  Copyright IBM Corp. 2005
   6  *  extended error reporting for DASD ECKD devices
   7  *  Author(s): Stefan Weinhuber <wein@de.ibm.com>
   8  */
   9
  10 #define KMSG_COMPONENT "dasd-eckd"
  11
  12 #include <linux/init.h>
  13 #include <linux/fs.h>
  14 #include <linux/kernel.h>
  15 #include <linux/miscdevice.h>
  16 #include <linux/module.h>
  17 #include <linux/moduleparam.h>
  18 #include <linux/device.h>
  19 #include <linux/poll.h>
  20 #include <linux/mutex.h>
  21 #include <linux/err.h>
  22 #include <linux/slab.h>
  23
  24 #include <linux/uaccess.h>
  25 #include <linux/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 timespec64 ts;
 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         ktime_get_real_ts64(&ts);
 314         header.tv_sec = ts.tv_sec;
 315         header.tv_usec = ts.tv_nsec / NSEC_PER_USEC;
 316         strlcpy(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 timespec64 ts;
 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         ktime_get_real_ts64(&ts);
 357         header.tv_sec = ts.tv_sec;
 358         header.tv_usec = ts.tv_nsec / NSEC_PER_USEC;
 359         strlcpy(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         case DASD_EER_NOSPC:
 390                 dasd_eer_write_standard_trigger(device, NULL, id);
 391                 break;
 392         case DASD_EER_STATECHANGE:
 393                 dasd_eer_write_snss_trigger(device, cqr, id);
 394                 break;
 395         default: /* unknown trigger, so we write it without any sense data */
 396                 dasd_eer_write_standard_trigger(device, NULL, id);
 397                 break;
 398         }
 399 }
 400 EXPORT_SYMBOL(dasd_eer_write);
 401
 402 /*
 403  * Start a sense subsystem status request.
 404  * Needs to be called with the device held.
 405  */
 406 void dasd_eer_snss(struct dasd_device *device)
 407 {
 408         struct dasd_ccw_req *cqr;
 409
 410         cqr = device->eer_cqr;
 411         if (!cqr)       /* Device not eer enabled. */
 412                 return;
 413         if (test_and_set_bit(DASD_FLAG_EER_IN_USE, &device->flags)) {
 414                 /* Sense subsystem status request in use. */
 415                 set_bit(DASD_FLAG_EER_SNSS, &device->flags);
 416                 return;
 417         }
 418         /* cdev is already locked, can't use dasd_add_request_head */
 419         clear_bit(DASD_FLAG_EER_SNSS, &device->flags);
 420         cqr->status = DASD_CQR_QUEUED;
 421         list_add(&cqr->devlist, &device->ccw_queue);
 422         dasd_schedule_device_bh(device);
 423 }
 424
 425 /*
 426  * Callback function for use with sense subsystem status request.
 427  */
 428 static void dasd_eer_snss_cb(struct dasd_ccw_req *cqr, void *data)
 429 {
 430         struct dasd_device *device = cqr->startdev;
 431         unsigned long flags;
 432
 433         dasd_eer_write(device, cqr, DASD_EER_STATECHANGE);
 434         spin_lock_irqsave(get_ccwdev_lock(device->cdev), flags);
 435         if (device->eer_cqr == cqr) {
 436                 clear_bit(DASD_FLAG_EER_IN_USE, &device->flags);
 437                 if (test_bit(DASD_FLAG_EER_SNSS, &device->flags))
 438                         /* Another SNSS has been requested in the meantime. */
 439                         dasd_eer_snss(device);
 440                 cqr = NULL;
 441         }
 442         spin_unlock_irqrestore(get_ccwdev_lock(device->cdev), flags);
 443         if (cqr)
 444                 /*
 445                  * Extended error recovery has been switched off while
 446                  * the SNSS request was running. It could even have
 447                  * been switched off and on again in which case there
 448                  * is a new ccw in device->eer_cqr. Free the "old"
 449                  * snss request now.
 450                  */
 451                 dasd_sfree_request(cqr, device);
 452 }
 453
 454 /*
 455  * Enable error reporting on a given device.
 456  */
 457 int dasd_eer_enable(struct dasd_device *device)
 458 {
 459         struct dasd_ccw_req *cqr = NULL;
 460         unsigned long flags;
 461         struct ccw1 *ccw;
 462         int rc = 0;
 463
 464         spin_lock_irqsave(get_ccwdev_lock(device->cdev), flags);
 465         if (device->eer_cqr)
 466                 goto out;
 467         else if (!device->discipline ||
 468                  strcmp(device->discipline->name, "ECKD"))
 469                 rc = -EMEDIUMTYPE;
 470         else if (test_bit(DASD_FLAG_OFFLINE, &device->flags))
 471                 rc = -EBUSY;
 472
 473         if (rc)
 474                 goto out;
 475
 476         cqr = dasd_smalloc_request(DASD_ECKD_MAGIC, 1 /* SNSS */,
 477                                    SNSS_DATA_SIZE, device, NULL);
 478         if (IS_ERR(cqr)) {
 479                 rc = -ENOMEM;
 480                 cqr = NULL;
 481                 goto out;
 482         }
 483
 484         cqr->startdev = device;
 485         cqr->retries = 255;
 486         cqr->expires = 10 * HZ;
 487         clear_bit(DASD_CQR_FLAGS_USE_ERP, &cqr->flags);
 488         set_bit(DASD_CQR_ALLOW_SLOCK, &cqr->flags);
 489
 490         ccw = cqr->cpaddr;
 491         ccw->cmd_code = DASD_ECKD_CCW_SNSS;
 492         ccw->count = SNSS_DATA_SIZE;
 493         ccw->flags = 0;
 494         ccw->cda = (__u32)(addr_t) cqr->data;
 495
 496         cqr->buildclk = get_tod_clock();
 497         cqr->status = DASD_CQR_FILLED;
 498         cqr->callback = dasd_eer_snss_cb;
 499
 500         if (!device->eer_cqr) {
 501                 device->eer_cqr = cqr;
 502                 cqr = NULL;
 503         }
 504
 505 out:
 506         spin_unlock_irqrestore(get_ccwdev_lock(device->cdev), flags);
 507
 508         if (cqr)
 509                 dasd_sfree_request(cqr, device);
 510
 511         return rc;
 512 }
 513
 514 /*
 515  * Disable error reporting on a given device.
 516  */
 517 void dasd_eer_disable(struct dasd_device *device)
 518 {
 519         struct dasd_ccw_req *cqr;
 520         unsigned long flags;
 521         int in_use;
 522
 523         if (!device->eer_cqr)
 524                 return;
 525         spin_lock_irqsave(get_ccwdev_lock(device->cdev), flags);
 526         cqr = device->eer_cqr;
 527         device->eer_cqr = NULL;
 528         clear_bit(DASD_FLAG_EER_SNSS, &device->flags);
 529         in_use = test_and_clear_bit(DASD_FLAG_EER_IN_USE, &device->flags);
 530         spin_unlock_irqrestore(get_ccwdev_lock(device->cdev), flags);
 531         if (cqr && !in_use)
 532                 dasd_sfree_request(cqr, device);
 533 }
 534
 535 /*
 536  * SECTION: the device operations
 537  */
 538
 539 /*
 540  * On the one side we need a lock to access our internal buffer, on the
 541  * other side a copy_to_user can sleep. So we need to copy the data we have
 542  * to transfer in a readbuffer, which is protected by the readbuffer_mutex.
 543  */
 544 static char readbuffer[PAGE_SIZE];
 545 static DEFINE_MUTEX(readbuffer_mutex);
 546
 547 static int dasd_eer_open(struct inode *inp, struct file *filp)
 548 {
 549         struct eerbuffer *eerb;
 550         unsigned long flags;
 551
 552         eerb = kzalloc(sizeof(struct eerbuffer), GFP_KERNEL);
 553         if (!eerb)
 554                 return -ENOMEM;
 555         eerb->buffer_page_count = eer_pages;
 556         if (eerb->buffer_page_count < 1 ||
 557             eerb->buffer_page_count > INT_MAX / PAGE_SIZE) {
 558                 kfree(eerb);
 559                 DBF_EVENT(DBF_WARNING, "can't open device since module "
 560                         "parameter eer_pages is smaller than 1 or"
 561                         " bigger than %d", (int)(INT_MAX / PAGE_SIZE));
 562                 return -EINVAL;
 563         }
 564         eerb->buffersize = eerb->buffer_page_count * PAGE_SIZE;
 565         eerb->buffer = kmalloc_array(eerb->buffer_page_count, sizeof(char *),
 566                                      GFP_KERNEL);
 567         if (!eerb->buffer) {
 568                 kfree(eerb);
 569                 return -ENOMEM;
 570         }
 571         if (dasd_eer_allocate_buffer_pages(eerb->buffer,
 572                                            eerb->buffer_page_count)) {
 573                 kfree(eerb->buffer);
 574                 kfree(eerb);
 575                 return -ENOMEM;
 576         }
 577         filp->private_data = eerb;
 578         spin_lock_irqsave(&bufferlock, flags);
 579         list_add(&eerb->list, &bufferlist);
 580         spin_unlock_irqrestore(&bufferlock, flags);
 581
 582         return nonseekable_open(inp,filp);
 583 }
 584
 585 static int dasd_eer_close(struct inode *inp, struct file *filp)
 586 {
 587         struct eerbuffer *eerb;
 588         unsigned long flags;
 589
 590         eerb = (struct eerbuffer *) filp->private_data;
 591         spin_lock_irqsave(&bufferlock, flags);
 592         list_del(&eerb->list);
 593         spin_unlock_irqrestore(&bufferlock, flags);
 594         dasd_eer_free_buffer_pages(eerb->buffer, eerb->buffer_page_count);
 595         kfree(eerb->buffer);
 596         kfree(eerb);
 597
 598         return 0;
 599 }
 600
 601 static ssize_t dasd_eer_read(struct file *filp, char __user *buf,
 602                              size_t count, loff_t *ppos)
 603 {
 604         int tc,rc;
 605         int tailcount,effective_count;
 606         unsigned long flags;
 607         struct eerbuffer *eerb;
 608
 609         eerb = (struct eerbuffer *) filp->private_data;
 610         if (mutex_lock_interruptible(&readbuffer_mutex))
 611                 return -ERESTARTSYS;
 612
 613         spin_lock_irqsave(&bufferlock, flags);
 614
 615         if (eerb->residual < 0) { /* the remainder of this record */
 616                                   /* has been deleted             */
 617                 eerb->residual = 0;
 618                 spin_unlock_irqrestore(&bufferlock, flags);
 619                 mutex_unlock(&readbuffer_mutex);
 620                 return -EIO;
 621         } else if (eerb->residual > 0) {
 622                 /* OK we still have a second half of a record to deliver */
 623                 effective_count = min(eerb->residual, (int) count);
 624                 eerb->residual -= effective_count;
 625         } else {
 626                 tc = 0;
 627                 while (!tc) {
 628                         tc = dasd_eer_read_buffer(eerb, (char *) &tailcount,
 629                                                   sizeof(tailcount));
 630                         if (!tc) {
 631                                 /* no data available */
 632                                 spin_unlock_irqrestore(&bufferlock, flags);
 633                                 mutex_unlock(&readbuffer_mutex);
 634                                 if (filp->f_flags & O_NONBLOCK)
 635                                         return -EAGAIN;
 636                                 rc = wait_event_interruptible(
 637                                         dasd_eer_read_wait_queue,
 638                                         eerb->head != eerb->tail);
 639                                 if (rc)
 640                                         return rc;
 641                                 if (mutex_lock_interruptible(&readbuffer_mutex))
 642                                         return -ERESTARTSYS;
 643                                 spin_lock_irqsave(&bufferlock, flags);
 644                         }
 645                 }
 646                 WARN_ON(tc != sizeof(tailcount));
 647                 effective_count = min(tailcount,(int)count);
 648                 eerb->residual = tailcount - effective_count;
 649         }
 650
 651         tc = dasd_eer_read_buffer(eerb, readbuffer, effective_count);
 652         WARN_ON(tc != effective_count);
 653
 654         spin_unlock_irqrestore(&bufferlock, flags);
 655
 656         if (copy_to_user(buf, readbuffer, effective_count)) {
 657                 mutex_unlock(&readbuffer_mutex);
 658                 return -EFAULT;
 659         }
 660
 661         mutex_unlock(&readbuffer_mutex);
 662         return effective_count;
 663 }
 664
 665 static __poll_t dasd_eer_poll(struct file *filp, poll_table *ptable)
 666 {
 667         __poll_t mask;
 668         unsigned long flags;
 669         struct eerbuffer *eerb;
 670
 671         eerb = (struct eerbuffer *) filp->private_data;
 672         poll_wait(filp, &dasd_eer_read_wait_queue, ptable);
 673         spin_lock_irqsave(&bufferlock, flags);
 674         if (eerb->head != eerb->tail)
 675                 mask = EPOLLIN | EPOLLRDNORM ;
 676         else
 677                 mask = 0;
 678         spin_unlock_irqrestore(&bufferlock, flags);
 679         return mask;
 680 }
 681
 682 static const struct file_operations dasd_eer_fops = {
 683         .open           = &dasd_eer_open,
 684         .release        = &dasd_eer_close,
 685         .read           = &dasd_eer_read,
 686         .poll           = &dasd_eer_poll,
 687         .owner          = THIS_MODULE,
 688         .llseek         = noop_llseek,
 689 };
 690
 691 static struct miscdevice *dasd_eer_dev = NULL;
 692
 693 int __init dasd_eer_init(void)
 694 {
 695         int rc;
 696
 697         dasd_eer_dev = kzalloc(sizeof(*dasd_eer_dev), GFP_KERNEL);
 698         if (!dasd_eer_dev)
 699                 return -ENOMEM;
 700
 701         dasd_eer_dev->minor = MISC_DYNAMIC_MINOR;
 702         dasd_eer_dev->name  = "dasd_eer";
 703         dasd_eer_dev->fops  = &dasd_eer_fops;
 704
 705         rc = misc_register(dasd_eer_dev);
 706         if (rc) {
 707                 kfree(dasd_eer_dev);
 708                 dasd_eer_dev = NULL;
 709                 DBF_EVENT(DBF_ERR, "%s", "dasd_eer_init could not "
 710                        "register misc device");
 711                 return rc;
 712         }
 713
 714         return 0;
 715 }
 716
 717 void dasd_eer_exit(void)
 718 {
 719         if (dasd_eer_dev) {
 720                 misc_deregister(dasd_eer_dev);
 721                 kfree(dasd_eer_dev);
 722                 dasd_eer_dev = NULL;
 723         }
 724 }