kernel/relay.c

   1 /*
   2  * Public API and common code for kernel->userspace relay file support.
   3  *
   4  * See Documentation/filesystems/relayfs.txt for an overview of relayfs.
   5  *
   6  * Copyright (C) 2002-2005 - Tom Zanussi (zanussi@us.ibm.com), IBM Corp
   7  * Copyright (C) 1999-2005 - Karim Yaghmour (karim@opersys.com)
   8  *
   9  * Moved to kernel/relay.c by Paul Mundt, 2006.
  10  *
  11  * This file is released under the GPL.
  12  */
  13 #include <linux/errno.h>
  14 #include <linux/stddef.h>
  15 #include <linux/slab.h>
  16 #include <linux/module.h>
  17 #include <linux/string.h>
  18 #include <linux/relay.h>
  19 #include <linux/vmalloc.h>
  20 #include <linux/mm.h>
  21
  22 /*
  23  * close() vm_op implementation for relay file mapping.
  24  */
  25 static void relay_file_mmap_close(struct vm_area_struct *vma)
  26 {
  27         struct rchan_buf *buf = vma->vm_private_data;
  28         buf->chan->cb->buf_unmapped(buf, vma->vm_file);
  29 }
  30
  31 /*
  32  * nopage() vm_op implementation for relay file mapping.
  33  */
  34 static struct page *relay_buf_nopage(struct vm_area_struct *vma,
  35                                      unsigned long address,
  36                                      int *type)
  37 {
  38         struct page *page;
  39         struct rchan_buf *buf = vma->vm_private_data;
  40         unsigned long offset = address - vma->vm_start;
  41
  42         if (address > vma->vm_end)
  43                 return NOPAGE_SIGBUS; /* Disallow mremap */
  44         if (!buf)
  45                 return NOPAGE_OOM;
  46
  47         page = vmalloc_to_page(buf->start + offset);
  48         if (!page)
  49                 return NOPAGE_OOM;
  50         get_page(page);
  51
  52         if (type)
  53                 *type = VM_FAULT_MINOR;
  54
  55         return page;
  56 }
  57
  58 /*
  59  * vm_ops for relay file mappings.
  60  */
  61 static struct vm_operations_struct relay_file_mmap_ops = {
  62         .nopage = relay_buf_nopage,
  63         .close = relay_file_mmap_close,
  64 };
  65
  66 /**
  67  *      relay_mmap_buf: - mmap channel buffer to process address space
  68  *      @buf: relay channel buffer
  69  *      @vma: vm_area_struct describing memory to be mapped
  70  *
  71  *      Returns 0 if ok, negative on error
  72  *
  73  *      Caller should already have grabbed mmap_sem.
  74  */
  75 int relay_mmap_buf(struct rchan_buf *buf, struct vm_area_struct *vma)
  76 {
  77         unsigned long length = vma->vm_end - vma->vm_start;
  78         struct file *filp = vma->vm_file;
  79
  80         if (!buf)
  81                 return -EBADF;
  82
  83         if (length != (unsigned long)buf->chan->alloc_size)
  84                 return -EINVAL;
  85
  86         vma->vm_ops = &relay_file_mmap_ops;
  87         vma->vm_private_data = buf;
  88         buf->chan->cb->buf_mapped(buf, filp);
  89
  90         return 0;
  91 }
  92
  93 /**
  94  *      relay_alloc_buf - allocate a channel buffer
  95  *      @buf: the buffer struct
  96  *      @size: total size of the buffer
  97  *
  98  *      Returns a pointer to the resulting buffer, NULL if unsuccessful. The
  99  *      passed in size will get page aligned, if it isn't already.
 100  */
 101 static void *relay_alloc_buf(struct rchan_buf *buf, size_t *size)
 102 {
 103         void *mem;
 104         unsigned int i, j, n_pages;
 105
 106         *size = PAGE_ALIGN(*size);
 107         n_pages = *size >> PAGE_SHIFT;
 108
 109         buf->page_array = kcalloc(n_pages, sizeof(struct page *), GFP_KERNEL);
 110         if (!buf->page_array)
 111                 return NULL;
 112
 113         for (i = 0; i < n_pages; i++) {
 114                 buf->page_array[i] = alloc_page(GFP_KERNEL);
 115                 if (unlikely(!buf->page_array[i]))
 116                         goto depopulate;
 117         }
 118         mem = vmap(buf->page_array, n_pages, VM_MAP, PAGE_KERNEL);
 119         if (!mem)
 120                 goto depopulate;
 121
 122         memset(mem, 0, *size);
 123         buf->page_count = n_pages;
 124         return mem;
 125
 126 depopulate:
 127         for (j = 0; j < i; j++)
 128                 __free_page(buf->page_array[j]);
 129         kfree(buf->page_array);
 130         return NULL;
 131 }
 132
 133 /**
 134  *      relay_create_buf - allocate and initialize a channel buffer
 135  *      @alloc_size: size of the buffer to allocate
 136  *      @n_subbufs: number of sub-buffers in the channel
 137  *
 138  *      Returns channel buffer if successful, NULL otherwise
 139  */
 140 struct rchan_buf *relay_create_buf(struct rchan *chan)
 141 {
 142         struct rchan_buf *buf = kcalloc(1, sizeof(struct rchan_buf), GFP_KERNEL);
 143         if (!buf)
 144                 return NULL;
 145
 146         buf->padding = kmalloc(chan->n_subbufs * sizeof(size_t *), GFP_KERNEL);
 147         if (!buf->padding)
 148                 goto free_buf;
 149
 150         buf->start = relay_alloc_buf(buf, &chan->alloc_size);
 151         if (!buf->start)
 152                 goto free_buf;
 153
 154         buf->chan = chan;
 155         kref_get(&buf->chan->kref);
 156         return buf;
 157
 158 free_buf:
 159         kfree(buf->padding);
 160         kfree(buf);
 161         return NULL;
 162 }
 163
 164 /**
 165  *      relay_destroy_channel - free the channel struct
 166  *
 167  *      Should only be called from kref_put().
 168  */
 169 void relay_destroy_channel(struct kref *kref)
 170 {
 171         struct rchan *chan = container_of(kref, struct rchan, kref);
 172         kfree(chan);
 173 }
 174
 175 /**
 176  *      relay_destroy_buf - destroy an rchan_buf struct and associated buffer
 177  *      @buf: the buffer struct
 178  */
 179 void relay_destroy_buf(struct rchan_buf *buf)
 180 {
 181         struct rchan *chan = buf->chan;
 182         unsigned int i;
 183
 184         if (likely(buf->start)) {
 185                 vunmap(buf->start);
 186                 for (i = 0; i < buf->page_count; i++)
 187                         __free_page(buf->page_array[i]);
 188                 kfree(buf->page_array);
 189         }
 190         kfree(buf->padding);
 191         kfree(buf);
 192         kref_put(&chan->kref, relay_destroy_channel);
 193 }
 194
 195 /**
 196  *      relay_remove_buf - remove a channel buffer
 197  *
 198  *      Removes the file from the fileystem, which also frees the
 199  *      rchan_buf_struct and the channel buffer.  Should only be called from
 200  *      kref_put().
 201  */
 202 void relay_remove_buf(struct kref *kref)
 203 {
 204         struct rchan_buf *buf = container_of(kref, struct rchan_buf, kref);
 205         buf->chan->cb->remove_buf_file(buf->dentry);
 206         relay_destroy_buf(buf);
 207 }
 208
 209 /**
 210  *      relay_buf_empty - boolean, is the channel buffer empty?
 211  *      @buf: channel buffer
 212  *
 213  *      Returns 1 if the buffer is empty, 0 otherwise.
 214  */
 215 int relay_buf_empty(struct rchan_buf *buf)
 216 {
 217         return (buf->subbufs_produced - buf->subbufs_consumed) ? 0 : 1;
 218 }
 219 EXPORT_SYMBOL_GPL(relay_buf_empty);
 220
 221 /**
 222  *      relay_buf_full - boolean, is the channel buffer full?
 223  *      @buf: channel buffer
 224  *
 225  *      Returns 1 if the buffer is full, 0 otherwise.
 226  */
 227 int relay_buf_full(struct rchan_buf *buf)
 228 {
 229         size_t ready = buf->subbufs_produced - buf->subbufs_consumed;
 230         return (ready >= buf->chan->n_subbufs) ? 1 : 0;
 231 }
 232 EXPORT_SYMBOL_GPL(relay_buf_full);
 233
 234 /*
 235  * High-level relay kernel API and associated functions.
 236  */
 237
 238 /*
 239  * rchan_callback implementations defining default channel behavior.  Used
 240  * in place of corresponding NULL values in client callback struct.
 241  */
 242
 243 /*
 244  * subbuf_start() default callback.  Does nothing.
 245  */
 246 static int subbuf_start_default_callback (struct rchan_buf *buf,
 247                                           void *subbuf,
 248                                           void *prev_subbuf,
 249                                           size_t prev_padding)
 250 {
 251         if (relay_buf_full(buf))
 252                 return 0;
 253
 254         return 1;
 255 }
 256
 257 /*
 258  * buf_mapped() default callback.  Does nothing.
 259  */
 260 static void buf_mapped_default_callback(struct rchan_buf *buf,
 261                                         struct file *filp)
 262 {
 263 }
 264
 265 /*
 266  * buf_unmapped() default callback.  Does nothing.
 267  */
 268 static void buf_unmapped_default_callback(struct rchan_buf *buf,
 269                                           struct file *filp)
 270 {
 271 }
 272
 273 /*
 274  * create_buf_file_create() default callback.  Does nothing.
 275  */
 276 static struct dentry *create_buf_file_default_callback(const char *filename,
 277                                                        struct dentry *parent,
 278                                                        int mode,
 279                                                        struct rchan_buf *buf,
 280                                                        int *is_global)
 281 {
 282         return NULL;
 283 }
 284
 285 /*
 286  * remove_buf_file() default callback.  Does nothing.
 287  */
 288 static int remove_buf_file_default_callback(struct dentry *dentry)
 289 {
 290         return -EINVAL;
 291 }
 292
 293 /* relay channel default callbacks */
 294 static struct rchan_callbacks default_channel_callbacks = {
 295         .subbuf_start = subbuf_start_default_callback,
 296         .buf_mapped = buf_mapped_default_callback,
 297         .buf_unmapped = buf_unmapped_default_callback,
 298         .create_buf_file = create_buf_file_default_callback,
 299         .remove_buf_file = remove_buf_file_default_callback,
 300 };
 301
 302 /**
 303  *      wakeup_readers - wake up readers waiting on a channel
 304  *      @private: the channel buffer
 305  *
 306  *      This is the work function used to defer reader waking.  The
 307  *      reason waking is deferred is that calling directly from write
 308  *      causes problems if you're writing from say the scheduler.
 309  */
 310 static void wakeup_readers(void *private)
 311 {
 312         struct rchan_buf *buf = private;
 313         wake_up_interruptible(&buf->read_wait);
 314 }
 315
 316 /**
 317  *      __relay_reset - reset a channel buffer
 318  *      @buf: the channel buffer
 319  *      @init: 1 if this is a first-time initialization
 320  *
 321  *      See relay_reset for description of effect.
 322  */
 323 static inline void __relay_reset(struct rchan_buf *buf, unsigned int init)
 324 {
 325         size_t i;
 326
 327         if (init) {
 328                 init_waitqueue_head(&buf->read_wait);
 329                 kref_init(&buf->kref);
 330                 INIT_WORK(&buf->wake_readers, NULL, NULL);
 331         } else {
 332                 cancel_delayed_work(&buf->wake_readers);
 333                 flush_scheduled_work();
 334         }
 335
 336         buf->subbufs_produced = 0;
 337         buf->subbufs_consumed = 0;
 338         buf->bytes_consumed = 0;
 339         buf->finalized = 0;
 340         buf->data = buf->start;
 341         buf->offset = 0;
 342
 343         for (i = 0; i < buf->chan->n_subbufs; i++)
 344                 buf->padding[i] = 0;
 345
 346         buf->chan->cb->subbuf_start(buf, buf->data, NULL, 0);
 347 }
 348
 349 /**
 350  *      relay_reset - reset the channel
 351  *      @chan: the channel
 352  *
 353  *      This has the effect of erasing all data from all channel buffers
 354  *      and restarting the channel in its initial state.  The buffers
 355  *      are not freed, so any mappings are still in effect.
 356  *
 357  *      NOTE: Care should be taken that the channel isn't actually
 358  *      being used by anything when this call is made.
 359  */
 360 void relay_reset(struct rchan *chan)
 361 {
 362         unsigned int i;
 363         struct rchan_buf *prev = NULL;
 364
 365         if (!chan)
 366                 return;
 367
 368         for (i = 0; i < NR_CPUS; i++) {
 369                 if (!chan->buf[i] || chan->buf[i] == prev)
 370                         break;
 371                 __relay_reset(chan->buf[i], 0);
 372                 prev = chan->buf[i];
 373         }
 374 }
 375 EXPORT_SYMBOL_GPL(relay_reset);
 376
 377 /**
 378  *      relay_open_buf - create a new relay channel buffer
 379  *
 380  *      Internal - used by relay_open().
 381  */
 382 static struct rchan_buf *relay_open_buf(struct rchan *chan,
 383                                         const char *filename,
 384                                         struct dentry *parent,
 385                                         int *is_global)
 386 {
 387         struct rchan_buf *buf;
 388         struct dentry *dentry;
 389
 390         if (*is_global)
 391                 return chan->buf[0];
 392
 393         buf = relay_create_buf(chan);
 394         if (!buf)
 395                 return NULL;
 396
 397         /* Create file in fs */
 398         dentry = chan->cb->create_buf_file(filename, parent, S_IRUSR,
 399                                            buf, is_global);
 400         if (!dentry) {
 401                 relay_destroy_buf(buf);
 402                 return NULL;
 403         }
 404
 405         buf->dentry = dentry;
 406         __relay_reset(buf, 1);
 407
 408         return buf;
 409 }
 410
 411 /**
 412  *      relay_close_buf - close a channel buffer
 413  *      @buf: channel buffer
 414  *
 415  *      Marks the buffer finalized and restores the default callbacks.
 416  *      The channel buffer and channel buffer data structure are then freed
 417  *      automatically when the last reference is given up.
 418  */
 419 static inline void relay_close_buf(struct rchan_buf *buf)
 420 {
 421         buf->finalized = 1;
 422         cancel_delayed_work(&buf->wake_readers);
 423         flush_scheduled_work();
 424         kref_put(&buf->kref, relay_remove_buf);
 425 }
 426
 427 static inline void setup_callbacks(struct rchan *chan,
 428                                    struct rchan_callbacks *cb)
 429 {
 430         if (!cb) {
 431                 chan->cb = &default_channel_callbacks;
 432                 return;
 433         }
 434
 435         if (!cb->subbuf_start)
 436                 cb->subbuf_start = subbuf_start_default_callback;
 437         if (!cb->buf_mapped)
 438                 cb->buf_mapped = buf_mapped_default_callback;
 439         if (!cb->buf_unmapped)
 440                 cb->buf_unmapped = buf_unmapped_default_callback;
 441         if (!cb->create_buf_file)
 442                 cb->create_buf_file = create_buf_file_default_callback;
 443         if (!cb->remove_buf_file)
 444                 cb->remove_buf_file = remove_buf_file_default_callback;
 445         chan->cb = cb;
 446 }
 447
 448 /**
 449  *      relay_open - create a new relay channel
 450  *      @base_filename: base name of files to create
 451  *      @parent: dentry of parent directory, NULL for root directory
 452  *      @subbuf_size: size of sub-buffers
 453  *      @n_subbufs: number of sub-buffers
 454  *      @cb: client callback functions
 455  *
 456  *      Returns channel pointer if successful, NULL otherwise.
 457  *
 458  *      Creates a channel buffer for each cpu using the sizes and
 459  *      attributes specified.  The created channel buffer files
 460  *      will be named base_filename0...base_filenameN-1.  File
 461  *      permissions will be S_IRUSR.
 462  */
 463 struct rchan *relay_open(const char *base_filename,
 464                          struct dentry *parent,
 465                          size_t subbuf_size,
 466                          size_t n_subbufs,
 467                          struct rchan_callbacks *cb)
 468 {
 469         unsigned int i;
 470         struct rchan *chan;
 471         char *tmpname;
 472         int is_global = 0;
 473
 474         if (!base_filename)
 475                 return NULL;
 476
 477         if (!(subbuf_size && n_subbufs))
 478                 return NULL;
 479
 480         chan = kcalloc(1, sizeof(struct rchan), GFP_KERNEL);
 481         if (!chan)
 482                 return NULL;
 483
 484         chan->version = RELAYFS_CHANNEL_VERSION;
 485         chan->n_subbufs = n_subbufs;
 486         chan->subbuf_size = subbuf_size;
 487         chan->alloc_size = FIX_SIZE(subbuf_size * n_subbufs);
 488         setup_callbacks(chan, cb);
 489         kref_init(&chan->kref);
 490
 491         tmpname = kmalloc(NAME_MAX + 1, GFP_KERNEL);
 492         if (!tmpname)
 493                 goto free_chan;
 494
 495         for_each_online_cpu(i) {
 496                 sprintf(tmpname, "%s%d", base_filename, i);
 497                 chan->buf[i] = relay_open_buf(chan, tmpname, parent,
 498                                               &is_global);
 499                 if (!chan->buf[i])
 500                         goto free_bufs;
 501
 502                 chan->buf[i]->cpu = i;
 503         }
 504
 505         kfree(tmpname);
 506         return chan;
 507
 508 free_bufs:
 509         for (i = 0; i < NR_CPUS; i++) {
 510                 if (!chan->buf[i])
 511                         break;
 512                 relay_close_buf(chan->buf[i]);
 513                 if (is_global)
 514                         break;
 515         }
 516         kfree(tmpname);
 517
 518 free_chan:
 519         kref_put(&chan->kref, relay_destroy_channel);
 520         return NULL;
 521 }
 522 EXPORT_SYMBOL_GPL(relay_open);
 523
 524 /**
 525  *      relay_switch_subbuf - switch to a new sub-buffer
 526  *      @buf: channel buffer
 527  *      @length: size of current event
 528  *
 529  *      Returns either the length passed in or 0 if full.
 530  *
 531  *      Performs sub-buffer-switch tasks such as invoking callbacks,
 532  *      updating padding counts, waking up readers, etc.
 533  */
 534 size_t relay_switch_subbuf(struct rchan_buf *buf, size_t length)
 535 {
 536         void *old, *new;
 537         size_t old_subbuf, new_subbuf;
 538
 539         if (unlikely(length > buf->chan->subbuf_size))
 540                 goto toobig;
 541
 542         if (buf->offset != buf->chan->subbuf_size + 1) {
 543                 buf->prev_padding = buf->chan->subbuf_size - buf->offset;
 544                 old_subbuf = buf->subbufs_produced % buf->chan->n_subbufs;
 545                 buf->padding[old_subbuf] = buf->prev_padding;
 546                 buf->subbufs_produced++;
 547                 buf->dentry->d_inode->i_size += buf->chan->subbuf_size -
 548                         buf->padding[old_subbuf];
 549                 smp_mb();
 550                 if (waitqueue_active(&buf->read_wait)) {
 551                         PREPARE_WORK(&buf->wake_readers, wakeup_readers, buf);
 552                         schedule_delayed_work(&buf->wake_readers, 1);
 553                 }
 554         }
 555
 556         old = buf->data;
 557         new_subbuf = buf->subbufs_produced % buf->chan->n_subbufs;
 558         new = buf->start + new_subbuf * buf->chan->subbuf_size;
 559         buf->offset = 0;
 560         if (!buf->chan->cb->subbuf_start(buf, new, old, buf->prev_padding)) {
 561                 buf->offset = buf->chan->subbuf_size + 1;
 562                 return 0;
 563         }
 564         buf->data = new;
 565         buf->padding[new_subbuf] = 0;
 566
 567         if (unlikely(length + buf->offset > buf->chan->subbuf_size))
 568                 goto toobig;
 569
 570         return length;
 571
 572 toobig:
 573         buf->chan->last_toobig = length;
 574         return 0;
 575 }
 576 EXPORT_SYMBOL_GPL(relay_switch_subbuf);
 577
 578 /**
 579  *      relay_subbufs_consumed - update the buffer's sub-buffers-consumed count
 580  *      @chan: the channel
 581  *      @cpu: the cpu associated with the channel buffer to update
 582  *      @subbufs_consumed: number of sub-buffers to add to current buf's count
 583  *
 584  *      Adds to the channel buffer's consumed sub-buffer count.
 585  *      subbufs_consumed should be the number of sub-buffers newly consumed,
 586  *      not the total consumed.
 587  *
 588  *      NOTE: kernel clients don't need to call this function if the channel
 589  *      mode is 'overwrite'.
 590  */
 591 void relay_subbufs_consumed(struct rchan *chan,
 592                             unsigned int cpu,
 593                             size_t subbufs_consumed)
 594 {
 595         struct rchan_buf *buf;
 596
 597         if (!chan)
 598                 return;
 599
 600         if (cpu >= NR_CPUS || !chan->buf[cpu])
 601                 return;
 602
 603         buf = chan->buf[cpu];
 604         buf->subbufs_consumed += subbufs_consumed;
 605         if (buf->subbufs_consumed > buf->subbufs_produced)
 606                 buf->subbufs_consumed = buf->subbufs_produced;
 607 }
 608 EXPORT_SYMBOL_GPL(relay_subbufs_consumed);
 609
 610 /**
 611  *      relay_close - close the channel
 612  *      @chan: the channel
 613  *
 614  *      Closes all channel buffers and frees the channel.
 615  */
 616 void relay_close(struct rchan *chan)
 617 {
 618         unsigned int i;
 619         struct rchan_buf *prev = NULL;
 620
 621         if (!chan)
 622                 return;
 623
 624         for (i = 0; i < NR_CPUS; i++) {
 625                 if (!chan->buf[i] || chan->buf[i] == prev)
 626                         break;
 627                 relay_close_buf(chan->buf[i]);
 628                 prev = chan->buf[i];
 629         }
 630
 631         if (chan->last_toobig)
 632                 printk(KERN_WARNING "relay: one or more items not logged "
 633                        "[item size (%Zd) > sub-buffer size (%Zd)]\n",
 634                        chan->last_toobig, chan->subbuf_size);
 635
 636         kref_put(&chan->kref, relay_destroy_channel);
 637 }
 638 EXPORT_SYMBOL_GPL(relay_close);
 639
 640 /**
 641  *      relay_flush - close the channel
 642  *      @chan: the channel
 643  *
 644  *      Flushes all channel buffers i.e. forces buffer switch.
 645  */
 646 void relay_flush(struct rchan *chan)
 647 {
 648         unsigned int i;
 649         struct rchan_buf *prev = NULL;
 650
 651         if (!chan)
 652                 return;
 653
 654         for (i = 0; i < NR_CPUS; i++) {
 655                 if (!chan->buf[i] || chan->buf[i] == prev)
 656                         break;
 657                 relay_switch_subbuf(chan->buf[i], 0);
 658                 prev = chan->buf[i];
 659         }
 660 }
 661 EXPORT_SYMBOL_GPL(relay_flush);
 662
 663 /**
 664  *      relay_file_open - open file op for relay files
 665  *      @inode: the inode
 666  *      @filp: the file
 667  *
 668  *      Increments the channel buffer refcount.
 669  */
 670 static int relay_file_open(struct inode *inode, struct file *filp)
 671 {
 672         struct rchan_buf *buf = inode->u.generic_ip;
 673         kref_get(&buf->kref);
 674         filp->private_data = buf;
 675
 676         return 0;
 677 }
 678
 679 /**
 680  *      relay_file_mmap - mmap file op for relay files
 681  *      @filp: the file
 682  *      @vma: the vma describing what to map
 683  *
 684  *      Calls upon relay_mmap_buf to map the file into user space.
 685  */
 686 static int relay_file_mmap(struct file *filp, struct vm_area_struct *vma)
 687 {
 688         struct rchan_buf *buf = filp->private_data;
 689         return relay_mmap_buf(buf, vma);
 690 }
 691
 692 /**
 693  *      relay_file_poll - poll file op for relay files
 694  *      @filp: the file
 695  *      @wait: poll table
 696  *
 697  *      Poll implemention.
 698  */
 699 static unsigned int relay_file_poll(struct file *filp, poll_table *wait)
 700 {
 701         unsigned int mask = 0;
 702         struct rchan_buf *buf = filp->private_data;
 703
 704         if (buf->finalized)
 705                 return POLLERR;
 706
 707         if (filp->f_mode & FMODE_READ) {
 708                 poll_wait(filp, &buf->read_wait, wait);
 709                 if (!relay_buf_empty(buf))
 710                         mask |= POLLIN | POLLRDNORM;
 711         }
 712
 713         return mask;
 714 }
 715
 716 /**
 717  *      relay_file_release - release file op for relay files
 718  *      @inode: the inode
 719  *      @filp: the file
 720  *
 721  *      Decrements the channel refcount, as the filesystem is
 722  *      no longer using it.
 723  */
 724 static int relay_file_release(struct inode *inode, struct file *filp)
 725 {
 726         struct rchan_buf *buf = filp->private_data;
 727         kref_put(&buf->kref, relay_remove_buf);
 728
 729         return 0;
 730 }
 731
 732 /**
 733  *      relay_file_read_consume - update the consumed count for the buffer
 734  */
 735 static void relay_file_read_consume(struct rchan_buf *buf,
 736                                     size_t read_pos,
 737                                     size_t bytes_consumed)
 738 {
 739         size_t subbuf_size = buf->chan->subbuf_size;
 740         size_t n_subbufs = buf->chan->n_subbufs;
 741         size_t read_subbuf;
 742
 743         if (buf->bytes_consumed + bytes_consumed > subbuf_size) {
 744                 relay_subbufs_consumed(buf->chan, buf->cpu, 1);
 745                 buf->bytes_consumed = 0;
 746         }
 747
 748         buf->bytes_consumed += bytes_consumed;
 749         read_subbuf = read_pos / buf->chan->subbuf_size;
 750         if (buf->bytes_consumed + buf->padding[read_subbuf] == subbuf_size) {
 751                 if ((read_subbuf == buf->subbufs_produced % n_subbufs) &&
 752                     (buf->offset == subbuf_size))
 753                         return;
 754                 relay_subbufs_consumed(buf->chan, buf->cpu, 1);
 755                 buf->bytes_consumed = 0;
 756         }
 757 }
 758
 759 /**
 760  *      relay_file_read_avail - boolean, are there unconsumed bytes available?
 761  */
 762 static int relay_file_read_avail(struct rchan_buf *buf, size_t read_pos)
 763 {
 764         size_t subbuf_size = buf->chan->subbuf_size;
 765         size_t n_subbufs = buf->chan->n_subbufs;
 766         size_t produced = buf->subbufs_produced;
 767         size_t consumed = buf->subbufs_consumed;
 768
 769         relay_file_read_consume(buf, read_pos, 0);
 770
 771         if (unlikely(buf->offset > subbuf_size)) {
 772                 if (produced == consumed)
 773                         return 0;
 774                 return 1;
 775         }
 776
 777         if (unlikely(produced - consumed >= n_subbufs)) {
 778                 consumed = (produced / n_subbufs) * n_subbufs;
 779                 buf->subbufs_consumed = consumed;
 780         }
 781
 782         produced = (produced % n_subbufs) * subbuf_size + buf->offset;
 783         consumed = (consumed % n_subbufs) * subbuf_size + buf->bytes_consumed;
 784
 785         if (consumed > produced)
 786                 produced += n_subbufs * subbuf_size;
 787
 788         if (consumed == produced)
 789                 return 0;
 790
 791         return 1;
 792 }
 793
 794 /**
 795  *      relay_file_read_subbuf_avail - return bytes available in sub-buffer
 796  */
 797 static size_t relay_file_read_subbuf_avail(size_t read_pos,
 798                                            struct rchan_buf *buf)
 799 {
 800         size_t padding, avail = 0;
 801         size_t read_subbuf, read_offset, write_subbuf, write_offset;
 802         size_t subbuf_size = buf->chan->subbuf_size;
 803
 804         write_subbuf = (buf->data - buf->start) / subbuf_size;
 805         write_offset = buf->offset > subbuf_size ? subbuf_size : buf->offset;
 806         read_subbuf = read_pos / subbuf_size;
 807         read_offset = read_pos % subbuf_size;
 808         padding = buf->padding[read_subbuf];
 809
 810         if (read_subbuf == write_subbuf) {
 811                 if (read_offset + padding < write_offset)
 812                         avail = write_offset - (read_offset + padding);
 813         } else
 814                 avail = (subbuf_size - padding) - read_offset;
 815
 816         return avail;
 817 }
 818
 819 /**
 820  *      relay_file_read_start_pos - find the first available byte to read
 821  *
 822  *      If the read_pos is in the middle of padding, return the
 823  *      position of the first actually available byte, otherwise
 824  *      return the original value.
 825  */
 826 static size_t relay_file_read_start_pos(size_t read_pos,
 827                                         struct rchan_buf *buf)
 828 {
 829         size_t read_subbuf, padding, padding_start, padding_end;
 830         size_t subbuf_size = buf->chan->subbuf_size;
 831         size_t n_subbufs = buf->chan->n_subbufs;
 832
 833         read_subbuf = read_pos / subbuf_size;
 834         padding = buf->padding[read_subbuf];
 835         padding_start = (read_subbuf + 1) * subbuf_size - padding;
 836         padding_end = (read_subbuf + 1) * subbuf_size;
 837         if (read_pos >= padding_start && read_pos < padding_end) {
 838                 read_subbuf = (read_subbuf + 1) % n_subbufs;
 839                 read_pos = read_subbuf * subbuf_size;
 840         }
 841
 842         return read_pos;
 843 }
 844
 845 /**
 846  *      relay_file_read_end_pos - return the new read position
 847  */
 848 static size_t relay_file_read_end_pos(struct rchan_buf *buf,
 849                                       size_t read_pos,
 850                                       size_t count)
 851 {
 852         size_t read_subbuf, padding, end_pos;
 853         size_t subbuf_size = buf->chan->subbuf_size;
 854         size_t n_subbufs = buf->chan->n_subbufs;
 855
 856         read_subbuf = read_pos / subbuf_size;
 857         padding = buf->padding[read_subbuf];
 858         if (read_pos % subbuf_size + count + padding == subbuf_size)
 859                 end_pos = (read_subbuf + 1) * subbuf_size;
 860         else
 861                 end_pos = read_pos + count;
 862         if (end_pos >= subbuf_size * n_subbufs)
 863                 end_pos = 0;
 864
 865         return end_pos;
 866 }
 867
 868 /**
 869  *      subbuf_read_actor - read up to one subbuf's worth of data
 870  */
 871 static int subbuf_read_actor(size_t read_start,
 872                              struct rchan_buf *buf,
 873                              size_t avail,
 874                              read_descriptor_t *desc,
 875                              read_actor_t actor)
 876 {
 877         void *from;
 878         int ret = 0;
 879
 880         from = buf->start + read_start;
 881         ret = avail;
 882         if (copy_to_user(desc->arg.data, from, avail)) {
 883                 desc->error = -EFAULT;
 884                 ret = 0;
 885         }
 886         desc->arg.data += ret;
 887         desc->written += ret;
 888         desc->count -= ret;
 889
 890         return ret;
 891 }
 892
 893 /**
 894  *      subbuf_send_actor - send up to one subbuf's worth of data
 895  */
 896 static int subbuf_send_actor(size_t read_start,
 897                              struct rchan_buf *buf,
 898                              size_t avail,
 899                              read_descriptor_t *desc,
 900                              read_actor_t actor)
 901 {
 902         unsigned long pidx, poff;
 903         unsigned int subbuf_pages;
 904         int ret = 0;
 905
 906         subbuf_pages = buf->chan->alloc_size >> PAGE_SHIFT;
 907         pidx = (read_start / PAGE_SIZE) % subbuf_pages;
 908         poff = read_start & ~PAGE_MASK;
 909         while (avail) {
 910                 struct page *p = buf->page_array[pidx];
 911                 unsigned int len;
 912
 913                 len = PAGE_SIZE - poff;
 914                 if (len > avail)
 915                         len = avail;
 916
 917                 len = actor(desc, p, poff, len);
 918                 if (desc->error)
 919                         break;
 920
 921                 avail -= len;
 922                 ret += len;
 923                 poff = 0;
 924                 pidx = (pidx + 1) % subbuf_pages;
 925         }
 926
 927         return ret;
 928 }
 929
 930 typedef int (*subbuf_actor_t) (size_t read_start,
 931                                struct rchan_buf *buf,
 932                                size_t avail,
 933                                read_descriptor_t *desc,
 934                                read_actor_t actor);
 935
 936 /**
 937  *      relay_file_read_subbufs - read count bytes, bridging subbuf boundaries
 938  */
 939 static inline ssize_t relay_file_read_subbufs(struct file *filp,
 940                                               loff_t *ppos,
 941                                               size_t count,
 942                                               subbuf_actor_t subbuf_actor,
 943                                               read_actor_t actor,
 944                                               void *target)
 945 {
 946         struct rchan_buf *buf = filp->private_data;
 947         size_t read_start, avail;
 948         read_descriptor_t desc;
 949         int ret;
 950
 951         if (!count)
 952                 return 0;
 953
 954         desc.written = 0;
 955         desc.count = count;
 956         desc.arg.data = target;
 957         desc.error = 0;
 958
 959         mutex_lock(&filp->f_dentry->d_inode->i_mutex);
 960         do {
 961                 if (!relay_file_read_avail(buf, *ppos))
 962                         break;
 963
 964                 read_start = relay_file_read_start_pos(*ppos, buf);
 965                 avail = relay_file_read_subbuf_avail(read_start, buf);
 966                 if (!avail)
 967                         break;
 968
 969                 avail = min(desc.count, avail);
 970                 ret = subbuf_actor(read_start, buf, avail, &desc, actor);
 971                 if (desc.error < 0)
 972                         break;
 973
 974                 if (ret) {
 975                         relay_file_read_consume(buf, read_start, ret);
 976                         *ppos = relay_file_read_end_pos(buf, read_start, ret);
 977                 }
 978         } while (desc.count && ret);
 979         mutex_unlock(&filp->f_dentry->d_inode->i_mutex);
 980
 981         return desc.written;
 982 }
 983
 984 static ssize_t relay_file_read(struct file *filp,
 985                                char __user *buffer,
 986                                size_t count,
 987                                loff_t *ppos)
 988 {
 989         return relay_file_read_subbufs(filp, ppos, count, subbuf_read_actor,
 990                                        NULL, buffer);
 991 }
 992
 993 static ssize_t relay_file_sendfile(struct file *filp,
 994                                    loff_t *ppos,
 995                                    size_t count,
 996                                    read_actor_t actor,
 997                                    void *target)
 998 {
 999         return relay_file_read_subbufs(filp, ppos, count, subbuf_send_actor,
1000                                        actor, target);
1001 }
1002
1003 struct file_operations relay_file_operations = {
1004         .open           = relay_file_open,
1005         .poll           = relay_file_poll,
1006         .mmap           = relay_file_mmap,
1007         .read           = relay_file_read,
1008         .llseek         = no_llseek,
1009         .release        = relay_file_release,
1010         .sendfile       = relay_file_sendfile,
1011 };
1012 EXPORT_SYMBOL_GPL(relay_file_operations);