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  *      @chan: the relay channel
 136  *
 137  *      Returns channel buffer if successful, %NULL otherwise.
 138  */
 139 struct rchan_buf *relay_create_buf(struct rchan *chan)
 140 {
 141         struct rchan_buf *buf = kcalloc(1, sizeof(struct rchan_buf), GFP_KERNEL);
 142         if (!buf)
 143                 return NULL;
 144
 145         buf->padding = kmalloc(chan->n_subbufs * sizeof(size_t *), GFP_KERNEL);
 146         if (!buf->padding)
 147                 goto free_buf;
 148
 149         buf->start = relay_alloc_buf(buf, &chan->alloc_size);
 150         if (!buf->start)
 151                 goto free_buf;
 152
 153         buf->chan = chan;
 154         kref_get(&buf->chan->kref);
 155         return buf;
 156
 157 free_buf:
 158         kfree(buf->padding);
 159         kfree(buf);
 160         return NULL;
 161 }
 162
 163 /**
 164  *      relay_destroy_channel - free the channel struct
 165  *      @kref: target kernel reference that contains the relay channel
 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  *      @kref: target kernel reference that contains the relay buffer
 198  *
 199  *      Removes the file from the fileystem, which also frees the
 200  *      rchan_buf_struct and the channel buffer.  Should only be called from
 201  *      kref_put().
 202  */
 203 void relay_remove_buf(struct kref *kref)
 204 {
 205         struct rchan_buf *buf = container_of(kref, struct rchan_buf, kref);
 206         buf->chan->cb->remove_buf_file(buf->dentry);
 207         relay_destroy_buf(buf);
 208 }
 209
 210 /**
 211  *      relay_buf_empty - boolean, is the channel buffer empty?
 212  *      @buf: channel buffer
 213  *
 214  *      Returns 1 if the buffer is empty, 0 otherwise.
 215  */
 216 int relay_buf_empty(struct rchan_buf *buf)
 217 {
 218         return (buf->subbufs_produced - buf->subbufs_consumed) ? 0 : 1;
 219 }
 220 EXPORT_SYMBOL_GPL(relay_buf_empty);
 221
 222 /**
 223  *      relay_buf_full - boolean, is the channel buffer full?
 224  *      @buf: channel buffer
 225  *
 226  *      Returns 1 if the buffer is full, 0 otherwise.
 227  */
 228 int relay_buf_full(struct rchan_buf *buf)
 229 {
 230         size_t ready = buf->subbufs_produced - buf->subbufs_consumed;
 231         return (ready >= buf->chan->n_subbufs) ? 1 : 0;
 232 }
 233 EXPORT_SYMBOL_GPL(relay_buf_full);
 234
 235 /*
 236  * High-level relay kernel API and associated functions.
 237  */
 238
 239 /*
 240  * rchan_callback implementations defining default channel behavior.  Used
 241  * in place of corresponding NULL values in client callback struct.
 242  */
 243
 244 /*
 245  * subbuf_start() default callback.  Does nothing.
 246  */
 247 static int subbuf_start_default_callback (struct rchan_buf *buf,
 248                                           void *subbuf,
 249                                           void *prev_subbuf,
 250                                           size_t prev_padding)
 251 {
 252         if (relay_buf_full(buf))
 253                 return 0;
 254
 255         return 1;
 256 }
 257
 258 /*
 259  * buf_mapped() default callback.  Does nothing.
 260  */
 261 static void buf_mapped_default_callback(struct rchan_buf *buf,
 262                                         struct file *filp)
 263 {
 264 }
 265
 266 /*
 267  * buf_unmapped() default callback.  Does nothing.
 268  */
 269 static void buf_unmapped_default_callback(struct rchan_buf *buf,
 270                                           struct file *filp)
 271 {
 272 }
 273
 274 /*
 275  * create_buf_file_create() default callback.  Does nothing.
 276  */
 277 static struct dentry *create_buf_file_default_callback(const char *filename,
 278                                                        struct dentry *parent,
 279                                                        int mode,
 280                                                        struct rchan_buf *buf,
 281                                                        int *is_global)
 282 {
 283         return NULL;
 284 }
 285
 286 /*
 287  * remove_buf_file() default callback.  Does nothing.
 288  */
 289 static int remove_buf_file_default_callback(struct dentry *dentry)
 290 {
 291         return -EINVAL;
 292 }
 293
 294 /* relay channel default callbacks */
 295 static struct rchan_callbacks default_channel_callbacks = {
 296         .subbuf_start = subbuf_start_default_callback,
 297         .buf_mapped = buf_mapped_default_callback,
 298         .buf_unmapped = buf_unmapped_default_callback,
 299         .create_buf_file = create_buf_file_default_callback,
 300         .remove_buf_file = remove_buf_file_default_callback,
 301 };
 302
 303 /**
 304  *      wakeup_readers - wake up readers waiting on a channel
 305  *      @private: the channel buffer
 306  *
 307  *      This is the work function used to defer reader waking.  The
 308  *      reason waking is deferred is that calling directly from write
 309  *      causes problems if you're writing from say the scheduler.
 310  */
 311 static void wakeup_readers(void *private)
 312 {
 313         struct rchan_buf *buf = private;
 314         wake_up_interruptible(&buf->read_wait);
 315 }
 316
 317 /**
 318  *      __relay_reset - reset a channel buffer
 319  *      @buf: the channel buffer
 320  *      @init: 1 if this is a first-time initialization
 321  *
 322  *      See relay_reset for description of effect.
 323  */
 324 static inline void __relay_reset(struct rchan_buf *buf, unsigned int init)
 325 {
 326         size_t i;
 327
 328         if (init) {
 329                 init_waitqueue_head(&buf->read_wait);
 330                 kref_init(&buf->kref);
 331                 INIT_WORK(&buf->wake_readers, NULL, NULL);
 332         } else {
 333                 cancel_delayed_work(&buf->wake_readers);
 334                 flush_scheduled_work();
 335         }
 336
 337         buf->subbufs_produced = 0;
 338         buf->subbufs_consumed = 0;
 339         buf->bytes_consumed = 0;
 340         buf->finalized = 0;
 341         buf->data = buf->start;
 342         buf->offset = 0;
 343
 344         for (i = 0; i < buf->chan->n_subbufs; i++)
 345                 buf->padding[i] = 0;
 346
 347         buf->chan->cb->subbuf_start(buf, buf->data, NULL, 0);
 348 }
 349
 350 /**
 351  *      relay_reset - reset the channel
 352  *      @chan: the channel
 353  *
 354  *      This has the effect of erasing all data from all channel buffers
 355  *      and restarting the channel in its initial state.  The buffers
 356  *      are not freed, so any mappings are still in effect.
 357  *
 358  *      NOTE: Care should be taken that the channel isn't actually
 359  *      being used by anything when this call is made.
 360  */
 361 void relay_reset(struct rchan *chan)
 362 {
 363         unsigned int i;
 364         struct rchan_buf *prev = NULL;
 365
 366         if (!chan)
 367                 return;
 368
 369         for (i = 0; i < NR_CPUS; i++) {
 370                 if (!chan->buf[i] || chan->buf[i] == prev)
 371                         break;
 372                 __relay_reset(chan->buf[i], 0);
 373                 prev = chan->buf[i];
 374         }
 375 }
 376 EXPORT_SYMBOL_GPL(relay_reset);
 377
 378 /*
 379  *      relay_open_buf - create a new relay channel buffer
 380  *
 381  *      Internal - used by relay_open().
 382  */
 383 static struct rchan_buf *relay_open_buf(struct rchan *chan,
 384                                         const char *filename,
 385                                         struct dentry *parent,
 386                                         int *is_global)
 387 {
 388         struct rchan_buf *buf;
 389         struct dentry *dentry;
 390
 391         if (*is_global)
 392                 return chan->buf[0];
 393
 394         buf = relay_create_buf(chan);
 395         if (!buf)
 396                 return NULL;
 397
 398         /* Create file in fs */
 399         dentry = chan->cb->create_buf_file(filename, parent, S_IRUSR,
 400                                            buf, is_global);
 401         if (!dentry) {
 402                 relay_destroy_buf(buf);
 403                 return NULL;
 404         }
 405
 406         buf->dentry = dentry;
 407         __relay_reset(buf, 1);
 408
 409         return buf;
 410 }
 411
 412 /**
 413  *      relay_close_buf - close a channel buffer
 414  *      @buf: channel buffer
 415  *
 416  *      Marks the buffer finalized and restores the default callbacks.
 417  *      The channel buffer and channel buffer data structure are then freed
 418  *      automatically when the last reference is given up.
 419  */
 420 static inline void relay_close_buf(struct rchan_buf *buf)
 421 {
 422         buf->finalized = 1;
 423         cancel_delayed_work(&buf->wake_readers);
 424         flush_scheduled_work();
 425         kref_put(&buf->kref, relay_remove_buf);
 426 }
 427
 428 static inline void setup_callbacks(struct rchan *chan,
 429                                    struct rchan_callbacks *cb)
 430 {
 431         if (!cb) {
 432                 chan->cb = &default_channel_callbacks;
 433                 return;
 434         }
 435
 436         if (!cb->subbuf_start)
 437                 cb->subbuf_start = subbuf_start_default_callback;
 438         if (!cb->buf_mapped)
 439                 cb->buf_mapped = buf_mapped_default_callback;
 440         if (!cb->buf_unmapped)
 441                 cb->buf_unmapped = buf_unmapped_default_callback;
 442         if (!cb->create_buf_file)
 443                 cb->create_buf_file = create_buf_file_default_callback;
 444         if (!cb->remove_buf_file)
 445                 cb->remove_buf_file = remove_buf_file_default_callback;
 446         chan->cb = cb;
 447 }
 448
 449 /**
 450  *      relay_open - create a new relay channel
 451  *      @base_filename: base name of files to create
 452  *      @parent: dentry of parent directory, %NULL for root directory
 453  *      @subbuf_size: size of sub-buffers
 454  *      @n_subbufs: number of sub-buffers
 455  *      @cb: client callback functions
 456  *
 457  *      Returns channel pointer if successful, %NULL otherwise.
 458  *
 459  *      Creates a channel buffer for each cpu using the sizes and
 460  *      attributes specified.  The created channel buffer files
 461  *      will be named base_filename0...base_filenameN-1.  File
 462  *      permissions will be S_IRUSR.
 463  */
 464 struct rchan *relay_open(const char *base_filename,
 465                          struct dentry *parent,
 466                          size_t subbuf_size,
 467                          size_t n_subbufs,
 468                          struct rchan_callbacks *cb)
 469 {
 470         unsigned int i;
 471         struct rchan *chan;
 472         char *tmpname;
 473         int is_global = 0;
 474
 475         if (!base_filename)
 476                 return NULL;
 477
 478         if (!(subbuf_size && n_subbufs))
 479                 return NULL;
 480
 481         chan = kcalloc(1, sizeof(struct rchan), GFP_KERNEL);
 482         if (!chan)
 483                 return NULL;
 484
 485         chan->version = RELAYFS_CHANNEL_VERSION;
 486         chan->n_subbufs = n_subbufs;
 487         chan->subbuf_size = subbuf_size;
 488         chan->alloc_size = FIX_SIZE(subbuf_size * n_subbufs);
 489         setup_callbacks(chan, cb);
 490         kref_init(&chan->kref);
 491
 492         tmpname = kmalloc(NAME_MAX + 1, GFP_KERNEL);
 493         if (!tmpname)
 494                 goto free_chan;
 495
 496         for_each_online_cpu(i) {
 497                 sprintf(tmpname, "%s%d", base_filename, i);
 498                 chan->buf[i] = relay_open_buf(chan, tmpname, parent,
 499                                               &is_global);
 500                 if (!chan->buf[i])
 501                         goto free_bufs;
 502
 503                 chan->buf[i]->cpu = i;
 504         }
 505
 506         kfree(tmpname);
 507         return chan;
 508
 509 free_bufs:
 510         for (i = 0; i < NR_CPUS; i++) {
 511                 if (!chan->buf[i])
 512                         break;
 513                 relay_close_buf(chan->buf[i]);
 514                 if (is_global)
 515                         break;
 516         }
 517         kfree(tmpname);
 518
 519 free_chan:
 520         kref_put(&chan->kref, relay_destroy_channel);
 521         return NULL;
 522 }
 523 EXPORT_SYMBOL_GPL(relay_open);
 524
 525 /**
 526  *      relay_switch_subbuf - switch to a new sub-buffer
 527  *      @buf: channel buffer
 528  *      @length: size of current event
 529  *
 530  *      Returns either the length passed in or 0 if full.
 531  *
 532  *      Performs sub-buffer-switch tasks such as invoking callbacks,
 533  *      updating padding counts, waking up readers, etc.
 534  */
 535 size_t relay_switch_subbuf(struct rchan_buf *buf, size_t length)
 536 {
 537         void *old, *new;
 538         size_t old_subbuf, new_subbuf;
 539
 540         if (unlikely(length > buf->chan->subbuf_size))
 541                 goto toobig;
 542
 543         if (buf->offset != buf->chan->subbuf_size + 1) {
 544                 buf->prev_padding = buf->chan->subbuf_size - buf->offset;
 545                 old_subbuf = buf->subbufs_produced % buf->chan->n_subbufs;
 546                 buf->padding[old_subbuf] = buf->prev_padding;
 547                 buf->subbufs_produced++;
 548                 buf->dentry->d_inode->i_size += buf->chan->subbuf_size -
 549                         buf->padding[old_subbuf];
 550                 smp_mb();
 551                 if (waitqueue_active(&buf->read_wait)) {
 552                         PREPARE_WORK(&buf->wake_readers, wakeup_readers, buf);
 553                         schedule_delayed_work(&buf->wake_readers, 1);
 554                 }
 555         }
 556
 557         old = buf->data;
 558         new_subbuf = buf->subbufs_produced % buf->chan->n_subbufs;
 559         new = buf->start + new_subbuf * buf->chan->subbuf_size;
 560         buf->offset = 0;
 561         if (!buf->chan->cb->subbuf_start(buf, new, old, buf->prev_padding)) {
 562                 buf->offset = buf->chan->subbuf_size + 1;
 563                 return 0;
 564         }
 565         buf->data = new;
 566         buf->padding[new_subbuf] = 0;
 567
 568         if (unlikely(length + buf->offset > buf->chan->subbuf_size))
 569                 goto toobig;
 570
 571         return length;
 572
 573 toobig:
 574         buf->chan->last_toobig = length;
 575         return 0;
 576 }
 577 EXPORT_SYMBOL_GPL(relay_switch_subbuf);
 578
 579 /**
 580  *      relay_subbufs_consumed - update the buffer's sub-buffers-consumed count
 581  *      @chan: the channel
 582  *      @cpu: the cpu associated with the channel buffer to update
 583  *      @subbufs_consumed: number of sub-buffers to add to current buf's count
 584  *
 585  *      Adds to the channel buffer's consumed sub-buffer count.
 586  *      subbufs_consumed should be the number of sub-buffers newly consumed,
 587  *      not the total consumed.
 588  *
 589  *      NOTE: Kernel clients don't need to call this function if the channel
 590  *      mode is 'overwrite'.
 591  */
 592 void relay_subbufs_consumed(struct rchan *chan,
 593                             unsigned int cpu,
 594                             size_t subbufs_consumed)
 595 {
 596         struct rchan_buf *buf;
 597
 598         if (!chan)
 599                 return;
 600
 601         if (cpu >= NR_CPUS || !chan->buf[cpu])
 602                 return;
 603
 604         buf = chan->buf[cpu];
 605         buf->subbufs_consumed += subbufs_consumed;
 606         if (buf->subbufs_consumed > buf->subbufs_produced)
 607                 buf->subbufs_consumed = buf->subbufs_produced;
 608 }
 609 EXPORT_SYMBOL_GPL(relay_subbufs_consumed);
 610
 611 /**
 612  *      relay_close - close the channel
 613  *      @chan: the channel
 614  *
 615  *      Closes all channel buffers and frees the channel.
 616  */
 617 void relay_close(struct rchan *chan)
 618 {
 619         unsigned int i;
 620         struct rchan_buf *prev = NULL;
 621
 622         if (!chan)
 623                 return;
 624
 625         for (i = 0; i < NR_CPUS; i++) {
 626                 if (!chan->buf[i] || chan->buf[i] == prev)
 627                         break;
 628                 relay_close_buf(chan->buf[i]);
 629                 prev = chan->buf[i];
 630         }
 631
 632         if (chan->last_toobig)
 633                 printk(KERN_WARNING "relay: one or more items not logged "
 634                        "[item size (%Zd) > sub-buffer size (%Zd)]\n",
 635                        chan->last_toobig, chan->subbuf_size);
 636
 637         kref_put(&chan->kref, relay_destroy_channel);
 638 }
 639 EXPORT_SYMBOL_GPL(relay_close);
 640
 641 /**
 642  *      relay_flush - close the channel
 643  *      @chan: the channel
 644  *
 645  *      Flushes all channel buffers, i.e. forces buffer switch.
 646  */
 647 void relay_flush(struct rchan *chan)
 648 {
 649         unsigned int i;
 650         struct rchan_buf *prev = NULL;
 651
 652         if (!chan)
 653                 return;
 654
 655         for (i = 0; i < NR_CPUS; i++) {
 656                 if (!chan->buf[i] || chan->buf[i] == prev)
 657                         break;
 658                 relay_switch_subbuf(chan->buf[i], 0);
 659                 prev = chan->buf[i];
 660         }
 661 }
 662 EXPORT_SYMBOL_GPL(relay_flush);
 663
 664 /**
 665  *      relay_file_open - open file op for relay files
 666  *      @inode: the inode
 667  *      @filp: the file
 668  *
 669  *      Increments the channel buffer refcount.
 670  */
 671 static int relay_file_open(struct inode *inode, struct file *filp)
 672 {
 673         struct rchan_buf *buf = inode->i_private;
 674         kref_get(&buf->kref);
 675         filp->private_data = buf;
 676
 677         return 0;
 678 }
 679
 680 /**
 681  *      relay_file_mmap - mmap file op for relay files
 682  *      @filp: the file
 683  *      @vma: the vma describing what to map
 684  *
 685  *      Calls upon relay_mmap_buf to map the file into user space.
 686  */
 687 static int relay_file_mmap(struct file *filp, struct vm_area_struct *vma)
 688 {
 689         struct rchan_buf *buf = filp->private_data;
 690         return relay_mmap_buf(buf, vma);
 691 }
 692
 693 /**
 694  *      relay_file_poll - poll file op for relay files
 695  *      @filp: the file
 696  *      @wait: poll table
 697  *
 698  *      Poll implemention.
 699  */
 700 static unsigned int relay_file_poll(struct file *filp, poll_table *wait)
 701 {
 702         unsigned int mask = 0;
 703         struct rchan_buf *buf = filp->private_data;
 704
 705         if (buf->finalized)
 706                 return POLLERR;
 707
 708         if (filp->f_mode & FMODE_READ) {
 709                 poll_wait(filp, &buf->read_wait, wait);
 710                 if (!relay_buf_empty(buf))
 711                         mask |= POLLIN | POLLRDNORM;
 712         }
 713
 714         return mask;
 715 }
 716
 717 /**
 718  *      relay_file_release - release file op for relay files
 719  *      @inode: the inode
 720  *      @filp: the file
 721  *
 722  *      Decrements the channel refcount, as the filesystem is
 723  *      no longer using it.
 724  */
 725 static int relay_file_release(struct inode *inode, struct file *filp)
 726 {
 727         struct rchan_buf *buf = filp->private_data;
 728         kref_put(&buf->kref, relay_remove_buf);
 729
 730         return 0;
 731 }
 732
 733 /*
 734  *      relay_file_read_consume - update the consumed count for the buffer
 735  */
 736 static void relay_file_read_consume(struct rchan_buf *buf,
 737                                     size_t read_pos,
 738                                     size_t bytes_consumed)
 739 {
 740         size_t subbuf_size = buf->chan->subbuf_size;
 741         size_t n_subbufs = buf->chan->n_subbufs;
 742         size_t read_subbuf;
 743
 744         if (buf->bytes_consumed + bytes_consumed > subbuf_size) {
 745                 relay_subbufs_consumed(buf->chan, buf->cpu, 1);
 746                 buf->bytes_consumed = 0;
 747         }
 748
 749         buf->bytes_consumed += bytes_consumed;
 750         read_subbuf = read_pos / buf->chan->subbuf_size;
 751         if (buf->bytes_consumed + buf->padding[read_subbuf] == subbuf_size) {
 752                 if ((read_subbuf == buf->subbufs_produced % n_subbufs) &&
 753                     (buf->offset == subbuf_size))
 754                         return;
 755                 relay_subbufs_consumed(buf->chan, buf->cpu, 1);
 756                 buf->bytes_consumed = 0;
 757         }
 758 }
 759
 760 /*
 761  *      relay_file_read_avail - boolean, are there unconsumed bytes available?
 762  */
 763 static int relay_file_read_avail(struct rchan_buf *buf, size_t read_pos)
 764 {
 765         size_t subbuf_size = buf->chan->subbuf_size;
 766         size_t n_subbufs = buf->chan->n_subbufs;
 767         size_t produced = buf->subbufs_produced;
 768         size_t consumed = buf->subbufs_consumed;
 769
 770         relay_file_read_consume(buf, read_pos, 0);
 771
 772         if (unlikely(buf->offset > subbuf_size)) {
 773                 if (produced == consumed)
 774                         return 0;
 775                 return 1;
 776         }
 777
 778         if (unlikely(produced - consumed >= n_subbufs)) {
 779                 consumed = (produced / n_subbufs) * n_subbufs;
 780                 buf->subbufs_consumed = consumed;
 781         }
 782
 783         produced = (produced % n_subbufs) * subbuf_size + buf->offset;
 784         consumed = (consumed % n_subbufs) * subbuf_size + buf->bytes_consumed;
 785
 786         if (consumed > produced)
 787                 produced += n_subbufs * subbuf_size;
 788
 789         if (consumed == produced)
 790                 return 0;
 791
 792         return 1;
 793 }
 794
 795 /**
 796  *      relay_file_read_subbuf_avail - return bytes available in sub-buffer
 797  *      @read_pos: file read position
 798  *      @buf: relay channel buffer
 799  */
 800 static size_t relay_file_read_subbuf_avail(size_t read_pos,
 801                                            struct rchan_buf *buf)
 802 {
 803         size_t padding, avail = 0;
 804         size_t read_subbuf, read_offset, write_subbuf, write_offset;
 805         size_t subbuf_size = buf->chan->subbuf_size;
 806
 807         write_subbuf = (buf->data - buf->start) / subbuf_size;
 808         write_offset = buf->offset > subbuf_size ? subbuf_size : buf->offset;
 809         read_subbuf = read_pos / subbuf_size;
 810         read_offset = read_pos % subbuf_size;
 811         padding = buf->padding[read_subbuf];
 812
 813         if (read_subbuf == write_subbuf) {
 814                 if (read_offset + padding < write_offset)
 815                         avail = write_offset - (read_offset + padding);
 816         } else
 817                 avail = (subbuf_size - padding) - read_offset;
 818
 819         return avail;
 820 }
 821
 822 /**
 823  *      relay_file_read_start_pos - find the first available byte to read
 824  *      @read_pos: file read position
 825  *      @buf: relay channel buffer
 826  *
 827  *      If the read_pos is in the middle of padding, return the
 828  *      position of the first actually available byte, otherwise
 829  *      return the original value.
 830  */
 831 static size_t relay_file_read_start_pos(size_t read_pos,
 832                                         struct rchan_buf *buf)
 833 {
 834         size_t read_subbuf, padding, padding_start, padding_end;
 835         size_t subbuf_size = buf->chan->subbuf_size;
 836         size_t n_subbufs = buf->chan->n_subbufs;
 837
 838         read_subbuf = read_pos / subbuf_size;
 839         padding = buf->padding[read_subbuf];
 840         padding_start = (read_subbuf + 1) * subbuf_size - padding;
 841         padding_end = (read_subbuf + 1) * subbuf_size;
 842         if (read_pos >= padding_start && read_pos < padding_end) {
 843                 read_subbuf = (read_subbuf + 1) % n_subbufs;
 844                 read_pos = read_subbuf * subbuf_size;
 845         }
 846
 847         return read_pos;
 848 }
 849
 850 /**
 851  *      relay_file_read_end_pos - return the new read position
 852  *      @read_pos: file read position
 853  *      @buf: relay channel buffer
 854  *      @count: number of bytes to be read
 855  */
 856 static size_t relay_file_read_end_pos(struct rchan_buf *buf,
 857                                       size_t read_pos,
 858                                       size_t count)
 859 {
 860         size_t read_subbuf, padding, end_pos;
 861         size_t subbuf_size = buf->chan->subbuf_size;
 862         size_t n_subbufs = buf->chan->n_subbufs;
 863
 864         read_subbuf = read_pos / subbuf_size;
 865         padding = buf->padding[read_subbuf];
 866         if (read_pos % subbuf_size + count + padding == subbuf_size)
 867                 end_pos = (read_subbuf + 1) * subbuf_size;
 868         else
 869                 end_pos = read_pos + count;
 870         if (end_pos >= subbuf_size * n_subbufs)
 871                 end_pos = 0;
 872
 873         return end_pos;
 874 }
 875
 876 /*
 877  *      subbuf_read_actor - read up to one subbuf's worth of data
 878  */
 879 static int subbuf_read_actor(size_t read_start,
 880                              struct rchan_buf *buf,
 881                              size_t avail,
 882                              read_descriptor_t *desc,
 883                              read_actor_t actor)
 884 {
 885         void *from;
 886         int ret = 0;
 887
 888         from = buf->start + read_start;
 889         ret = avail;
 890         if (copy_to_user(desc->arg.data, from, avail)) {
 891                 desc->error = -EFAULT;
 892                 ret = 0;
 893         }
 894         desc->arg.data += ret;
 895         desc->written += ret;
 896         desc->count -= ret;
 897
 898         return ret;
 899 }
 900
 901 /*
 902  *      subbuf_send_actor - send up to one subbuf's worth of data
 903  */
 904 static int subbuf_send_actor(size_t read_start,
 905                              struct rchan_buf *buf,
 906                              size_t avail,
 907                              read_descriptor_t *desc,
 908                              read_actor_t actor)
 909 {
 910         unsigned long pidx, poff;
 911         unsigned int subbuf_pages;
 912         int ret = 0;
 913
 914         subbuf_pages = buf->chan->alloc_size >> PAGE_SHIFT;
 915         pidx = (read_start / PAGE_SIZE) % subbuf_pages;
 916         poff = read_start & ~PAGE_MASK;
 917         while (avail) {
 918                 struct page *p = buf->page_array[pidx];
 919                 unsigned int len;
 920
 921                 len = PAGE_SIZE - poff;
 922                 if (len > avail)
 923                         len = avail;
 924
 925                 len = actor(desc, p, poff, len);
 926                 if (desc->error)
 927                         break;
 928
 929                 avail -= len;
 930                 ret += len;
 931                 poff = 0;
 932                 pidx = (pidx + 1) % subbuf_pages;
 933         }
 934
 935         return ret;
 936 }
 937
 938 typedef int (*subbuf_actor_t) (size_t read_start,
 939                                struct rchan_buf *buf,
 940                                size_t avail,
 941                                read_descriptor_t *desc,
 942                                read_actor_t actor);
 943
 944 /*
 945  *      relay_file_read_subbufs - read count bytes, bridging subbuf boundaries
 946  */
 947 static inline ssize_t relay_file_read_subbufs(struct file *filp,
 948                                               loff_t *ppos,
 949                                               size_t count,
 950                                               subbuf_actor_t subbuf_actor,
 951                                               read_actor_t actor,
 952                                               void *target)
 953 {
 954         struct rchan_buf *buf = filp->private_data;
 955         size_t read_start, avail;
 956         read_descriptor_t desc;
 957         int ret;
 958
 959         if (!count)
 960                 return 0;
 961
 962         desc.written = 0;
 963         desc.count = count;
 964         desc.arg.data = target;
 965         desc.error = 0;
 966
 967         mutex_lock(&filp->f_dentry->d_inode->i_mutex);
 968         do {
 969                 if (!relay_file_read_avail(buf, *ppos))
 970                         break;
 971
 972                 read_start = relay_file_read_start_pos(*ppos, buf);
 973                 avail = relay_file_read_subbuf_avail(read_start, buf);
 974                 if (!avail)
 975                         break;
 976
 977                 avail = min(desc.count, avail);
 978                 ret = subbuf_actor(read_start, buf, avail, &desc, actor);
 979                 if (desc.error < 0)
 980                         break;
 981
 982                 if (ret) {
 983                         relay_file_read_consume(buf, read_start, ret);
 984                         *ppos = relay_file_read_end_pos(buf, read_start, ret);
 985                 }
 986         } while (desc.count && ret);
 987         mutex_unlock(&filp->f_dentry->d_inode->i_mutex);
 988
 989         return desc.written;
 990 }
 991
 992 static ssize_t relay_file_read(struct file *filp,
 993                                char __user *buffer,
 994                                size_t count,
 995                                loff_t *ppos)
 996 {
 997         return relay_file_read_subbufs(filp, ppos, count, subbuf_read_actor,
 998                                        NULL, buffer);
 999 }
1000
1001 static ssize_t relay_file_sendfile(struct file *filp,
1002                                    loff_t *ppos,
1003                                    size_t count,
1004                                    read_actor_t actor,
1005                                    void *target)
1006 {
1007         return relay_file_read_subbufs(filp, ppos, count, subbuf_send_actor,
1008                                        actor, target);
1009 }
1010
1011 struct file_operations relay_file_operations = {
1012         .open           = relay_file_open,
1013         .poll           = relay_file_poll,
1014         .mmap           = relay_file_mmap,
1015         .read           = relay_file_read,
1016         .llseek         = no_llseek,
1017         .release        = relay_file_release,
1018         .sendfile       = relay_file_sendfile,
1019 };
1020 EXPORT_SYMBOL_GPL(relay_file_operations);