kernel/relay.c

   1 /*
   2  * Public API and common code for kernel->userspace relay file support.
   3  *
   4  * See Documentation/filesystems/relay.txt for an overview.
   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  * November 2006 - CPU hotplug support by Mathieu Desnoyers
  11  *      (mathieu.desnoyers@polymtl.ca)
  12  *
  13  * This file is released under the GPL.
  14  */
  15 #include <linux/errno.h>
  16 #include <linux/stddef.h>
  17 #include <linux/slab.h>
  18 #include <linux/export.h>
  19 #include <linux/string.h>
  20 #include <linux/relay.h>
  21 #include <linux/vmalloc.h>
  22 #include <linux/mm.h>
  23 #include <linux/cpu.h>
  24 #include <linux/splice.h>
  25
  26 /* list of open channels, for cpu hotplug */
  27 static DEFINE_MUTEX(relay_channels_mutex);
  28 static LIST_HEAD(relay_channels);
  29
  30 /*
  31  * close() vm_op implementation for relay file mapping.
  32  */
  33 static void relay_file_mmap_close(struct vm_area_struct *vma)
  34 {
  35         struct rchan_buf *buf = vma->vm_private_data;
  36         buf->chan->cb->buf_unmapped(buf, vma->vm_file);
  37 }
  38
  39 /*
  40  * fault() vm_op implementation for relay file mapping.
  41  */
  42 static int relay_buf_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
  43 {
  44         struct page *page;
  45         struct rchan_buf *buf = vma->vm_private_data;
  46         pgoff_t pgoff = vmf->pgoff;
  47
  48         if (!buf)
  49                 return VM_FAULT_OOM;
  50
  51         page = vmalloc_to_page(buf->start + (pgoff << PAGE_SHIFT));
  52         if (!page)
  53                 return VM_FAULT_SIGBUS;
  54         get_page(page);
  55         vmf->page = page;
  56
  57         return 0;
  58 }
  59
  60 /*
  61  * vm_ops for relay file mappings.
  62  */
  63 static const struct vm_operations_struct relay_file_mmap_ops = {
  64         .fault = relay_buf_fault,
  65         .close = relay_file_mmap_close,
  66 };
  67
  68 /*
  69  * allocate an array of pointers of struct page
  70  */
  71 static struct page **relay_alloc_page_array(unsigned int n_pages)
  72 {
  73         const size_t pa_size = n_pages * sizeof(struct page *);
  74         if (pa_size > PAGE_SIZE)
  75                 return vzalloc(pa_size);
  76         return kzalloc(pa_size, GFP_KERNEL);
  77 }
  78
  79 /*
  80  * free an array of pointers of struct page
  81  */
  82 static void relay_free_page_array(struct page **array)
  83 {
  84         kvfree(array);
  85 }
  86
  87 /**
  88  *      relay_mmap_buf: - mmap channel buffer to process address space
  89  *      @buf: relay channel buffer
  90  *      @vma: vm_area_struct describing memory to be mapped
  91  *
  92  *      Returns 0 if ok, negative on error
  93  *
  94  *      Caller should already have grabbed mmap_sem.
  95  */
  96 static int relay_mmap_buf(struct rchan_buf *buf, struct vm_area_struct *vma)
  97 {
  98         unsigned long length = vma->vm_end - vma->vm_start;
  99         struct file *filp = vma->vm_file;
 100
 101         if (!buf)
 102                 return -EBADF;
 103
 104         if (length != (unsigned long)buf->chan->alloc_size)
 105                 return -EINVAL;
 106
 107         vma->vm_ops = &relay_file_mmap_ops;
 108         vma->vm_flags |= VM_DONTEXPAND;
 109         vma->vm_private_data = buf;
 110         buf->chan->cb->buf_mapped(buf, filp);
 111
 112         return 0;
 113 }
 114
 115 /**
 116  *      relay_alloc_buf - allocate a channel buffer
 117  *      @buf: the buffer struct
 118  *      @size: total size of the buffer
 119  *
 120  *      Returns a pointer to the resulting buffer, %NULL if unsuccessful. The
 121  *      passed in size will get page aligned, if it isn't already.
 122  */
 123 static void *relay_alloc_buf(struct rchan_buf *buf, size_t *size)
 124 {
 125         void *mem;
 126         unsigned int i, j, n_pages;
 127
 128         *size = PAGE_ALIGN(*size);
 129         n_pages = *size >> PAGE_SHIFT;
 130
 131         buf->page_array = relay_alloc_page_array(n_pages);
 132         if (!buf->page_array)
 133                 return NULL;
 134
 135         for (i = 0; i < n_pages; i++) {
 136                 buf->page_array[i] = alloc_page(GFP_KERNEL);
 137                 if (unlikely(!buf->page_array[i]))
 138                         goto depopulate;
 139                 set_page_private(buf->page_array[i], (unsigned long)buf);
 140         }
 141         mem = vmap(buf->page_array, n_pages, VM_MAP, PAGE_KERNEL);
 142         if (!mem)
 143                 goto depopulate;
 144
 145         memset(mem, 0, *size);
 146         buf->page_count = n_pages;
 147         return mem;
 148
 149 depopulate:
 150         for (j = 0; j < i; j++)
 151                 __free_page(buf->page_array[j]);
 152         relay_free_page_array(buf->page_array);
 153         return NULL;
 154 }
 155
 156 /**
 157  *      relay_create_buf - allocate and initialize a channel buffer
 158  *      @chan: the relay channel
 159  *
 160  *      Returns channel buffer if successful, %NULL otherwise.
 161  */
 162 static struct rchan_buf *relay_create_buf(struct rchan *chan)
 163 {
 164         struct rchan_buf *buf;
 165
 166         if (chan->n_subbufs > UINT_MAX / sizeof(size_t *))
 167                 return NULL;
 168
 169         buf = kzalloc(sizeof(struct rchan_buf), GFP_KERNEL);
 170         if (!buf)
 171                 return NULL;
 172         buf->padding = kmalloc(chan->n_subbufs * sizeof(size_t *), GFP_KERNEL);
 173         if (!buf->padding)
 174                 goto free_buf;
 175
 176         buf->start = relay_alloc_buf(buf, &chan->alloc_size);
 177         if (!buf->start)
 178                 goto free_buf;
 179
 180         buf->chan = chan;
 181         kref_get(&buf->chan->kref);
 182         return buf;
 183
 184 free_buf:
 185         kfree(buf->padding);
 186         kfree(buf);
 187         return NULL;
 188 }
 189
 190 /**
 191  *      relay_destroy_channel - free the channel struct
 192  *      @kref: target kernel reference that contains the relay channel
 193  *
 194  *      Should only be called from kref_put().
 195  */
 196 static void relay_destroy_channel(struct kref *kref)
 197 {
 198         struct rchan *chan = container_of(kref, struct rchan, kref);
 199         kfree(chan);
 200 }
 201
 202 /**
 203  *      relay_destroy_buf - destroy an rchan_buf struct and associated buffer
 204  *      @buf: the buffer struct
 205  */
 206 static void relay_destroy_buf(struct rchan_buf *buf)
 207 {
 208         struct rchan *chan = buf->chan;
 209         unsigned int i;
 210
 211         if (likely(buf->start)) {
 212                 vunmap(buf->start);
 213                 for (i = 0; i < buf->page_count; i++)
 214                         __free_page(buf->page_array[i]);
 215                 relay_free_page_array(buf->page_array);
 216         }
 217         *per_cpu_ptr(chan->buf, buf->cpu) = NULL;
 218         kfree(buf->padding);
 219         kfree(buf);
 220         kref_put(&chan->kref, relay_destroy_channel);
 221 }
 222
 223 /**
 224  *      relay_remove_buf - remove a channel buffer
 225  *      @kref: target kernel reference that contains the relay buffer
 226  *
 227  *      Removes the file from the filesystem, which also frees the
 228  *      rchan_buf_struct and the channel buffer.  Should only be called from
 229  *      kref_put().
 230  */
 231 static void relay_remove_buf(struct kref *kref)
 232 {
 233         struct rchan_buf *buf = container_of(kref, struct rchan_buf, kref);
 234         relay_destroy_buf(buf);
 235 }
 236
 237 /**
 238  *      relay_buf_empty - boolean, is the channel buffer empty?
 239  *      @buf: channel buffer
 240  *
 241  *      Returns 1 if the buffer is empty, 0 otherwise.
 242  */
 243 static int relay_buf_empty(struct rchan_buf *buf)
 244 {
 245         return (buf->subbufs_produced - buf->subbufs_consumed) ? 0 : 1;
 246 }
 247
 248 /**
 249  *      relay_buf_full - boolean, is the channel buffer full?
 250  *      @buf: channel buffer
 251  *
 252  *      Returns 1 if the buffer is full, 0 otherwise.
 253  */
 254 int relay_buf_full(struct rchan_buf *buf)
 255 {
 256         size_t ready = buf->subbufs_produced - buf->subbufs_consumed;
 257         return (ready >= buf->chan->n_subbufs) ? 1 : 0;
 258 }
 259 EXPORT_SYMBOL_GPL(relay_buf_full);
 260
 261 /*
 262  * High-level relay kernel API and associated functions.
 263  */
 264
 265 /*
 266  * rchan_callback implementations defining default channel behavior.  Used
 267  * in place of corresponding NULL values in client callback struct.
 268  */
 269
 270 /*
 271  * subbuf_start() default callback.  Does nothing.
 272  */
 273 static int subbuf_start_default_callback (struct rchan_buf *buf,
 274                                           void *subbuf,
 275                                           void *prev_subbuf,
 276                                           size_t prev_padding)
 277 {
 278         if (relay_buf_full(buf))
 279                 return 0;
 280
 281         return 1;
 282 }
 283
 284 /*
 285  * buf_mapped() default callback.  Does nothing.
 286  */
 287 static void buf_mapped_default_callback(struct rchan_buf *buf,
 288                                         struct file *filp)
 289 {
 290 }
 291
 292 /*
 293  * buf_unmapped() default callback.  Does nothing.
 294  */
 295 static void buf_unmapped_default_callback(struct rchan_buf *buf,
 296                                           struct file *filp)
 297 {
 298 }
 299
 300 /*
 301  * create_buf_file_create() default callback.  Does nothing.
 302  */
 303 static struct dentry *create_buf_file_default_callback(const char *filename,
 304                                                        struct dentry *parent,
 305                                                        umode_t mode,
 306                                                        struct rchan_buf *buf,
 307                                                        int *is_global)
 308 {
 309         return NULL;
 310 }
 311
 312 /*
 313  * remove_buf_file() default callback.  Does nothing.
 314  */
 315 static int remove_buf_file_default_callback(struct dentry *dentry)
 316 {
 317         return -EINVAL;
 318 }
 319
 320 /* relay channel default callbacks */
 321 static struct rchan_callbacks default_channel_callbacks = {
 322         .subbuf_start = subbuf_start_default_callback,
 323         .buf_mapped = buf_mapped_default_callback,
 324         .buf_unmapped = buf_unmapped_default_callback,
 325         .create_buf_file = create_buf_file_default_callback,
 326         .remove_buf_file = remove_buf_file_default_callback,
 327 };
 328
 329 /**
 330  *      wakeup_readers - wake up readers waiting on a channel
 331  *      @data: contains the channel buffer
 332  *
 333  *      This is the timer function used to defer reader waking.
 334  */
 335 static void wakeup_readers(unsigned long data)
 336 {
 337         struct rchan_buf *buf = (struct rchan_buf *)data;
 338         wake_up_interruptible(&buf->read_wait);
 339 }
 340
 341 /**
 342  *      __relay_reset - reset a channel buffer
 343  *      @buf: the channel buffer
 344  *      @init: 1 if this is a first-time initialization
 345  *
 346  *      See relay_reset() for description of effect.
 347  */
 348 static void __relay_reset(struct rchan_buf *buf, unsigned int init)
 349 {
 350         size_t i;
 351
 352         if (init) {
 353                 init_waitqueue_head(&buf->read_wait);
 354                 kref_init(&buf->kref);
 355                 setup_timer(&buf->timer, wakeup_readers, (unsigned long)buf);
 356         } else
 357                 del_timer_sync(&buf->timer);
 358
 359         buf->subbufs_produced = 0;
 360         buf->subbufs_consumed = 0;
 361         buf->bytes_consumed = 0;
 362         buf->finalized = 0;
 363         buf->data = buf->start;
 364         buf->offset = 0;
 365
 366         for (i = 0; i < buf->chan->n_subbufs; i++)
 367                 buf->padding[i] = 0;
 368
 369         buf->chan->cb->subbuf_start(buf, buf->data, NULL, 0);
 370 }
 371
 372 /**
 373  *      relay_reset - reset the channel
 374  *      @chan: the channel
 375  *
 376  *      This has the effect of erasing all data from all channel buffers
 377  *      and restarting the channel in its initial state.  The buffers
 378  *      are not freed, so any mappings are still in effect.
 379  *
 380  *      NOTE. Care should be taken that the channel isn't actually
 381  *      being used by anything when this call is made.
 382  */
 383 void relay_reset(struct rchan *chan)
 384 {
 385         struct rchan_buf *buf;
 386         unsigned int i;
 387
 388         if (!chan)
 389                 return;
 390
 391         if (chan->is_global && (buf = *per_cpu_ptr(chan->buf, 0))) {
 392                 __relay_reset(buf, 0);
 393                 return;
 394         }
 395
 396         mutex_lock(&relay_channels_mutex);
 397         for_each_possible_cpu(i)
 398                 if ((buf = *per_cpu_ptr(chan->buf, i)))
 399                         __relay_reset(buf, 0);
 400         mutex_unlock(&relay_channels_mutex);
 401 }
 402 EXPORT_SYMBOL_GPL(relay_reset);
 403
 404 static inline void relay_set_buf_dentry(struct rchan_buf *buf,
 405                                         struct dentry *dentry)
 406 {
 407         buf->dentry = dentry;
 408         d_inode(buf->dentry)->i_size = buf->early_bytes;
 409 }
 410
 411 static struct dentry *relay_create_buf_file(struct rchan *chan,
 412                                             struct rchan_buf *buf,
 413                                             unsigned int cpu)
 414 {
 415         struct dentry *dentry;
 416         char *tmpname;
 417
 418         tmpname = kzalloc(NAME_MAX + 1, GFP_KERNEL);
 419         if (!tmpname)
 420                 return NULL;
 421         snprintf(tmpname, NAME_MAX, "%s%d", chan->base_filename, cpu);
 422
 423         /* Create file in fs */
 424         dentry = chan->cb->create_buf_file(tmpname, chan->parent,
 425                                            S_IRUSR, buf,
 426                                            &chan->is_global);
 427
 428         kfree(tmpname);
 429
 430         return dentry;
 431 }
 432
 433 /*
 434  *      relay_open_buf - create a new relay channel buffer
 435  *
 436  *      used by relay_open() and CPU hotplug.
 437  */
 438 static struct rchan_buf *relay_open_buf(struct rchan *chan, unsigned int cpu)
 439 {
 440         struct rchan_buf *buf = NULL;
 441         struct dentry *dentry;
 442
 443         if (chan->is_global)
 444                 return *per_cpu_ptr(chan->buf, 0);
 445
 446         buf = relay_create_buf(chan);
 447         if (!buf)
 448                 return NULL;
 449
 450         if (chan->has_base_filename) {
 451                 dentry = relay_create_buf_file(chan, buf, cpu);
 452                 if (!dentry)
 453                         goto free_buf;
 454                 relay_set_buf_dentry(buf, dentry);
 455         } else {
 456                 /* Only retrieve global info, nothing more, nothing less */
 457                 dentry = chan->cb->create_buf_file(NULL, NULL,
 458                                                    S_IRUSR, buf,
 459                                                    &chan->is_global);
 460                 if (WARN_ON(dentry))
 461                         goto free_buf;
 462         }
 463
 464         buf->cpu = cpu;
 465         __relay_reset(buf, 1);
 466
 467         if(chan->is_global) {
 468                 *per_cpu_ptr(chan->buf, 0) = buf;
 469                 buf->cpu = 0;
 470         }
 471
 472         return buf;
 473
 474 free_buf:
 475         relay_destroy_buf(buf);
 476         return NULL;
 477 }
 478
 479 /**
 480  *      relay_close_buf - close a channel buffer
 481  *      @buf: channel buffer
 482  *
 483  *      Marks the buffer finalized and restores the default callbacks.
 484  *      The channel buffer and channel buffer data structure are then freed
 485  *      automatically when the last reference is given up.
 486  */
 487 static void relay_close_buf(struct rchan_buf *buf)
 488 {
 489         buf->finalized = 1;
 490         del_timer_sync(&buf->timer);
 491         buf->chan->cb->remove_buf_file(buf->dentry);
 492         kref_put(&buf->kref, relay_remove_buf);
 493 }
 494
 495 static void setup_callbacks(struct rchan *chan,
 496                                    struct rchan_callbacks *cb)
 497 {
 498         if (!cb) {
 499                 chan->cb = &default_channel_callbacks;
 500                 return;
 501         }
 502
 503         if (!cb->subbuf_start)
 504                 cb->subbuf_start = subbuf_start_default_callback;
 505         if (!cb->buf_mapped)
 506                 cb->buf_mapped = buf_mapped_default_callback;
 507         if (!cb->buf_unmapped)
 508                 cb->buf_unmapped = buf_unmapped_default_callback;
 509         if (!cb->create_buf_file)
 510                 cb->create_buf_file = create_buf_file_default_callback;
 511         if (!cb->remove_buf_file)
 512                 cb->remove_buf_file = remove_buf_file_default_callback;
 513         chan->cb = cb;
 514 }
 515
 516 int relay_prepare_cpu(unsigned int cpu)
 517 {
 518         struct rchan *chan;
 519         struct rchan_buf *buf;
 520
 521         mutex_lock(&relay_channels_mutex);
 522         list_for_each_entry(chan, &relay_channels, list) {
 523                 if ((buf = *per_cpu_ptr(chan->buf, cpu)))
 524                         continue;
 525                 buf = relay_open_buf(chan, cpu);
 526                 if (!buf) {
 527                         pr_err("relay: cpu %d buffer creation failed\n", cpu);
 528                         mutex_unlock(&relay_channels_mutex);
 529                         return -ENOMEM;
 530                 }
 531                 *per_cpu_ptr(chan->buf, cpu) = buf;
 532         }
 533         mutex_unlock(&relay_channels_mutex);
 534         return 0;
 535 }
 536
 537 /**
 538  *      relay_open - create a new relay channel
 539  *      @base_filename: base name of files to create, %NULL for buffering only
 540  *      @parent: dentry of parent directory, %NULL for root directory or buffer
 541  *      @subbuf_size: size of sub-buffers
 542  *      @n_subbufs: number of sub-buffers
 543  *      @cb: client callback functions
 544  *      @private_data: user-defined data
 545  *
 546  *      Returns channel pointer if successful, %NULL otherwise.
 547  *
 548  *      Creates a channel buffer for each cpu using the sizes and
 549  *      attributes specified.  The created channel buffer files
 550  *      will be named base_filename0...base_filenameN-1.  File
 551  *      permissions will be %S_IRUSR.
 552  *
 553  *      If opening a buffer (@parent = NULL) that you later wish to register
 554  *      in a filesystem, call relay_late_setup_files() once the @parent dentry
 555  *      is available.
 556  */
 557 struct rchan *relay_open(const char *base_filename,
 558                          struct dentry *parent,
 559                          size_t subbuf_size,
 560                          size_t n_subbufs,
 561                          struct rchan_callbacks *cb,
 562                          void *private_data)
 563 {
 564         unsigned int i;
 565         struct rchan *chan;
 566         struct rchan_buf *buf;
 567
 568         if (!(subbuf_size && n_subbufs))
 569                 return NULL;
 570         if (subbuf_size > UINT_MAX / n_subbufs)
 571                 return NULL;
 572
 573         chan = kzalloc(sizeof(struct rchan), GFP_KERNEL);
 574         if (!chan)
 575                 return NULL;
 576
 577         chan->buf = alloc_percpu(struct rchan_buf *);
 578         chan->version = RELAYFS_CHANNEL_VERSION;
 579         chan->n_subbufs = n_subbufs;
 580         chan->subbuf_size = subbuf_size;
 581         chan->alloc_size = PAGE_ALIGN(subbuf_size * n_subbufs);
 582         chan->parent = parent;
 583         chan->private_data = private_data;
 584         if (base_filename) {
 585                 chan->has_base_filename = 1;
 586                 strlcpy(chan->base_filename, base_filename, NAME_MAX);
 587         }
 588         setup_callbacks(chan, cb);
 589         kref_init(&chan->kref);
 590
 591         mutex_lock(&relay_channels_mutex);
 592         for_each_online_cpu(i) {
 593                 buf = relay_open_buf(chan, i);
 594                 if (!buf)
 595                         goto free_bufs;
 596                 *per_cpu_ptr(chan->buf, i) = buf;
 597         }
 598         list_add(&chan->list, &relay_channels);
 599         mutex_unlock(&relay_channels_mutex);
 600
 601         return chan;
 602
 603 free_bufs:
 604         for_each_possible_cpu(i) {
 605                 if ((buf = *per_cpu_ptr(chan->buf, i)))
 606                         relay_close_buf(buf);
 607         }
 608
 609         kref_put(&chan->kref, relay_destroy_channel);
 610         mutex_unlock(&relay_channels_mutex);
 611         kfree(chan);
 612         return NULL;
 613 }
 614 EXPORT_SYMBOL_GPL(relay_open);
 615
 616 struct rchan_percpu_buf_dispatcher {
 617         struct rchan_buf *buf;
 618         struct dentry *dentry;
 619 };
 620
 621 /* Called in atomic context. */
 622 static void __relay_set_buf_dentry(void *info)
 623 {
 624         struct rchan_percpu_buf_dispatcher *p = info;
 625
 626         relay_set_buf_dentry(p->buf, p->dentry);
 627 }
 628
 629 /**
 630  *      relay_late_setup_files - triggers file creation
 631  *      @chan: channel to operate on
 632  *      @base_filename: base name of files to create
 633  *      @parent: dentry of parent directory, %NULL for root directory
 634  *
 635  *      Returns 0 if successful, non-zero otherwise.
 636  *
 637  *      Use to setup files for a previously buffer-only channel created
 638  *      by relay_open() with a NULL parent dentry.
 639  *
 640  *      For example, this is useful for perfomring early tracing in kernel,
 641  *      before VFS is up and then exposing the early results once the dentry
 642  *      is available.
 643  */
 644 int relay_late_setup_files(struct rchan *chan,
 645                            const char *base_filename,
 646                            struct dentry *parent)
 647 {
 648         int err = 0;
 649         unsigned int i, curr_cpu;
 650         unsigned long flags;
 651         struct dentry *dentry;
 652         struct rchan_buf *buf;
 653         struct rchan_percpu_buf_dispatcher disp;
 654
 655         if (!chan || !base_filename)
 656                 return -EINVAL;
 657
 658         strlcpy(chan->base_filename, base_filename, NAME_MAX);
 659
 660         mutex_lock(&relay_channels_mutex);
 661         /* Is chan already set up? */
 662         if (unlikely(chan->has_base_filename)) {
 663                 mutex_unlock(&relay_channels_mutex);
 664                 return -EEXIST;
 665         }
 666         chan->has_base_filename = 1;
 667         chan->parent = parent;
 668
 669         if (chan->is_global) {
 670                 err = -EINVAL;
 671                 buf = *per_cpu_ptr(chan->buf, 0);
 672                 if (!WARN_ON_ONCE(!buf)) {
 673                         dentry = relay_create_buf_file(chan, buf, 0);
 674                         if (dentry && !WARN_ON_ONCE(!chan->is_global)) {
 675                                 relay_set_buf_dentry(buf, dentry);
 676                                 err = 0;
 677                         }
 678                 }
 679                 mutex_unlock(&relay_channels_mutex);
 680                 return err;
 681         }
 682
 683         curr_cpu = get_cpu();
 684         /*
 685          * The CPU hotplug notifier ran before us and created buffers with
 686          * no files associated. So it's safe to call relay_setup_buf_file()
 687          * on all currently online CPUs.
 688          */
 689         for_each_online_cpu(i) {
 690                 buf = *per_cpu_ptr(chan->buf, i);
 691                 if (unlikely(!buf)) {
 692                         WARN_ONCE(1, KERN_ERR "CPU has no buffer!\n");
 693                         err = -EINVAL;
 694                         break;
 695                 }
 696
 697                 dentry = relay_create_buf_file(chan, buf, i);
 698                 if (unlikely(!dentry)) {
 699                         err = -EINVAL;
 700                         break;
 701                 }
 702
 703                 if (curr_cpu == i) {
 704                         local_irq_save(flags);
 705                         relay_set_buf_dentry(buf, dentry);
 706                         local_irq_restore(flags);
 707                 } else {
 708                         disp.buf = buf;
 709                         disp.dentry = dentry;
 710                         smp_mb();
 711                         /* relay_channels_mutex must be held, so wait. */
 712                         err = smp_call_function_single(i,
 713                                                        __relay_set_buf_dentry,
 714                                                        &disp, 1);
 715                 }
 716                 if (unlikely(err))
 717                         break;
 718         }
 719         put_cpu();
 720         mutex_unlock(&relay_channels_mutex);
 721
 722         return err;
 723 }
 724 EXPORT_SYMBOL_GPL(relay_late_setup_files);
 725
 726 /**
 727  *      relay_switch_subbuf - switch to a new sub-buffer
 728  *      @buf: channel buffer
 729  *      @length: size of current event
 730  *
 731  *      Returns either the length passed in or 0 if full.
 732  *
 733  *      Performs sub-buffer-switch tasks such as invoking callbacks,
 734  *      updating padding counts, waking up readers, etc.
 735  */
 736 size_t relay_switch_subbuf(struct rchan_buf *buf, size_t length)
 737 {
 738         void *old, *new;
 739         size_t old_subbuf, new_subbuf;
 740
 741         if (unlikely(length > buf->chan->subbuf_size))
 742                 goto toobig;
 743
 744         if (buf->offset != buf->chan->subbuf_size + 1) {
 745                 buf->prev_padding = buf->chan->subbuf_size - buf->offset;
 746                 old_subbuf = buf->subbufs_produced % buf->chan->n_subbufs;
 747                 buf->padding[old_subbuf] = buf->prev_padding;
 748                 buf->subbufs_produced++;
 749                 if (buf->dentry)
 750                         d_inode(buf->dentry)->i_size +=
 751                                 buf->chan->subbuf_size -
 752                                 buf->padding[old_subbuf];
 753                 else
 754                         buf->early_bytes += buf->chan->subbuf_size -
 755                                             buf->padding[old_subbuf];
 756                 smp_mb();
 757                 if (waitqueue_active(&buf->read_wait))
 758                         /*
 759                          * Calling wake_up_interruptible() from here
 760                          * will deadlock if we happen to be logging
 761                          * from the scheduler (trying to re-grab
 762                          * rq->lock), so defer it.
 763                          */
 764                         mod_timer(&buf->timer, jiffies + 1);
 765         }
 766
 767         old = buf->data;
 768         new_subbuf = buf->subbufs_produced % buf->chan->n_subbufs;
 769         new = buf->start + new_subbuf * buf->chan->subbuf_size;
 770         buf->offset = 0;
 771         if (!buf->chan->cb->subbuf_start(buf, new, old, buf->prev_padding)) {
 772                 buf->offset = buf->chan->subbuf_size + 1;
 773                 return 0;
 774         }
 775         buf->data = new;
 776         buf->padding[new_subbuf] = 0;
 777
 778         if (unlikely(length + buf->offset > buf->chan->subbuf_size))
 779                 goto toobig;
 780
 781         return length;
 782
 783 toobig:
 784         buf->chan->last_toobig = length;
 785         return 0;
 786 }
 787 EXPORT_SYMBOL_GPL(relay_switch_subbuf);
 788
 789 /**
 790  *      relay_subbufs_consumed - update the buffer's sub-buffers-consumed count
 791  *      @chan: the channel
 792  *      @cpu: the cpu associated with the channel buffer to update
 793  *      @subbufs_consumed: number of sub-buffers to add to current buf's count
 794  *
 795  *      Adds to the channel buffer's consumed sub-buffer count.
 796  *      subbufs_consumed should be the number of sub-buffers newly consumed,
 797  *      not the total consumed.
 798  *
 799  *      NOTE. Kernel clients don't need to call this function if the channel
 800  *      mode is 'overwrite'.
 801  */
 802 void relay_subbufs_consumed(struct rchan *chan,
 803                             unsigned int cpu,
 804                             size_t subbufs_consumed)
 805 {
 806         struct rchan_buf *buf;
 807
 808         if (!chan)
 809                 return;
 810
 811         buf = *per_cpu_ptr(chan->buf, cpu);
 812         if (cpu >= NR_CPUS || !buf || subbufs_consumed > chan->n_subbufs)
 813                 return;
 814
 815         if (subbufs_consumed > buf->subbufs_produced - buf->subbufs_consumed)
 816                 buf->subbufs_consumed = buf->subbufs_produced;
 817         else
 818                 buf->subbufs_consumed += subbufs_consumed;
 819 }
 820 EXPORT_SYMBOL_GPL(relay_subbufs_consumed);
 821
 822 /**
 823  *      relay_close - close the channel
 824  *      @chan: the channel
 825  *
 826  *      Closes all channel buffers and frees the channel.
 827  */
 828 void relay_close(struct rchan *chan)
 829 {
 830         struct rchan_buf *buf;
 831         unsigned int i;
 832
 833         if (!chan)
 834                 return;
 835
 836         mutex_lock(&relay_channels_mutex);
 837         if (chan->is_global && (buf = *per_cpu_ptr(chan->buf, 0)))
 838                 relay_close_buf(buf);
 839         else
 840                 for_each_possible_cpu(i)
 841                         if ((buf = *per_cpu_ptr(chan->buf, i)))
 842                                 relay_close_buf(buf);
 843
 844         if (chan->last_toobig)
 845                 printk(KERN_WARNING "relay: one or more items not logged "
 846                        "[item size (%Zd) > sub-buffer size (%Zd)]\n",
 847                        chan->last_toobig, chan->subbuf_size);
 848
 849         list_del(&chan->list);
 850         kref_put(&chan->kref, relay_destroy_channel);
 851         mutex_unlock(&relay_channels_mutex);
 852 }
 853 EXPORT_SYMBOL_GPL(relay_close);
 854
 855 /**
 856  *      relay_flush - close the channel
 857  *      @chan: the channel
 858  *
 859  *      Flushes all channel buffers, i.e. forces buffer switch.
 860  */
 861 void relay_flush(struct rchan *chan)
 862 {
 863         struct rchan_buf *buf;
 864         unsigned int i;
 865
 866         if (!chan)
 867                 return;
 868
 869         if (chan->is_global && (buf = *per_cpu_ptr(chan->buf, 0))) {
 870                 relay_switch_subbuf(buf, 0);
 871                 return;
 872         }
 873
 874         mutex_lock(&relay_channels_mutex);
 875         for_each_possible_cpu(i)
 876                 if ((buf = *per_cpu_ptr(chan->buf, i)))
 877                         relay_switch_subbuf(buf, 0);
 878         mutex_unlock(&relay_channels_mutex);
 879 }
 880 EXPORT_SYMBOL_GPL(relay_flush);
 881
 882 /**
 883  *      relay_file_open - open file op for relay files
 884  *      @inode: the inode
 885  *      @filp: the file
 886  *
 887  *      Increments the channel buffer refcount.
 888  */
 889 static int relay_file_open(struct inode *inode, struct file *filp)
 890 {
 891         struct rchan_buf *buf = inode->i_private;
 892         kref_get(&buf->kref);
 893         filp->private_data = buf;
 894
 895         return nonseekable_open(inode, filp);
 896 }
 897
 898 /**
 899  *      relay_file_mmap - mmap file op for relay files
 900  *      @filp: the file
 901  *      @vma: the vma describing what to map
 902  *
 903  *      Calls upon relay_mmap_buf() to map the file into user space.
 904  */
 905 static int relay_file_mmap(struct file *filp, struct vm_area_struct *vma)
 906 {
 907         struct rchan_buf *buf = filp->private_data;
 908         return relay_mmap_buf(buf, vma);
 909 }
 910
 911 /**
 912  *      relay_file_poll - poll file op for relay files
 913  *      @filp: the file
 914  *      @wait: poll table
 915  *
 916  *      Poll implemention.
 917  */
 918 static unsigned int relay_file_poll(struct file *filp, poll_table *wait)
 919 {
 920         unsigned int mask = 0;
 921         struct rchan_buf *buf = filp->private_data;
 922
 923         if (buf->finalized)
 924                 return POLLERR;
 925
 926         if (filp->f_mode & FMODE_READ) {
 927                 poll_wait(filp, &buf->read_wait, wait);
 928                 if (!relay_buf_empty(buf))
 929                         mask |= POLLIN | POLLRDNORM;
 930         }
 931
 932         return mask;
 933 }
 934
 935 /**
 936  *      relay_file_release - release file op for relay files
 937  *      @inode: the inode
 938  *      @filp: the file
 939  *
 940  *      Decrements the channel refcount, as the filesystem is
 941  *      no longer using it.
 942  */
 943 static int relay_file_release(struct inode *inode, struct file *filp)
 944 {
 945         struct rchan_buf *buf = filp->private_data;
 946         kref_put(&buf->kref, relay_remove_buf);
 947
 948         return 0;
 949 }
 950
 951 /*
 952  *      relay_file_read_consume - update the consumed count for the buffer
 953  */
 954 static void relay_file_read_consume(struct rchan_buf *buf,
 955                                     size_t read_pos,
 956                                     size_t bytes_consumed)
 957 {
 958         size_t subbuf_size = buf->chan->subbuf_size;
 959         size_t n_subbufs = buf->chan->n_subbufs;
 960         size_t read_subbuf;
 961
 962         if (buf->subbufs_produced == buf->subbufs_consumed &&
 963             buf->offset == buf->bytes_consumed)
 964                 return;
 965
 966         if (buf->bytes_consumed + bytes_consumed > subbuf_size) {
 967                 relay_subbufs_consumed(buf->chan, buf->cpu, 1);
 968                 buf->bytes_consumed = 0;
 969         }
 970
 971         buf->bytes_consumed += bytes_consumed;
 972         if (!read_pos)
 973                 read_subbuf = buf->subbufs_consumed % n_subbufs;
 974         else
 975                 read_subbuf = read_pos / buf->chan->subbuf_size;
 976         if (buf->bytes_consumed + buf->padding[read_subbuf] == subbuf_size) {
 977                 if ((read_subbuf == buf->subbufs_produced % n_subbufs) &&
 978                     (buf->offset == subbuf_size))
 979                         return;
 980                 relay_subbufs_consumed(buf->chan, buf->cpu, 1);
 981                 buf->bytes_consumed = 0;
 982         }
 983 }
 984
 985 /*
 986  *      relay_file_read_avail - boolean, are there unconsumed bytes available?
 987  */
 988 static int relay_file_read_avail(struct rchan_buf *buf, size_t read_pos)
 989 {
 990         size_t subbuf_size = buf->chan->subbuf_size;
 991         size_t n_subbufs = buf->chan->n_subbufs;
 992         size_t produced = buf->subbufs_produced;
 993         size_t consumed = buf->subbufs_consumed;
 994
 995         relay_file_read_consume(buf, read_pos, 0);
 996
 997         consumed = buf->subbufs_consumed;
 998
 999         if (unlikely(buf->offset > subbuf_size)) {
1000                 if (produced == consumed)
1001                         return 0;
1002                 return 1;
1003         }
1004
1005         if (unlikely(produced - consumed >= n_subbufs)) {
1006                 consumed = produced - n_subbufs + 1;
1007                 buf->subbufs_consumed = consumed;
1008                 buf->bytes_consumed = 0;
1009         }
1010
1011         produced = (produced % n_subbufs) * subbuf_size + buf->offset;
1012         consumed = (consumed % n_subbufs) * subbuf_size + buf->bytes_consumed;
1013
1014         if (consumed > produced)
1015                 produced += n_subbufs * subbuf_size;
1016
1017         if (consumed == produced) {
1018                 if (buf->offset == subbuf_size &&
1019                     buf->subbufs_produced > buf->subbufs_consumed)
1020                         return 1;
1021                 return 0;
1022         }
1023
1024         return 1;
1025 }
1026
1027 /**
1028  *      relay_file_read_subbuf_avail - return bytes available in sub-buffer
1029  *      @read_pos: file read position
1030  *      @buf: relay channel buffer
1031  */
1032 static size_t relay_file_read_subbuf_avail(size_t read_pos,
1033                                            struct rchan_buf *buf)
1034 {
1035         size_t padding, avail = 0;
1036         size_t read_subbuf, read_offset, write_subbuf, write_offset;
1037         size_t subbuf_size = buf->chan->subbuf_size;
1038
1039         write_subbuf = (buf->data - buf->start) / subbuf_size;
1040         write_offset = buf->offset > subbuf_size ? subbuf_size : buf->offset;
1041         read_subbuf = read_pos / subbuf_size;
1042         read_offset = read_pos % subbuf_size;
1043         padding = buf->padding[read_subbuf];
1044
1045         if (read_subbuf == write_subbuf) {
1046                 if (read_offset + padding < write_offset)
1047                         avail = write_offset - (read_offset + padding);
1048         } else
1049                 avail = (subbuf_size - padding) - read_offset;
1050
1051         return avail;
1052 }
1053
1054 /**
1055  *      relay_file_read_start_pos - find the first available byte to read
1056  *      @read_pos: file read position
1057  *      @buf: relay channel buffer
1058  *
1059  *      If the @read_pos is in the middle of padding, return the
1060  *      position of the first actually available byte, otherwise
1061  *      return the original value.
1062  */
1063 static size_t relay_file_read_start_pos(size_t read_pos,
1064                                         struct rchan_buf *buf)
1065 {
1066         size_t read_subbuf, padding, padding_start, padding_end;
1067         size_t subbuf_size = buf->chan->subbuf_size;
1068         size_t n_subbufs = buf->chan->n_subbufs;
1069         size_t consumed = buf->subbufs_consumed % n_subbufs;
1070
1071         if (!read_pos)
1072                 read_pos = consumed * subbuf_size + buf->bytes_consumed;
1073         read_subbuf = read_pos / subbuf_size;
1074         padding = buf->padding[read_subbuf];
1075         padding_start = (read_subbuf + 1) * subbuf_size - padding;
1076         padding_end = (read_subbuf + 1) * subbuf_size;
1077         if (read_pos >= padding_start && read_pos < padding_end) {
1078                 read_subbuf = (read_subbuf + 1) % n_subbufs;
1079                 read_pos = read_subbuf * subbuf_size;
1080         }
1081
1082         return read_pos;
1083 }
1084
1085 /**
1086  *      relay_file_read_end_pos - return the new read position
1087  *      @read_pos: file read position
1088  *      @buf: relay channel buffer
1089  *      @count: number of bytes to be read
1090  */
1091 static size_t relay_file_read_end_pos(struct rchan_buf *buf,
1092                                       size_t read_pos,
1093                                       size_t count)
1094 {
1095         size_t read_subbuf, padding, end_pos;
1096         size_t subbuf_size = buf->chan->subbuf_size;
1097         size_t n_subbufs = buf->chan->n_subbufs;
1098
1099         read_subbuf = read_pos / subbuf_size;
1100         padding = buf->padding[read_subbuf];
1101         if (read_pos % subbuf_size + count + padding == subbuf_size)
1102                 end_pos = (read_subbuf + 1) * subbuf_size;
1103         else
1104                 end_pos = read_pos + count;
1105         if (end_pos >= subbuf_size * n_subbufs)
1106                 end_pos = 0;
1107
1108         return end_pos;
1109 }
1110
1111 /*
1112  *      subbuf_read_actor - read up to one subbuf's worth of data
1113  */
1114 static int subbuf_read_actor(size_t read_start,
1115                              struct rchan_buf *buf,
1116                              size_t avail,
1117                              read_descriptor_t *desc)
1118 {
1119         void *from;
1120         int ret = 0;
1121
1122         from = buf->start + read_start;
1123         ret = avail;
1124         if (copy_to_user(desc->arg.buf, from, avail)) {
1125                 desc->error = -EFAULT;
1126                 ret = 0;
1127         }
1128         desc->arg.data += ret;
1129         desc->written += ret;
1130         desc->count -= ret;
1131
1132         return ret;
1133 }
1134
1135 typedef int (*subbuf_actor_t) (size_t read_start,
1136                                struct rchan_buf *buf,
1137                                size_t avail,
1138                                read_descriptor_t *desc);
1139
1140 /*
1141  *      relay_file_read_subbufs - read count bytes, bridging subbuf boundaries
1142  */
1143 static ssize_t relay_file_read_subbufs(struct file *filp, loff_t *ppos,
1144                                         subbuf_actor_t subbuf_actor,
1145                                         read_descriptor_t *desc)
1146 {
1147         struct rchan_buf *buf = filp->private_data;
1148         size_t read_start, avail;
1149         int ret;
1150
1151         if (!desc->count)
1152                 return 0;
1153
1154         inode_lock(file_inode(filp));
1155         do {
1156                 if (!relay_file_read_avail(buf, *ppos))
1157                         break;
1158
1159                 read_start = relay_file_read_start_pos(*ppos, buf);
1160                 avail = relay_file_read_subbuf_avail(read_start, buf);
1161                 if (!avail)
1162                         break;
1163
1164                 avail = min(desc->count, avail);
1165                 ret = subbuf_actor(read_start, buf, avail, desc);
1166                 if (desc->error < 0)
1167                         break;
1168
1169                 if (ret) {
1170                         relay_file_read_consume(buf, read_start, ret);
1171                         *ppos = relay_file_read_end_pos(buf, read_start, ret);
1172                 }
1173         } while (desc->count && ret);
1174         inode_unlock(file_inode(filp));
1175
1176         return desc->written;
1177 }
1178
1179 static ssize_t relay_file_read(struct file *filp,
1180                                char __user *buffer,
1181                                size_t count,
1182                                loff_t *ppos)
1183 {
1184         read_descriptor_t desc;
1185         desc.written = 0;
1186         desc.count = count;
1187         desc.arg.buf = buffer;
1188         desc.error = 0;
1189         return relay_file_read_subbufs(filp, ppos, subbuf_read_actor, &desc);
1190 }
1191
1192 static void relay_consume_bytes(struct rchan_buf *rbuf, int bytes_consumed)
1193 {
1194         rbuf->bytes_consumed += bytes_consumed;
1195
1196         if (rbuf->bytes_consumed >= rbuf->chan->subbuf_size) {
1197                 relay_subbufs_consumed(rbuf->chan, rbuf->cpu, 1);
1198                 rbuf->bytes_consumed %= rbuf->chan->subbuf_size;
1199         }
1200 }
1201
1202 static void relay_pipe_buf_release(struct pipe_inode_info *pipe,
1203                                    struct pipe_buffer *buf)
1204 {
1205         struct rchan_buf *rbuf;
1206
1207         rbuf = (struct rchan_buf *)page_private(buf->page);
1208         relay_consume_bytes(rbuf, buf->private);
1209 }
1210
1211 static const struct pipe_buf_operations relay_pipe_buf_ops = {
1212         .can_merge = 0,
1213         .confirm = generic_pipe_buf_confirm,
1214         .release = relay_pipe_buf_release,
1215         .steal = generic_pipe_buf_steal,
1216         .get = generic_pipe_buf_get,
1217 };
1218
1219 static void relay_page_release(struct splice_pipe_desc *spd, unsigned int i)
1220 {
1221 }
1222
1223 /*
1224  *      subbuf_splice_actor - splice up to one subbuf's worth of data
1225  */
1226 static ssize_t subbuf_splice_actor(struct file *in,
1227                                loff_t *ppos,
1228                                struct pipe_inode_info *pipe,
1229                                size_t len,
1230                                unsigned int flags,
1231                                int *nonpad_ret)
1232 {
1233         unsigned int pidx, poff, total_len, subbuf_pages, nr_pages;
1234         struct rchan_buf *rbuf = in->private_data;
1235         unsigned int subbuf_size = rbuf->chan->subbuf_size;
1236         uint64_t pos = (uint64_t) *ppos;
1237         uint32_t alloc_size = (uint32_t) rbuf->chan->alloc_size;
1238         size_t read_start = (size_t) do_div(pos, alloc_size);
1239         size_t read_subbuf = read_start / subbuf_size;
1240         size_t padding = rbuf->padding[read_subbuf];
1241         size_t nonpad_end = read_subbuf * subbuf_size + subbuf_size - padding;
1242         struct page *pages[PIPE_DEF_BUFFERS];
1243         struct partial_page partial[PIPE_DEF_BUFFERS];
1244         struct splice_pipe_desc spd = {
1245                 .pages = pages,
1246                 .nr_pages = 0,
1247                 .nr_pages_max = PIPE_DEF_BUFFERS,
1248                 .partial = partial,
1249                 .flags = flags,
1250                 .ops = &relay_pipe_buf_ops,
1251                 .spd_release = relay_page_release,
1252         };
1253         ssize_t ret;
1254
1255         if (rbuf->subbufs_produced == rbuf->subbufs_consumed)
1256                 return 0;
1257         if (splice_grow_spd(pipe, &spd))
1258                 return -ENOMEM;
1259
1260         /*
1261          * Adjust read len, if longer than what is available
1262          */
1263         if (len > (subbuf_size - read_start % subbuf_size))
1264                 len = subbuf_size - read_start % subbuf_size;
1265
1266         subbuf_pages = rbuf->chan->alloc_size >> PAGE_SHIFT;
1267         pidx = (read_start / PAGE_SIZE) % subbuf_pages;
1268         poff = read_start & ~PAGE_MASK;
1269         nr_pages = min_t(unsigned int, subbuf_pages, spd.nr_pages_max);
1270
1271         for (total_len = 0; spd.nr_pages < nr_pages; spd.nr_pages++) {
1272                 unsigned int this_len, this_end, private;
1273                 unsigned int cur_pos = read_start + total_len;
1274
1275                 if (!len)
1276                         break;
1277
1278                 this_len = min_t(unsigned long, len, PAGE_SIZE - poff);
1279                 private = this_len;
1280
1281                 spd.pages[spd.nr_pages] = rbuf->page_array[pidx];
1282                 spd.partial[spd.nr_pages].offset = poff;
1283
1284                 this_end = cur_pos + this_len;
1285                 if (this_end >= nonpad_end) {
1286                         this_len = nonpad_end - cur_pos;
1287                         private = this_len + padding;
1288                 }
1289                 spd.partial[spd.nr_pages].len = this_len;
1290                 spd.partial[spd.nr_pages].private = private;
1291
1292                 len -= this_len;
1293                 total_len += this_len;
1294                 poff = 0;
1295                 pidx = (pidx + 1) % subbuf_pages;
1296
1297                 if (this_end >= nonpad_end) {
1298                         spd.nr_pages++;
1299                         break;
1300                 }
1301         }
1302
1303         ret = 0;
1304         if (!spd.nr_pages)
1305                 goto out;
1306
1307         ret = *nonpad_ret = splice_to_pipe(pipe, &spd);
1308         if (ret < 0 || ret < total_len)
1309                 goto out;
1310
1311         if (read_start + ret == nonpad_end)
1312                 ret += padding;
1313
1314 out:
1315         splice_shrink_spd(&spd);
1316         return ret;
1317 }
1318
1319 static ssize_t relay_file_splice_read(struct file *in,
1320                                       loff_t *ppos,
1321                                       struct pipe_inode_info *pipe,
1322                                       size_t len,
1323                                       unsigned int flags)
1324 {
1325         ssize_t spliced;
1326         int ret;
1327         int nonpad_ret = 0;
1328
1329         ret = 0;
1330         spliced = 0;
1331
1332         while (len && !spliced) {
1333                 ret = subbuf_splice_actor(in, ppos, pipe, len, flags, &nonpad_ret);
1334                 if (ret < 0)
1335                         break;
1336                 else if (!ret) {
1337                         if (flags & SPLICE_F_NONBLOCK)
1338                                 ret = -EAGAIN;
1339                         break;
1340                 }
1341
1342                 *ppos += ret;
1343                 if (ret > len)
1344                         len = 0;
1345                 else
1346                         len -= ret;
1347                 spliced += nonpad_ret;
1348                 nonpad_ret = 0;
1349         }
1350
1351         if (spliced)
1352                 return spliced;
1353
1354         return ret;
1355 }
1356
1357 const struct file_operations relay_file_operations = {
1358         .open           = relay_file_open,
1359         .poll           = relay_file_poll,
1360         .mmap           = relay_file_mmap,
1361         .read           = relay_file_read,
1362         .llseek         = no_llseek,
1363         .release        = relay_file_release,
1364         .splice_read    = relay_file_splice_read,
1365 };
1366 EXPORT_SYMBOL_GPL(relay_file_operations);