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         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         unsigned int i;
 386
 387         if (!chan)
 388                 return;
 389
 390         if (chan->is_global && chan->buf[0]) {
 391                 __relay_reset(chan->buf[0], 0);
 392                 return;
 393         }
 394
 395         mutex_lock(&relay_channels_mutex);
 396         for_each_possible_cpu(i)
 397                 if (chan->buf[i])
 398                         __relay_reset(chan->buf[i], 0);
 399         mutex_unlock(&relay_channels_mutex);
 400 }
 401 EXPORT_SYMBOL_GPL(relay_reset);
 402
 403 static inline void relay_set_buf_dentry(struct rchan_buf *buf,
 404                                         struct dentry *dentry)
 405 {
 406         buf->dentry = dentry;
 407         d_inode(buf->dentry)->i_size = buf->early_bytes;
 408 }
 409
 410 static struct dentry *relay_create_buf_file(struct rchan *chan,
 411                                             struct rchan_buf *buf,
 412                                             unsigned int cpu)
 413 {
 414         struct dentry *dentry;
 415         char *tmpname;
 416
 417         tmpname = kzalloc(NAME_MAX + 1, GFP_KERNEL);
 418         if (!tmpname)
 419                 return NULL;
 420         snprintf(tmpname, NAME_MAX, "%s%d", chan->base_filename, cpu);
 421
 422         /* Create file in fs */
 423         dentry = chan->cb->create_buf_file(tmpname, chan->parent,
 424                                            S_IRUSR, buf,
 425                                            &chan->is_global);
 426
 427         kfree(tmpname);
 428
 429         return dentry;
 430 }
 431
 432 /*
 433  *      relay_open_buf - create a new relay channel buffer
 434  *
 435  *      used by relay_open() and CPU hotplug.
 436  */
 437 static struct rchan_buf *relay_open_buf(struct rchan *chan, unsigned int cpu)
 438 {
 439         struct rchan_buf *buf = NULL;
 440         struct dentry *dentry;
 441
 442         if (chan->is_global)
 443                 return chan->buf[0];
 444
 445         buf = relay_create_buf(chan);
 446         if (!buf)
 447                 return NULL;
 448
 449         if (chan->has_base_filename) {
 450                 dentry = relay_create_buf_file(chan, buf, cpu);
 451                 if (!dentry)
 452                         goto free_buf;
 453                 relay_set_buf_dentry(buf, dentry);
 454         } else {
 455                 /* Only retrieve global info, nothing more, nothing less */
 456                 dentry = chan->cb->create_buf_file(NULL, NULL,
 457                                                    S_IRUSR, buf,
 458                                                    &chan->is_global);
 459                 if (WARN_ON(dentry))
 460                         goto free_buf;
 461         }
 462
 463         buf->cpu = cpu;
 464         __relay_reset(buf, 1);
 465
 466         if(chan->is_global) {
 467                 chan->buf[0] = buf;
 468                 buf->cpu = 0;
 469         }
 470
 471         return buf;
 472
 473 free_buf:
 474         relay_destroy_buf(buf);
 475         return NULL;
 476 }
 477
 478 /**
 479  *      relay_close_buf - close a channel buffer
 480  *      @buf: channel buffer
 481  *
 482  *      Marks the buffer finalized and restores the default callbacks.
 483  *      The channel buffer and channel buffer data structure are then freed
 484  *      automatically when the last reference is given up.
 485  */
 486 static void relay_close_buf(struct rchan_buf *buf)
 487 {
 488         buf->finalized = 1;
 489         del_timer_sync(&buf->timer);
 490         buf->chan->cb->remove_buf_file(buf->dentry);
 491         kref_put(&buf->kref, relay_remove_buf);
 492 }
 493
 494 static void setup_callbacks(struct rchan *chan,
 495                                    struct rchan_callbacks *cb)
 496 {
 497         if (!cb) {
 498                 chan->cb = &default_channel_callbacks;
 499                 return;
 500         }
 501
 502         if (!cb->subbuf_start)
 503                 cb->subbuf_start = subbuf_start_default_callback;
 504         if (!cb->buf_mapped)
 505                 cb->buf_mapped = buf_mapped_default_callback;
 506         if (!cb->buf_unmapped)
 507                 cb->buf_unmapped = buf_unmapped_default_callback;
 508         if (!cb->create_buf_file)
 509                 cb->create_buf_file = create_buf_file_default_callback;
 510         if (!cb->remove_buf_file)
 511                 cb->remove_buf_file = remove_buf_file_default_callback;
 512         chan->cb = cb;
 513 }
 514
 515 /**
 516  *      relay_hotcpu_callback - CPU hotplug callback
 517  *      @nb: notifier block
 518  *      @action: hotplug action to take
 519  *      @hcpu: CPU number
 520  *
 521  *      Returns the success/failure of the operation. (%NOTIFY_OK, %NOTIFY_BAD)
 522  */
 523 static int relay_hotcpu_callback(struct notifier_block *nb,
 524                                 unsigned long action,
 525                                 void *hcpu)
 526 {
 527         unsigned int hotcpu = (unsigned long)hcpu;
 528         struct rchan *chan;
 529
 530         switch(action) {
 531         case CPU_UP_PREPARE:
 532         case CPU_UP_PREPARE_FROZEN:
 533                 mutex_lock(&relay_channels_mutex);
 534                 list_for_each_entry(chan, &relay_channels, list) {
 535                         if (chan->buf[hotcpu])
 536                                 continue;
 537                         chan->buf[hotcpu] = relay_open_buf(chan, hotcpu);
 538                         if(!chan->buf[hotcpu]) {
 539                                 printk(KERN_ERR
 540                                         "relay_hotcpu_callback: cpu %d buffer "
 541                                         "creation failed\n", hotcpu);
 542                                 mutex_unlock(&relay_channels_mutex);
 543                                 return notifier_from_errno(-ENOMEM);
 544                         }
 545                 }
 546                 mutex_unlock(&relay_channels_mutex);
 547                 break;
 548         case CPU_DEAD:
 549         case CPU_DEAD_FROZEN:
 550                 /* No need to flush the cpu : will be flushed upon
 551                  * final relay_flush() call. */
 552                 break;
 553         }
 554         return NOTIFY_OK;
 555 }
 556
 557 /**
 558  *      relay_open - create a new relay channel
 559  *      @base_filename: base name of files to create, %NULL for buffering only
 560  *      @parent: dentry of parent directory, %NULL for root directory or buffer
 561  *      @subbuf_size: size of sub-buffers
 562  *      @n_subbufs: number of sub-buffers
 563  *      @cb: client callback functions
 564  *      @private_data: user-defined data
 565  *
 566  *      Returns channel pointer if successful, %NULL otherwise.
 567  *
 568  *      Creates a channel buffer for each cpu using the sizes and
 569  *      attributes specified.  The created channel buffer files
 570  *      will be named base_filename0...base_filenameN-1.  File
 571  *      permissions will be %S_IRUSR.
 572  *
 573  *      If opening a buffer (@parent = NULL) that you later wish to register
 574  *      in a filesystem, call relay_late_setup_files() once the @parent dentry
 575  *      is available.
 576  */
 577 struct rchan *relay_open(const char *base_filename,
 578                          struct dentry *parent,
 579                          size_t subbuf_size,
 580                          size_t n_subbufs,
 581                          struct rchan_callbacks *cb,
 582                          void *private_data)
 583 {
 584         unsigned int i;
 585         struct rchan *chan;
 586
 587         if (!(subbuf_size && n_subbufs))
 588                 return NULL;
 589         if (subbuf_size > UINT_MAX / n_subbufs)
 590                 return NULL;
 591
 592         chan = kzalloc(sizeof(struct rchan), GFP_KERNEL);
 593         if (!chan)
 594                 return NULL;
 595
 596         chan->version = RELAYFS_CHANNEL_VERSION;
 597         chan->n_subbufs = n_subbufs;
 598         chan->subbuf_size = subbuf_size;
 599         chan->alloc_size = PAGE_ALIGN(subbuf_size * n_subbufs);
 600         chan->parent = parent;
 601         chan->private_data = private_data;
 602         if (base_filename) {
 603                 chan->has_base_filename = 1;
 604                 strlcpy(chan->base_filename, base_filename, NAME_MAX);
 605         }
 606         setup_callbacks(chan, cb);
 607         kref_init(&chan->kref);
 608
 609         mutex_lock(&relay_channels_mutex);
 610         for_each_online_cpu(i) {
 611                 chan->buf[i] = relay_open_buf(chan, i);
 612                 if (!chan->buf[i])
 613                         goto free_bufs;
 614         }
 615         list_add(&chan->list, &relay_channels);
 616         mutex_unlock(&relay_channels_mutex);
 617
 618         return chan;
 619
 620 free_bufs:
 621         for_each_possible_cpu(i) {
 622                 if (chan->buf[i])
 623                         relay_close_buf(chan->buf[i]);
 624         }
 625
 626         kref_put(&chan->kref, relay_destroy_channel);
 627         mutex_unlock(&relay_channels_mutex);
 628         kfree(chan);
 629         return NULL;
 630 }
 631 EXPORT_SYMBOL_GPL(relay_open);
 632
 633 struct rchan_percpu_buf_dispatcher {
 634         struct rchan_buf *buf;
 635         struct dentry *dentry;
 636 };
 637
 638 /* Called in atomic context. */
 639 static void __relay_set_buf_dentry(void *info)
 640 {
 641         struct rchan_percpu_buf_dispatcher *p = info;
 642
 643         relay_set_buf_dentry(p->buf, p->dentry);
 644 }
 645
 646 /**
 647  *      relay_late_setup_files - triggers file creation
 648  *      @chan: channel to operate on
 649  *      @base_filename: base name of files to create
 650  *      @parent: dentry of parent directory, %NULL for root directory
 651  *
 652  *      Returns 0 if successful, non-zero otherwise.
 653  *
 654  *      Use to setup files for a previously buffer-only channel created
 655  *      by relay_open() with a NULL parent dentry.
 656  *
 657  *      For example, this is useful for perfomring early tracing in kernel,
 658  *      before VFS is up and then exposing the early results once the dentry
 659  *      is available.
 660  */
 661 int relay_late_setup_files(struct rchan *chan,
 662                            const char *base_filename,
 663                            struct dentry *parent)
 664 {
 665         int err = 0;
 666         unsigned int i, curr_cpu;
 667         unsigned long flags;
 668         struct dentry *dentry;
 669         struct rchan_percpu_buf_dispatcher disp;
 670
 671         if (!chan || !base_filename)
 672                 return -EINVAL;
 673
 674         strlcpy(chan->base_filename, base_filename, NAME_MAX);
 675
 676         mutex_lock(&relay_channels_mutex);
 677         /* Is chan already set up? */
 678         if (unlikely(chan->has_base_filename)) {
 679                 mutex_unlock(&relay_channels_mutex);
 680                 return -EEXIST;
 681         }
 682         chan->has_base_filename = 1;
 683         chan->parent = parent;
 684
 685         if (chan->is_global) {
 686                 err = -EINVAL;
 687                 if (!WARN_ON_ONCE(!chan->buf[0])) {
 688                         dentry = relay_create_buf_file(chan, chan->buf[0], 0);
 689                         if (dentry && !WARN_ON_ONCE(!chan->is_global)) {
 690                                 relay_set_buf_dentry(chan->buf[0], dentry);
 691                                 err = 0;
 692                         }
 693                 }
 694                 mutex_unlock(&relay_channels_mutex);
 695                 return err;
 696         }
 697
 698         curr_cpu = get_cpu();
 699         /*
 700          * The CPU hotplug notifier ran before us and created buffers with
 701          * no files associated. So it's safe to call relay_setup_buf_file()
 702          * on all currently online CPUs.
 703          */
 704         for_each_online_cpu(i) {
 705                 if (unlikely(!chan->buf[i])) {
 706                         WARN_ONCE(1, KERN_ERR "CPU has no buffer!\n");
 707                         err = -EINVAL;
 708                         break;
 709                 }
 710
 711                 dentry = relay_create_buf_file(chan, chan->buf[i], i);
 712                 if (unlikely(!dentry)) {
 713                         err = -EINVAL;
 714                         break;
 715                 }
 716
 717                 if (curr_cpu == i) {
 718                         local_irq_save(flags);
 719                         relay_set_buf_dentry(chan->buf[i], dentry);
 720                         local_irq_restore(flags);
 721                 } else {
 722                         disp.buf = chan->buf[i];
 723                         disp.dentry = dentry;
 724                         smp_mb();
 725                         /* relay_channels_mutex must be held, so wait. */
 726                         err = smp_call_function_single(i,
 727                                                        __relay_set_buf_dentry,
 728                                                        &disp, 1);
 729                 }
 730                 if (unlikely(err))
 731                         break;
 732         }
 733         put_cpu();
 734         mutex_unlock(&relay_channels_mutex);
 735
 736         return err;
 737 }
 738 EXPORT_SYMBOL_GPL(relay_late_setup_files);
 739
 740 /**
 741  *      relay_switch_subbuf - switch to a new sub-buffer
 742  *      @buf: channel buffer
 743  *      @length: size of current event
 744  *
 745  *      Returns either the length passed in or 0 if full.
 746  *
 747  *      Performs sub-buffer-switch tasks such as invoking callbacks,
 748  *      updating padding counts, waking up readers, etc.
 749  */
 750 size_t relay_switch_subbuf(struct rchan_buf *buf, size_t length)
 751 {
 752         void *old, *new;
 753         size_t old_subbuf, new_subbuf;
 754
 755         if (unlikely(length > buf->chan->subbuf_size))
 756                 goto toobig;
 757
 758         if (buf->offset != buf->chan->subbuf_size + 1) {
 759                 buf->prev_padding = buf->chan->subbuf_size - buf->offset;
 760                 old_subbuf = buf->subbufs_produced % buf->chan->n_subbufs;
 761                 buf->padding[old_subbuf] = buf->prev_padding;
 762                 buf->subbufs_produced++;
 763                 if (buf->dentry)
 764                         d_inode(buf->dentry)->i_size +=
 765                                 buf->chan->subbuf_size -
 766                                 buf->padding[old_subbuf];
 767                 else
 768                         buf->early_bytes += buf->chan->subbuf_size -
 769                                             buf->padding[old_subbuf];
 770                 smp_mb();
 771                 if (waitqueue_active(&buf->read_wait))
 772                         /*
 773                          * Calling wake_up_interruptible() from here
 774                          * will deadlock if we happen to be logging
 775                          * from the scheduler (trying to re-grab
 776                          * rq->lock), so defer it.
 777                          */
 778                         mod_timer(&buf->timer, jiffies + 1);
 779         }
 780
 781         old = buf->data;
 782         new_subbuf = buf->subbufs_produced % buf->chan->n_subbufs;
 783         new = buf->start + new_subbuf * buf->chan->subbuf_size;
 784         buf->offset = 0;
 785         if (!buf->chan->cb->subbuf_start(buf, new, old, buf->prev_padding)) {
 786                 buf->offset = buf->chan->subbuf_size + 1;
 787                 return 0;
 788         }
 789         buf->data = new;
 790         buf->padding[new_subbuf] = 0;
 791
 792         if (unlikely(length + buf->offset > buf->chan->subbuf_size))
 793                 goto toobig;
 794
 795         return length;
 796
 797 toobig:
 798         buf->chan->last_toobig = length;
 799         return 0;
 800 }
 801 EXPORT_SYMBOL_GPL(relay_switch_subbuf);
 802
 803 /**
 804  *      relay_subbufs_consumed - update the buffer's sub-buffers-consumed count
 805  *      @chan: the channel
 806  *      @cpu: the cpu associated with the channel buffer to update
 807  *      @subbufs_consumed: number of sub-buffers to add to current buf's count
 808  *
 809  *      Adds to the channel buffer's consumed sub-buffer count.
 810  *      subbufs_consumed should be the number of sub-buffers newly consumed,
 811  *      not the total consumed.
 812  *
 813  *      NOTE. Kernel clients don't need to call this function if the channel
 814  *      mode is 'overwrite'.
 815  */
 816 void relay_subbufs_consumed(struct rchan *chan,
 817                             unsigned int cpu,
 818                             size_t subbufs_consumed)
 819 {
 820         struct rchan_buf *buf;
 821
 822         if (!chan)
 823                 return;
 824
 825         if (cpu >= NR_CPUS || !chan->buf[cpu] ||
 826                                         subbufs_consumed > chan->n_subbufs)
 827                 return;
 828
 829         buf = chan->buf[cpu];
 830         if (subbufs_consumed > buf->subbufs_produced - buf->subbufs_consumed)
 831                 buf->subbufs_consumed = buf->subbufs_produced;
 832         else
 833                 buf->subbufs_consumed += subbufs_consumed;
 834 }
 835 EXPORT_SYMBOL_GPL(relay_subbufs_consumed);
 836
 837 /**
 838  *      relay_close - close the channel
 839  *      @chan: the channel
 840  *
 841  *      Closes all channel buffers and frees the channel.
 842  */
 843 void relay_close(struct rchan *chan)
 844 {
 845         unsigned int i;
 846
 847         if (!chan)
 848                 return;
 849
 850         mutex_lock(&relay_channels_mutex);
 851         if (chan->is_global && chan->buf[0])
 852                 relay_close_buf(chan->buf[0]);
 853         else
 854                 for_each_possible_cpu(i)
 855                         if (chan->buf[i])
 856                                 relay_close_buf(chan->buf[i]);
 857
 858         if (chan->last_toobig)
 859                 printk(KERN_WARNING "relay: one or more items not logged "
 860                        "[item size (%Zd) > sub-buffer size (%Zd)]\n",
 861                        chan->last_toobig, chan->subbuf_size);
 862
 863         list_del(&chan->list);
 864         kref_put(&chan->kref, relay_destroy_channel);
 865         mutex_unlock(&relay_channels_mutex);
 866 }
 867 EXPORT_SYMBOL_GPL(relay_close);
 868
 869 /**
 870  *      relay_flush - close the channel
 871  *      @chan: the channel
 872  *
 873  *      Flushes all channel buffers, i.e. forces buffer switch.
 874  */
 875 void relay_flush(struct rchan *chan)
 876 {
 877         unsigned int i;
 878
 879         if (!chan)
 880                 return;
 881
 882         if (chan->is_global && chan->buf[0]) {
 883                 relay_switch_subbuf(chan->buf[0], 0);
 884                 return;
 885         }
 886
 887         mutex_lock(&relay_channels_mutex);
 888         for_each_possible_cpu(i)
 889                 if (chan->buf[i])
 890                         relay_switch_subbuf(chan->buf[i], 0);
 891         mutex_unlock(&relay_channels_mutex);
 892 }
 893 EXPORT_SYMBOL_GPL(relay_flush);
 894
 895 /**
 896  *      relay_file_open - open file op for relay files
 897  *      @inode: the inode
 898  *      @filp: the file
 899  *
 900  *      Increments the channel buffer refcount.
 901  */
 902 static int relay_file_open(struct inode *inode, struct file *filp)
 903 {
 904         struct rchan_buf *buf = inode->i_private;
 905         kref_get(&buf->kref);
 906         filp->private_data = buf;
 907
 908         return nonseekable_open(inode, filp);
 909 }
 910
 911 /**
 912  *      relay_file_mmap - mmap file op for relay files
 913  *      @filp: the file
 914  *      @vma: the vma describing what to map
 915  *
 916  *      Calls upon relay_mmap_buf() to map the file into user space.
 917  */
 918 static int relay_file_mmap(struct file *filp, struct vm_area_struct *vma)
 919 {
 920         struct rchan_buf *buf = filp->private_data;
 921         return relay_mmap_buf(buf, vma);
 922 }
 923
 924 /**
 925  *      relay_file_poll - poll file op for relay files
 926  *      @filp: the file
 927  *      @wait: poll table
 928  *
 929  *      Poll implemention.
 930  */
 931 static unsigned int relay_file_poll(struct file *filp, poll_table *wait)
 932 {
 933         unsigned int mask = 0;
 934         struct rchan_buf *buf = filp->private_data;
 935
 936         if (buf->finalized)
 937                 return POLLERR;
 938
 939         if (filp->f_mode & FMODE_READ) {
 940                 poll_wait(filp, &buf->read_wait, wait);
 941                 if (!relay_buf_empty(buf))
 942                         mask |= POLLIN | POLLRDNORM;
 943         }
 944
 945         return mask;
 946 }
 947
 948 /**
 949  *      relay_file_release - release file op for relay files
 950  *      @inode: the inode
 951  *      @filp: the file
 952  *
 953  *      Decrements the channel refcount, as the filesystem is
 954  *      no longer using it.
 955  */
 956 static int relay_file_release(struct inode *inode, struct file *filp)
 957 {
 958         struct rchan_buf *buf = filp->private_data;
 959         kref_put(&buf->kref, relay_remove_buf);
 960
 961         return 0;
 962 }
 963
 964 /*
 965  *      relay_file_read_consume - update the consumed count for the buffer
 966  */
 967 static void relay_file_read_consume(struct rchan_buf *buf,
 968                                     size_t read_pos,
 969                                     size_t bytes_consumed)
 970 {
 971         size_t subbuf_size = buf->chan->subbuf_size;
 972         size_t n_subbufs = buf->chan->n_subbufs;
 973         size_t read_subbuf;
 974
 975         if (buf->subbufs_produced == buf->subbufs_consumed &&
 976             buf->offset == buf->bytes_consumed)
 977                 return;
 978
 979         if (buf->bytes_consumed + bytes_consumed > subbuf_size) {
 980                 relay_subbufs_consumed(buf->chan, buf->cpu, 1);
 981                 buf->bytes_consumed = 0;
 982         }
 983
 984         buf->bytes_consumed += bytes_consumed;
 985         if (!read_pos)
 986                 read_subbuf = buf->subbufs_consumed % n_subbufs;
 987         else
 988                 read_subbuf = read_pos / buf->chan->subbuf_size;
 989         if (buf->bytes_consumed + buf->padding[read_subbuf] == subbuf_size) {
 990                 if ((read_subbuf == buf->subbufs_produced % n_subbufs) &&
 991                     (buf->offset == subbuf_size))
 992                         return;
 993                 relay_subbufs_consumed(buf->chan, buf->cpu, 1);
 994                 buf->bytes_consumed = 0;
 995         }
 996 }
 997
 998 /*
 999  *      relay_file_read_avail - boolean, are there unconsumed bytes available?
1000  */
1001 static int relay_file_read_avail(struct rchan_buf *buf, size_t read_pos)
1002 {
1003         size_t subbuf_size = buf->chan->subbuf_size;
1004         size_t n_subbufs = buf->chan->n_subbufs;
1005         size_t produced = buf->subbufs_produced;
1006         size_t consumed = buf->subbufs_consumed;
1007
1008         relay_file_read_consume(buf, read_pos, 0);
1009
1010         consumed = buf->subbufs_consumed;
1011
1012         if (unlikely(buf->offset > subbuf_size)) {
1013                 if (produced == consumed)
1014                         return 0;
1015                 return 1;
1016         }
1017
1018         if (unlikely(produced - consumed >= n_subbufs)) {
1019                 consumed = produced - n_subbufs + 1;
1020                 buf->subbufs_consumed = consumed;
1021                 buf->bytes_consumed = 0;
1022         }
1023
1024         produced = (produced % n_subbufs) * subbuf_size + buf->offset;
1025         consumed = (consumed % n_subbufs) * subbuf_size + buf->bytes_consumed;
1026
1027         if (consumed > produced)
1028                 produced += n_subbufs * subbuf_size;
1029
1030         if (consumed == produced) {
1031                 if (buf->offset == subbuf_size &&
1032                     buf->subbufs_produced > buf->subbufs_consumed)
1033                         return 1;
1034                 return 0;
1035         }
1036
1037         return 1;
1038 }
1039
1040 /**
1041  *      relay_file_read_subbuf_avail - return bytes available in sub-buffer
1042  *      @read_pos: file read position
1043  *      @buf: relay channel buffer
1044  */
1045 static size_t relay_file_read_subbuf_avail(size_t read_pos,
1046                                            struct rchan_buf *buf)
1047 {
1048         size_t padding, avail = 0;
1049         size_t read_subbuf, read_offset, write_subbuf, write_offset;
1050         size_t subbuf_size = buf->chan->subbuf_size;
1051
1052         write_subbuf = (buf->data - buf->start) / subbuf_size;
1053         write_offset = buf->offset > subbuf_size ? subbuf_size : buf->offset;
1054         read_subbuf = read_pos / subbuf_size;
1055         read_offset = read_pos % subbuf_size;
1056         padding = buf->padding[read_subbuf];
1057
1058         if (read_subbuf == write_subbuf) {
1059                 if (read_offset + padding < write_offset)
1060                         avail = write_offset - (read_offset + padding);
1061         } else
1062                 avail = (subbuf_size - padding) - read_offset;
1063
1064         return avail;
1065 }
1066
1067 /**
1068  *      relay_file_read_start_pos - find the first available byte to read
1069  *      @read_pos: file read position
1070  *      @buf: relay channel buffer
1071  *
1072  *      If the @read_pos is in the middle of padding, return the
1073  *      position of the first actually available byte, otherwise
1074  *      return the original value.
1075  */
1076 static size_t relay_file_read_start_pos(size_t read_pos,
1077                                         struct rchan_buf *buf)
1078 {
1079         size_t read_subbuf, padding, padding_start, padding_end;
1080         size_t subbuf_size = buf->chan->subbuf_size;
1081         size_t n_subbufs = buf->chan->n_subbufs;
1082         size_t consumed = buf->subbufs_consumed % n_subbufs;
1083
1084         if (!read_pos)
1085                 read_pos = consumed * subbuf_size + buf->bytes_consumed;
1086         read_subbuf = read_pos / subbuf_size;
1087         padding = buf->padding[read_subbuf];
1088         padding_start = (read_subbuf + 1) * subbuf_size - padding;
1089         padding_end = (read_subbuf + 1) * subbuf_size;
1090         if (read_pos >= padding_start && read_pos < padding_end) {
1091                 read_subbuf = (read_subbuf + 1) % n_subbufs;
1092                 read_pos = read_subbuf * subbuf_size;
1093         }
1094
1095         return read_pos;
1096 }
1097
1098 /**
1099  *      relay_file_read_end_pos - return the new read position
1100  *      @read_pos: file read position
1101  *      @buf: relay channel buffer
1102  *      @count: number of bytes to be read
1103  */
1104 static size_t relay_file_read_end_pos(struct rchan_buf *buf,
1105                                       size_t read_pos,
1106                                       size_t count)
1107 {
1108         size_t read_subbuf, padding, end_pos;
1109         size_t subbuf_size = buf->chan->subbuf_size;
1110         size_t n_subbufs = buf->chan->n_subbufs;
1111
1112         read_subbuf = read_pos / subbuf_size;
1113         padding = buf->padding[read_subbuf];
1114         if (read_pos % subbuf_size + count + padding == subbuf_size)
1115                 end_pos = (read_subbuf + 1) * subbuf_size;
1116         else
1117                 end_pos = read_pos + count;
1118         if (end_pos >= subbuf_size * n_subbufs)
1119                 end_pos = 0;
1120
1121         return end_pos;
1122 }
1123
1124 /*
1125  *      subbuf_read_actor - read up to one subbuf's worth of data
1126  */
1127 static int subbuf_read_actor(size_t read_start,
1128                              struct rchan_buf *buf,
1129                              size_t avail,
1130                              read_descriptor_t *desc)
1131 {
1132         void *from;
1133         int ret = 0;
1134
1135         from = buf->start + read_start;
1136         ret = avail;
1137         if (copy_to_user(desc->arg.buf, from, avail)) {
1138                 desc->error = -EFAULT;
1139                 ret = 0;
1140         }
1141         desc->arg.data += ret;
1142         desc->written += ret;
1143         desc->count -= ret;
1144
1145         return ret;
1146 }
1147
1148 typedef int (*subbuf_actor_t) (size_t read_start,
1149                                struct rchan_buf *buf,
1150                                size_t avail,
1151                                read_descriptor_t *desc);
1152
1153 /*
1154  *      relay_file_read_subbufs - read count bytes, bridging subbuf boundaries
1155  */
1156 static ssize_t relay_file_read_subbufs(struct file *filp, loff_t *ppos,
1157                                         subbuf_actor_t subbuf_actor,
1158                                         read_descriptor_t *desc)
1159 {
1160         struct rchan_buf *buf = filp->private_data;
1161         size_t read_start, avail;
1162         int ret;
1163
1164         if (!desc->count)
1165                 return 0;
1166
1167         inode_lock(file_inode(filp));
1168         do {
1169                 if (!relay_file_read_avail(buf, *ppos))
1170                         break;
1171
1172                 read_start = relay_file_read_start_pos(*ppos, buf);
1173                 avail = relay_file_read_subbuf_avail(read_start, buf);
1174                 if (!avail)
1175                         break;
1176
1177                 avail = min(desc->count, avail);
1178                 ret = subbuf_actor(read_start, buf, avail, desc);
1179                 if (desc->error < 0)
1180                         break;
1181
1182                 if (ret) {
1183                         relay_file_read_consume(buf, read_start, ret);
1184                         *ppos = relay_file_read_end_pos(buf, read_start, ret);
1185                 }
1186         } while (desc->count && ret);
1187         inode_unlock(file_inode(filp));
1188
1189         return desc->written;
1190 }
1191
1192 static ssize_t relay_file_read(struct file *filp,
1193                                char __user *buffer,
1194                                size_t count,
1195                                loff_t *ppos)
1196 {
1197         read_descriptor_t desc;
1198         desc.written = 0;
1199         desc.count = count;
1200         desc.arg.buf = buffer;
1201         desc.error = 0;
1202         return relay_file_read_subbufs(filp, ppos, subbuf_read_actor, &desc);
1203 }
1204
1205 static void relay_consume_bytes(struct rchan_buf *rbuf, int bytes_consumed)
1206 {
1207         rbuf->bytes_consumed += bytes_consumed;
1208
1209         if (rbuf->bytes_consumed >= rbuf->chan->subbuf_size) {
1210                 relay_subbufs_consumed(rbuf->chan, rbuf->cpu, 1);
1211                 rbuf->bytes_consumed %= rbuf->chan->subbuf_size;
1212         }
1213 }
1214
1215 static void relay_pipe_buf_release(struct pipe_inode_info *pipe,
1216                                    struct pipe_buffer *buf)
1217 {
1218         struct rchan_buf *rbuf;
1219
1220         rbuf = (struct rchan_buf *)page_private(buf->page);
1221         relay_consume_bytes(rbuf, buf->private);
1222 }
1223
1224 static const struct pipe_buf_operations relay_pipe_buf_ops = {
1225         .can_merge = 0,
1226         .confirm = generic_pipe_buf_confirm,
1227         .release = relay_pipe_buf_release,
1228         .steal = generic_pipe_buf_steal,
1229         .get = generic_pipe_buf_get,
1230 };
1231
1232 static void relay_page_release(struct splice_pipe_desc *spd, unsigned int i)
1233 {
1234 }
1235
1236 /*
1237  *      subbuf_splice_actor - splice up to one subbuf's worth of data
1238  */
1239 static ssize_t subbuf_splice_actor(struct file *in,
1240                                loff_t *ppos,
1241                                struct pipe_inode_info *pipe,
1242                                size_t len,
1243                                unsigned int flags,
1244                                int *nonpad_ret)
1245 {
1246         unsigned int pidx, poff, total_len, subbuf_pages, nr_pages;
1247         struct rchan_buf *rbuf = in->private_data;
1248         unsigned int subbuf_size = rbuf->chan->subbuf_size;
1249         uint64_t pos = (uint64_t) *ppos;
1250         uint32_t alloc_size = (uint32_t) rbuf->chan->alloc_size;
1251         size_t read_start = (size_t) do_div(pos, alloc_size);
1252         size_t read_subbuf = read_start / subbuf_size;
1253         size_t padding = rbuf->padding[read_subbuf];
1254         size_t nonpad_end = read_subbuf * subbuf_size + subbuf_size - padding;
1255         struct page *pages[PIPE_DEF_BUFFERS];
1256         struct partial_page partial[PIPE_DEF_BUFFERS];
1257         struct splice_pipe_desc spd = {
1258                 .pages = pages,
1259                 .nr_pages = 0,
1260                 .nr_pages_max = PIPE_DEF_BUFFERS,
1261                 .partial = partial,
1262                 .flags = flags,
1263                 .ops = &relay_pipe_buf_ops,
1264                 .spd_release = relay_page_release,
1265         };
1266         ssize_t ret;
1267
1268         if (rbuf->subbufs_produced == rbuf->subbufs_consumed)
1269                 return 0;
1270         if (splice_grow_spd(pipe, &spd))
1271                 return -ENOMEM;
1272
1273         /*
1274          * Adjust read len, if longer than what is available
1275          */
1276         if (len > (subbuf_size - read_start % subbuf_size))
1277                 len = subbuf_size - read_start % subbuf_size;
1278
1279         subbuf_pages = rbuf->chan->alloc_size >> PAGE_SHIFT;
1280         pidx = (read_start / PAGE_SIZE) % subbuf_pages;
1281         poff = read_start & ~PAGE_MASK;
1282         nr_pages = min_t(unsigned int, subbuf_pages, spd.nr_pages_max);
1283
1284         for (total_len = 0; spd.nr_pages < nr_pages; spd.nr_pages++) {
1285                 unsigned int this_len, this_end, private;
1286                 unsigned int cur_pos = read_start + total_len;
1287
1288                 if (!len)
1289                         break;
1290
1291                 this_len = min_t(unsigned long, len, PAGE_SIZE - poff);
1292                 private = this_len;
1293
1294                 spd.pages[spd.nr_pages] = rbuf->page_array[pidx];
1295                 spd.partial[spd.nr_pages].offset = poff;
1296
1297                 this_end = cur_pos + this_len;
1298                 if (this_end >= nonpad_end) {
1299                         this_len = nonpad_end - cur_pos;
1300                         private = this_len + padding;
1301                 }
1302                 spd.partial[spd.nr_pages].len = this_len;
1303                 spd.partial[spd.nr_pages].private = private;
1304
1305                 len -= this_len;
1306                 total_len += this_len;
1307                 poff = 0;
1308                 pidx = (pidx + 1) % subbuf_pages;
1309
1310                 if (this_end >= nonpad_end) {
1311                         spd.nr_pages++;
1312                         break;
1313                 }
1314         }
1315
1316         ret = 0;
1317         if (!spd.nr_pages)
1318                 goto out;
1319
1320         ret = *nonpad_ret = splice_to_pipe(pipe, &spd);
1321         if (ret < 0 || ret < total_len)
1322                 goto out;
1323
1324         if (read_start + ret == nonpad_end)
1325                 ret += padding;
1326
1327 out:
1328         splice_shrink_spd(&spd);
1329         return ret;
1330 }
1331
1332 static ssize_t relay_file_splice_read(struct file *in,
1333                                       loff_t *ppos,
1334                                       struct pipe_inode_info *pipe,
1335                                       size_t len,
1336                                       unsigned int flags)
1337 {
1338         ssize_t spliced;
1339         int ret;
1340         int nonpad_ret = 0;
1341
1342         ret = 0;
1343         spliced = 0;
1344
1345         while (len && !spliced) {
1346                 ret = subbuf_splice_actor(in, ppos, pipe, len, flags, &nonpad_ret);
1347                 if (ret < 0)
1348                         break;
1349                 else if (!ret) {
1350                         if (flags & SPLICE_F_NONBLOCK)
1351                                 ret = -EAGAIN;
1352                         break;
1353                 }
1354
1355                 *ppos += ret;
1356                 if (ret > len)
1357                         len = 0;
1358                 else
1359                         len -= ret;
1360                 spliced += nonpad_ret;
1361                 nonpad_ret = 0;
1362         }
1363
1364         if (spliced)
1365                 return spliced;
1366
1367         return ret;
1368 }
1369
1370 const struct file_operations relay_file_operations = {
1371         .open           = relay_file_open,
1372         .poll           = relay_file_poll,
1373         .mmap           = relay_file_mmap,
1374         .read           = relay_file_read,
1375         .llseek         = no_llseek,
1376         .release        = relay_file_release,
1377         .splice_read    = relay_file_splice_read,
1378 };
1379 EXPORT_SYMBOL_GPL(relay_file_operations);
1380
1381 static __init int relay_init(void)
1382 {
1383
1384         hotcpu_notifier(relay_hotcpu_callback, 0);
1385         return 0;
1386 }
1387
1388 early_initcall(relay_init);