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