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 = kzalloc(sizeof(struct rchan_buf), GFP_KERNEL);
 168         if (!buf)
 169                 return NULL;
 170
 171         buf->padding = kmalloc(chan->n_subbufs * sizeof(size_t *), GFP_KERNEL);
 172         if (!buf->padding)
 173                 goto free_buf;
 174
 175         buf->start = relay_alloc_buf(buf, &chan->alloc_size);
 176         if (!buf->start)
 177                 goto free_buf;
 178
 179         buf->chan = chan;
 180         kref_get(&buf->chan->kref);
 181         return buf;
 182
 183 free_buf:
 184         kfree(buf->padding);
 185         kfree(buf);
 186         return NULL;
 187 }
 188
 189 /**
 190  *      relay_destroy_channel - free the channel struct
 191  *      @kref: target kernel reference that contains the relay channel
 192  *
 193  *      Should only be called from kref_put().
 194  */
 195 static void relay_destroy_channel(struct kref *kref)
 196 {
 197         struct rchan *chan = container_of(kref, struct rchan, kref);
 198         kfree(chan);
 199 }
 200
 201 /**
 202  *      relay_destroy_buf - destroy an rchan_buf struct and associated buffer
 203  *      @buf: the buffer struct
 204  */
 205 static void relay_destroy_buf(struct rchan_buf *buf)
 206 {
 207         struct rchan *chan = buf->chan;
 208         unsigned int i;
 209
 210         if (likely(buf->start)) {
 211                 vunmap(buf->start);
 212                 for (i = 0; i < buf->page_count; i++)
 213                         __free_page(buf->page_array[i]);
 214                 relay_free_page_array(buf->page_array);
 215         }
 216         chan->buf[buf->cpu] = NULL;
 217         kfree(buf->padding);
 218         kfree(buf);
 219         kref_put(&chan->kref, relay_destroy_channel);
 220 }
 221
 222 /**
 223  *      relay_remove_buf - remove a channel buffer
 224  *      @kref: target kernel reference that contains the relay buffer
 225  *
 226  *      Removes the file from the fileystem, which also frees the
 227  *      rchan_buf_struct and the channel buffer.  Should only be called from
 228  *      kref_put().
 229  */
 230 static void relay_remove_buf(struct kref *kref)
 231 {
 232         struct rchan_buf *buf = container_of(kref, struct rchan_buf, kref);
 233         buf->chan->cb->remove_buf_file(buf->dentry);
 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                                                        int 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         buf->dentry->d_inode->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         }
 455
 456         buf->cpu = cpu;
 457         __relay_reset(buf, 1);
 458
 459         if(chan->is_global) {
 460                 chan->buf[0] = buf;
 461                 buf->cpu = 0;
 462         }
 463
 464         return buf;
 465
 466 free_buf:
 467         relay_destroy_buf(buf);
 468         return NULL;
 469 }
 470
 471 /**
 472  *      relay_close_buf - close a channel buffer
 473  *      @buf: channel buffer
 474  *
 475  *      Marks the buffer finalized and restores the default callbacks.
 476  *      The channel buffer and channel buffer data structure are then freed
 477  *      automatically when the last reference is given up.
 478  */
 479 static void relay_close_buf(struct rchan_buf *buf)
 480 {
 481         buf->finalized = 1;
 482         del_timer_sync(&buf->timer);
 483         kref_put(&buf->kref, relay_remove_buf);
 484 }
 485
 486 static void setup_callbacks(struct rchan *chan,
 487                                    struct rchan_callbacks *cb)
 488 {
 489         if (!cb) {
 490                 chan->cb = &default_channel_callbacks;
 491                 return;
 492         }
 493
 494         if (!cb->subbuf_start)
 495                 cb->subbuf_start = subbuf_start_default_callback;
 496         if (!cb->buf_mapped)
 497                 cb->buf_mapped = buf_mapped_default_callback;
 498         if (!cb->buf_unmapped)
 499                 cb->buf_unmapped = buf_unmapped_default_callback;
 500         if (!cb->create_buf_file)
 501                 cb->create_buf_file = create_buf_file_default_callback;
 502         if (!cb->remove_buf_file)
 503                 cb->remove_buf_file = remove_buf_file_default_callback;
 504         chan->cb = cb;
 505 }
 506
 507 /**
 508  *      relay_hotcpu_callback - CPU hotplug callback
 509  *      @nb: notifier block
 510  *      @action: hotplug action to take
 511  *      @hcpu: CPU number
 512  *
 513  *      Returns the success/failure of the operation. (%NOTIFY_OK, %NOTIFY_BAD)
 514  */
 515 static int __cpuinit relay_hotcpu_callback(struct notifier_block *nb,
 516                                 unsigned long action,
 517                                 void *hcpu)
 518 {
 519         unsigned int hotcpu = (unsigned long)hcpu;
 520         struct rchan *chan;
 521
 522         switch(action) {
 523         case CPU_UP_PREPARE:
 524         case CPU_UP_PREPARE_FROZEN:
 525                 mutex_lock(&relay_channels_mutex);
 526                 list_for_each_entry(chan, &relay_channels, list) {
 527                         if (chan->buf[hotcpu])
 528                                 continue;
 529                         chan->buf[hotcpu] = relay_open_buf(chan, hotcpu);
 530                         if(!chan->buf[hotcpu]) {
 531                                 printk(KERN_ERR
 532                                         "relay_hotcpu_callback: cpu %d buffer "
 533                                         "creation failed\n", hotcpu);
 534                                 mutex_unlock(&relay_channels_mutex);
 535                                 return notifier_from_errno(-ENOMEM);
 536                         }
 537                 }
 538                 mutex_unlock(&relay_channels_mutex);
 539                 break;
 540         case CPU_DEAD:
 541         case CPU_DEAD_FROZEN:
 542                 /* No need to flush the cpu : will be flushed upon
 543                  * final relay_flush() call. */
 544                 break;
 545         }
 546         return NOTIFY_OK;
 547 }
 548
 549 /**
 550  *      relay_open - create a new relay channel
 551  *      @base_filename: base name of files to create, %NULL for buffering only
 552  *      @parent: dentry of parent directory, %NULL for root directory or buffer
 553  *      @subbuf_size: size of sub-buffers
 554  *      @n_subbufs: number of sub-buffers
 555  *      @cb: client callback functions
 556  *      @private_data: user-defined data
 557  *
 558  *      Returns channel pointer if successful, %NULL otherwise.
 559  *
 560  *      Creates a channel buffer for each cpu using the sizes and
 561  *      attributes specified.  The created channel buffer files
 562  *      will be named base_filename0...base_filenameN-1.  File
 563  *      permissions will be %S_IRUSR.
 564  */
 565 struct rchan *relay_open(const char *base_filename,
 566                          struct dentry *parent,
 567                          size_t subbuf_size,
 568                          size_t n_subbufs,
 569                          struct rchan_callbacks *cb,
 570                          void *private_data)
 571 {
 572         unsigned int i;
 573         struct rchan *chan;
 574
 575         if (!(subbuf_size && n_subbufs))
 576                 return NULL;
 577
 578         chan = kzalloc(sizeof(struct rchan), GFP_KERNEL);
 579         if (!chan)
 580                 return NULL;
 581
 582         chan->version = RELAYFS_CHANNEL_VERSION;
 583         chan->n_subbufs = n_subbufs;
 584         chan->subbuf_size = subbuf_size;
 585         chan->alloc_size = FIX_SIZE(subbuf_size * n_subbufs);
 586         chan->parent = parent;
 587         chan->private_data = private_data;
 588         if (base_filename) {
 589                 chan->has_base_filename = 1;
 590                 strlcpy(chan->base_filename, base_filename, NAME_MAX);
 591         }
 592         setup_callbacks(chan, cb);
 593         kref_init(&chan->kref);
 594
 595         mutex_lock(&relay_channels_mutex);
 596         for_each_online_cpu(i) {
 597                 chan->buf[i] = relay_open_buf(chan, i);
 598                 if (!chan->buf[i])
 599                         goto free_bufs;
 600         }
 601         list_add(&chan->list, &relay_channels);
 602         mutex_unlock(&relay_channels_mutex);
 603
 604         return chan;
 605
 606 free_bufs:
 607         for_each_possible_cpu(i) {
 608                 if (chan->buf[i])
 609                         relay_close_buf(chan->buf[i]);
 610         }
 611
 612         kref_put(&chan->kref, relay_destroy_channel);
 613         mutex_unlock(&relay_channels_mutex);
 614         return NULL;
 615 }
 616 EXPORT_SYMBOL_GPL(relay_open);
 617
 618 struct rchan_percpu_buf_dispatcher {
 619         struct rchan_buf *buf;
 620         struct dentry *dentry;
 621 };
 622
 623 /* Called in atomic context. */
 624 static void __relay_set_buf_dentry(void *info)
 625 {
 626         struct rchan_percpu_buf_dispatcher *p = info;
 627
 628         relay_set_buf_dentry(p->buf, p->dentry);
 629 }
 630
 631 /**
 632  *      relay_late_setup_files - triggers file creation
 633  *      @chan: channel to operate on
 634  *      @base_filename: base name of files to create
 635  *      @parent: dentry of parent directory, %NULL for root directory
 636  *
 637  *      Returns 0 if successful, non-zero otherwise.
 638  *
 639  *      Use to setup files for a previously buffer-only channel.
 640  *      Useful to do early tracing in kernel, before VFS is up, for example.
 641  */
 642 int relay_late_setup_files(struct rchan *chan,
 643                            const char *base_filename,
 644                            struct dentry *parent)
 645 {
 646         int err = 0;
 647         unsigned int i, curr_cpu;
 648         unsigned long flags;
 649         struct dentry *dentry;
 650         struct rchan_percpu_buf_dispatcher disp;
 651
 652         if (!chan || !base_filename)
 653                 return -EINVAL;
 654
 655         strlcpy(chan->base_filename, base_filename, NAME_MAX);
 656
 657         mutex_lock(&relay_channels_mutex);
 658         /* Is chan already set up? */
 659         if (unlikely(chan->has_base_filename)) {
 660                 mutex_unlock(&relay_channels_mutex);
 661                 return -EEXIST;
 662         }
 663         chan->has_base_filename = 1;
 664         chan->parent = parent;
 665         curr_cpu = get_cpu();
 666         /*
 667          * The CPU hotplug notifier ran before us and created buffers with
 668          * no files associated. So it's safe to call relay_setup_buf_file()
 669          * on all currently online CPUs.
 670          */
 671         for_each_online_cpu(i) {
 672                 if (unlikely(!chan->buf[i])) {
 673                         WARN_ONCE(1, KERN_ERR "CPU has no buffer!\n");
 674                         err = -EINVAL;
 675                         break;
 676                 }
 677
 678                 dentry = relay_create_buf_file(chan, chan->buf[i], i);
 679                 if (unlikely(!dentry)) {
 680                         err = -EINVAL;
 681                         break;
 682                 }
 683
 684                 if (curr_cpu == i) {
 685                         local_irq_save(flags);
 686                         relay_set_buf_dentry(chan->buf[i], dentry);
 687                         local_irq_restore(flags);
 688                 } else {
 689                         disp.buf = chan->buf[i];
 690                         disp.dentry = dentry;
 691                         smp_mb();
 692                         /* relay_channels_mutex must be held, so wait. */
 693                         err = smp_call_function_single(i,
 694                                                        __relay_set_buf_dentry,
 695                                                        &disp, 1);
 696                 }
 697                 if (unlikely(err))
 698                         break;
 699         }
 700         put_cpu();
 701         mutex_unlock(&relay_channels_mutex);
 702
 703         return err;
 704 }
 705
 706 /**
 707  *      relay_switch_subbuf - switch to a new sub-buffer
 708  *      @buf: channel buffer
 709  *      @length: size of current event
 710  *
 711  *      Returns either the length passed in or 0 if full.
 712  *
 713  *      Performs sub-buffer-switch tasks such as invoking callbacks,
 714  *      updating padding counts, waking up readers, etc.
 715  */
 716 size_t relay_switch_subbuf(struct rchan_buf *buf, size_t length)
 717 {
 718         void *old, *new;
 719         size_t old_subbuf, new_subbuf;
 720
 721         if (unlikely(length > buf->chan->subbuf_size))
 722                 goto toobig;
 723
 724         if (buf->offset != buf->chan->subbuf_size + 1) {
 725                 buf->prev_padding = buf->chan->subbuf_size - buf->offset;
 726                 old_subbuf = buf->subbufs_produced % buf->chan->n_subbufs;
 727                 buf->padding[old_subbuf] = buf->prev_padding;
 728                 buf->subbufs_produced++;
 729                 if (buf->dentry)
 730                         buf->dentry->d_inode->i_size +=
 731                                 buf->chan->subbuf_size -
 732                                 buf->padding[old_subbuf];
 733                 else
 734                         buf->early_bytes += buf->chan->subbuf_size -
 735                                             buf->padding[old_subbuf];
 736                 smp_mb();
 737                 if (waitqueue_active(&buf->read_wait))
 738                         /*
 739                          * Calling wake_up_interruptible() from here
 740                          * will deadlock if we happen to be logging
 741                          * from the scheduler (trying to re-grab
 742                          * rq->lock), so defer it.
 743                          */
 744                         mod_timer(&buf->timer, jiffies + 1);
 745         }
 746
 747         old = buf->data;
 748         new_subbuf = buf->subbufs_produced % buf->chan->n_subbufs;
 749         new = buf->start + new_subbuf * buf->chan->subbuf_size;
 750         buf->offset = 0;
 751         if (!buf->chan->cb->subbuf_start(buf, new, old, buf->prev_padding)) {
 752                 buf->offset = buf->chan->subbuf_size + 1;
 753                 return 0;
 754         }
 755         buf->data = new;
 756         buf->padding[new_subbuf] = 0;
 757
 758         if (unlikely(length + buf->offset > buf->chan->subbuf_size))
 759                 goto toobig;
 760
 761         return length;
 762
 763 toobig:
 764         buf->chan->last_toobig = length;
 765         return 0;
 766 }
 767 EXPORT_SYMBOL_GPL(relay_switch_subbuf);
 768
 769 /**
 770  *      relay_subbufs_consumed - update the buffer's sub-buffers-consumed count
 771  *      @chan: the channel
 772  *      @cpu: the cpu associated with the channel buffer to update
 773  *      @subbufs_consumed: number of sub-buffers to add to current buf's count
 774  *
 775  *      Adds to the channel buffer's consumed sub-buffer count.
 776  *      subbufs_consumed should be the number of sub-buffers newly consumed,
 777  *      not the total consumed.
 778  *
 779  *      NOTE. Kernel clients don't need to call this function if the channel
 780  *      mode is 'overwrite'.
 781  */
 782 void relay_subbufs_consumed(struct rchan *chan,
 783                             unsigned int cpu,
 784                             size_t subbufs_consumed)
 785 {
 786         struct rchan_buf *buf;
 787
 788         if (!chan)
 789                 return;
 790
 791         if (cpu >= NR_CPUS || !chan->buf[cpu] ||
 792                                         subbufs_consumed > chan->n_subbufs)
 793                 return;
 794
 795         buf = chan->buf[cpu];
 796         if (subbufs_consumed > buf->subbufs_produced - buf->subbufs_consumed)
 797                 buf->subbufs_consumed = buf->subbufs_produced;
 798         else
 799                 buf->subbufs_consumed += subbufs_consumed;
 800 }
 801 EXPORT_SYMBOL_GPL(relay_subbufs_consumed);
 802
 803 /**
 804  *      relay_close - close the channel
 805  *      @chan: the channel
 806  *
 807  *      Closes all channel buffers and frees the channel.
 808  */
 809 void relay_close(struct rchan *chan)
 810 {
 811         unsigned int i;
 812
 813         if (!chan)
 814                 return;
 815
 816         mutex_lock(&relay_channels_mutex);
 817         if (chan->is_global && chan->buf[0])
 818                 relay_close_buf(chan->buf[0]);
 819         else
 820                 for_each_possible_cpu(i)
 821                         if (chan->buf[i])
 822                                 relay_close_buf(chan->buf[i]);
 823
 824         if (chan->last_toobig)
 825                 printk(KERN_WARNING "relay: one or more items not logged "
 826                        "[item size (%Zd) > sub-buffer size (%Zd)]\n",
 827                        chan->last_toobig, chan->subbuf_size);
 828
 829         list_del(&chan->list);
 830         kref_put(&chan->kref, relay_destroy_channel);
 831         mutex_unlock(&relay_channels_mutex);
 832 }
 833 EXPORT_SYMBOL_GPL(relay_close);
 834
 835 /**
 836  *      relay_flush - close the channel
 837  *      @chan: the channel
 838  *
 839  *      Flushes all channel buffers, i.e. forces buffer switch.
 840  */
 841 void relay_flush(struct rchan *chan)
 842 {
 843         unsigned int i;
 844
 845         if (!chan)
 846                 return;
 847
 848         if (chan->is_global && chan->buf[0]) {
 849                 relay_switch_subbuf(chan->buf[0], 0);
 850                 return;
 851         }
 852
 853         mutex_lock(&relay_channels_mutex);
 854         for_each_possible_cpu(i)
 855                 if (chan->buf[i])
 856                         relay_switch_subbuf(chan->buf[i], 0);
 857         mutex_unlock(&relay_channels_mutex);
 858 }
 859 EXPORT_SYMBOL_GPL(relay_flush);
 860
 861 /**
 862  *      relay_file_open - open file op for relay files
 863  *      @inode: the inode
 864  *      @filp: the file
 865  *
 866  *      Increments the channel buffer refcount.
 867  */
 868 static int relay_file_open(struct inode *inode, struct file *filp)
 869 {
 870         struct rchan_buf *buf = inode->i_private;
 871         kref_get(&buf->kref);
 872         filp->private_data = buf;
 873
 874         return nonseekable_open(inode, filp);
 875 }
 876
 877 /**
 878  *      relay_file_mmap - mmap file op for relay files
 879  *      @filp: the file
 880  *      @vma: the vma describing what to map
 881  *
 882  *      Calls upon relay_mmap_buf() to map the file into user space.
 883  */
 884 static int relay_file_mmap(struct file *filp, struct vm_area_struct *vma)
 885 {
 886         struct rchan_buf *buf = filp->private_data;
 887         return relay_mmap_buf(buf, vma);
 888 }
 889
 890 /**
 891  *      relay_file_poll - poll file op for relay files
 892  *      @filp: the file
 893  *      @wait: poll table
 894  *
 895  *      Poll implemention.
 896  */
 897 static unsigned int relay_file_poll(struct file *filp, poll_table *wait)
 898 {
 899         unsigned int mask = 0;
 900         struct rchan_buf *buf = filp->private_data;
 901
 902         if (buf->finalized)
 903                 return POLLERR;
 904
 905         if (filp->f_mode & FMODE_READ) {
 906                 poll_wait(filp, &buf->read_wait, wait);
 907                 if (!relay_buf_empty(buf))
 908                         mask |= POLLIN | POLLRDNORM;
 909         }
 910
 911         return mask;
 912 }
 913
 914 /**
 915  *      relay_file_release - release file op for relay files
 916  *      @inode: the inode
 917  *      @filp: the file
 918  *
 919  *      Decrements the channel refcount, as the filesystem is
 920  *      no longer using it.
 921  */
 922 static int relay_file_release(struct inode *inode, struct file *filp)
 923 {
 924         struct rchan_buf *buf = filp->private_data;
 925         kref_put(&buf->kref, relay_remove_buf);
 926
 927         return 0;
 928 }
 929
 930 /*
 931  *      relay_file_read_consume - update the consumed count for the buffer
 932  */
 933 static void relay_file_read_consume(struct rchan_buf *buf,
 934                                     size_t read_pos,
 935                                     size_t bytes_consumed)
 936 {
 937         size_t subbuf_size = buf->chan->subbuf_size;
 938         size_t n_subbufs = buf->chan->n_subbufs;
 939         size_t read_subbuf;
 940
 941         if (buf->subbufs_produced == buf->subbufs_consumed &&
 942             buf->offset == buf->bytes_consumed)
 943                 return;
 944
 945         if (buf->bytes_consumed + bytes_consumed > subbuf_size) {
 946                 relay_subbufs_consumed(buf->chan, buf->cpu, 1);
 947                 buf->bytes_consumed = 0;
 948         }
 949
 950         buf->bytes_consumed += bytes_consumed;
 951         if (!read_pos)
 952                 read_subbuf = buf->subbufs_consumed % n_subbufs;
 953         else
 954                 read_subbuf = read_pos / buf->chan->subbuf_size;
 955         if (buf->bytes_consumed + buf->padding[read_subbuf] == subbuf_size) {
 956                 if ((read_subbuf == buf->subbufs_produced % n_subbufs) &&
 957                     (buf->offset == subbuf_size))
 958                         return;
 959                 relay_subbufs_consumed(buf->chan, buf->cpu, 1);
 960                 buf->bytes_consumed = 0;
 961         }
 962 }
 963
 964 /*
 965  *      relay_file_read_avail - boolean, are there unconsumed bytes available?
 966  */
 967 static int relay_file_read_avail(struct rchan_buf *buf, size_t read_pos)
 968 {
 969         size_t subbuf_size = buf->chan->subbuf_size;
 970         size_t n_subbufs = buf->chan->n_subbufs;
 971         size_t produced = buf->subbufs_produced;
 972         size_t consumed = buf->subbufs_consumed;
 973
 974         relay_file_read_consume(buf, read_pos, 0);
 975
 976         consumed = buf->subbufs_consumed;
 977
 978         if (unlikely(buf->offset > subbuf_size)) {
 979                 if (produced == consumed)
 980                         return 0;
 981                 return 1;
 982         }
 983
 984         if (unlikely(produced - consumed >= n_subbufs)) {
 985                 consumed = produced - n_subbufs + 1;
 986                 buf->subbufs_consumed = consumed;
 987                 buf->bytes_consumed = 0;
 988         }
 989
 990         produced = (produced % n_subbufs) * subbuf_size + buf->offset;
 991         consumed = (consumed % n_subbufs) * subbuf_size + buf->bytes_consumed;
 992
 993         if (consumed > produced)
 994                 produced += n_subbufs * subbuf_size;
 995
 996         if (consumed == produced) {
 997                 if (buf->offset == subbuf_size &&
 998                     buf->subbufs_produced > buf->subbufs_consumed)
 999                         return 1;
1000                 return 0;
1001         }
1002
1003         return 1;
1004 }
1005
1006 /**
1007  *      relay_file_read_subbuf_avail - return bytes available in sub-buffer
1008  *      @read_pos: file read position
1009  *      @buf: relay channel buffer
1010  */
1011 static size_t relay_file_read_subbuf_avail(size_t read_pos,
1012                                            struct rchan_buf *buf)
1013 {
1014         size_t padding, avail = 0;
1015         size_t read_subbuf, read_offset, write_subbuf, write_offset;
1016         size_t subbuf_size = buf->chan->subbuf_size;
1017
1018         write_subbuf = (buf->data - buf->start) / subbuf_size;
1019         write_offset = buf->offset > subbuf_size ? subbuf_size : buf->offset;
1020         read_subbuf = read_pos / subbuf_size;
1021         read_offset = read_pos % subbuf_size;
1022         padding = buf->padding[read_subbuf];
1023
1024         if (read_subbuf == write_subbuf) {
1025                 if (read_offset + padding < write_offset)
1026                         avail = write_offset - (read_offset + padding);
1027         } else
1028                 avail = (subbuf_size - padding) - read_offset;
1029
1030         return avail;
1031 }
1032
1033 /**
1034  *      relay_file_read_start_pos - find the first available byte to read
1035  *      @read_pos: file read position
1036  *      @buf: relay channel buffer
1037  *
1038  *      If the @read_pos is in the middle of padding, return the
1039  *      position of the first actually available byte, otherwise
1040  *      return the original value.
1041  */
1042 static size_t relay_file_read_start_pos(size_t read_pos,
1043                                         struct rchan_buf *buf)
1044 {
1045         size_t read_subbuf, padding, padding_start, padding_end;
1046         size_t subbuf_size = buf->chan->subbuf_size;
1047         size_t n_subbufs = buf->chan->n_subbufs;
1048         size_t consumed = buf->subbufs_consumed % n_subbufs;
1049
1050         if (!read_pos)
1051                 read_pos = consumed * subbuf_size + buf->bytes_consumed;
1052         read_subbuf = read_pos / subbuf_size;
1053         padding = buf->padding[read_subbuf];
1054         padding_start = (read_subbuf + 1) * subbuf_size - padding;
1055         padding_end = (read_subbuf + 1) * subbuf_size;
1056         if (read_pos >= padding_start && read_pos < padding_end) {
1057                 read_subbuf = (read_subbuf + 1) % n_subbufs;
1058                 read_pos = read_subbuf * subbuf_size;
1059         }
1060
1061         return read_pos;
1062 }
1063
1064 /**
1065  *      relay_file_read_end_pos - return the new read position
1066  *      @read_pos: file read position
1067  *      @buf: relay channel buffer
1068  *      @count: number of bytes to be read
1069  */
1070 static size_t relay_file_read_end_pos(struct rchan_buf *buf,
1071                                       size_t read_pos,
1072                                       size_t count)
1073 {
1074         size_t read_subbuf, padding, end_pos;
1075         size_t subbuf_size = buf->chan->subbuf_size;
1076         size_t n_subbufs = buf->chan->n_subbufs;
1077
1078         read_subbuf = read_pos / subbuf_size;
1079         padding = buf->padding[read_subbuf];
1080         if (read_pos % subbuf_size + count + padding == subbuf_size)
1081                 end_pos = (read_subbuf + 1) * subbuf_size;
1082         else
1083                 end_pos = read_pos + count;
1084         if (end_pos >= subbuf_size * n_subbufs)
1085                 end_pos = 0;
1086
1087         return end_pos;
1088 }
1089
1090 /*
1091  *      subbuf_read_actor - read up to one subbuf's worth of data
1092  */
1093 static int subbuf_read_actor(size_t read_start,
1094                              struct rchan_buf *buf,
1095                              size_t avail,
1096                              read_descriptor_t *desc,
1097                              read_actor_t actor)
1098 {
1099         void *from;
1100         int ret = 0;
1101
1102         from = buf->start + read_start;
1103         ret = avail;
1104         if (copy_to_user(desc->arg.buf, from, avail)) {
1105                 desc->error = -EFAULT;
1106                 ret = 0;
1107         }
1108         desc->arg.data += ret;
1109         desc->written += ret;
1110         desc->count -= ret;
1111
1112         return ret;
1113 }
1114
1115 typedef int (*subbuf_actor_t) (size_t read_start,
1116                                struct rchan_buf *buf,
1117                                size_t avail,
1118                                read_descriptor_t *desc,
1119                                read_actor_t actor);
1120
1121 /*
1122  *      relay_file_read_subbufs - read count bytes, bridging subbuf boundaries
1123  */
1124 static ssize_t relay_file_read_subbufs(struct file *filp, loff_t *ppos,
1125                                         subbuf_actor_t subbuf_actor,
1126                                         read_actor_t actor,
1127                                         read_descriptor_t *desc)
1128 {
1129         struct rchan_buf *buf = filp->private_data;
1130         size_t read_start, avail;
1131         int ret;
1132
1133         if (!desc->count)
1134                 return 0;
1135
1136         mutex_lock(&filp->f_path.dentry->d_inode->i_mutex);
1137         do {
1138                 if (!relay_file_read_avail(buf, *ppos))
1139                         break;
1140
1141                 read_start = relay_file_read_start_pos(*ppos, buf);
1142                 avail = relay_file_read_subbuf_avail(read_start, buf);
1143                 if (!avail)
1144                         break;
1145
1146                 avail = min(desc->count, avail);
1147                 ret = subbuf_actor(read_start, buf, avail, desc, actor);
1148                 if (desc->error < 0)
1149                         break;
1150
1151                 if (ret) {
1152                         relay_file_read_consume(buf, read_start, ret);
1153                         *ppos = relay_file_read_end_pos(buf, read_start, ret);
1154                 }
1155         } while (desc->count && ret);
1156         mutex_unlock(&filp->f_path.dentry->d_inode->i_mutex);
1157
1158         return desc->written;
1159 }
1160
1161 static ssize_t relay_file_read(struct file *filp,
1162                                char __user *buffer,
1163                                size_t count,
1164                                loff_t *ppos)
1165 {
1166         read_descriptor_t desc;
1167         desc.written = 0;
1168         desc.count = count;
1169         desc.arg.buf = buffer;
1170         desc.error = 0;
1171         return relay_file_read_subbufs(filp, ppos, subbuf_read_actor,
1172                                        NULL, &desc);
1173 }
1174
1175 static void relay_consume_bytes(struct rchan_buf *rbuf, int bytes_consumed)
1176 {
1177         rbuf->bytes_consumed += bytes_consumed;
1178
1179         if (rbuf->bytes_consumed >= rbuf->chan->subbuf_size) {
1180                 relay_subbufs_consumed(rbuf->chan, rbuf->cpu, 1);
1181                 rbuf->bytes_consumed %= rbuf->chan->subbuf_size;
1182         }
1183 }
1184
1185 static void relay_pipe_buf_release(struct pipe_inode_info *pipe,
1186                                    struct pipe_buffer *buf)
1187 {
1188         struct rchan_buf *rbuf;
1189
1190         rbuf = (struct rchan_buf *)page_private(buf->page);
1191         relay_consume_bytes(rbuf, buf->private);
1192 }
1193
1194 static const struct pipe_buf_operations relay_pipe_buf_ops = {
1195         .can_merge = 0,
1196         .map = generic_pipe_buf_map,
1197         .unmap = generic_pipe_buf_unmap,
1198         .confirm = generic_pipe_buf_confirm,
1199         .release = relay_pipe_buf_release,
1200         .steal = generic_pipe_buf_steal,
1201         .get = generic_pipe_buf_get,
1202 };
1203
1204 static void relay_page_release(struct splice_pipe_desc *spd, unsigned int i)
1205 {
1206 }
1207
1208 /*
1209  *      subbuf_splice_actor - splice up to one subbuf's worth of data
1210  */
1211 static ssize_t subbuf_splice_actor(struct file *in,
1212                                loff_t *ppos,
1213                                struct pipe_inode_info *pipe,
1214                                size_t len,
1215                                unsigned int flags,
1216                                int *nonpad_ret)
1217 {
1218         unsigned int pidx, poff, total_len, subbuf_pages, nr_pages;
1219         struct rchan_buf *rbuf = in->private_data;
1220         unsigned int subbuf_size = rbuf->chan->subbuf_size;
1221         uint64_t pos = (uint64_t) *ppos;
1222         uint32_t alloc_size = (uint32_t) rbuf->chan->alloc_size;
1223         size_t read_start = (size_t) do_div(pos, alloc_size);
1224         size_t read_subbuf = read_start / subbuf_size;
1225         size_t padding = rbuf->padding[read_subbuf];
1226         size_t nonpad_end = read_subbuf * subbuf_size + subbuf_size - padding;
1227         struct page *pages[PIPE_DEF_BUFFERS];
1228         struct partial_page partial[PIPE_DEF_BUFFERS];
1229         struct splice_pipe_desc spd = {
1230                 .pages = pages,
1231                 .nr_pages = 0,
1232                 .partial = partial,
1233                 .flags = flags,
1234                 .ops = &relay_pipe_buf_ops,
1235                 .spd_release = relay_page_release,
1236         };
1237         ssize_t ret;
1238
1239         if (rbuf->subbufs_produced == rbuf->subbufs_consumed)
1240                 return 0;
1241         if (splice_grow_spd(pipe, &spd))
1242                 return -ENOMEM;
1243
1244         /*
1245          * Adjust read len, if longer than what is available
1246          */
1247         if (len > (subbuf_size - read_start % subbuf_size))
1248                 len = subbuf_size - read_start % subbuf_size;
1249
1250         subbuf_pages = rbuf->chan->alloc_size >> PAGE_SHIFT;
1251         pidx = (read_start / PAGE_SIZE) % subbuf_pages;
1252         poff = read_start & ~PAGE_MASK;
1253         nr_pages = min_t(unsigned int, subbuf_pages, pipe->buffers);
1254
1255         for (total_len = 0; spd.nr_pages < nr_pages; spd.nr_pages++) {
1256                 unsigned int this_len, this_end, private;
1257                 unsigned int cur_pos = read_start + total_len;
1258
1259                 if (!len)
1260                         break;
1261
1262                 this_len = min_t(unsigned long, len, PAGE_SIZE - poff);
1263                 private = this_len;
1264
1265                 spd.pages[spd.nr_pages] = rbuf->page_array[pidx];
1266                 spd.partial[spd.nr_pages].offset = poff;
1267
1268                 this_end = cur_pos + this_len;
1269                 if (this_end >= nonpad_end) {
1270                         this_len = nonpad_end - cur_pos;
1271                         private = this_len + padding;
1272                 }
1273                 spd.partial[spd.nr_pages].len = this_len;
1274                 spd.partial[spd.nr_pages].private = private;
1275
1276                 len -= this_len;
1277                 total_len += this_len;
1278                 poff = 0;
1279                 pidx = (pidx + 1) % subbuf_pages;
1280
1281                 if (this_end >= nonpad_end) {
1282                         spd.nr_pages++;
1283                         break;
1284                 }
1285         }
1286
1287         ret = 0;
1288         if (!spd.nr_pages)
1289                 goto out;
1290
1291         ret = *nonpad_ret = splice_to_pipe(pipe, &spd);
1292         if (ret < 0 || ret < total_len)
1293                 goto out;
1294
1295         if (read_start + ret == nonpad_end)
1296                 ret += padding;
1297
1298 out:
1299         splice_shrink_spd(pipe, &spd);
1300         return ret;
1301 }
1302
1303 static ssize_t relay_file_splice_read(struct file *in,
1304                                       loff_t *ppos,
1305                                       struct pipe_inode_info *pipe,
1306                                       size_t len,
1307                                       unsigned int flags)
1308 {
1309         ssize_t spliced;
1310         int ret;
1311         int nonpad_ret = 0;
1312
1313         ret = 0;
1314         spliced = 0;
1315
1316         while (len && !spliced) {
1317                 ret = subbuf_splice_actor(in, ppos, pipe, len, flags, &nonpad_ret);
1318                 if (ret < 0)
1319                         break;
1320                 else if (!ret) {
1321                         if (flags & SPLICE_F_NONBLOCK)
1322                                 ret = -EAGAIN;
1323                         break;
1324                 }
1325
1326                 *ppos += ret;
1327                 if (ret > len)
1328                         len = 0;
1329                 else
1330                         len -= ret;
1331                 spliced += nonpad_ret;
1332                 nonpad_ret = 0;
1333         }
1334
1335         if (spliced)
1336                 return spliced;
1337
1338         return ret;
1339 }
1340
1341 const struct file_operations relay_file_operations = {
1342         .open           = relay_file_open,
1343         .poll           = relay_file_poll,
1344         .mmap           = relay_file_mmap,
1345         .read           = relay_file_read,
1346         .llseek         = no_llseek,
1347         .release        = relay_file_release,
1348         .splice_read    = relay_file_splice_read,
1349 };
1350 EXPORT_SYMBOL_GPL(relay_file_operations);
1351
1352 static __init int relay_init(void)
1353 {
1354
1355         hotcpu_notifier(relay_hotcpu_callback, 0);
1356         return 0;
1357 }
1358
1359 early_initcall(relay_init);