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