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