linux/mm/backing-dev.c
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   1
   2#include <linux/wait.h>
   3#include <linux/backing-dev.h>
   4#include <linux/kthread.h>
   5#include <linux/freezer.h>
   6#include <linux/fs.h>
   7#include <linux/pagemap.h>
   8#include <linux/mm.h>
   9#include <linux/sched.h>
  10#include <linux/module.h>
  11#include <linux/writeback.h>
  12#include <linux/device.h>
  13#include <trace/events/writeback.h>
  14
  15static atomic_long_t bdi_seq = ATOMIC_LONG_INIT(0);
  16
  17struct backing_dev_info default_backing_dev_info = {
  18        .name           = "default",
  19        .ra_pages       = VM_MAX_READAHEAD * 1024 / PAGE_CACHE_SIZE,
  20        .state          = 0,
  21        .capabilities   = BDI_CAP_MAP_COPY,
  22};
  23EXPORT_SYMBOL_GPL(default_backing_dev_info);
  24
  25struct backing_dev_info noop_backing_dev_info = {
  26        .name           = "noop",
  27        .capabilities   = BDI_CAP_NO_ACCT_AND_WRITEBACK,
  28};
  29EXPORT_SYMBOL_GPL(noop_backing_dev_info);
  30
  31static struct class *bdi_class;
  32
  33/*
  34 * bdi_lock protects updates to bdi_list. bdi_list has RCU reader side
  35 * locking.
  36 */
  37DEFINE_SPINLOCK(bdi_lock);
  38LIST_HEAD(bdi_list);
  39
  40/* bdi_wq serves all asynchronous writeback tasks */
  41struct workqueue_struct *bdi_wq;
  42
  43void bdi_lock_two(struct bdi_writeback *wb1, struct bdi_writeback *wb2)
  44{
  45        if (wb1 < wb2) {
  46                spin_lock(&wb1->list_lock);
  47                spin_lock_nested(&wb2->list_lock, 1);
  48        } else {
  49                spin_lock(&wb2->list_lock);
  50                spin_lock_nested(&wb1->list_lock, 1);
  51        }
  52}
  53
  54#ifdef CONFIG_DEBUG_FS
  55#include <linux/debugfs.h>
  56#include <linux/seq_file.h>
  57
  58static struct dentry *bdi_debug_root;
  59
  60static void bdi_debug_init(void)
  61{
  62        bdi_debug_root = debugfs_create_dir("bdi", NULL);
  63}
  64
  65static int bdi_debug_stats_show(struct seq_file *m, void *v)
  66{
  67        struct backing_dev_info *bdi = m->private;
  68        struct bdi_writeback *wb = &bdi->wb;
  69        unsigned long background_thresh;
  70        unsigned long dirty_thresh;
  71        unsigned long bdi_thresh;
  72        unsigned long nr_dirty, nr_io, nr_more_io;
  73        struct inode *inode;
  74
  75        nr_dirty = nr_io = nr_more_io = 0;
  76        spin_lock(&wb->list_lock);
  77        list_for_each_entry(inode, &wb->b_dirty, i_wb_list)
  78                nr_dirty++;
  79        list_for_each_entry(inode, &wb->b_io, i_wb_list)
  80                nr_io++;
  81        list_for_each_entry(inode, &wb->b_more_io, i_wb_list)
  82                nr_more_io++;
  83        spin_unlock(&wb->list_lock);
  84
  85        global_dirty_limits(&background_thresh, &dirty_thresh);
  86        bdi_thresh = bdi_dirty_limit(bdi, dirty_thresh);
  87
  88#define K(x) ((x) << (PAGE_SHIFT - 10))
  89        seq_printf(m,
  90                   "BdiWriteback:       %10lu kB\n"
  91                   "BdiReclaimable:     %10lu kB\n"
  92                   "BdiDirtyThresh:     %10lu kB\n"
  93                   "DirtyThresh:        %10lu kB\n"
  94                   "BackgroundThresh:   %10lu kB\n"
  95                   "BdiDirtied:         %10lu kB\n"
  96                   "BdiWritten:         %10lu kB\n"
  97                   "BdiWriteBandwidth:  %10lu kBps\n"
  98                   "b_dirty:            %10lu\n"
  99                   "b_io:               %10lu\n"
 100                   "b_more_io:          %10lu\n"
 101                   "bdi_list:           %10u\n"
 102                   "state:              %10lx\n",
 103                   (unsigned long) K(bdi_stat(bdi, BDI_WRITEBACK)),
 104                   (unsigned long) K(bdi_stat(bdi, BDI_RECLAIMABLE)),
 105                   K(bdi_thresh),
 106                   K(dirty_thresh),
 107                   K(background_thresh),
 108                   (unsigned long) K(bdi_stat(bdi, BDI_DIRTIED)),
 109                   (unsigned long) K(bdi_stat(bdi, BDI_WRITTEN)),
 110                   (unsigned long) K(bdi->write_bandwidth),
 111                   nr_dirty,
 112                   nr_io,
 113                   nr_more_io,
 114                   !list_empty(&bdi->bdi_list), bdi->state);
 115#undef K
 116
 117        return 0;
 118}
 119
 120static int bdi_debug_stats_open(struct inode *inode, struct file *file)
 121{
 122        return single_open(file, bdi_debug_stats_show, inode->i_private);
 123}
 124
 125static const struct file_operations bdi_debug_stats_fops = {
 126        .open           = bdi_debug_stats_open,
 127        .read           = seq_read,
 128        .llseek         = seq_lseek,
 129        .release        = single_release,
 130};
 131
 132static void bdi_debug_register(struct backing_dev_info *bdi, const char *name)
 133{
 134        bdi->debug_dir = debugfs_create_dir(name, bdi_debug_root);
 135        bdi->debug_stats = debugfs_create_file("stats", 0444, bdi->debug_dir,
 136                                               bdi, &bdi_debug_stats_fops);
 137}
 138
 139static void bdi_debug_unregister(struct backing_dev_info *bdi)
 140{
 141        debugfs_remove(bdi->debug_stats);
 142        debugfs_remove(bdi->debug_dir);
 143}
 144#else
 145static inline void bdi_debug_init(void)
 146{
 147}
 148static inline void bdi_debug_register(struct backing_dev_info *bdi,
 149                                      const char *name)
 150{
 151}
 152static inline void bdi_debug_unregister(struct backing_dev_info *bdi)
 153{
 154}
 155#endif
 156
 157static ssize_t read_ahead_kb_store(struct device *dev,
 158                                  struct device_attribute *attr,
 159                                  const char *buf, size_t count)
 160{
 161        struct backing_dev_info *bdi = dev_get_drvdata(dev);
 162        unsigned long read_ahead_kb;
 163        ssize_t ret;
 164
 165        ret = kstrtoul(buf, 10, &read_ahead_kb);
 166        if (ret < 0)
 167                return ret;
 168
 169        bdi->ra_pages = read_ahead_kb >> (PAGE_SHIFT - 10);
 170
 171        return count;
 172}
 173
 174#define K(pages) ((pages) << (PAGE_SHIFT - 10))
 175
 176#define BDI_SHOW(name, expr)                                            \
 177static ssize_t name##_show(struct device *dev,                          \
 178                           struct device_attribute *attr, char *page)   \
 179{                                                                       \
 180        struct backing_dev_info *bdi = dev_get_drvdata(dev);            \
 181                                                                        \
 182        return snprintf(page, PAGE_SIZE-1, "%lld\n", (long long)expr);  \
 183}
 184
 185BDI_SHOW(read_ahead_kb, K(bdi->ra_pages))
 186
 187static ssize_t min_ratio_store(struct device *dev,
 188                struct device_attribute *attr, const char *buf, size_t count)
 189{
 190        struct backing_dev_info *bdi = dev_get_drvdata(dev);
 191        unsigned int ratio;
 192        ssize_t ret;
 193
 194        ret = kstrtouint(buf, 10, &ratio);
 195        if (ret < 0)
 196                return ret;
 197
 198        ret = bdi_set_min_ratio(bdi, ratio);
 199        if (!ret)
 200                ret = count;
 201
 202        return ret;
 203}
 204BDI_SHOW(min_ratio, bdi->min_ratio)
 205
 206static ssize_t max_ratio_store(struct device *dev,
 207                struct device_attribute *attr, const char *buf, size_t count)
 208{
 209        struct backing_dev_info *bdi = dev_get_drvdata(dev);
 210        unsigned int ratio;
 211        ssize_t ret;
 212
 213        ret = kstrtouint(buf, 10, &ratio);
 214        if (ret < 0)
 215                return ret;
 216
 217        ret = bdi_set_max_ratio(bdi, ratio);
 218        if (!ret)
 219                ret = count;
 220
 221        return ret;
 222}
 223BDI_SHOW(max_ratio, bdi->max_ratio)
 224
 225static ssize_t stable_pages_required_show(struct device *dev,
 226                                          struct device_attribute *attr,
 227                                          char *page)
 228{
 229        struct backing_dev_info *bdi = dev_get_drvdata(dev);
 230
 231        return snprintf(page, PAGE_SIZE-1, "%d\n",
 232                        bdi_cap_stable_pages_required(bdi) ? 1 : 0);
 233}
 234
 235static struct device_attribute bdi_dev_attrs[] = {
 236        __ATTR_RW(read_ahead_kb),
 237        __ATTR_RW(min_ratio),
 238        __ATTR_RW(max_ratio),
 239        __ATTR_RO(stable_pages_required),
 240        __ATTR_NULL,
 241};
 242
 243static __init int bdi_class_init(void)
 244{
 245        bdi_class = class_create(THIS_MODULE, "bdi");
 246        if (IS_ERR(bdi_class))
 247                return PTR_ERR(bdi_class);
 248
 249        bdi_class->dev_attrs = bdi_dev_attrs;
 250        bdi_debug_init();
 251        return 0;
 252}
 253postcore_initcall(bdi_class_init);
 254
 255static int __init default_bdi_init(void)
 256{
 257        int err;
 258
 259        bdi_wq = alloc_workqueue("writeback", WQ_MEM_RECLAIM | WQ_FREEZABLE |
 260                                              WQ_UNBOUND | WQ_SYSFS, 0);
 261        if (!bdi_wq)
 262                return -ENOMEM;
 263
 264        err = bdi_init(&default_backing_dev_info);
 265        if (!err)
 266                bdi_register(&default_backing_dev_info, NULL, "default");
 267        err = bdi_init(&noop_backing_dev_info);
 268
 269        return err;
 270}
 271subsys_initcall(default_bdi_init);
 272
 273int bdi_has_dirty_io(struct backing_dev_info *bdi)
 274{
 275        return wb_has_dirty_io(&bdi->wb);
 276}
 277
 278/*
 279 * This function is used when the first inode for this bdi is marked dirty. It
 280 * wakes-up the corresponding bdi thread which should then take care of the
 281 * periodic background write-out of dirty inodes. Since the write-out would
 282 * starts only 'dirty_writeback_interval' centisecs from now anyway, we just
 283 * set up a timer which wakes the bdi thread up later.
 284 *
 285 * Note, we wouldn't bother setting up the timer, but this function is on the
 286 * fast-path (used by '__mark_inode_dirty()'), so we save few context switches
 287 * by delaying the wake-up.
 288 */
 289void bdi_wakeup_thread_delayed(struct backing_dev_info *bdi)
 290{
 291        unsigned long timeout;
 292
 293        timeout = msecs_to_jiffies(dirty_writeback_interval * 10);
 294        mod_delayed_work(bdi_wq, &bdi->wb.dwork, timeout);
 295}
 296
 297/*
 298 * Remove bdi from bdi_list, and ensure that it is no longer visible
 299 */
 300static void bdi_remove_from_list(struct backing_dev_info *bdi)
 301{
 302        spin_lock_bh(&bdi_lock);
 303        list_del_rcu(&bdi->bdi_list);
 304        spin_unlock_bh(&bdi_lock);
 305
 306        synchronize_rcu_expedited();
 307
 308        /* bdi_list is now unused, clear it to mark @bdi dying */
 309        INIT_LIST_HEAD(&bdi->bdi_list);
 310}
 311
 312int bdi_register(struct backing_dev_info *bdi, struct device *parent,
 313                const char *fmt, ...)
 314{
 315        va_list args;
 316        struct device *dev;
 317
 318        if (bdi->dev)   /* The driver needs to use separate queues per device */
 319                return 0;
 320
 321        va_start(args, fmt);
 322        dev = device_create_vargs(bdi_class, parent, MKDEV(0, 0), bdi, fmt, args);
 323        va_end(args);
 324        if (IS_ERR(dev))
 325                return PTR_ERR(dev);
 326
 327        bdi->dev = dev;
 328
 329        bdi_debug_register(bdi, dev_name(dev));
 330        set_bit(BDI_registered, &bdi->state);
 331
 332        spin_lock_bh(&bdi_lock);
 333        list_add_tail_rcu(&bdi->bdi_list, &bdi_list);
 334        spin_unlock_bh(&bdi_lock);
 335
 336        trace_writeback_bdi_register(bdi);
 337        return 0;
 338}
 339EXPORT_SYMBOL(bdi_register);
 340
 341int bdi_register_dev(struct backing_dev_info *bdi, dev_t dev)
 342{
 343        return bdi_register(bdi, NULL, "%u:%u", MAJOR(dev), MINOR(dev));
 344}
 345EXPORT_SYMBOL(bdi_register_dev);
 346
 347/*
 348 * Remove bdi from the global list and shutdown any threads we have running
 349 */
 350static void bdi_wb_shutdown(struct backing_dev_info *bdi)
 351{
 352        if (!bdi_cap_writeback_dirty(bdi))
 353                return;
 354
 355        /*
 356         * Make sure nobody finds us on the bdi_list anymore
 357         */
 358        bdi_remove_from_list(bdi);
 359
 360        /*
 361         * Drain work list and shutdown the delayed_work.  At this point,
 362         * @bdi->bdi_list is empty telling bdi_Writeback_workfn() that @bdi
 363         * is dying and its work_list needs to be drained no matter what.
 364         */
 365        mod_delayed_work(bdi_wq, &bdi->wb.dwork, 0);
 366        flush_delayed_work(&bdi->wb.dwork);
 367        WARN_ON(!list_empty(&bdi->work_list));
 368
 369        /*
 370         * This shouldn't be necessary unless @bdi for some reason has
 371         * unflushed dirty IO after work_list is drained.  Do it anyway
 372         * just in case.
 373         */
 374        cancel_delayed_work_sync(&bdi->wb.dwork);
 375}
 376
 377/*
 378 * This bdi is going away now, make sure that no super_blocks point to it
 379 */
 380static void bdi_prune_sb(struct backing_dev_info *bdi)
 381{
 382        struct super_block *sb;
 383
 384        spin_lock(&sb_lock);
 385        list_for_each_entry(sb, &super_blocks, s_list) {
 386                if (sb->s_bdi == bdi)
 387                        sb->s_bdi = &default_backing_dev_info;
 388        }
 389        spin_unlock(&sb_lock);
 390}
 391
 392void bdi_unregister(struct backing_dev_info *bdi)
 393{
 394        struct device *dev = bdi->dev;
 395
 396        if (dev) {
 397                bdi_set_min_ratio(bdi, 0);
 398                trace_writeback_bdi_unregister(bdi);
 399                bdi_prune_sb(bdi);
 400
 401                bdi_wb_shutdown(bdi);
 402                bdi_debug_unregister(bdi);
 403
 404                spin_lock_bh(&bdi->wb_lock);
 405                bdi->dev = NULL;
 406                spin_unlock_bh(&bdi->wb_lock);
 407
 408                device_unregister(dev);
 409        }
 410}
 411EXPORT_SYMBOL(bdi_unregister);
 412
 413static void bdi_wb_init(struct bdi_writeback *wb, struct backing_dev_info *bdi)
 414{
 415        memset(wb, 0, sizeof(*wb));
 416
 417        wb->bdi = bdi;
 418        wb->last_old_flush = jiffies;
 419        INIT_LIST_HEAD(&wb->b_dirty);
 420        INIT_LIST_HEAD(&wb->b_io);
 421        INIT_LIST_HEAD(&wb->b_more_io);
 422        spin_lock_init(&wb->list_lock);
 423        INIT_DELAYED_WORK(&wb->dwork, bdi_writeback_workfn);
 424}
 425
 426/*
 427 * Initial write bandwidth: 100 MB/s
 428 */
 429#define INIT_BW         (100 << (20 - PAGE_SHIFT))
 430
 431int bdi_init(struct backing_dev_info *bdi)
 432{
 433        int i, err;
 434
 435        bdi->dev = NULL;
 436
 437        bdi->min_ratio = 0;
 438        bdi->max_ratio = 100;
 439        bdi->max_prop_frac = FPROP_FRAC_BASE;
 440        spin_lock_init(&bdi->wb_lock);
 441        INIT_LIST_HEAD(&bdi->bdi_list);
 442        INIT_LIST_HEAD(&bdi->work_list);
 443
 444        bdi_wb_init(&bdi->wb, bdi);
 445
 446        for (i = 0; i < NR_BDI_STAT_ITEMS; i++) {
 447                err = percpu_counter_init(&bdi->bdi_stat[i], 0);
 448                if (err)
 449                        goto err;
 450        }
 451
 452        bdi->dirty_exceeded = 0;
 453
 454        bdi->bw_time_stamp = jiffies;
 455        bdi->written_stamp = 0;
 456
 457        bdi->balanced_dirty_ratelimit = INIT_BW;
 458        bdi->dirty_ratelimit = INIT_BW;
 459        bdi->write_bandwidth = INIT_BW;
 460        bdi->avg_write_bandwidth = INIT_BW;
 461
 462        err = fprop_local_init_percpu(&bdi->completions);
 463
 464        if (err) {
 465err:
 466                while (i--)
 467                        percpu_counter_destroy(&bdi->bdi_stat[i]);
 468        }
 469
 470        return err;
 471}
 472EXPORT_SYMBOL(bdi_init);
 473
 474void bdi_destroy(struct backing_dev_info *bdi)
 475{
 476        int i;
 477
 478        /*
 479         * Splice our entries to the default_backing_dev_info, if this
 480         * bdi disappears
 481         */
 482        if (bdi_has_dirty_io(bdi)) {
 483                struct bdi_writeback *dst = &default_backing_dev_info.wb;
 484
 485                bdi_lock_two(&bdi->wb, dst);
 486                list_splice(&bdi->wb.b_dirty, &dst->b_dirty);
 487                list_splice(&bdi->wb.b_io, &dst->b_io);
 488                list_splice(&bdi->wb.b_more_io, &dst->b_more_io);
 489                spin_unlock(&bdi->wb.list_lock);
 490                spin_unlock(&dst->list_lock);
 491        }
 492
 493        bdi_unregister(bdi);
 494
 495        /*
 496         * If bdi_unregister() had already been called earlier, the dwork
 497         * could still be pending because bdi_prune_sb() can race with the
 498         * bdi_wakeup_thread_delayed() calls from __mark_inode_dirty().
 499         */
 500        cancel_delayed_work_sync(&bdi->wb.dwork);
 501
 502        for (i = 0; i < NR_BDI_STAT_ITEMS; i++)
 503                percpu_counter_destroy(&bdi->bdi_stat[i]);
 504
 505        fprop_local_destroy_percpu(&bdi->completions);
 506}
 507EXPORT_SYMBOL(bdi_destroy);
 508
 509/*
 510 * For use from filesystems to quickly init and register a bdi associated
 511 * with dirty writeback
 512 */
 513int bdi_setup_and_register(struct backing_dev_info *bdi, char *name,
 514                           unsigned int cap)
 515{
 516        int err;
 517
 518        bdi->name = name;
 519        bdi->capabilities = cap;
 520        err = bdi_init(bdi);
 521        if (err)
 522                return err;
 523
 524        err = bdi_register(bdi, NULL, "%.28s-%ld", name,
 525                           atomic_long_inc_return(&bdi_seq));
 526        if (err) {
 527                bdi_destroy(bdi);
 528                return err;
 529        }
 530
 531        return 0;
 532}
 533EXPORT_SYMBOL(bdi_setup_and_register);
 534
 535static wait_queue_head_t congestion_wqh[2] = {
 536                __WAIT_QUEUE_HEAD_INITIALIZER(congestion_wqh[0]),
 537                __WAIT_QUEUE_HEAD_INITIALIZER(congestion_wqh[1])
 538        };
 539static atomic_t nr_bdi_congested[2];
 540
 541void clear_bdi_congested(struct backing_dev_info *bdi, int sync)
 542{
 543        enum bdi_state bit;
 544        wait_queue_head_t *wqh = &congestion_wqh[sync];
 545
 546        bit = sync ? BDI_sync_congested : BDI_async_congested;
 547        if (test_and_clear_bit(bit, &bdi->state))
 548                atomic_dec(&nr_bdi_congested[sync]);
 549        smp_mb__after_clear_bit();
 550        if (waitqueue_active(wqh))
 551                wake_up(wqh);
 552}
 553EXPORT_SYMBOL(clear_bdi_congested);
 554
 555void set_bdi_congested(struct backing_dev_info *bdi, int sync)
 556{
 557        enum bdi_state bit;
 558
 559        bit = sync ? BDI_sync_congested : BDI_async_congested;
 560        if (!test_and_set_bit(bit, &bdi->state))
 561                atomic_inc(&nr_bdi_congested[sync]);
 562}
 563EXPORT_SYMBOL(set_bdi_congested);
 564
 565/**
 566 * congestion_wait - wait for a backing_dev to become uncongested
 567 * @sync: SYNC or ASYNC IO
 568 * @timeout: timeout in jiffies
 569 *
 570 * Waits for up to @timeout jiffies for a backing_dev (any backing_dev) to exit
 571 * write congestion.  If no backing_devs are congested then just wait for the
 572 * next write to be completed.
 573 */
 574long congestion_wait(int sync, long timeout)
 575{
 576        long ret;
 577        unsigned long start = jiffies;
 578        DEFINE_WAIT(wait);
 579        wait_queue_head_t *wqh = &congestion_wqh[sync];
 580
 581        prepare_to_wait(wqh, &wait, TASK_UNINTERRUPTIBLE);
 582        ret = io_schedule_timeout(timeout);
 583        finish_wait(wqh, &wait);
 584
 585        trace_writeback_congestion_wait(jiffies_to_usecs(timeout),
 586                                        jiffies_to_usecs(jiffies - start));
 587
 588        return ret;
 589}
 590EXPORT_SYMBOL(congestion_wait);
 591
 592/**
 593 * wait_iff_congested - Conditionally wait for a backing_dev to become uncongested or a zone to complete writes
 594 * @zone: A zone to check if it is heavily congested
 595 * @sync: SYNC or ASYNC IO
 596 * @timeout: timeout in jiffies
 597 *
 598 * In the event of a congested backing_dev (any backing_dev) and the given
 599 * @zone has experienced recent congestion, this waits for up to @timeout
 600 * jiffies for either a BDI to exit congestion of the given @sync queue
 601 * or a write to complete.
 602 *
 603 * In the absence of zone congestion, cond_resched() is called to yield
 604 * the processor if necessary but otherwise does not sleep.
 605 *
 606 * The return value is 0 if the sleep is for the full timeout. Otherwise,
 607 * it is the number of jiffies that were still remaining when the function
 608 * returned. return_value == timeout implies the function did not sleep.
 609 */
 610long wait_iff_congested(struct zone *zone, int sync, long timeout)
 611{
 612        long ret;
 613        unsigned long start = jiffies;
 614        DEFINE_WAIT(wait);
 615        wait_queue_head_t *wqh = &congestion_wqh[sync];
 616
 617        /*
 618         * If there is no congestion, or heavy congestion is not being
 619         * encountered in the current zone, yield if necessary instead
 620         * of sleeping on the congestion queue
 621         */
 622        if (atomic_read(&nr_bdi_congested[sync]) == 0 ||
 623                        !zone_is_reclaim_congested(zone)) {
 624                cond_resched();
 625
 626                /* In case we scheduled, work out time remaining */
 627                ret = timeout - (jiffies - start);
 628                if (ret < 0)
 629                        ret = 0;
 630
 631                goto out;
 632        }
 633
 634        /* Sleep until uncongested or a write happens */
 635        prepare_to_wait(wqh, &wait, TASK_UNINTERRUPTIBLE);
 636        ret = io_schedule_timeout(timeout);
 637        finish_wait(wqh, &wait);
 638
 639out:
 640        trace_writeback_wait_iff_congested(jiffies_to_usecs(timeout),
 641                                        jiffies_to_usecs(jiffies - start));
 642
 643        return ret;
 644}
 645EXPORT_SYMBOL(wait_iff_congested);
 646
 647int pdflush_proc_obsolete(struct ctl_table *table, int write,
 648                        void __user *buffer, size_t *lenp, loff_t *ppos)
 649{
 650        char kbuf[] = "0\n";
 651
 652        if (*ppos) {
 653                *lenp = 0;
 654                return 0;
 655        }
 656
 657        if (copy_to_user(buffer, kbuf, sizeof(kbuf)))
 658                return -EFAULT;
 659        printk_once(KERN_WARNING "%s exported in /proc is scheduled for removal\n",
 660                        table->procname);
 661
 662        *lenp = 2;
 663        *ppos += *lenp;
 664        return 2;
 665}
 666
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