linux/fs/kernfs/file.c
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   1// SPDX-License-Identifier: GPL-2.0-only
   2/*
   3 * fs/kernfs/file.c - kernfs file implementation
   4 *
   5 * Copyright (c) 2001-3 Patrick Mochel
   6 * Copyright (c) 2007 SUSE Linux Products GmbH
   7 * Copyright (c) 2007, 2013 Tejun Heo <tj@kernel.org>
   8 */
   9
  10#include <linux/fs.h>
  11#include <linux/seq_file.h>
  12#include <linux/slab.h>
  13#include <linux/poll.h>
  14#include <linux/pagemap.h>
  15#include <linux/sched/mm.h>
  16#include <linux/fsnotify.h>
  17
  18#include "kernfs-internal.h"
  19
  20/*
  21 * There's one kernfs_open_file for each open file and one kernfs_open_node
  22 * for each kernfs_node with one or more open files.
  23 *
  24 * kernfs_node->attr.open points to kernfs_open_node.  attr.open is
  25 * protected by kernfs_open_node_lock.
  26 *
  27 * filp->private_data points to seq_file whose ->private points to
  28 * kernfs_open_file.  kernfs_open_files are chained at
  29 * kernfs_open_node->files, which is protected by kernfs_open_file_mutex.
  30 */
  31static DEFINE_SPINLOCK(kernfs_open_node_lock);
  32static DEFINE_MUTEX(kernfs_open_file_mutex);
  33
  34struct kernfs_open_node {
  35        atomic_t                refcnt;
  36        atomic_t                event;
  37        wait_queue_head_t       poll;
  38        struct list_head        files; /* goes through kernfs_open_file.list */
  39};
  40
  41/*
  42 * kernfs_notify() may be called from any context and bounces notifications
  43 * through a work item.  To minimize space overhead in kernfs_node, the
  44 * pending queue is implemented as a singly linked list of kernfs_nodes.
  45 * The list is terminated with the self pointer so that whether a
  46 * kernfs_node is on the list or not can be determined by testing the next
  47 * pointer for NULL.
  48 */
  49#define KERNFS_NOTIFY_EOL                       ((void *)&kernfs_notify_list)
  50
  51static DEFINE_SPINLOCK(kernfs_notify_lock);
  52static struct kernfs_node *kernfs_notify_list = KERNFS_NOTIFY_EOL;
  53
  54static struct kernfs_open_file *kernfs_of(struct file *file)
  55{
  56        return ((struct seq_file *)file->private_data)->private;
  57}
  58
  59/*
  60 * Determine the kernfs_ops for the given kernfs_node.  This function must
  61 * be called while holding an active reference.
  62 */
  63static const struct kernfs_ops *kernfs_ops(struct kernfs_node *kn)
  64{
  65        if (kn->flags & KERNFS_LOCKDEP)
  66                lockdep_assert_held(kn);
  67        return kn->attr.ops;
  68}
  69
  70/*
  71 * As kernfs_seq_stop() is also called after kernfs_seq_start() or
  72 * kernfs_seq_next() failure, it needs to distinguish whether it's stopping
  73 * a seq_file iteration which is fully initialized with an active reference
  74 * or an aborted kernfs_seq_start() due to get_active failure.  The
  75 * position pointer is the only context for each seq_file iteration and
  76 * thus the stop condition should be encoded in it.  As the return value is
  77 * directly visible to userland, ERR_PTR(-ENODEV) is the only acceptable
  78 * choice to indicate get_active failure.
  79 *
  80 * Unfortunately, this is complicated due to the optional custom seq_file
  81 * operations which may return ERR_PTR(-ENODEV) too.  kernfs_seq_stop()
  82 * can't distinguish whether ERR_PTR(-ENODEV) is from get_active failure or
  83 * custom seq_file operations and thus can't decide whether put_active
  84 * should be performed or not only on ERR_PTR(-ENODEV).
  85 *
  86 * This is worked around by factoring out the custom seq_stop() and
  87 * put_active part into kernfs_seq_stop_active(), skipping it from
  88 * kernfs_seq_stop() if ERR_PTR(-ENODEV) while invoking it directly after
  89 * custom seq_file operations fail with ERR_PTR(-ENODEV) - this ensures
  90 * that kernfs_seq_stop_active() is skipped only after get_active failure.
  91 */
  92static void kernfs_seq_stop_active(struct seq_file *sf, void *v)
  93{
  94        struct kernfs_open_file *of = sf->private;
  95        const struct kernfs_ops *ops = kernfs_ops(of->kn);
  96
  97        if (ops->seq_stop)
  98                ops->seq_stop(sf, v);
  99        kernfs_put_active(of->kn);
 100}
 101
 102static void *kernfs_seq_start(struct seq_file *sf, loff_t *ppos)
 103{
 104        struct kernfs_open_file *of = sf->private;
 105        const struct kernfs_ops *ops;
 106
 107        /*
 108         * @of->mutex nests outside active ref and is primarily to ensure that
 109         * the ops aren't called concurrently for the same open file.
 110         */
 111        mutex_lock(&of->mutex);
 112        if (!kernfs_get_active(of->kn))
 113                return ERR_PTR(-ENODEV);
 114
 115        ops = kernfs_ops(of->kn);
 116        if (ops->seq_start) {
 117                void *next = ops->seq_start(sf, ppos);
 118                /* see the comment above kernfs_seq_stop_active() */
 119                if (next == ERR_PTR(-ENODEV))
 120                        kernfs_seq_stop_active(sf, next);
 121                return next;
 122        } else {
 123                /*
 124                 * The same behavior and code as single_open().  Returns
 125                 * !NULL if pos is at the beginning; otherwise, NULL.
 126                 */
 127                return NULL + !*ppos;
 128        }
 129}
 130
 131static void *kernfs_seq_next(struct seq_file *sf, void *v, loff_t *ppos)
 132{
 133        struct kernfs_open_file *of = sf->private;
 134        const struct kernfs_ops *ops = kernfs_ops(of->kn);
 135
 136        if (ops->seq_next) {
 137                void *next = ops->seq_next(sf, v, ppos);
 138                /* see the comment above kernfs_seq_stop_active() */
 139                if (next == ERR_PTR(-ENODEV))
 140                        kernfs_seq_stop_active(sf, next);
 141                return next;
 142        } else {
 143                /*
 144                 * The same behavior and code as single_open(), always
 145                 * terminate after the initial read.
 146                 */
 147                ++*ppos;
 148                return NULL;
 149        }
 150}
 151
 152static void kernfs_seq_stop(struct seq_file *sf, void *v)
 153{
 154        struct kernfs_open_file *of = sf->private;
 155
 156        if (v != ERR_PTR(-ENODEV))
 157                kernfs_seq_stop_active(sf, v);
 158        mutex_unlock(&of->mutex);
 159}
 160
 161static int kernfs_seq_show(struct seq_file *sf, void *v)
 162{
 163        struct kernfs_open_file *of = sf->private;
 164
 165        of->event = atomic_read(&of->kn->attr.open->event);
 166
 167        return of->kn->attr.ops->seq_show(sf, v);
 168}
 169
 170static const struct seq_operations kernfs_seq_ops = {
 171        .start = kernfs_seq_start,
 172        .next = kernfs_seq_next,
 173        .stop = kernfs_seq_stop,
 174        .show = kernfs_seq_show,
 175};
 176
 177/*
 178 * As reading a bin file can have side-effects, the exact offset and bytes
 179 * specified in read(2) call should be passed to the read callback making
 180 * it difficult to use seq_file.  Implement simplistic custom buffering for
 181 * bin files.
 182 */
 183static ssize_t kernfs_file_direct_read(struct kernfs_open_file *of,
 184                                       char __user *user_buf, size_t count,
 185                                       loff_t *ppos)
 186{
 187        ssize_t len = min_t(size_t, count, PAGE_SIZE);
 188        const struct kernfs_ops *ops;
 189        char *buf;
 190
 191        buf = of->prealloc_buf;
 192        if (buf)
 193                mutex_lock(&of->prealloc_mutex);
 194        else
 195                buf = kmalloc(len, GFP_KERNEL);
 196        if (!buf)
 197                return -ENOMEM;
 198
 199        /*
 200         * @of->mutex nests outside active ref and is used both to ensure that
 201         * the ops aren't called concurrently for the same open file.
 202         */
 203        mutex_lock(&of->mutex);
 204        if (!kernfs_get_active(of->kn)) {
 205                len = -ENODEV;
 206                mutex_unlock(&of->mutex);
 207                goto out_free;
 208        }
 209
 210        of->event = atomic_read(&of->kn->attr.open->event);
 211        ops = kernfs_ops(of->kn);
 212        if (ops->read)
 213                len = ops->read(of, buf, len, *ppos);
 214        else
 215                len = -EINVAL;
 216
 217        kernfs_put_active(of->kn);
 218        mutex_unlock(&of->mutex);
 219
 220        if (len < 0)
 221                goto out_free;
 222
 223        if (copy_to_user(user_buf, buf, len)) {
 224                len = -EFAULT;
 225                goto out_free;
 226        }
 227
 228        *ppos += len;
 229
 230 out_free:
 231        if (buf == of->prealloc_buf)
 232                mutex_unlock(&of->prealloc_mutex);
 233        else
 234                kfree(buf);
 235        return len;
 236}
 237
 238/**
 239 * kernfs_fop_read - kernfs vfs read callback
 240 * @file: file pointer
 241 * @user_buf: data to write
 242 * @count: number of bytes
 243 * @ppos: starting offset
 244 */
 245static ssize_t kernfs_fop_read(struct file *file, char __user *user_buf,
 246                               size_t count, loff_t *ppos)
 247{
 248        struct kernfs_open_file *of = kernfs_of(file);
 249
 250        if (of->kn->flags & KERNFS_HAS_SEQ_SHOW)
 251                return seq_read(file, user_buf, count, ppos);
 252        else
 253                return kernfs_file_direct_read(of, user_buf, count, ppos);
 254}
 255
 256/**
 257 * kernfs_fop_write - kernfs vfs write callback
 258 * @file: file pointer
 259 * @user_buf: data to write
 260 * @count: number of bytes
 261 * @ppos: starting offset
 262 *
 263 * Copy data in from userland and pass it to the matching kernfs write
 264 * operation.
 265 *
 266 * There is no easy way for us to know if userspace is only doing a partial
 267 * write, so we don't support them. We expect the entire buffer to come on
 268 * the first write.  Hint: if you're writing a value, first read the file,
 269 * modify only the the value you're changing, then write entire buffer
 270 * back.
 271 */
 272static ssize_t kernfs_fop_write(struct file *file, const char __user *user_buf,
 273                                size_t count, loff_t *ppos)
 274{
 275        struct kernfs_open_file *of = kernfs_of(file);
 276        const struct kernfs_ops *ops;
 277        ssize_t len;
 278        char *buf;
 279
 280        if (of->atomic_write_len) {
 281                len = count;
 282                if (len > of->atomic_write_len)
 283                        return -E2BIG;
 284        } else {
 285                len = min_t(size_t, count, PAGE_SIZE);
 286        }
 287
 288        buf = of->prealloc_buf;
 289        if (buf)
 290                mutex_lock(&of->prealloc_mutex);
 291        else
 292                buf = kmalloc(len + 1, GFP_KERNEL);
 293        if (!buf)
 294                return -ENOMEM;
 295
 296        if (copy_from_user(buf, user_buf, len)) {
 297                len = -EFAULT;
 298                goto out_free;
 299        }
 300        buf[len] = '\0';        /* guarantee string termination */
 301
 302        /*
 303         * @of->mutex nests outside active ref and is used both to ensure that
 304         * the ops aren't called concurrently for the same open file.
 305         */
 306        mutex_lock(&of->mutex);
 307        if (!kernfs_get_active(of->kn)) {
 308                mutex_unlock(&of->mutex);
 309                len = -ENODEV;
 310                goto out_free;
 311        }
 312
 313        ops = kernfs_ops(of->kn);
 314        if (ops->write)
 315                len = ops->write(of, buf, len, *ppos);
 316        else
 317                len = -EINVAL;
 318
 319        kernfs_put_active(of->kn);
 320        mutex_unlock(&of->mutex);
 321
 322        if (len > 0)
 323                *ppos += len;
 324
 325out_free:
 326        if (buf == of->prealloc_buf)
 327                mutex_unlock(&of->prealloc_mutex);
 328        else
 329                kfree(buf);
 330        return len;
 331}
 332
 333static void kernfs_vma_open(struct vm_area_struct *vma)
 334{
 335        struct file *file = vma->vm_file;
 336        struct kernfs_open_file *of = kernfs_of(file);
 337
 338        if (!of->vm_ops)
 339                return;
 340
 341        if (!kernfs_get_active(of->kn))
 342                return;
 343
 344        if (of->vm_ops->open)
 345                of->vm_ops->open(vma);
 346
 347        kernfs_put_active(of->kn);
 348}
 349
 350static vm_fault_t kernfs_vma_fault(struct vm_fault *vmf)
 351{
 352        struct file *file = vmf->vma->vm_file;
 353        struct kernfs_open_file *of = kernfs_of(file);
 354        vm_fault_t ret;
 355
 356        if (!of->vm_ops)
 357                return VM_FAULT_SIGBUS;
 358
 359        if (!kernfs_get_active(of->kn))
 360                return VM_FAULT_SIGBUS;
 361
 362        ret = VM_FAULT_SIGBUS;
 363        if (of->vm_ops->fault)
 364                ret = of->vm_ops->fault(vmf);
 365
 366        kernfs_put_active(of->kn);
 367        return ret;
 368}
 369
 370static vm_fault_t kernfs_vma_page_mkwrite(struct vm_fault *vmf)
 371{
 372        struct file *file = vmf->vma->vm_file;
 373        struct kernfs_open_file *of = kernfs_of(file);
 374        vm_fault_t ret;
 375
 376        if (!of->vm_ops)
 377                return VM_FAULT_SIGBUS;
 378
 379        if (!kernfs_get_active(of->kn))
 380                return VM_FAULT_SIGBUS;
 381
 382        ret = 0;
 383        if (of->vm_ops->page_mkwrite)
 384                ret = of->vm_ops->page_mkwrite(vmf);
 385        else
 386                file_update_time(file);
 387
 388        kernfs_put_active(of->kn);
 389        return ret;
 390}
 391
 392static int kernfs_vma_access(struct vm_area_struct *vma, unsigned long addr,
 393                             void *buf, int len, int write)
 394{
 395        struct file *file = vma->vm_file;
 396        struct kernfs_open_file *of = kernfs_of(file);
 397        int ret;
 398
 399        if (!of->vm_ops)
 400                return -EINVAL;
 401
 402        if (!kernfs_get_active(of->kn))
 403                return -EINVAL;
 404
 405        ret = -EINVAL;
 406        if (of->vm_ops->access)
 407                ret = of->vm_ops->access(vma, addr, buf, len, write);
 408
 409        kernfs_put_active(of->kn);
 410        return ret;
 411}
 412
 413#ifdef CONFIG_NUMA
 414static int kernfs_vma_set_policy(struct vm_area_struct *vma,
 415                                 struct mempolicy *new)
 416{
 417        struct file *file = vma->vm_file;
 418        struct kernfs_open_file *of = kernfs_of(file);
 419        int ret;
 420
 421        if (!of->vm_ops)
 422                return 0;
 423
 424        if (!kernfs_get_active(of->kn))
 425                return -EINVAL;
 426
 427        ret = 0;
 428        if (of->vm_ops->set_policy)
 429                ret = of->vm_ops->set_policy(vma, new);
 430
 431        kernfs_put_active(of->kn);
 432        return ret;
 433}
 434
 435static struct mempolicy *kernfs_vma_get_policy(struct vm_area_struct *vma,
 436                                               unsigned long addr)
 437{
 438        struct file *file = vma->vm_file;
 439        struct kernfs_open_file *of = kernfs_of(file);
 440        struct mempolicy *pol;
 441
 442        if (!of->vm_ops)
 443                return vma->vm_policy;
 444
 445        if (!kernfs_get_active(of->kn))
 446                return vma->vm_policy;
 447
 448        pol = vma->vm_policy;
 449        if (of->vm_ops->get_policy)
 450                pol = of->vm_ops->get_policy(vma, addr);
 451
 452        kernfs_put_active(of->kn);
 453        return pol;
 454}
 455
 456#endif
 457
 458static const struct vm_operations_struct kernfs_vm_ops = {
 459        .open           = kernfs_vma_open,
 460        .fault          = kernfs_vma_fault,
 461        .page_mkwrite   = kernfs_vma_page_mkwrite,
 462        .access         = kernfs_vma_access,
 463#ifdef CONFIG_NUMA
 464        .set_policy     = kernfs_vma_set_policy,
 465        .get_policy     = kernfs_vma_get_policy,
 466#endif
 467};
 468
 469static int kernfs_fop_mmap(struct file *file, struct vm_area_struct *vma)
 470{
 471        struct kernfs_open_file *of = kernfs_of(file);
 472        const struct kernfs_ops *ops;
 473        int rc;
 474
 475        /*
 476         * mmap path and of->mutex are prone to triggering spurious lockdep
 477         * warnings and we don't want to add spurious locking dependency
 478         * between the two.  Check whether mmap is actually implemented
 479         * without grabbing @of->mutex by testing HAS_MMAP flag.  See the
 480         * comment in kernfs_file_open() for more details.
 481         */
 482        if (!(of->kn->flags & KERNFS_HAS_MMAP))
 483                return -ENODEV;
 484
 485        mutex_lock(&of->mutex);
 486
 487        rc = -ENODEV;
 488        if (!kernfs_get_active(of->kn))
 489                goto out_unlock;
 490
 491        ops = kernfs_ops(of->kn);
 492        rc = ops->mmap(of, vma);
 493        if (rc)
 494                goto out_put;
 495
 496        /*
 497         * PowerPC's pci_mmap of legacy_mem uses shmem_zero_setup()
 498         * to satisfy versions of X which crash if the mmap fails: that
 499         * substitutes a new vm_file, and we don't then want bin_vm_ops.
 500         */
 501        if (vma->vm_file != file)
 502                goto out_put;
 503
 504        rc = -EINVAL;
 505        if (of->mmapped && of->vm_ops != vma->vm_ops)
 506                goto out_put;
 507
 508        /*
 509         * It is not possible to successfully wrap close.
 510         * So error if someone is trying to use close.
 511         */
 512        rc = -EINVAL;
 513        if (vma->vm_ops && vma->vm_ops->close)
 514                goto out_put;
 515
 516        rc = 0;
 517        of->mmapped = true;
 518        of->vm_ops = vma->vm_ops;
 519        vma->vm_ops = &kernfs_vm_ops;
 520out_put:
 521        kernfs_put_active(of->kn);
 522out_unlock:
 523        mutex_unlock(&of->mutex);
 524
 525        return rc;
 526}
 527
 528/**
 529 *      kernfs_get_open_node - get or create kernfs_open_node
 530 *      @kn: target kernfs_node
 531 *      @of: kernfs_open_file for this instance of open
 532 *
 533 *      If @kn->attr.open exists, increment its reference count; otherwise,
 534 *      create one.  @of is chained to the files list.
 535 *
 536 *      LOCKING:
 537 *      Kernel thread context (may sleep).
 538 *
 539 *      RETURNS:
 540 *      0 on success, -errno on failure.
 541 */
 542static int kernfs_get_open_node(struct kernfs_node *kn,
 543                                struct kernfs_open_file *of)
 544{
 545        struct kernfs_open_node *on, *new_on = NULL;
 546
 547 retry:
 548        mutex_lock(&kernfs_open_file_mutex);
 549        spin_lock_irq(&kernfs_open_node_lock);
 550
 551        if (!kn->attr.open && new_on) {
 552                kn->attr.open = new_on;
 553                new_on = NULL;
 554        }
 555
 556        on = kn->attr.open;
 557        if (on) {
 558                atomic_inc(&on->refcnt);
 559                list_add_tail(&of->list, &on->files);
 560        }
 561
 562        spin_unlock_irq(&kernfs_open_node_lock);
 563        mutex_unlock(&kernfs_open_file_mutex);
 564
 565        if (on) {
 566                kfree(new_on);
 567                return 0;
 568        }
 569
 570        /* not there, initialize a new one and retry */
 571        new_on = kmalloc(sizeof(*new_on), GFP_KERNEL);
 572        if (!new_on)
 573                return -ENOMEM;
 574
 575        atomic_set(&new_on->refcnt, 0);
 576        atomic_set(&new_on->event, 1);
 577        init_waitqueue_head(&new_on->poll);
 578        INIT_LIST_HEAD(&new_on->files);
 579        goto retry;
 580}
 581
 582/**
 583 *      kernfs_put_open_node - put kernfs_open_node
 584 *      @kn: target kernfs_nodet
 585 *      @of: associated kernfs_open_file
 586 *
 587 *      Put @kn->attr.open and unlink @of from the files list.  If
 588 *      reference count reaches zero, disassociate and free it.
 589 *
 590 *      LOCKING:
 591 *      None.
 592 */
 593static void kernfs_put_open_node(struct kernfs_node *kn,
 594                                 struct kernfs_open_file *of)
 595{
 596        struct kernfs_open_node *on = kn->attr.open;
 597        unsigned long flags;
 598
 599        mutex_lock(&kernfs_open_file_mutex);
 600        spin_lock_irqsave(&kernfs_open_node_lock, flags);
 601
 602        if (of)
 603                list_del(&of->list);
 604
 605        if (atomic_dec_and_test(&on->refcnt))
 606                kn->attr.open = NULL;
 607        else
 608                on = NULL;
 609
 610        spin_unlock_irqrestore(&kernfs_open_node_lock, flags);
 611        mutex_unlock(&kernfs_open_file_mutex);
 612
 613        kfree(on);
 614}
 615
 616static int kernfs_fop_open(struct inode *inode, struct file *file)
 617{
 618        struct kernfs_node *kn = inode->i_private;
 619        struct kernfs_root *root = kernfs_root(kn);
 620        const struct kernfs_ops *ops;
 621        struct kernfs_open_file *of;
 622        bool has_read, has_write, has_mmap;
 623        int error = -EACCES;
 624
 625        if (!kernfs_get_active(kn))
 626                return -ENODEV;
 627
 628        ops = kernfs_ops(kn);
 629
 630        has_read = ops->seq_show || ops->read || ops->mmap;
 631        has_write = ops->write || ops->mmap;
 632        has_mmap = ops->mmap;
 633
 634        /* see the flag definition for details */
 635        if (root->flags & KERNFS_ROOT_EXTRA_OPEN_PERM_CHECK) {
 636                if ((file->f_mode & FMODE_WRITE) &&
 637                    (!(inode->i_mode & S_IWUGO) || !has_write))
 638                        goto err_out;
 639
 640                if ((file->f_mode & FMODE_READ) &&
 641                    (!(inode->i_mode & S_IRUGO) || !has_read))
 642                        goto err_out;
 643        }
 644
 645        /* allocate a kernfs_open_file for the file */
 646        error = -ENOMEM;
 647        of = kzalloc(sizeof(struct kernfs_open_file), GFP_KERNEL);
 648        if (!of)
 649                goto err_out;
 650
 651        /*
 652         * The following is done to give a different lockdep key to
 653         * @of->mutex for files which implement mmap.  This is a rather
 654         * crude way to avoid false positive lockdep warning around
 655         * mm->mmap_lock - mmap nests @of->mutex under mm->mmap_lock and
 656         * reading /sys/block/sda/trace/act_mask grabs sr_mutex, under
 657         * which mm->mmap_lock nests, while holding @of->mutex.  As each
 658         * open file has a separate mutex, it's okay as long as those don't
 659         * happen on the same file.  At this point, we can't easily give
 660         * each file a separate locking class.  Let's differentiate on
 661         * whether the file has mmap or not for now.
 662         *
 663         * Both paths of the branch look the same.  They're supposed to
 664         * look that way and give @of->mutex different static lockdep keys.
 665         */
 666        if (has_mmap)
 667                mutex_init(&of->mutex);
 668        else
 669                mutex_init(&of->mutex);
 670
 671        of->kn = kn;
 672        of->file = file;
 673
 674        /*
 675         * Write path needs to atomic_write_len outside active reference.
 676         * Cache it in open_file.  See kernfs_fop_write() for details.
 677         */
 678        of->atomic_write_len = ops->atomic_write_len;
 679
 680        error = -EINVAL;
 681        /*
 682         * ->seq_show is incompatible with ->prealloc,
 683         * as seq_read does its own allocation.
 684         * ->read must be used instead.
 685         */
 686        if (ops->prealloc && ops->seq_show)
 687                goto err_free;
 688        if (ops->prealloc) {
 689                int len = of->atomic_write_len ?: PAGE_SIZE;
 690                of->prealloc_buf = kmalloc(len + 1, GFP_KERNEL);
 691                error = -ENOMEM;
 692                if (!of->prealloc_buf)
 693                        goto err_free;
 694                mutex_init(&of->prealloc_mutex);
 695        }
 696
 697        /*
 698         * Always instantiate seq_file even if read access doesn't use
 699         * seq_file or is not requested.  This unifies private data access
 700         * and readable regular files are the vast majority anyway.
 701         */
 702        if (ops->seq_show)
 703                error = seq_open(file, &kernfs_seq_ops);
 704        else
 705                error = seq_open(file, NULL);
 706        if (error)
 707                goto err_free;
 708
 709        of->seq_file = file->private_data;
 710        of->seq_file->private = of;
 711
 712        /* seq_file clears PWRITE unconditionally, restore it if WRITE */
 713        if (file->f_mode & FMODE_WRITE)
 714                file->f_mode |= FMODE_PWRITE;
 715
 716        /* make sure we have open node struct */
 717        error = kernfs_get_open_node(kn, of);
 718        if (error)
 719                goto err_seq_release;
 720
 721        if (ops->open) {
 722                /* nobody has access to @of yet, skip @of->mutex */
 723                error = ops->open(of);
 724                if (error)
 725                        goto err_put_node;
 726        }
 727
 728        /* open succeeded, put active references */
 729        kernfs_put_active(kn);
 730        return 0;
 731
 732err_put_node:
 733        kernfs_put_open_node(kn, of);
 734err_seq_release:
 735        seq_release(inode, file);
 736err_free:
 737        kfree(of->prealloc_buf);
 738        kfree(of);
 739err_out:
 740        kernfs_put_active(kn);
 741        return error;
 742}
 743
 744/* used from release/drain to ensure that ->release() is called exactly once */
 745static void kernfs_release_file(struct kernfs_node *kn,
 746                                struct kernfs_open_file *of)
 747{
 748        /*
 749         * @of is guaranteed to have no other file operations in flight and
 750         * we just want to synchronize release and drain paths.
 751         * @kernfs_open_file_mutex is enough.  @of->mutex can't be used
 752         * here because drain path may be called from places which can
 753         * cause circular dependency.
 754         */
 755        lockdep_assert_held(&kernfs_open_file_mutex);
 756
 757        if (!of->released) {
 758                /*
 759                 * A file is never detached without being released and we
 760                 * need to be able to release files which are deactivated
 761                 * and being drained.  Don't use kernfs_ops().
 762                 */
 763                kn->attr.ops->release(of);
 764                of->released = true;
 765        }
 766}
 767
 768static int kernfs_fop_release(struct inode *inode, struct file *filp)
 769{
 770        struct kernfs_node *kn = inode->i_private;
 771        struct kernfs_open_file *of = kernfs_of(filp);
 772
 773        if (kn->flags & KERNFS_HAS_RELEASE) {
 774                mutex_lock(&kernfs_open_file_mutex);
 775                kernfs_release_file(kn, of);
 776                mutex_unlock(&kernfs_open_file_mutex);
 777        }
 778
 779        kernfs_put_open_node(kn, of);
 780        seq_release(inode, filp);
 781        kfree(of->prealloc_buf);
 782        kfree(of);
 783
 784        return 0;
 785}
 786
 787void kernfs_drain_open_files(struct kernfs_node *kn)
 788{
 789        struct kernfs_open_node *on;
 790        struct kernfs_open_file *of;
 791
 792        if (!(kn->flags & (KERNFS_HAS_MMAP | KERNFS_HAS_RELEASE)))
 793                return;
 794
 795        spin_lock_irq(&kernfs_open_node_lock);
 796        on = kn->attr.open;
 797        if (on)
 798                atomic_inc(&on->refcnt);
 799        spin_unlock_irq(&kernfs_open_node_lock);
 800        if (!on)
 801                return;
 802
 803        mutex_lock(&kernfs_open_file_mutex);
 804
 805        list_for_each_entry(of, &on->files, list) {
 806                struct inode *inode = file_inode(of->file);
 807
 808                if (kn->flags & KERNFS_HAS_MMAP)
 809                        unmap_mapping_range(inode->i_mapping, 0, 0, 1);
 810
 811                if (kn->flags & KERNFS_HAS_RELEASE)
 812                        kernfs_release_file(kn, of);
 813        }
 814
 815        mutex_unlock(&kernfs_open_file_mutex);
 816
 817        kernfs_put_open_node(kn, NULL);
 818}
 819
 820/*
 821 * Kernfs attribute files are pollable.  The idea is that you read
 822 * the content and then you use 'poll' or 'select' to wait for
 823 * the content to change.  When the content changes (assuming the
 824 * manager for the kobject supports notification), poll will
 825 * return EPOLLERR|EPOLLPRI, and select will return the fd whether
 826 * it is waiting for read, write, or exceptions.
 827 * Once poll/select indicates that the value has changed, you
 828 * need to close and re-open the file, or seek to 0 and read again.
 829 * Reminder: this only works for attributes which actively support
 830 * it, and it is not possible to test an attribute from userspace
 831 * to see if it supports poll (Neither 'poll' nor 'select' return
 832 * an appropriate error code).  When in doubt, set a suitable timeout value.
 833 */
 834__poll_t kernfs_generic_poll(struct kernfs_open_file *of, poll_table *wait)
 835{
 836        struct kernfs_node *kn = kernfs_dentry_node(of->file->f_path.dentry);
 837        struct kernfs_open_node *on = kn->attr.open;
 838
 839        poll_wait(of->file, &on->poll, wait);
 840
 841        if (of->event != atomic_read(&on->event))
 842                return DEFAULT_POLLMASK|EPOLLERR|EPOLLPRI;
 843
 844        return DEFAULT_POLLMASK;
 845}
 846
 847static __poll_t kernfs_fop_poll(struct file *filp, poll_table *wait)
 848{
 849        struct kernfs_open_file *of = kernfs_of(filp);
 850        struct kernfs_node *kn = kernfs_dentry_node(filp->f_path.dentry);
 851        __poll_t ret;
 852
 853        if (!kernfs_get_active(kn))
 854                return DEFAULT_POLLMASK|EPOLLERR|EPOLLPRI;
 855
 856        if (kn->attr.ops->poll)
 857                ret = kn->attr.ops->poll(of, wait);
 858        else
 859                ret = kernfs_generic_poll(of, wait);
 860
 861        kernfs_put_active(kn);
 862        return ret;
 863}
 864
 865static void kernfs_notify_workfn(struct work_struct *work)
 866{
 867        struct kernfs_node *kn;
 868        struct kernfs_super_info *info;
 869repeat:
 870        /* pop one off the notify_list */
 871        spin_lock_irq(&kernfs_notify_lock);
 872        kn = kernfs_notify_list;
 873        if (kn == KERNFS_NOTIFY_EOL) {
 874                spin_unlock_irq(&kernfs_notify_lock);
 875                return;
 876        }
 877        kernfs_notify_list = kn->attr.notify_next;
 878        kn->attr.notify_next = NULL;
 879        spin_unlock_irq(&kernfs_notify_lock);
 880
 881        /* kick fsnotify */
 882        mutex_lock(&kernfs_mutex);
 883
 884        list_for_each_entry(info, &kernfs_root(kn)->supers, node) {
 885                struct kernfs_node *parent;
 886                struct inode *p_inode = NULL;
 887                struct inode *inode;
 888                struct qstr name;
 889
 890                /*
 891                 * We want fsnotify_modify() on @kn but as the
 892                 * modifications aren't originating from userland don't
 893                 * have the matching @file available.  Look up the inodes
 894                 * and generate the events manually.
 895                 */
 896                inode = ilookup(info->sb, kernfs_ino(kn));
 897                if (!inode)
 898                        continue;
 899
 900                name = (struct qstr)QSTR_INIT(kn->name, strlen(kn->name));
 901                parent = kernfs_get_parent(kn);
 902                if (parent) {
 903                        p_inode = ilookup(info->sb, kernfs_ino(parent));
 904                        if (p_inode) {
 905                                fsnotify(FS_MODIFY | FS_EVENT_ON_CHILD,
 906                                         inode, FSNOTIFY_EVENT_INODE,
 907                                         p_inode, &name, inode, 0);
 908                                iput(p_inode);
 909                        }
 910
 911                        kernfs_put(parent);
 912                }
 913
 914                if (!p_inode)
 915                        fsnotify_inode(inode, FS_MODIFY);
 916
 917                iput(inode);
 918        }
 919
 920        mutex_unlock(&kernfs_mutex);
 921        kernfs_put(kn);
 922        goto repeat;
 923}
 924
 925/**
 926 * kernfs_notify - notify a kernfs file
 927 * @kn: file to notify
 928 *
 929 * Notify @kn such that poll(2) on @kn wakes up.  Maybe be called from any
 930 * context.
 931 */
 932void kernfs_notify(struct kernfs_node *kn)
 933{
 934        static DECLARE_WORK(kernfs_notify_work, kernfs_notify_workfn);
 935        unsigned long flags;
 936        struct kernfs_open_node *on;
 937
 938        if (WARN_ON(kernfs_type(kn) != KERNFS_FILE))
 939                return;
 940
 941        /* kick poll immediately */
 942        spin_lock_irqsave(&kernfs_open_node_lock, flags);
 943        on = kn->attr.open;
 944        if (on) {
 945                atomic_inc(&on->event);
 946                wake_up_interruptible(&on->poll);
 947        }
 948        spin_unlock_irqrestore(&kernfs_open_node_lock, flags);
 949
 950        /* schedule work to kick fsnotify */
 951        spin_lock_irqsave(&kernfs_notify_lock, flags);
 952        if (!kn->attr.notify_next) {
 953                kernfs_get(kn);
 954                kn->attr.notify_next = kernfs_notify_list;
 955                kernfs_notify_list = kn;
 956                schedule_work(&kernfs_notify_work);
 957        }
 958        spin_unlock_irqrestore(&kernfs_notify_lock, flags);
 959}
 960EXPORT_SYMBOL_GPL(kernfs_notify);
 961
 962const struct file_operations kernfs_file_fops = {
 963        .read           = kernfs_fop_read,
 964        .write          = kernfs_fop_write,
 965        .llseek         = generic_file_llseek,
 966        .mmap           = kernfs_fop_mmap,
 967        .open           = kernfs_fop_open,
 968        .release        = kernfs_fop_release,
 969        .poll           = kernfs_fop_poll,
 970        .fsync          = noop_fsync,
 971};
 972
 973/**
 974 * __kernfs_create_file - kernfs internal function to create a file
 975 * @parent: directory to create the file in
 976 * @name: name of the file
 977 * @mode: mode of the file
 978 * @uid: uid of the file
 979 * @gid: gid of the file
 980 * @size: size of the file
 981 * @ops: kernfs operations for the file
 982 * @priv: private data for the file
 983 * @ns: optional namespace tag of the file
 984 * @key: lockdep key for the file's active_ref, %NULL to disable lockdep
 985 *
 986 * Returns the created node on success, ERR_PTR() value on error.
 987 */
 988struct kernfs_node *__kernfs_create_file(struct kernfs_node *parent,
 989                                         const char *name,
 990                                         umode_t mode, kuid_t uid, kgid_t gid,
 991                                         loff_t size,
 992                                         const struct kernfs_ops *ops,
 993                                         void *priv, const void *ns,
 994                                         struct lock_class_key *key)
 995{
 996        struct kernfs_node *kn;
 997        unsigned flags;
 998        int rc;
 999
1000        flags = KERNFS_FILE;
1001
1002        kn = kernfs_new_node(parent, name, (mode & S_IALLUGO) | S_IFREG,
1003                             uid, gid, flags);
1004        if (!kn)
1005                return ERR_PTR(-ENOMEM);
1006
1007        kn->attr.ops = ops;
1008        kn->attr.size = size;
1009        kn->ns = ns;
1010        kn->priv = priv;
1011
1012#ifdef CONFIG_DEBUG_LOCK_ALLOC
1013        if (key) {
1014                lockdep_init_map(&kn->dep_map, "kn->active", key, 0);
1015                kn->flags |= KERNFS_LOCKDEP;
1016        }
1017#endif
1018
1019        /*
1020         * kn->attr.ops is accesible only while holding active ref.  We
1021         * need to know whether some ops are implemented outside active
1022         * ref.  Cache their existence in flags.
1023         */
1024        if (ops->seq_show)
1025                kn->flags |= KERNFS_HAS_SEQ_SHOW;
1026        if (ops->mmap)
1027                kn->flags |= KERNFS_HAS_MMAP;
1028        if (ops->release)
1029                kn->flags |= KERNFS_HAS_RELEASE;
1030
1031        rc = kernfs_add_one(kn);
1032        if (rc) {
1033                kernfs_put(kn);
1034                return ERR_PTR(rc);
1035        }
1036        return kn;
1037}
1038