linux/fs/file.c
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   1/*
   2 *  linux/fs/file.c
   3 *
   4 *  Copyright (C) 1998-1999, Stephen Tweedie and Bill Hawes
   5 *
   6 *  Manage the dynamic fd arrays in the process files_struct.
   7 */
   8
   9#include <linux/syscalls.h>
  10#include <linux/export.h>
  11#include <linux/fs.h>
  12#include <linux/mm.h>
  13#include <linux/mmzone.h>
  14#include <linux/time.h>
  15#include <linux/sched.h>
  16#include <linux/slab.h>
  17#include <linux/vmalloc.h>
  18#include <linux/file.h>
  19#include <linux/fdtable.h>
  20#include <linux/bitops.h>
  21#include <linux/interrupt.h>
  22#include <linux/spinlock.h>
  23#include <linux/rcupdate.h>
  24#include <linux/workqueue.h>
  25
  26struct fdtable_defer {
  27        spinlock_t lock;
  28        struct work_struct wq;
  29        struct fdtable *next;
  30};
  31
  32int sysctl_nr_open __read_mostly = 1024*1024;
  33int sysctl_nr_open_min = BITS_PER_LONG;
  34int sysctl_nr_open_max = 1024 * 1024; /* raised later */
  35
  36/*
  37 * We use this list to defer free fdtables that have vmalloced
  38 * sets/arrays. By keeping a per-cpu list, we avoid having to embed
  39 * the work_struct in fdtable itself which avoids a 64 byte (i386) increase in
  40 * this per-task structure.
  41 */
  42static DEFINE_PER_CPU(struct fdtable_defer, fdtable_defer_list);
  43
  44static void *alloc_fdmem(size_t size)
  45{
  46        /*
  47         * Very large allocations can stress page reclaim, so fall back to
  48         * vmalloc() if the allocation size will be considered "large" by the VM.
  49         */
  50        if (size <= (PAGE_SIZE << PAGE_ALLOC_COSTLY_ORDER)) {
  51                void *data = kmalloc(size, GFP_KERNEL|__GFP_NOWARN);
  52                if (data != NULL)
  53                        return data;
  54        }
  55        return vmalloc(size);
  56}
  57
  58static void free_fdmem(void *ptr)
  59{
  60        is_vmalloc_addr(ptr) ? vfree(ptr) : kfree(ptr);
  61}
  62
  63static void __free_fdtable(struct fdtable *fdt)
  64{
  65        free_fdmem(fdt->fd);
  66        free_fdmem(fdt->open_fds);
  67        kfree(fdt);
  68}
  69
  70static void free_fdtable_work(struct work_struct *work)
  71{
  72        struct fdtable_defer *f =
  73                container_of(work, struct fdtable_defer, wq);
  74        struct fdtable *fdt;
  75
  76        spin_lock_bh(&f->lock);
  77        fdt = f->next;
  78        f->next = NULL;
  79        spin_unlock_bh(&f->lock);
  80        while(fdt) {
  81                struct fdtable *next = fdt->next;
  82
  83                __free_fdtable(fdt);
  84                fdt = next;
  85        }
  86}
  87
  88static void free_fdtable_rcu(struct rcu_head *rcu)
  89{
  90        struct fdtable *fdt = container_of(rcu, struct fdtable, rcu);
  91        struct fdtable_defer *fddef;
  92
  93        BUG_ON(!fdt);
  94        BUG_ON(fdt->max_fds <= NR_OPEN_DEFAULT);
  95
  96        if (!is_vmalloc_addr(fdt->fd) && !is_vmalloc_addr(fdt->open_fds)) {
  97                kfree(fdt->fd);
  98                kfree(fdt->open_fds);
  99                kfree(fdt);
 100        } else {
 101                fddef = &get_cpu_var(fdtable_defer_list);
 102                spin_lock(&fddef->lock);
 103                fdt->next = fddef->next;
 104                fddef->next = fdt;
 105                /* vmallocs are handled from the workqueue context */
 106                schedule_work(&fddef->wq);
 107                spin_unlock(&fddef->lock);
 108                put_cpu_var(fdtable_defer_list);
 109        }
 110}
 111
 112/*
 113 * Expand the fdset in the files_struct.  Called with the files spinlock
 114 * held for write.
 115 */
 116static void copy_fdtable(struct fdtable *nfdt, struct fdtable *ofdt)
 117{
 118        unsigned int cpy, set;
 119
 120        BUG_ON(nfdt->max_fds < ofdt->max_fds);
 121
 122        cpy = ofdt->max_fds * sizeof(struct file *);
 123        set = (nfdt->max_fds - ofdt->max_fds) * sizeof(struct file *);
 124        memcpy(nfdt->fd, ofdt->fd, cpy);
 125        memset((char *)(nfdt->fd) + cpy, 0, set);
 126
 127        cpy = ofdt->max_fds / BITS_PER_BYTE;
 128        set = (nfdt->max_fds - ofdt->max_fds) / BITS_PER_BYTE;
 129        memcpy(nfdt->open_fds, ofdt->open_fds, cpy);
 130        memset((char *)(nfdt->open_fds) + cpy, 0, set);
 131        memcpy(nfdt->close_on_exec, ofdt->close_on_exec, cpy);
 132        memset((char *)(nfdt->close_on_exec) + cpy, 0, set);
 133}
 134
 135static struct fdtable * alloc_fdtable(unsigned int nr)
 136{
 137        struct fdtable *fdt;
 138        void *data;
 139
 140        /*
 141         * Figure out how many fds we actually want to support in this fdtable.
 142         * Allocation steps are keyed to the size of the fdarray, since it
 143         * grows far faster than any of the other dynamic data. We try to fit
 144         * the fdarray into comfortable page-tuned chunks: starting at 1024B
 145         * and growing in powers of two from there on.
 146         */
 147        nr /= (1024 / sizeof(struct file *));
 148        nr = roundup_pow_of_two(nr + 1);
 149        nr *= (1024 / sizeof(struct file *));
 150        /*
 151         * Note that this can drive nr *below* what we had passed if sysctl_nr_open
 152         * had been set lower between the check in expand_files() and here.  Deal
 153         * with that in caller, it's cheaper that way.
 154         *
 155         * We make sure that nr remains a multiple of BITS_PER_LONG - otherwise
 156         * bitmaps handling below becomes unpleasant, to put it mildly...
 157         */
 158        if (unlikely(nr > sysctl_nr_open))
 159                nr = ((sysctl_nr_open - 1) | (BITS_PER_LONG - 1)) + 1;
 160
 161        fdt = kmalloc(sizeof(struct fdtable), GFP_KERNEL);
 162        if (!fdt)
 163                goto out;
 164        fdt->max_fds = nr;
 165        data = alloc_fdmem(nr * sizeof(struct file *));
 166        if (!data)
 167                goto out_fdt;
 168        fdt->fd = data;
 169
 170        data = alloc_fdmem(max_t(size_t,
 171                                 2 * nr / BITS_PER_BYTE, L1_CACHE_BYTES));
 172        if (!data)
 173                goto out_arr;
 174        fdt->open_fds = data;
 175        data += nr / BITS_PER_BYTE;
 176        fdt->close_on_exec = data;
 177        fdt->next = NULL;
 178
 179        return fdt;
 180
 181out_arr:
 182        free_fdmem(fdt->fd);
 183out_fdt:
 184        kfree(fdt);
 185out:
 186        return NULL;
 187}
 188
 189/*
 190 * Expand the file descriptor table.
 191 * This function will allocate a new fdtable and both fd array and fdset, of
 192 * the given size.
 193 * Return <0 error code on error; 1 on successful completion.
 194 * The files->file_lock should be held on entry, and will be held on exit.
 195 */
 196static int expand_fdtable(struct files_struct *files, int nr)
 197        __releases(files->file_lock)
 198        __acquires(files->file_lock)
 199{
 200        struct fdtable *new_fdt, *cur_fdt;
 201
 202        spin_unlock(&files->file_lock);
 203        new_fdt = alloc_fdtable(nr);
 204        spin_lock(&files->file_lock);
 205        if (!new_fdt)
 206                return -ENOMEM;
 207        /*
 208         * extremely unlikely race - sysctl_nr_open decreased between the check in
 209         * caller and alloc_fdtable().  Cheaper to catch it here...
 210         */
 211        if (unlikely(new_fdt->max_fds <= nr)) {
 212                __free_fdtable(new_fdt);
 213                return -EMFILE;
 214        }
 215        /*
 216         * Check again since another task may have expanded the fd table while
 217         * we dropped the lock
 218         */
 219        cur_fdt = files_fdtable(files);
 220        if (nr >= cur_fdt->max_fds) {
 221                /* Continue as planned */
 222                copy_fdtable(new_fdt, cur_fdt);
 223                rcu_assign_pointer(files->fdt, new_fdt);
 224                if (cur_fdt->max_fds > NR_OPEN_DEFAULT)
 225                        call_rcu(&cur_fdt->rcu, free_fdtable_rcu);
 226        } else {
 227                /* Somebody else expanded, so undo our attempt */
 228                __free_fdtable(new_fdt);
 229        }
 230        return 1;
 231}
 232
 233/*
 234 * Expand files.
 235 * This function will expand the file structures, if the requested size exceeds
 236 * the current capacity and there is room for expansion.
 237 * Return <0 error code on error; 0 when nothing done; 1 when files were
 238 * expanded and execution may have blocked.
 239 * The files->file_lock should be held on entry, and will be held on exit.
 240 */
 241static int expand_files(struct files_struct *files, int nr)
 242{
 243        struct fdtable *fdt;
 244
 245        fdt = files_fdtable(files);
 246
 247        /* Do we need to expand? */
 248        if (nr < fdt->max_fds)
 249                return 0;
 250
 251        /* Can we expand? */
 252        if (nr >= sysctl_nr_open)
 253                return -EMFILE;
 254
 255        /* All good, so we try */
 256        return expand_fdtable(files, nr);
 257}
 258
 259static inline void __set_close_on_exec(int fd, struct fdtable *fdt)
 260{
 261        __set_bit(fd, fdt->close_on_exec);
 262}
 263
 264static inline void __clear_close_on_exec(int fd, struct fdtable *fdt)
 265{
 266        __clear_bit(fd, fdt->close_on_exec);
 267}
 268
 269static inline void __set_open_fd(int fd, struct fdtable *fdt)
 270{
 271        __set_bit(fd, fdt->open_fds);
 272}
 273
 274static inline void __clear_open_fd(int fd, struct fdtable *fdt)
 275{
 276        __clear_bit(fd, fdt->open_fds);
 277}
 278
 279static int count_open_files(struct fdtable *fdt)
 280{
 281        int size = fdt->max_fds;
 282        int i;
 283
 284        /* Find the last open fd */
 285        for (i = size / BITS_PER_LONG; i > 0; ) {
 286                if (fdt->open_fds[--i])
 287                        break;
 288        }
 289        i = (i + 1) * BITS_PER_LONG;
 290        return i;
 291}
 292
 293/*
 294 * Allocate a new files structure and copy contents from the
 295 * passed in files structure.
 296 * errorp will be valid only when the returned files_struct is NULL.
 297 */
 298struct files_struct *dup_fd(struct files_struct *oldf, int *errorp)
 299{
 300        struct files_struct *newf;
 301        struct file **old_fds, **new_fds;
 302        int open_files, size, i;
 303        struct fdtable *old_fdt, *new_fdt;
 304
 305        *errorp = -ENOMEM;
 306        newf = kmem_cache_alloc(files_cachep, GFP_KERNEL);
 307        if (!newf)
 308                goto out;
 309
 310        atomic_set(&newf->count, 1);
 311
 312        spin_lock_init(&newf->file_lock);
 313        newf->next_fd = 0;
 314        new_fdt = &newf->fdtab;
 315        new_fdt->max_fds = NR_OPEN_DEFAULT;
 316        new_fdt->close_on_exec = newf->close_on_exec_init;
 317        new_fdt->open_fds = newf->open_fds_init;
 318        new_fdt->fd = &newf->fd_array[0];
 319        new_fdt->next = NULL;
 320
 321        spin_lock(&oldf->file_lock);
 322        old_fdt = files_fdtable(oldf);
 323        open_files = count_open_files(old_fdt);
 324
 325        /*
 326         * Check whether we need to allocate a larger fd array and fd set.
 327         */
 328        while (unlikely(open_files > new_fdt->max_fds)) {
 329                spin_unlock(&oldf->file_lock);
 330
 331                if (new_fdt != &newf->fdtab)
 332                        __free_fdtable(new_fdt);
 333
 334                new_fdt = alloc_fdtable(open_files - 1);
 335                if (!new_fdt) {
 336                        *errorp = -ENOMEM;
 337                        goto out_release;
 338                }
 339
 340                /* beyond sysctl_nr_open; nothing to do */
 341                if (unlikely(new_fdt->max_fds < open_files)) {
 342                        __free_fdtable(new_fdt);
 343                        *errorp = -EMFILE;
 344                        goto out_release;
 345                }
 346
 347                /*
 348                 * Reacquire the oldf lock and a pointer to its fd table
 349                 * who knows it may have a new bigger fd table. We need
 350                 * the latest pointer.
 351                 */
 352                spin_lock(&oldf->file_lock);
 353                old_fdt = files_fdtable(oldf);
 354                open_files = count_open_files(old_fdt);
 355        }
 356
 357        old_fds = old_fdt->fd;
 358        new_fds = new_fdt->fd;
 359
 360        memcpy(new_fdt->open_fds, old_fdt->open_fds, open_files / 8);
 361        memcpy(new_fdt->close_on_exec, old_fdt->close_on_exec, open_files / 8);
 362
 363        for (i = open_files; i != 0; i--) {
 364                struct file *f = *old_fds++;
 365                if (f) {
 366                        get_file(f);
 367                } else {
 368                        /*
 369                         * The fd may be claimed in the fd bitmap but not yet
 370                         * instantiated in the files array if a sibling thread
 371                         * is partway through open().  So make sure that this
 372                         * fd is available to the new process.
 373                         */
 374                        __clear_open_fd(open_files - i, new_fdt);
 375                }
 376                rcu_assign_pointer(*new_fds++, f);
 377        }
 378        spin_unlock(&oldf->file_lock);
 379
 380        /* compute the remainder to be cleared */
 381        size = (new_fdt->max_fds - open_files) * sizeof(struct file *);
 382
 383        /* This is long word aligned thus could use a optimized version */
 384        memset(new_fds, 0, size);
 385
 386        if (new_fdt->max_fds > open_files) {
 387                int left = (new_fdt->max_fds - open_files) / 8;
 388                int start = open_files / BITS_PER_LONG;
 389
 390                memset(&new_fdt->open_fds[start], 0, left);
 391                memset(&new_fdt->close_on_exec[start], 0, left);
 392        }
 393
 394        rcu_assign_pointer(newf->fdt, new_fdt);
 395
 396        return newf;
 397
 398out_release:
 399        kmem_cache_free(files_cachep, newf);
 400out:
 401        return NULL;
 402}
 403
 404static void close_files(struct files_struct * files)
 405{
 406        int i, j;
 407        struct fdtable *fdt;
 408
 409        j = 0;
 410
 411        /*
 412         * It is safe to dereference the fd table without RCU or
 413         * ->file_lock because this is the last reference to the
 414         * files structure.  But use RCU to shut RCU-lockdep up.
 415         */
 416        rcu_read_lock();
 417        fdt = files_fdtable(files);
 418        rcu_read_unlock();
 419        for (;;) {
 420                unsigned long set;
 421                i = j * BITS_PER_LONG;
 422                if (i >= fdt->max_fds)
 423                        break;
 424                set = fdt->open_fds[j++];
 425                while (set) {
 426                        if (set & 1) {
 427                                struct file * file = xchg(&fdt->fd[i], NULL);
 428                                if (file) {
 429                                        filp_close(file, files);
 430                                        cond_resched();
 431                                }
 432                        }
 433                        i++;
 434                        set >>= 1;
 435                }
 436        }
 437}
 438
 439struct files_struct *get_files_struct(struct task_struct *task)
 440{
 441        struct files_struct *files;
 442
 443        task_lock(task);
 444        files = task->files;
 445        if (files)
 446                atomic_inc(&files->count);
 447        task_unlock(task);
 448
 449        return files;
 450}
 451
 452void put_files_struct(struct files_struct *files)
 453{
 454        struct fdtable *fdt;
 455
 456        if (atomic_dec_and_test(&files->count)) {
 457                close_files(files);
 458                /* not really needed, since nobody can see us */
 459                rcu_read_lock();
 460                fdt = files_fdtable(files);
 461                rcu_read_unlock();
 462                /* free the arrays if they are not embedded */
 463                if (fdt != &files->fdtab)
 464                        __free_fdtable(fdt);
 465                kmem_cache_free(files_cachep, files);
 466        }
 467}
 468
 469void reset_files_struct(struct files_struct *files)
 470{
 471        struct task_struct *tsk = current;
 472        struct files_struct *old;
 473
 474        old = tsk->files;
 475        task_lock(tsk);
 476        tsk->files = files;
 477        task_unlock(tsk);
 478        put_files_struct(old);
 479}
 480
 481void exit_files(struct task_struct *tsk)
 482{
 483        struct files_struct * files = tsk->files;
 484
 485        if (files) {
 486                task_lock(tsk);
 487                tsk->files = NULL;
 488                task_unlock(tsk);
 489                put_files_struct(files);
 490        }
 491}
 492
 493static void fdtable_defer_list_init(int cpu)
 494{
 495        struct fdtable_defer *fddef = &per_cpu(fdtable_defer_list, cpu);
 496        spin_lock_init(&fddef->lock);
 497        INIT_WORK(&fddef->wq, free_fdtable_work);
 498        fddef->next = NULL;
 499}
 500
 501void __init files_defer_init(void)
 502{
 503        int i;
 504        for_each_possible_cpu(i)
 505                fdtable_defer_list_init(i);
 506        sysctl_nr_open_max = min((size_t)INT_MAX, ~(size_t)0/sizeof(void *)) &
 507                             -BITS_PER_LONG;
 508}
 509
 510struct files_struct init_files = {
 511        .count          = ATOMIC_INIT(1),
 512        .fdt            = &init_files.fdtab,
 513        .fdtab          = {
 514                .max_fds        = NR_OPEN_DEFAULT,
 515                .fd             = &init_files.fd_array[0],
 516                .close_on_exec  = init_files.close_on_exec_init,
 517                .open_fds       = init_files.open_fds_init,
 518        },
 519        .file_lock      = __SPIN_LOCK_UNLOCKED(init_task.file_lock),
 520};
 521
 522/*
 523 * allocate a file descriptor, mark it busy.
 524 */
 525int __alloc_fd(struct files_struct *files,
 526               unsigned start, unsigned end, unsigned flags)
 527{
 528        unsigned int fd;
 529        int error;
 530        struct fdtable *fdt;
 531
 532        spin_lock(&files->file_lock);
 533repeat:
 534        fdt = files_fdtable(files);
 535        fd = start;
 536        if (fd < files->next_fd)
 537                fd = files->next_fd;
 538
 539        if (fd < fdt->max_fds)
 540                fd = find_next_zero_bit(fdt->open_fds, fdt->max_fds, fd);
 541
 542        /*
 543         * N.B. For clone tasks sharing a files structure, this test
 544         * will limit the total number of files that can be opened.
 545         */
 546        error = -EMFILE;
 547        if (fd >= end)
 548                goto out;
 549
 550        error = expand_files(files, fd);
 551        if (error < 0)
 552                goto out;
 553
 554        /*
 555         * If we needed to expand the fs array we
 556         * might have blocked - try again.
 557         */
 558        if (error)
 559                goto repeat;
 560
 561        if (start <= files->next_fd)
 562                files->next_fd = fd + 1;
 563
 564        __set_open_fd(fd, fdt);
 565        if (flags & O_CLOEXEC)
 566                __set_close_on_exec(fd, fdt);
 567        else
 568                __clear_close_on_exec(fd, fdt);
 569        error = fd;
 570#if 1
 571        /* Sanity check */
 572        if (rcu_dereference_raw(fdt->fd[fd]) != NULL) {
 573                printk(KERN_WARNING "alloc_fd: slot %d not NULL!\n", fd);
 574                rcu_assign_pointer(fdt->fd[fd], NULL);
 575        }
 576#endif
 577
 578out:
 579        spin_unlock(&files->file_lock);
 580        return error;
 581}
 582
 583static int alloc_fd(unsigned start, unsigned flags)
 584{
 585        return __alloc_fd(current->files, start, rlimit(RLIMIT_NOFILE), flags);
 586}
 587
 588int get_unused_fd_flags(unsigned flags)
 589{
 590        return __alloc_fd(current->files, 0, rlimit(RLIMIT_NOFILE), flags);
 591}
 592EXPORT_SYMBOL(get_unused_fd_flags);
 593
 594static void __put_unused_fd(struct files_struct *files, unsigned int fd)
 595{
 596        struct fdtable *fdt = files_fdtable(files);
 597        __clear_open_fd(fd, fdt);
 598        if (fd < files->next_fd)
 599                files->next_fd = fd;
 600}
 601
 602void put_unused_fd(unsigned int fd)
 603{
 604        struct files_struct *files = current->files;
 605        spin_lock(&files->file_lock);
 606        __put_unused_fd(files, fd);
 607        spin_unlock(&files->file_lock);
 608}
 609
 610EXPORT_SYMBOL(put_unused_fd);
 611
 612/*
 613 * Install a file pointer in the fd array.
 614 *
 615 * The VFS is full of places where we drop the files lock between
 616 * setting the open_fds bitmap and installing the file in the file
 617 * array.  At any such point, we are vulnerable to a dup2() race
 618 * installing a file in the array before us.  We need to detect this and
 619 * fput() the struct file we are about to overwrite in this case.
 620 *
 621 * It should never happen - if we allow dup2() do it, _really_ bad things
 622 * will follow.
 623 *
 624 * NOTE: __fd_install() variant is really, really low-level; don't
 625 * use it unless you are forced to by truly lousy API shoved down
 626 * your throat.  'files' *MUST* be either current->files or obtained
 627 * by get_files_struct(current) done by whoever had given it to you,
 628 * or really bad things will happen.  Normally you want to use
 629 * fd_install() instead.
 630 */
 631
 632void __fd_install(struct files_struct *files, unsigned int fd,
 633                struct file *file)
 634{
 635        struct fdtable *fdt;
 636        spin_lock(&files->file_lock);
 637        fdt = files_fdtable(files);
 638        BUG_ON(fdt->fd[fd] != NULL);
 639        rcu_assign_pointer(fdt->fd[fd], file);
 640        spin_unlock(&files->file_lock);
 641}
 642
 643void fd_install(unsigned int fd, struct file *file)
 644{
 645        __fd_install(current->files, fd, file);
 646}
 647
 648EXPORT_SYMBOL(fd_install);
 649
 650/*
 651 * The same warnings as for __alloc_fd()/__fd_install() apply here...
 652 */
 653int __close_fd(struct files_struct *files, unsigned fd)
 654{
 655        struct file *file;
 656        struct fdtable *fdt;
 657
 658        spin_lock(&files->file_lock);
 659        fdt = files_fdtable(files);
 660        if (fd >= fdt->max_fds)
 661                goto out_unlock;
 662        file = fdt->fd[fd];
 663        if (!file)
 664                goto out_unlock;
 665        rcu_assign_pointer(fdt->fd[fd], NULL);
 666        __clear_close_on_exec(fd, fdt);
 667        __put_unused_fd(files, fd);
 668        spin_unlock(&files->file_lock);
 669        return filp_close(file, files);
 670
 671out_unlock:
 672        spin_unlock(&files->file_lock);
 673        return -EBADF;
 674}
 675
 676void do_close_on_exec(struct files_struct *files)
 677{
 678        unsigned i;
 679        struct fdtable *fdt;
 680
 681        /* exec unshares first */
 682        spin_lock(&files->file_lock);
 683        for (i = 0; ; i++) {
 684                unsigned long set;
 685                unsigned fd = i * BITS_PER_LONG;
 686                fdt = files_fdtable(files);
 687                if (fd >= fdt->max_fds)
 688                        break;
 689                set = fdt->close_on_exec[i];
 690                if (!set)
 691                        continue;
 692                fdt->close_on_exec[i] = 0;
 693                for ( ; set ; fd++, set >>= 1) {
 694                        struct file *file;
 695                        if (!(set & 1))
 696                                continue;
 697                        file = fdt->fd[fd];
 698                        if (!file)
 699                                continue;
 700                        rcu_assign_pointer(fdt->fd[fd], NULL);
 701                        __put_unused_fd(files, fd);
 702                        spin_unlock(&files->file_lock);
 703                        filp_close(file, files);
 704                        cond_resched();
 705                        spin_lock(&files->file_lock);
 706                }
 707
 708        }
 709        spin_unlock(&files->file_lock);
 710}
 711
 712struct file *fget(unsigned int fd)
 713{
 714        struct file *file;
 715        struct files_struct *files = current->files;
 716
 717        rcu_read_lock();
 718        file = fcheck_files(files, fd);
 719        if (file) {
 720                /* File object ref couldn't be taken */
 721                if (file->f_mode & FMODE_PATH ||
 722                    !atomic_long_inc_not_zero(&file->f_count))
 723                        file = NULL;
 724        }
 725        rcu_read_unlock();
 726
 727        return file;
 728}
 729
 730EXPORT_SYMBOL(fget);
 731
 732struct file *fget_raw(unsigned int fd)
 733{
 734        struct file *file;
 735        struct files_struct *files = current->files;
 736
 737        rcu_read_lock();
 738        file = fcheck_files(files, fd);
 739        if (file) {
 740                /* File object ref couldn't be taken */
 741                if (!atomic_long_inc_not_zero(&file->f_count))
 742                        file = NULL;
 743        }
 744        rcu_read_unlock();
 745
 746        return file;
 747}
 748
 749EXPORT_SYMBOL(fget_raw);
 750
 751/*
 752 * Lightweight file lookup - no refcnt increment if fd table isn't shared.
 753 *
 754 * You can use this instead of fget if you satisfy all of the following
 755 * conditions:
 756 * 1) You must call fput_light before exiting the syscall and returning control
 757 *    to userspace (i.e. you cannot remember the returned struct file * after
 758 *    returning to userspace).
 759 * 2) You must not call filp_close on the returned struct file * in between
 760 *    calls to fget_light and fput_light.
 761 * 3) You must not clone the current task in between the calls to fget_light
 762 *    and fput_light.
 763 *
 764 * The fput_needed flag returned by fget_light should be passed to the
 765 * corresponding fput_light.
 766 */
 767struct file *fget_light(unsigned int fd, int *fput_needed)
 768{
 769        struct file *file;
 770        struct files_struct *files = current->files;
 771
 772        *fput_needed = 0;
 773        if (atomic_read(&files->count) == 1) {
 774                file = fcheck_files(files, fd);
 775                if (file && (file->f_mode & FMODE_PATH))
 776                        file = NULL;
 777        } else {
 778                rcu_read_lock();
 779                file = fcheck_files(files, fd);
 780                if (file) {
 781                        if (!(file->f_mode & FMODE_PATH) &&
 782                            atomic_long_inc_not_zero(&file->f_count))
 783                                *fput_needed = 1;
 784                        else
 785                                /* Didn't get the reference, someone's freed */
 786                                file = NULL;
 787                }
 788                rcu_read_unlock();
 789        }
 790
 791        return file;
 792}
 793EXPORT_SYMBOL(fget_light);
 794
 795struct file *fget_raw_light(unsigned int fd, int *fput_needed)
 796{
 797        struct file *file;
 798        struct files_struct *files = current->files;
 799
 800        *fput_needed = 0;
 801        if (atomic_read(&files->count) == 1) {
 802                file = fcheck_files(files, fd);
 803        } else {
 804                rcu_read_lock();
 805                file = fcheck_files(files, fd);
 806                if (file) {
 807                        if (atomic_long_inc_not_zero(&file->f_count))
 808                                *fput_needed = 1;
 809                        else
 810                                /* Didn't get the reference, someone's freed */
 811                                file = NULL;
 812                }
 813                rcu_read_unlock();
 814        }
 815
 816        return file;
 817}
 818
 819void set_close_on_exec(unsigned int fd, int flag)
 820{
 821        struct files_struct *files = current->files;
 822        struct fdtable *fdt;
 823        spin_lock(&files->file_lock);
 824        fdt = files_fdtable(files);
 825        if (flag)
 826                __set_close_on_exec(fd, fdt);
 827        else
 828                __clear_close_on_exec(fd, fdt);
 829        spin_unlock(&files->file_lock);
 830}
 831
 832bool get_close_on_exec(unsigned int fd)
 833{
 834        struct files_struct *files = current->files;
 835        struct fdtable *fdt;
 836        bool res;
 837        rcu_read_lock();
 838        fdt = files_fdtable(files);
 839        res = close_on_exec(fd, fdt);
 840        rcu_read_unlock();
 841        return res;
 842}
 843
 844static int do_dup2(struct files_struct *files,
 845        struct file *file, unsigned fd, unsigned flags)
 846{
 847        struct file *tofree;
 848        struct fdtable *fdt;
 849
 850        /*
 851         * We need to detect attempts to do dup2() over allocated but still
 852         * not finished descriptor.  NB: OpenBSD avoids that at the price of
 853         * extra work in their equivalent of fget() - they insert struct
 854         * file immediately after grabbing descriptor, mark it larval if
 855         * more work (e.g. actual opening) is needed and make sure that
 856         * fget() treats larval files as absent.  Potentially interesting,
 857         * but while extra work in fget() is trivial, locking implications
 858         * and amount of surgery on open()-related paths in VFS are not.
 859         * FreeBSD fails with -EBADF in the same situation, NetBSD "solution"
 860         * deadlocks in rather amusing ways, AFAICS.  All of that is out of
 861         * scope of POSIX or SUS, since neither considers shared descriptor
 862         * tables and this condition does not arise without those.
 863         */
 864        fdt = files_fdtable(files);
 865        tofree = fdt->fd[fd];
 866        if (!tofree && fd_is_open(fd, fdt))
 867                goto Ebusy;
 868        get_file(file);
 869        rcu_assign_pointer(fdt->fd[fd], file);
 870        __set_open_fd(fd, fdt);
 871        if (flags & O_CLOEXEC)
 872                __set_close_on_exec(fd, fdt);
 873        else
 874                __clear_close_on_exec(fd, fdt);
 875        spin_unlock(&files->file_lock);
 876
 877        if (tofree)
 878                filp_close(tofree, files);
 879
 880        return fd;
 881
 882Ebusy:
 883        spin_unlock(&files->file_lock);
 884        return -EBUSY;
 885}
 886
 887int replace_fd(unsigned fd, struct file *file, unsigned flags)
 888{
 889        int err;
 890        struct files_struct *files = current->files;
 891
 892        if (!file)
 893                return __close_fd(files, fd);
 894
 895        if (fd >= rlimit(RLIMIT_NOFILE))
 896                return -EBADF;
 897
 898        spin_lock(&files->file_lock);
 899        err = expand_files(files, fd);
 900        if (unlikely(err < 0))
 901                goto out_unlock;
 902        return do_dup2(files, file, fd, flags);
 903
 904out_unlock:
 905        spin_unlock(&files->file_lock);
 906        return err;
 907}
 908
 909SYSCALL_DEFINE3(dup3, unsigned int, oldfd, unsigned int, newfd, int, flags)
 910{
 911        int err = -EBADF;
 912        struct file *file;
 913        struct files_struct *files = current->files;
 914
 915        if ((flags & ~O_CLOEXEC) != 0)
 916                return -EINVAL;
 917
 918        if (unlikely(oldfd == newfd))
 919                return -EINVAL;
 920
 921        if (newfd >= rlimit(RLIMIT_NOFILE))
 922                return -EBADF;
 923
 924        spin_lock(&files->file_lock);
 925        err = expand_files(files, newfd);
 926        file = fcheck(oldfd);
 927        if (unlikely(!file))
 928                goto Ebadf;
 929        if (unlikely(err < 0)) {
 930                if (err == -EMFILE)
 931                        goto Ebadf;
 932                goto out_unlock;
 933        }
 934        return do_dup2(files, file, newfd, flags);
 935
 936Ebadf:
 937        err = -EBADF;
 938out_unlock:
 939        spin_unlock(&files->file_lock);
 940        return err;
 941}
 942
 943SYSCALL_DEFINE2(dup2, unsigned int, oldfd, unsigned int, newfd)
 944{
 945        if (unlikely(newfd == oldfd)) { /* corner case */
 946                struct files_struct *files = current->files;
 947                int retval = oldfd;
 948
 949                rcu_read_lock();
 950                if (!fcheck_files(files, oldfd))
 951                        retval = -EBADF;
 952                rcu_read_unlock();
 953                return retval;
 954        }
 955        return sys_dup3(oldfd, newfd, 0);
 956}
 957
 958SYSCALL_DEFINE1(dup, unsigned int, fildes)
 959{
 960        int ret = -EBADF;
 961        struct file *file = fget_raw(fildes);
 962
 963        if (file) {
 964                ret = get_unused_fd();
 965                if (ret >= 0)
 966                        fd_install(ret, file);
 967                else
 968                        fput(file);
 969        }
 970        return ret;
 971}
 972
 973int f_dupfd(unsigned int from, struct file *file, unsigned flags)
 974{
 975        int err;
 976        if (from >= rlimit(RLIMIT_NOFILE))
 977                return -EINVAL;
 978        err = alloc_fd(from, flags);
 979        if (err >= 0) {
 980                get_file(file);
 981                fd_install(err, file);
 982        }
 983        return err;
 984}
 985
 986int iterate_fd(struct files_struct *files, unsigned n,
 987                int (*f)(const void *, struct file *, unsigned),
 988                const void *p)
 989{
 990        struct fdtable *fdt;
 991        int res = 0;
 992        if (!files)
 993                return 0;
 994        spin_lock(&files->file_lock);
 995        for (fdt = files_fdtable(files); n < fdt->max_fds; n++) {
 996                struct file *file;
 997                file = rcu_dereference_check_fdtable(files, fdt->fd[n]);
 998                if (!file)
 999                        continue;
1000                res = f(p, file, n);
1001                if (res)
1002                        break;
1003        }
1004        spin_unlock(&files->file_lock);
1005        return res;
1006}
1007EXPORT_SYMBOL(iterate_fd);
1008
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