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/export.h>
  10#include <linux/fs.h>
  11#include <linux/mm.h>
  12#include <linux/mmzone.h>
  13#include <linux/time.h>
  14#include <linux/sched.h>
  15#include <linux/slab.h>
  16#include <linux/vmalloc.h>
  17#include <linux/file.h>
  18#include <linux/fdtable.h>
  19#include <linux/bitops.h>
  20#include <linux/interrupt.h>
  21#include <linux/spinlock.h>
  22#include <linux/rcupdate.h>
  23#include <linux/workqueue.h>
  24
  25struct fdtable_defer {
  26        spinlock_t lock;
  27        struct work_struct wq;
  28        struct fdtable *next;
  29};
  30
  31int sysctl_nr_open __read_mostly = 1024*1024;
  32int sysctl_nr_open_min = BITS_PER_LONG;
  33int sysctl_nr_open_max = 1024 * 1024; /* raised later */
  34
  35/*
  36 * We use this list to defer free fdtables that have vmalloced
  37 * sets/arrays. By keeping a per-cpu list, we avoid having to embed
  38 * the work_struct in fdtable itself which avoids a 64 byte (i386) increase in
  39 * this per-task structure.
  40 */
  41static DEFINE_PER_CPU(struct fdtable_defer, fdtable_defer_list);
  42
  43static void *alloc_fdmem(size_t size)
  44{
  45        /*
  46         * Very large allocations can stress page reclaim, so fall back to
  47         * vmalloc() if the allocation size will be considered "large" by the VM.
  48         */
  49        if (size <= (PAGE_SIZE << PAGE_ALLOC_COSTLY_ORDER)) {
  50                void *data = kmalloc(size, GFP_KERNEL|__GFP_NOWARN);
  51                if (data != NULL)
  52                        return data;
  53        }
  54        return vmalloc(size);
  55}
  56
  57static void free_fdmem(void *ptr)
  58{
  59        is_vmalloc_addr(ptr) ? vfree(ptr) : kfree(ptr);
  60}
  61
  62static void __free_fdtable(struct fdtable *fdt)
  63{
  64        free_fdmem(fdt->fd);
  65        free_fdmem(fdt->open_fds);
  66        kfree(fdt);
  67}
  68
  69static void free_fdtable_work(struct work_struct *work)
  70{
  71        struct fdtable_defer *f =
  72                container_of(work, struct fdtable_defer, wq);
  73        struct fdtable *fdt;
  74
  75        spin_lock_bh(&f->lock);
  76        fdt = f->next;
  77        f->next = NULL;
  78        spin_unlock_bh(&f->lock);
  79        while(fdt) {
  80                struct fdtable *next = fdt->next;
  81
  82                __free_fdtable(fdt);
  83                fdt = next;
  84        }
  85}
  86
  87void free_fdtable_rcu(struct rcu_head *rcu)
  88{
  89        struct fdtable *fdt = container_of(rcu, struct fdtable, rcu);
  90        struct fdtable_defer *fddef;
  91
  92        BUG_ON(!fdt);
  93
  94        if (fdt->max_fds <= NR_OPEN_DEFAULT) {
  95                /*
  96                 * This fdtable is embedded in the files structure and that
  97                 * structure itself is getting destroyed.
  98                 */
  99                kmem_cache_free(files_cachep,
 100                                container_of(fdt, struct files_struct, fdtab));
 101                return;
 102        }
 103        if (!is_vmalloc_addr(fdt->fd) && !is_vmalloc_addr(fdt->open_fds)) {
 104                kfree(fdt->fd);
 105                kfree(fdt->open_fds);
 106                kfree(fdt);
 107        } else {
 108                fddef = &get_cpu_var(fdtable_defer_list);
 109                spin_lock(&fddef->lock);
 110                fdt->next = fddef->next;
 111                fddef->next = fdt;
 112                /* vmallocs are handled from the workqueue context */
 113                schedule_work(&fddef->wq);
 114                spin_unlock(&fddef->lock);
 115                put_cpu_var(fdtable_defer_list);
 116        }
 117}
 118
 119/*
 120 * Expand the fdset in the files_struct.  Called with the files spinlock
 121 * held for write.
 122 */
 123static void copy_fdtable(struct fdtable *nfdt, struct fdtable *ofdt)
 124{
 125        unsigned int cpy, set;
 126
 127        BUG_ON(nfdt->max_fds < ofdt->max_fds);
 128
 129        cpy = ofdt->max_fds * sizeof(struct file *);
 130        set = (nfdt->max_fds - ofdt->max_fds) * sizeof(struct file *);
 131        memcpy(nfdt->fd, ofdt->fd, cpy);
 132        memset((char *)(nfdt->fd) + cpy, 0, set);
 133
 134        cpy = ofdt->max_fds / BITS_PER_BYTE;
 135        set = (nfdt->max_fds - ofdt->max_fds) / BITS_PER_BYTE;
 136        memcpy(nfdt->open_fds, ofdt->open_fds, cpy);
 137        memset((char *)(nfdt->open_fds) + cpy, 0, set);
 138        memcpy(nfdt->close_on_exec, ofdt->close_on_exec, cpy);
 139        memset((char *)(nfdt->close_on_exec) + cpy, 0, set);
 140}
 141
 142static struct fdtable * alloc_fdtable(unsigned int nr)
 143{
 144        struct fdtable *fdt;
 145        void *data;
 146
 147        /*
 148         * Figure out how many fds we actually want to support in this fdtable.
 149         * Allocation steps are keyed to the size of the fdarray, since it
 150         * grows far faster than any of the other dynamic data. We try to fit
 151         * the fdarray into comfortable page-tuned chunks: starting at 1024B
 152         * and growing in powers of two from there on.
 153         */
 154        nr /= (1024 / sizeof(struct file *));
 155        nr = roundup_pow_of_two(nr + 1);
 156        nr *= (1024 / sizeof(struct file *));
 157        /*
 158         * Note that this can drive nr *below* what we had passed if sysctl_nr_open
 159         * had been set lower between the check in expand_files() and here.  Deal
 160         * with that in caller, it's cheaper that way.
 161         *
 162         * We make sure that nr remains a multiple of BITS_PER_LONG - otherwise
 163         * bitmaps handling below becomes unpleasant, to put it mildly...
 164         */
 165        if (unlikely(nr > sysctl_nr_open))
 166                nr = ((sysctl_nr_open - 1) | (BITS_PER_LONG - 1)) + 1;
 167
 168        fdt = kmalloc(sizeof(struct fdtable), GFP_KERNEL);
 169        if (!fdt)
 170                goto out;
 171        fdt->max_fds = nr;
 172        data = alloc_fdmem(nr * sizeof(struct file *));
 173        if (!data)
 174                goto out_fdt;
 175        fdt->fd = data;
 176
 177        data = alloc_fdmem(max_t(size_t,
 178                                 2 * nr / BITS_PER_BYTE, L1_CACHE_BYTES));
 179        if (!data)
 180                goto out_arr;
 181        fdt->open_fds = data;
 182        data += nr / BITS_PER_BYTE;
 183        fdt->close_on_exec = data;
 184        fdt->next = NULL;
 185
 186        return fdt;
 187
 188out_arr:
 189        free_fdmem(fdt->fd);
 190out_fdt:
 191        kfree(fdt);
 192out:
 193        return NULL;
 194}
 195
 196/*
 197 * Expand the file descriptor table.
 198 * This function will allocate a new fdtable and both fd array and fdset, of
 199 * the given size.
 200 * Return <0 error code on error; 1 on successful completion.
 201 * The files->file_lock should be held on entry, and will be held on exit.
 202 */
 203static int expand_fdtable(struct files_struct *files, int nr)
 204        __releases(files->file_lock)
 205        __acquires(files->file_lock)
 206{
 207        struct fdtable *new_fdt, *cur_fdt;
 208
 209        spin_unlock(&files->file_lock);
 210        new_fdt = alloc_fdtable(nr);
 211        spin_lock(&files->file_lock);
 212        if (!new_fdt)
 213                return -ENOMEM;
 214        /*
 215         * extremely unlikely race - sysctl_nr_open decreased between the check in
 216         * caller and alloc_fdtable().  Cheaper to catch it here...
 217         */
 218        if (unlikely(new_fdt->max_fds <= nr)) {
 219                __free_fdtable(new_fdt);
 220                return -EMFILE;
 221        }
 222        /*
 223         * Check again since another task may have expanded the fd table while
 224         * we dropped the lock
 225         */
 226        cur_fdt = files_fdtable(files);
 227        if (nr >= cur_fdt->max_fds) {
 228                /* Continue as planned */
 229                copy_fdtable(new_fdt, cur_fdt);
 230                rcu_assign_pointer(files->fdt, new_fdt);
 231                if (cur_fdt->max_fds > NR_OPEN_DEFAULT)
 232                        free_fdtable(cur_fdt);
 233        } else {
 234                /* Somebody else expanded, so undo our attempt */
 235                __free_fdtable(new_fdt);
 236        }
 237        return 1;
 238}
 239
 240/*
 241 * Expand files.
 242 * This function will expand the file structures, if the requested size exceeds
 243 * the current capacity and there is room for expansion.
 244 * Return <0 error code on error; 0 when nothing done; 1 when files were
 245 * expanded and execution may have blocked.
 246 * The files->file_lock should be held on entry, and will be held on exit.
 247 */
 248int expand_files(struct files_struct *files, int nr)
 249{
 250        struct fdtable *fdt;
 251
 252        fdt = files_fdtable(files);
 253
 254        /*
 255         * N.B. For clone tasks sharing a files structure, this test
 256         * will limit the total number of files that can be opened.
 257         */
 258        if (nr >= rlimit(RLIMIT_NOFILE))
 259                return -EMFILE;
 260
 261        /* Do we need to expand? */
 262        if (nr < fdt->max_fds)
 263                return 0;
 264
 265        /* Can we expand? */
 266        if (nr >= sysctl_nr_open)
 267                return -EMFILE;
 268
 269        /* All good, so we try */
 270        return expand_fdtable(files, nr);
 271}
 272
 273static int count_open_files(struct fdtable *fdt)
 274{
 275        int size = fdt->max_fds;
 276        int i;
 277
 278        /* Find the last open fd */
 279        for (i = size / BITS_PER_LONG; i > 0; ) {
 280                if (fdt->open_fds[--i])
 281                        break;
 282        }
 283        i = (i + 1) * BITS_PER_LONG;
 284        return i;
 285}
 286
 287/*
 288 * Allocate a new files structure and copy contents from the
 289 * passed in files structure.
 290 * errorp will be valid only when the returned files_struct is NULL.
 291 */
 292struct files_struct *dup_fd(struct files_struct *oldf, int *errorp)
 293{
 294        struct files_struct *newf;
 295        struct file **old_fds, **new_fds;
 296        int open_files, size, i;
 297        struct fdtable *old_fdt, *new_fdt;
 298
 299        *errorp = -ENOMEM;
 300        newf = kmem_cache_alloc(files_cachep, GFP_KERNEL);
 301        if (!newf)
 302                goto out;
 303
 304        atomic_set(&newf->count, 1);
 305
 306        spin_lock_init(&newf->file_lock);
 307        newf->next_fd = 0;
 308        new_fdt = &newf->fdtab;
 309        new_fdt->max_fds = NR_OPEN_DEFAULT;
 310        new_fdt->close_on_exec = newf->close_on_exec_init;
 311        new_fdt->open_fds = newf->open_fds_init;
 312        new_fdt->fd = &newf->fd_array[0];
 313        new_fdt->next = NULL;
 314
 315        spin_lock(&oldf->file_lock);
 316        old_fdt = files_fdtable(oldf);
 317        open_files = count_open_files(old_fdt);
 318
 319        /*
 320         * Check whether we need to allocate a larger fd array and fd set.
 321         */
 322        while (unlikely(open_files > new_fdt->max_fds)) {
 323                spin_unlock(&oldf->file_lock);
 324
 325                if (new_fdt != &newf->fdtab)
 326                        __free_fdtable(new_fdt);
 327
 328                new_fdt = alloc_fdtable(open_files - 1);
 329                if (!new_fdt) {
 330                        *errorp = -ENOMEM;
 331                        goto out_release;
 332                }
 333
 334                /* beyond sysctl_nr_open; nothing to do */
 335                if (unlikely(new_fdt->max_fds < open_files)) {
 336                        __free_fdtable(new_fdt);
 337                        *errorp = -EMFILE;
 338                        goto out_release;
 339                }
 340
 341                /*
 342                 * Reacquire the oldf lock and a pointer to its fd table
 343                 * who knows it may have a new bigger fd table. We need
 344                 * the latest pointer.
 345                 */
 346                spin_lock(&oldf->file_lock);
 347                old_fdt = files_fdtable(oldf);
 348                open_files = count_open_files(old_fdt);
 349        }
 350
 351        old_fds = old_fdt->fd;
 352        new_fds = new_fdt->fd;
 353
 354        memcpy(new_fdt->open_fds, old_fdt->open_fds, open_files / 8);
 355        memcpy(new_fdt->close_on_exec, old_fdt->close_on_exec, open_files / 8);
 356
 357        for (i = open_files; i != 0; i--) {
 358                struct file *f = *old_fds++;
 359                if (f) {
 360                        get_file(f);
 361                } else {
 362                        /*
 363                         * The fd may be claimed in the fd bitmap but not yet
 364                         * instantiated in the files array if a sibling thread
 365                         * is partway through open().  So make sure that this
 366                         * fd is available to the new process.
 367                         */
 368                        __clear_open_fd(open_files - i, new_fdt);
 369                }
 370                rcu_assign_pointer(*new_fds++, f);
 371        }
 372        spin_unlock(&oldf->file_lock);
 373
 374        /* compute the remainder to be cleared */
 375        size = (new_fdt->max_fds - open_files) * sizeof(struct file *);
 376
 377        /* This is long word aligned thus could use a optimized version */
 378        memset(new_fds, 0, size);
 379
 380        if (new_fdt->max_fds > open_files) {
 381                int left = (new_fdt->max_fds - open_files) / 8;
 382                int start = open_files / BITS_PER_LONG;
 383
 384                memset(&new_fdt->open_fds[start], 0, left);
 385                memset(&new_fdt->close_on_exec[start], 0, left);
 386        }
 387
 388        rcu_assign_pointer(newf->fdt, new_fdt);
 389
 390        return newf;
 391
 392out_release:
 393        kmem_cache_free(files_cachep, newf);
 394out:
 395        return NULL;
 396}
 397
 398static void __devinit fdtable_defer_list_init(int cpu)
 399{
 400        struct fdtable_defer *fddef = &per_cpu(fdtable_defer_list, cpu);
 401        spin_lock_init(&fddef->lock);
 402        INIT_WORK(&fddef->wq, free_fdtable_work);
 403        fddef->next = NULL;
 404}
 405
 406void __init files_defer_init(void)
 407{
 408        int i;
 409        for_each_possible_cpu(i)
 410                fdtable_defer_list_init(i);
 411        sysctl_nr_open_max = min((size_t)INT_MAX, ~(size_t)0/sizeof(void *)) &
 412                             -BITS_PER_LONG;
 413}
 414
 415struct files_struct init_files = {
 416        .count          = ATOMIC_INIT(1),
 417        .fdt            = &init_files.fdtab,
 418        .fdtab          = {
 419                .max_fds        = NR_OPEN_DEFAULT,
 420                .fd             = &init_files.fd_array[0],
 421                .close_on_exec  = init_files.close_on_exec_init,
 422                .open_fds       = init_files.open_fds_init,
 423        },
 424        .file_lock      = __SPIN_LOCK_UNLOCKED(init_task.file_lock),
 425};
 426
 427/*
 428 * allocate a file descriptor, mark it busy.
 429 */
 430int alloc_fd(unsigned start, unsigned flags)
 431{
 432        struct files_struct *files = current->files;
 433        unsigned int fd;
 434        int error;
 435        struct fdtable *fdt;
 436
 437        spin_lock(&files->file_lock);
 438repeat:
 439        fdt = files_fdtable(files);
 440        fd = start;
 441        if (fd < files->next_fd)
 442                fd = files->next_fd;
 443
 444        if (fd < fdt->max_fds)
 445                fd = find_next_zero_bit(fdt->open_fds, fdt->max_fds, fd);
 446
 447        error = expand_files(files, fd);
 448        if (error < 0)
 449                goto out;
 450
 451        /*
 452         * If we needed to expand the fs array we
 453         * might have blocked - try again.
 454         */
 455        if (error)
 456                goto repeat;
 457
 458        if (start <= files->next_fd)
 459                files->next_fd = fd + 1;
 460
 461        __set_open_fd(fd, fdt);
 462        if (flags & O_CLOEXEC)
 463                __set_close_on_exec(fd, fdt);
 464        else
 465                __clear_close_on_exec(fd, fdt);
 466        error = fd;
 467#if 1
 468        /* Sanity check */
 469        if (rcu_dereference_raw(fdt->fd[fd]) != NULL) {
 470                printk(KERN_WARNING "alloc_fd: slot %d not NULL!\n", fd);
 471                rcu_assign_pointer(fdt->fd[fd], NULL);
 472        }
 473#endif
 474
 475out:
 476        spin_unlock(&files->file_lock);
 477        return error;
 478}
 479
 480int get_unused_fd(void)
 481{
 482        return alloc_fd(0, 0);
 483}
 484EXPORT_SYMBOL(get_unused_fd);
 485
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