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/module.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(unsigned int 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        char *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 = (struct file **)data;
 176        data = alloc_fdmem(max_t(unsigned int,
 177                                 2 * nr / BITS_PER_BYTE, L1_CACHE_BYTES));
 178        if (!data)
 179                goto out_arr;
 180        fdt->open_fds = (fd_set *)data;
 181        data += nr / BITS_PER_BYTE;
 182        fdt->close_on_exec = (fd_set *)data;
 183        fdt->next = NULL;
 184
 185        return fdt;
 186
 187out_arr:
 188        free_fdmem(fdt->fd);
 189out_fdt:
 190        kfree(fdt);
 191out:
 192        return NULL;
 193}
 194
 195/*
 196 * Expand the file descriptor table.
 197 * This function will allocate a new fdtable and both fd array and fdset, of
 198 * the given size.
 199 * Return <0 error code on error; 1 on successful completion.
 200 * The files->file_lock should be held on entry, and will be held on exit.
 201 */
 202static int expand_fdtable(struct files_struct *files, int nr)
 203        __releases(files->file_lock)
 204        __acquires(files->file_lock)
 205{
 206        struct fdtable *new_fdt, *cur_fdt;
 207
 208        spin_unlock(&files->file_lock);
 209        new_fdt = alloc_fdtable(nr);
 210        spin_lock(&files->file_lock);
 211        if (!new_fdt)
 212                return -ENOMEM;
 213        /*
 214         * extremely unlikely race - sysctl_nr_open decreased between the check in
 215         * caller and alloc_fdtable().  Cheaper to catch it here...
 216         */
 217        if (unlikely(new_fdt->max_fds <= nr)) {
 218                __free_fdtable(new_fdt);
 219                return -EMFILE;
 220        }
 221        /*
 222         * Check again since another task may have expanded the fd table while
 223         * we dropped the lock
 224         */
 225        cur_fdt = files_fdtable(files);
 226        if (nr >= cur_fdt->max_fds) {
 227                /* Continue as planned */
 228                copy_fdtable(new_fdt, cur_fdt);
 229                rcu_assign_pointer(files->fdt, new_fdt);
 230                if (cur_fdt->max_fds > NR_OPEN_DEFAULT)
 231                        free_fdtable(cur_fdt);
 232        } else {
 233                /* Somebody else expanded, so undo our attempt */
 234                __free_fdtable(new_fdt);
 235        }
 236        return 1;
 237}
 238
 239/*
 240 * Expand files.
 241 * This function will expand the file structures, if the requested size exceeds
 242 * the current capacity and there is room for expansion.
 243 * Return <0 error code on error; 0 when nothing done; 1 when files were
 244 * expanded and execution may have blocked.
 245 * The files->file_lock should be held on entry, and will be held on exit.
 246 */
 247int expand_files(struct files_struct *files, int nr)
 248{
 249        struct fdtable *fdt;
 250
 251        fdt = files_fdtable(files);
 252
 253        /*
 254         * N.B. For clone tasks sharing a files structure, this test
 255         * will limit the total number of files that can be opened.
 256         */
 257        if (nr >= rlimit(RLIMIT_NOFILE))
 258                return -EMFILE;
 259
 260        /* Do we need to expand? */
 261        if (nr < fdt->max_fds)
 262                return 0;
 263
 264        /* Can we expand? */
 265        if (nr >= sysctl_nr_open)
 266                return -EMFILE;
 267
 268        /* All good, so we try */
 269        return expand_fdtable(files, nr);
 270}
 271
 272static int count_open_files(struct fdtable *fdt)
 273{
 274        int size = fdt->max_fds;
 275        int i;
 276
 277        /* Find the last open fd */
 278        for (i = size/(8*sizeof(long)); i > 0; ) {
 279                if (fdt->open_fds->fds_bits[--i])
 280                        break;
 281        }
 282        i = (i+1) * 8 * sizeof(long);
 283        return i;
 284}
 285
 286/*
 287 * Allocate a new files structure and copy contents from the
 288 * passed in files structure.
 289 * errorp will be valid only when the returned files_struct is NULL.
 290 */
 291struct files_struct *dup_fd(struct files_struct *oldf, int *errorp)
 292{
 293        struct files_struct *newf;
 294        struct file **old_fds, **new_fds;
 295        int open_files, size, i;
 296        struct fdtable *old_fdt, *new_fdt;
 297
 298        *errorp = -ENOMEM;
 299        newf = kmem_cache_alloc(files_cachep, GFP_KERNEL);
 300        if (!newf)
 301                goto out;
 302
 303        atomic_set(&newf->count, 1);
 304
 305        spin_lock_init(&newf->file_lock);
 306        newf->next_fd = 0;
 307        new_fdt = &newf->fdtab;
 308        new_fdt->max_fds = NR_OPEN_DEFAULT;
 309        new_fdt->close_on_exec = (fd_set *)&newf->close_on_exec_init;
 310        new_fdt->open_fds = (fd_set *)&newf->open_fds_init;
 311        new_fdt->fd = &newf->fd_array[0];
 312        new_fdt->next = NULL;
 313
 314        spin_lock(&oldf->file_lock);
 315        old_fdt = files_fdtable(oldf);
 316        open_files = count_open_files(old_fdt);
 317
 318        /*
 319         * Check whether we need to allocate a larger fd array and fd set.
 320         */
 321        while (unlikely(open_files > new_fdt->max_fds)) {
 322                spin_unlock(&oldf->file_lock);
 323
 324                if (new_fdt != &newf->fdtab)
 325                        __free_fdtable(new_fdt);
 326
 327                new_fdt = alloc_fdtable(open_files - 1);
 328                if (!new_fdt) {
 329                        *errorp = -ENOMEM;
 330                        goto out_release;
 331                }
 332
 333                /* beyond sysctl_nr_open; nothing to do */
 334                if (unlikely(new_fdt->max_fds < open_files)) {
 335                        __free_fdtable(new_fdt);
 336                        *errorp = -EMFILE;
 337                        goto out_release;
 338                }
 339
 340                /*
 341                 * Reacquire the oldf lock and a pointer to its fd table
 342                 * who knows it may have a new bigger fd table. We need
 343                 * the latest pointer.
 344                 */
 345                spin_lock(&oldf->file_lock);
 346                old_fdt = files_fdtable(oldf);
 347                open_files = count_open_files(old_fdt);
 348        }
 349
 350        old_fds = old_fdt->fd;
 351        new_fds = new_fdt->fd;
 352
 353        memcpy(new_fdt->open_fds->fds_bits,
 354                old_fdt->open_fds->fds_bits, open_files/8);
 355        memcpy(new_fdt->close_on_exec->fds_bits,
 356                old_fdt->close_on_exec->fds_bits, open_files/8);
 357
 358        for (i = open_files; i != 0; i--) {
 359                struct file *f = *old_fds++;
 360                if (f) {
 361                        get_file(f);
 362                } else {
 363                        /*
 364                         * The fd may be claimed in the fd bitmap but not yet
 365                         * instantiated in the files array if a sibling thread
 366                         * is partway through open().  So make sure that this
 367                         * fd is available to the new process.
 368                         */
 369                        FD_CLR(open_files - i, new_fdt->open_fds);
 370                }
 371                rcu_assign_pointer(*new_fds++, f);
 372        }
 373        spin_unlock(&oldf->file_lock);
 374
 375        /* compute the remainder to be cleared */
 376        size = (new_fdt->max_fds - open_files) * sizeof(struct file *);
 377
 378        /* This is long word aligned thus could use a optimized version */
 379        memset(new_fds, 0, size);
 380
 381        if (new_fdt->max_fds > open_files) {
 382                int left = (new_fdt->max_fds-open_files)/8;
 383                int start = open_files / (8 * sizeof(unsigned long));
 384
 385                memset(&new_fdt->open_fds->fds_bits[start], 0, left);
 386                memset(&new_fdt->close_on_exec->fds_bits[start], 0, left);
 387        }
 388
 389        rcu_assign_pointer(newf->fdt, new_fdt);
 390
 391        return newf;
 392
 393out_release:
 394        kmem_cache_free(files_cachep, newf);
 395out:
 396        return NULL;
 397}
 398
 399static void __devinit fdtable_defer_list_init(int cpu)
 400{
 401        struct fdtable_defer *fddef = &per_cpu(fdtable_defer_list, cpu);
 402        spin_lock_init(&fddef->lock);
 403        INIT_WORK(&fddef->wq, free_fdtable_work);
 404        fddef->next = NULL;
 405}
 406
 407void __init files_defer_init(void)
 408{
 409        int i;
 410        for_each_possible_cpu(i)
 411                fdtable_defer_list_init(i);
 412        sysctl_nr_open_max = min((size_t)INT_MAX, ~(size_t)0/sizeof(void *)) &
 413                             -BITS_PER_LONG;
 414}
 415
 416struct files_struct init_files = {
 417        .count          = ATOMIC_INIT(1),
 418        .fdt            = &init_files.fdtab,
 419        .fdtab          = {
 420                .max_fds        = NR_OPEN_DEFAULT,
 421                .fd             = &init_files.fd_array[0],
 422                .close_on_exec  = (fd_set *)&init_files.close_on_exec_init,
 423                .open_fds       = (fd_set *)&init_files.open_fds_init,
 424        },
 425        .file_lock      = __SPIN_LOCK_UNLOCKED(init_task.file_lock),
 426};
 427
 428/*
 429 * allocate a file descriptor, mark it busy.
 430 */
 431int alloc_fd(unsigned start, unsigned flags)
 432{
 433        struct files_struct *files = current->files;
 434        unsigned int fd;
 435        int error;
 436        struct fdtable *fdt;
 437
 438        spin_lock(&files->file_lock);
 439repeat:
 440        fdt = files_fdtable(files);
 441        fd = start;
 442        if (fd < files->next_fd)
 443                fd = files->next_fd;
 444
 445        if (fd < fdt->max_fds)
 446                fd = find_next_zero_bit(fdt->open_fds->fds_bits,
 447                                           fdt->max_fds, fd);
 448
 449        error = expand_files(files, fd);
 450        if (error < 0)
 451                goto out;
 452
 453        /*
 454         * If we needed to expand the fs array we
 455         * might have blocked - try again.
 456         */
 457        if (error)
 458                goto repeat;
 459
 460        if (start <= files->next_fd)
 461                files->next_fd = fd + 1;
 462
 463        FD_SET(fd, fdt->open_fds);
 464        if (flags & O_CLOEXEC)
 465                FD_SET(fd, fdt->close_on_exec);
 466        else
 467                FD_CLR(fd, fdt->close_on_exec);
 468        error = fd;
 469#if 1
 470        /* Sanity check */
 471        if (rcu_dereference_raw(fdt->fd[fd]) != NULL) {
 472                printk(KERN_WARNING "alloc_fd: slot %d not NULL!\n", fd);
 473                rcu_assign_pointer(fdt->fd[fd], NULL);
 474        }
 475#endif
 476
 477out:
 478        spin_unlock(&files->file_lock);
 479        return error;
 480}
 481
 482int get_unused_fd(void)
 483{
 484        return alloc_fd(0, 0);
 485}
 486EXPORT_SYMBOL(get_unused_fd);
 487
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