fs/file.c

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