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/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
  25 struct fdtable_defer {
  26         spinlock_t lock;
  27         struct work_struct wq;
  28         struct fdtable *next;
  29 };
  30
  31 int sysctl_nr_open __read_mostly = 1024*1024;
  32 int sysctl_nr_open_min = BITS_PER_LONG;
  33 int 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  */
  41 static DEFINE_PER_CPU(struct fdtable_defer, fdtable_defer_list);
  42
  43 static 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
  57 static void free_fdmem(void *ptr)
  58 {
  59         is_vmalloc_addr(ptr) ? vfree(ptr) : kfree(ptr);
  60 }
  61
  62 static void __free_fdtable(struct fdtable *fdt)
  63 {
  64         free_fdmem(fdt->fd);
  65         free_fdmem(fdt->open_fds);
  66         kfree(fdt);
  67 }
  68
  69 static 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
  87 void 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  */
 123 static 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
 142 static 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
 187 out_arr:
 188         free_fdmem(fdt->fd);
 189 out_fdt:
 190         kfree(fdt);
 191 out:
 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  */
 202 static 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  */
 247 int 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
 272 static 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  */
 291 struct 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
 393 out_release:
 394         kmem_cache_free(files_cachep, newf);
 395 out:
 396         return NULL;
 397 }
 398
 399 static 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
 407 void __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
 416 struct 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  */
 431 int 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);
 439 repeat:
 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
 477 out:
 478         spin_unlock(&files->file_lock);
 479         return error;
 480 }
 481
 482 int get_unused_fd(void)
 483 {
 484         return alloc_fd(0, 0);
 485 }
 486 EXPORT_SYMBOL(get_unused_fd);