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/fs.h>
  10 #include <linux/mm.h>
  11 #include <linux/time.h>
  12 #include <linux/slab.h>
  13 #include <linux/vmalloc.h>
  14 #include <linux/file.h>
  15 #include <linux/bitops.h>
  16 #include <linux/interrupt.h>
  17 #include <linux/spinlock.h>
  18 #include <linux/rcupdate.h>
  19 #include <linux/workqueue.h>
  20
  21 struct fdtable_defer {
  22         spinlock_t lock;
  23         struct work_struct wq;
  24         struct timer_list timer;
  25         struct fdtable *next;
  26 };
  27
  28 /*
  29  * We use this list to defer free fdtables that have vmalloced
  30  * sets/arrays. By keeping a per-cpu list, we avoid having to embed
  31  * the work_struct in fdtable itself which avoids a 64 byte (i386) increase in
  32  * this per-task structure.
  33  */
  34 static DEFINE_PER_CPU(struct fdtable_defer, fdtable_defer_list);
  35
  36
  37 /*
  38  * Allocate an fd array, using kmalloc or vmalloc.
  39  * Note: the array isn't cleared at allocation time.
  40  */
  41 struct file ** alloc_fd_array(int num)
  42 {
  43         struct file **new_fds;
  44         int size = num * sizeof(struct file *);
  45
  46         if (size <= PAGE_SIZE)
  47                 new_fds = (struct file **) kmalloc(size, GFP_KERNEL);
  48         else
  49                 new_fds = (struct file **) vmalloc(size);
  50         return new_fds;
  51 }
  52
  53 void free_fd_array(struct file **array, int num)
  54 {
  55         int size = num * sizeof(struct file *);
  56
  57         if (!array) {
  58                 printk (KERN_ERR "free_fd_array: array = 0 (num = %d)\n", num);
  59                 return;
  60         }
  61
  62         if (num <= NR_OPEN_DEFAULT) /* Don't free the embedded fd array! */
  63                 return;
  64         else if (size <= PAGE_SIZE)
  65                 kfree(array);
  66         else
  67                 vfree(array);
  68 }
  69
  70 static void __free_fdtable(struct fdtable *fdt)
  71 {
  72         int fdset_size, fdarray_size;
  73
  74         fdset_size = fdt->max_fdset / 8;
  75         fdarray_size = fdt->max_fds * sizeof(struct file *);
  76         free_fdset(fdt->open_fds, fdset_size);
  77         free_fdset(fdt->close_on_exec, fdset_size);
  78         free_fd_array(fdt->fd, fdarray_size);
  79         kfree(fdt);
  80 }
  81
  82 static void fdtable_timer(unsigned long data)
  83 {
  84         struct fdtable_defer *fddef = (struct fdtable_defer *)data;
  85
  86         spin_lock(&fddef->lock);
  87         /*
  88          * If someone already emptied the queue return.
  89          */
  90         if (!fddef->next)
  91                 goto out;
  92         if (!schedule_work(&fddef->wq))
  93                 mod_timer(&fddef->timer, 5);
  94 out:
  95         spin_unlock(&fddef->lock);
  96 }
  97
  98 static void free_fdtable_work(struct fdtable_defer *f)
  99 {
 100         struct fdtable *fdt;
 101
 102         spin_lock_bh(&f->lock);
 103         fdt = f->next;
 104         f->next = NULL;
 105         spin_unlock_bh(&f->lock);
 106         while(fdt) {
 107                 struct fdtable *next = fdt->next;
 108                 __free_fdtable(fdt);
 109                 fdt = next;
 110         }
 111 }
 112
 113 static void free_fdtable_rcu(struct rcu_head *rcu)
 114 {
 115         struct fdtable *fdt = container_of(rcu, struct fdtable, rcu);
 116         int fdset_size, fdarray_size;
 117         struct fdtable_defer *fddef;
 118
 119         BUG_ON(!fdt);
 120         fdset_size = fdt->max_fdset / 8;
 121         fdarray_size = fdt->max_fds * sizeof(struct file *);
 122
 123         if (fdt->free_files) {
 124                 /*
 125                  * The this fdtable was embedded in the files structure
 126                  * and the files structure itself was getting destroyed.
 127                  * It is now safe to free the files structure.
 128                  */
 129                 kmem_cache_free(files_cachep, fdt->free_files);
 130                 return;
 131         }
 132         if (fdt->max_fdset <= __FD_SETSIZE && fdt->max_fds <= NR_OPEN_DEFAULT) {
 133                 /*
 134                  * The fdtable was embedded
 135                  */
 136                 return;
 137         }
 138         if (fdset_size <= PAGE_SIZE && fdarray_size <= PAGE_SIZE) {
 139                 kfree(fdt->open_fds);
 140                 kfree(fdt->close_on_exec);
 141                 kfree(fdt->fd);
 142                 kfree(fdt);
 143         } else {
 144                 fddef = &get_cpu_var(fdtable_defer_list);
 145                 spin_lock(&fddef->lock);
 146                 fdt->next = fddef->next;
 147                 fddef->next = fdt;
 148                 /*
 149                  * vmallocs are handled from the workqueue context.
 150                  * If the per-cpu workqueue is running, then we
 151                  * defer work scheduling through a timer.
 152                  */
 153                 if (!schedule_work(&fddef->wq))
 154                         mod_timer(&fddef->timer, 5);
 155                 spin_unlock(&fddef->lock);
 156                 put_cpu_var(fdtable_defer_list);
 157         }
 158 }
 159
 160 void free_fdtable(struct fdtable *fdt)
 161 {
 162         if (fdt->free_files || fdt->max_fdset > __FD_SETSIZE ||
 163                                         fdt->max_fds > NR_OPEN_DEFAULT)
 164                 call_rcu(&fdt->rcu, free_fdtable_rcu);
 165 }
 166
 167 /*
 168  * Expand the fdset in the files_struct.  Called with the files spinlock
 169  * held for write.
 170  */
 171 static void copy_fdtable(struct fdtable *nfdt, struct fdtable *fdt)
 172 {
 173         int i;
 174         int count;
 175
 176         BUG_ON(nfdt->max_fdset < fdt->max_fdset);
 177         BUG_ON(nfdt->max_fds < fdt->max_fds);
 178         /* Copy the existing tables and install the new pointers */
 179
 180         i = fdt->max_fdset / (sizeof(unsigned long) * 8);
 181         count = (nfdt->max_fdset - fdt->max_fdset) / 8;
 182
 183         /*
 184          * Don't copy the entire array if the current fdset is
 185          * not yet initialised.
 186          */
 187         if (i) {
 188                 memcpy (nfdt->open_fds, fdt->open_fds,
 189                                                 fdt->max_fdset/8);
 190                 memcpy (nfdt->close_on_exec, fdt->close_on_exec,
 191                                                 fdt->max_fdset/8);
 192                 memset (&nfdt->open_fds->fds_bits[i], 0, count);
 193                 memset (&nfdt->close_on_exec->fds_bits[i], 0, count);
 194         }
 195
 196         /* Don't copy/clear the array if we are creating a new
 197            fd array for fork() */
 198         if (fdt->max_fds) {
 199                 memcpy(nfdt->fd, fdt->fd,
 200                         fdt->max_fds * sizeof(struct file *));
 201                 /* clear the remainder of the array */
 202                 memset(&nfdt->fd[fdt->max_fds], 0,
 203                        (nfdt->max_fds - fdt->max_fds) *
 204                                         sizeof(struct file *));
 205         }
 206         nfdt->next_fd = fdt->next_fd;
 207 }
 208
 209 /*
 210  * Allocate an fdset array, using kmalloc or vmalloc.
 211  * Note: the array isn't cleared at allocation time.
 212  */
 213 fd_set * alloc_fdset(int num)
 214 {
 215         fd_set *new_fdset;
 216         int size = num / 8;
 217
 218         if (size <= PAGE_SIZE)
 219                 new_fdset = (fd_set *) kmalloc(size, GFP_KERNEL);
 220         else
 221                 new_fdset = (fd_set *) vmalloc(size);
 222         return new_fdset;
 223 }
 224
 225 void free_fdset(fd_set *array, int num)
 226 {
 227         int size = num / 8;
 228
 229         if (num <= __FD_SETSIZE) /* Don't free an embedded fdset */
 230                 return;
 231         else if (size <= PAGE_SIZE)
 232                 kfree(array);
 233         else
 234                 vfree(array);
 235 }
 236
 237 static struct fdtable *alloc_fdtable(int nr)
 238 {
 239         struct fdtable *fdt = NULL;
 240         int nfds = 0;
 241         fd_set *new_openset = NULL, *new_execset = NULL;
 242         struct file **new_fds;
 243
 244         fdt = kmalloc(sizeof(*fdt), GFP_KERNEL);
 245         if (!fdt)
 246                 goto out;
 247         memset(fdt, 0, sizeof(*fdt));
 248
 249         nfds = __FD_SETSIZE;
 250         /* Expand to the max in easy steps */
 251         do {
 252                 if (nfds < (PAGE_SIZE * 8))
 253                         nfds = PAGE_SIZE * 8;
 254                 else {
 255                         nfds = nfds * 2;
 256                         if (nfds > NR_OPEN)
 257                                 nfds = NR_OPEN;
 258                 }
 259         } while (nfds <= nr);
 260
 261         new_openset = alloc_fdset(nfds);
 262         new_execset = alloc_fdset(nfds);
 263         if (!new_openset || !new_execset)
 264                 goto out;
 265         fdt->open_fds = new_openset;
 266         fdt->close_on_exec = new_execset;
 267         fdt->max_fdset = nfds;
 268
 269         nfds = NR_OPEN_DEFAULT;
 270         /*
 271          * Expand to the max in easy steps, and keep expanding it until
 272          * we have enough for the requested fd array size.
 273          */
 274         do {
 275 #if NR_OPEN_DEFAULT < 256
 276                 if (nfds < 256)
 277                         nfds = 256;
 278                 else
 279 #endif
 280                 if (nfds < (PAGE_SIZE / sizeof(struct file *)))
 281                         nfds = PAGE_SIZE / sizeof(struct file *);
 282                 else {
 283                         nfds = nfds * 2;
 284                         if (nfds > NR_OPEN)
 285                                 nfds = NR_OPEN;
 286                 }
 287         } while (nfds <= nr);
 288         new_fds = alloc_fd_array(nfds);
 289         if (!new_fds)
 290                 goto out;
 291         fdt->fd = new_fds;
 292         fdt->max_fds = nfds;
 293         fdt->free_files = NULL;
 294         return fdt;
 295 out:
 296         if (new_openset)
 297                 free_fdset(new_openset, nfds);
 298         if (new_execset)
 299                 free_fdset(new_execset, nfds);
 300         kfree(fdt);
 301         return NULL;
 302 }
 303
 304 /*
 305  * Expands the file descriptor table - it will allocate a new fdtable and
 306  * both fd array and fdset. It is expected to be called with the
 307  * files_lock held.
 308  */
 309 static int expand_fdtable(struct files_struct *files, int nr)
 310         __releases(files->file_lock)
 311         __acquires(files->file_lock)
 312 {
 313         int error = 0;
 314         struct fdtable *fdt;
 315         struct fdtable *nfdt = NULL;
 316
 317         spin_unlock(&files->file_lock);
 318         nfdt = alloc_fdtable(nr);
 319         if (!nfdt) {
 320                 error = -ENOMEM;
 321                 spin_lock(&files->file_lock);
 322                 goto out;
 323         }
 324
 325         spin_lock(&files->file_lock);
 326         fdt = files_fdtable(files);
 327         /*
 328          * Check again since another task may have expanded the
 329          * fd table while we dropped the lock
 330          */
 331         if (nr >= fdt->max_fds || nr >= fdt->max_fdset) {
 332                 copy_fdtable(nfdt, fdt);
 333         } else {
 334                 /* Somebody expanded while we dropped file_lock */
 335                 spin_unlock(&files->file_lock);
 336                 __free_fdtable(nfdt);
 337                 spin_lock(&files->file_lock);
 338                 goto out;
 339         }
 340         rcu_assign_pointer(files->fdt, nfdt);
 341         free_fdtable(fdt);
 342 out:
 343         return error;
 344 }
 345
 346 /*
 347  * Expand files.
 348  * Return <0 on error; 0 nothing done; 1 files expanded, we may have blocked.
 349  * Should be called with the files->file_lock spinlock held for write.
 350  */
 351 int expand_files(struct files_struct *files, int nr)
 352 {
 353         int err, expand = 0;
 354         struct fdtable *fdt;
 355
 356         fdt = files_fdtable(files);
 357         if (nr >= fdt->max_fdset || nr >= fdt->max_fds) {
 358                 if (fdt->max_fdset >= NR_OPEN ||
 359                         fdt->max_fds >= NR_OPEN || nr >= NR_OPEN) {
 360                         err = -EMFILE;
 361                         goto out;
 362                 }
 363                 expand = 1;
 364                 if ((err = expand_fdtable(files, nr)))
 365                         goto out;
 366         }
 367         err = expand;
 368 out:
 369         return err;
 370 }
 371
 372 static void __devinit fdtable_defer_list_init(int cpu)
 373 {
 374         struct fdtable_defer *fddef = &per_cpu(fdtable_defer_list, cpu);
 375         spin_lock_init(&fddef->lock);
 376         INIT_WORK(&fddef->wq, (void (*)(void *))free_fdtable_work, fddef);
 377         init_timer(&fddef->timer);
 378         fddef->timer.data = (unsigned long)fddef;
 379         fddef->timer.function = fdtable_timer;
 380         fddef->next = NULL;
 381 }
 382
 383 void __init files_defer_init(void)
 384 {
 385         int i;
 386         /* Really early - can't use for_each_cpu */
 387         for (i = 0; i < NR_CPUS; i++)
 388                 fdtable_defer_list_init(i);
 389 }