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         free_fdset(fdt->open_fds, fdt->max_fdset);
  73         free_fdset(fdt->close_on_exec, fdt->max_fdset);
  74         free_fd_array(fdt->fd, fdt->max_fds);
  75         kfree(fdt);
  76 }
  77
  78 static void fdtable_timer(unsigned long data)
  79 {
  80         struct fdtable_defer *fddef = (struct fdtable_defer *)data;
  81
  82         spin_lock(&fddef->lock);
  83         /*
  84          * If someone already emptied the queue return.
  85          */
  86         if (!fddef->next)
  87                 goto out;
  88         if (!schedule_work(&fddef->wq))
  89                 mod_timer(&fddef->timer, 5);
  90 out:
  91         spin_unlock(&fddef->lock);
  92 }
  93
  94 static void free_fdtable_work(struct fdtable_defer *f)
  95 {
  96         struct fdtable *fdt;
  97
  98         spin_lock_bh(&f->lock);
  99         fdt = f->next;
 100         f->next = NULL;
 101         spin_unlock_bh(&f->lock);
 102         while(fdt) {
 103                 struct fdtable *next = fdt->next;
 104                 __free_fdtable(fdt);
 105                 fdt = next;
 106         }
 107 }
 108
 109 static void free_fdtable_rcu(struct rcu_head *rcu)
 110 {
 111         struct fdtable *fdt = container_of(rcu, struct fdtable, rcu);
 112         int fdset_size, fdarray_size;
 113         struct fdtable_defer *fddef;
 114
 115         BUG_ON(!fdt);
 116         fdset_size = fdt->max_fdset / 8;
 117         fdarray_size = fdt->max_fds * sizeof(struct file *);
 118
 119         if (fdt->free_files) {
 120                 /*
 121                  * The this fdtable was embedded in the files structure
 122                  * and the files structure itself was getting destroyed.
 123                  * It is now safe to free the files structure.
 124                  */
 125                 kmem_cache_free(files_cachep, fdt->free_files);
 126                 return;
 127         }
 128         if (fdt->max_fdset <= EMBEDDED_FD_SET_SIZE &&
 129                 fdt->max_fds <= NR_OPEN_DEFAULT) {
 130                 /*
 131                  * The fdtable was embedded
 132                  */
 133                 return;
 134         }
 135         if (fdset_size <= PAGE_SIZE && fdarray_size <= PAGE_SIZE) {
 136                 kfree(fdt->open_fds);
 137                 kfree(fdt->close_on_exec);
 138                 kfree(fdt->fd);
 139                 kfree(fdt);
 140         } else {
 141                 fddef = &get_cpu_var(fdtable_defer_list);
 142                 spin_lock(&fddef->lock);
 143                 fdt->next = fddef->next;
 144                 fddef->next = fdt;
 145                 /*
 146                  * vmallocs are handled from the workqueue context.
 147                  * If the per-cpu workqueue is running, then we
 148                  * defer work scheduling through a timer.
 149                  */
 150                 if (!schedule_work(&fddef->wq))
 151                         mod_timer(&fddef->timer, 5);
 152                 spin_unlock(&fddef->lock);
 153                 put_cpu_var(fdtable_defer_list);
 154         }
 155 }
 156
 157 void free_fdtable(struct fdtable *fdt)
 158 {
 159         if (fdt->free_files ||
 160                 fdt->max_fdset > EMBEDDED_FD_SET_SIZE ||
 161                 fdt->max_fds > NR_OPEN_DEFAULT)
 162                 call_rcu(&fdt->rcu, free_fdtable_rcu);
 163 }
 164
 165 /*
 166  * Expand the fdset in the files_struct.  Called with the files spinlock
 167  * held for write.
 168  */
 169 static void copy_fdtable(struct fdtable *nfdt, struct fdtable *fdt)
 170 {
 171         int i;
 172         int count;
 173
 174         BUG_ON(nfdt->max_fdset < fdt->max_fdset);
 175         BUG_ON(nfdt->max_fds < fdt->max_fds);
 176         /* Copy the existing tables and install the new pointers */
 177
 178         i = fdt->max_fdset / (sizeof(unsigned long) * 8);
 179         count = (nfdt->max_fdset - fdt->max_fdset) / 8;
 180
 181         /*
 182          * Don't copy the entire array if the current fdset is
 183          * not yet initialised.
 184          */
 185         if (i) {
 186                 memcpy (nfdt->open_fds, fdt->open_fds,
 187                                                 fdt->max_fdset/8);
 188                 memcpy (nfdt->close_on_exec, fdt->close_on_exec,
 189                                                 fdt->max_fdset/8);
 190                 memset (&nfdt->open_fds->fds_bits[i], 0, count);
 191                 memset (&nfdt->close_on_exec->fds_bits[i], 0, count);
 192         }
 193
 194         /* Don't copy/clear the array if we are creating a new
 195            fd array for fork() */
 196         if (fdt->max_fds) {
 197                 memcpy(nfdt->fd, fdt->fd,
 198                         fdt->max_fds * sizeof(struct file *));
 199                 /* clear the remainder of the array */
 200                 memset(&nfdt->fd[fdt->max_fds], 0,
 201                        (nfdt->max_fds - fdt->max_fds) *
 202                                         sizeof(struct file *));
 203         }
 204 }
 205
 206 /*
 207  * Allocate an fdset array, using kmalloc or vmalloc.
 208  * Note: the array isn't cleared at allocation time.
 209  */
 210 fd_set * alloc_fdset(int num)
 211 {
 212         fd_set *new_fdset;
 213         int size = num / 8;
 214
 215         if (size <= PAGE_SIZE)
 216                 new_fdset = (fd_set *) kmalloc(size, GFP_KERNEL);
 217         else
 218                 new_fdset = (fd_set *) vmalloc(size);
 219         return new_fdset;
 220 }
 221
 222 void free_fdset(fd_set *array, int num)
 223 {
 224         if (num <= EMBEDDED_FD_SET_SIZE) /* Don't free an embedded fdset */
 225                 return;
 226         else if (num <= 8 * PAGE_SIZE)
 227                 kfree(array);
 228         else
 229                 vfree(array);
 230 }
 231
 232 static struct fdtable *alloc_fdtable(int nr)
 233 {
 234         struct fdtable *fdt = NULL;
 235         int nfds = 0;
 236         fd_set *new_openset = NULL, *new_execset = NULL;
 237         struct file **new_fds;
 238
 239         fdt = kzalloc(sizeof(*fdt), GFP_KERNEL);
 240         if (!fdt)
 241                 goto out;
 242
 243         nfds = 8 * L1_CACHE_BYTES;
 244         /* Expand to the max in easy steps */
 245         while (nfds <= nr) {
 246                 nfds = nfds * 2;
 247                 if (nfds > NR_OPEN)
 248                         nfds = NR_OPEN;
 249         }
 250
 251         new_openset = alloc_fdset(nfds);
 252         new_execset = alloc_fdset(nfds);
 253         if (!new_openset || !new_execset)
 254                 goto out;
 255         fdt->open_fds = new_openset;
 256         fdt->close_on_exec = new_execset;
 257         fdt->max_fdset = nfds;
 258
 259         nfds = NR_OPEN_DEFAULT;
 260         /*
 261          * Expand to the max in easy steps, and keep expanding it until
 262          * we have enough for the requested fd array size.
 263          */
 264         do {
 265 #if NR_OPEN_DEFAULT < 256
 266                 if (nfds < 256)
 267                         nfds = 256;
 268                 else
 269 #endif
 270                 if (nfds < (PAGE_SIZE / sizeof(struct file *)))
 271                         nfds = PAGE_SIZE / sizeof(struct file *);
 272                 else {
 273                         nfds = nfds * 2;
 274                         if (nfds > NR_OPEN)
 275                                 nfds = NR_OPEN;
 276                 }
 277         } while (nfds <= nr);
 278         new_fds = alloc_fd_array(nfds);
 279         if (!new_fds)
 280                 goto out;
 281         fdt->fd = new_fds;
 282         fdt->max_fds = nfds;
 283         fdt->free_files = NULL;
 284         return fdt;
 285 out:
 286         if (new_openset)
 287                 free_fdset(new_openset, nfds);
 288         if (new_execset)
 289                 free_fdset(new_execset, nfds);
 290         kfree(fdt);
 291         return NULL;
 292 }
 293
 294 /*
 295  * Expands the file descriptor table - it will allocate a new fdtable and
 296  * both fd array and fdset. It is expected to be called with the
 297  * files_lock held.
 298  */
 299 static int expand_fdtable(struct files_struct *files, int nr)
 300         __releases(files->file_lock)
 301         __acquires(files->file_lock)
 302 {
 303         int error = 0;
 304         struct fdtable *fdt;
 305         struct fdtable *nfdt = NULL;
 306
 307         spin_unlock(&files->file_lock);
 308         nfdt = alloc_fdtable(nr);
 309         if (!nfdt) {
 310                 error = -ENOMEM;
 311                 spin_lock(&files->file_lock);
 312                 goto out;
 313         }
 314
 315         spin_lock(&files->file_lock);
 316         fdt = files_fdtable(files);
 317         /*
 318          * Check again since another task may have expanded the
 319          * fd table while we dropped the lock
 320          */
 321         if (nr >= fdt->max_fds || nr >= fdt->max_fdset) {
 322                 copy_fdtable(nfdt, fdt);
 323         } else {
 324                 /* Somebody expanded while we dropped file_lock */
 325                 spin_unlock(&files->file_lock);
 326                 __free_fdtable(nfdt);
 327                 spin_lock(&files->file_lock);
 328                 goto out;
 329         }
 330         rcu_assign_pointer(files->fdt, nfdt);
 331         free_fdtable(fdt);
 332 out:
 333         return error;
 334 }
 335
 336 /*
 337  * Expand files.
 338  * Return <0 on error; 0 nothing done; 1 files expanded, we may have blocked.
 339  * Should be called with the files->file_lock spinlock held for write.
 340  */
 341 int expand_files(struct files_struct *files, int nr)
 342 {
 343         int err, expand = 0;
 344         struct fdtable *fdt;
 345
 346         fdt = files_fdtable(files);
 347         if (nr >= fdt->max_fdset || nr >= fdt->max_fds) {
 348                 if (fdt->max_fdset >= NR_OPEN ||
 349                         fdt->max_fds >= NR_OPEN || nr >= NR_OPEN) {
 350                         err = -EMFILE;
 351                         goto out;
 352                 }
 353                 expand = 1;
 354                 if ((err = expand_fdtable(files, nr)))
 355                         goto out;
 356         }
 357         err = expand;
 358 out:
 359         return err;
 360 }
 361
 362 static void __devinit fdtable_defer_list_init(int cpu)
 363 {
 364         struct fdtable_defer *fddef = &per_cpu(fdtable_defer_list, cpu);
 365         spin_lock_init(&fddef->lock);
 366         INIT_WORK(&fddef->wq, (void (*)(void *))free_fdtable_work, fddef);
 367         init_timer(&fddef->timer);
 368         fddef->timer.data = (unsigned long)fddef;
 369         fddef->timer.function = fdtable_timer;
 370         fddef->next = NULL;
 371 }
 372
 373 void __init files_defer_init(void)
 374 {
 375         int i;
 376         for_each_possible_cpu(i)
 377                 fdtable_defer_list_init(i);
 378 }