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 <= __FD_SETSIZE && fdt->max_fds <= NR_OPEN_DEFAULT) {
 129                 /*
 130                  * The fdtable was embedded
 131                  */
 132                 return;
 133         }
 134         if (fdset_size <= PAGE_SIZE && fdarray_size <= PAGE_SIZE) {
 135                 kfree(fdt->open_fds);
 136                 kfree(fdt->close_on_exec);
 137                 kfree(fdt->fd);
 138                 kfree(fdt);
 139         } else {
 140                 fddef = &get_cpu_var(fdtable_defer_list);
 141                 spin_lock(&fddef->lock);
 142                 fdt->next = fddef->next;
 143                 fddef->next = fdt;
 144                 /*
 145                  * vmallocs are handled from the workqueue context.
 146                  * If the per-cpu workqueue is running, then we
 147                  * defer work scheduling through a timer.
 148                  */
 149                 if (!schedule_work(&fddef->wq))
 150                         mod_timer(&fddef->timer, 5);
 151                 spin_unlock(&fddef->lock);
 152                 put_cpu_var(fdtable_defer_list);
 153         }
 154 }
 155
 156 void free_fdtable(struct fdtable *fdt)
 157 {
 158         if (fdt->free_files || fdt->max_fdset > __FD_SETSIZE ||
 159                                         fdt->max_fds > NR_OPEN_DEFAULT)
 160                 call_rcu(&fdt->rcu, free_fdtable_rcu);
 161 }
 162
 163 /*
 164  * Expand the fdset in the files_struct.  Called with the files spinlock
 165  * held for write.
 166  */
 167 static void copy_fdtable(struct fdtable *nfdt, struct fdtable *fdt)
 168 {
 169         int i;
 170         int count;
 171
 172         BUG_ON(nfdt->max_fdset < fdt->max_fdset);
 173         BUG_ON(nfdt->max_fds < fdt->max_fds);
 174         /* Copy the existing tables and install the new pointers */
 175
 176         i = fdt->max_fdset / (sizeof(unsigned long) * 8);
 177         count = (nfdt->max_fdset - fdt->max_fdset) / 8;
 178
 179         /*
 180          * Don't copy the entire array if the current fdset is
 181          * not yet initialised.
 182          */
 183         if (i) {
 184                 memcpy (nfdt->open_fds, fdt->open_fds,
 185                                                 fdt->max_fdset/8);
 186                 memcpy (nfdt->close_on_exec, fdt->close_on_exec,
 187                                                 fdt->max_fdset/8);
 188                 memset (&nfdt->open_fds->fds_bits[i], 0, count);
 189                 memset (&nfdt->close_on_exec->fds_bits[i], 0, count);
 190         }
 191
 192         /* Don't copy/clear the array if we are creating a new
 193            fd array for fork() */
 194         if (fdt->max_fds) {
 195                 memcpy(nfdt->fd, fdt->fd,
 196                         fdt->max_fds * sizeof(struct file *));
 197                 /* clear the remainder of the array */
 198                 memset(&nfdt->fd[fdt->max_fds], 0,
 199                        (nfdt->max_fds - fdt->max_fds) *
 200                                         sizeof(struct file *));
 201         }
 202         nfdt->next_fd = fdt->next_fd;
 203 }
 204
 205 /*
 206  * Allocate an fdset array, using kmalloc or vmalloc.
 207  * Note: the array isn't cleared at allocation time.
 208  */
 209 fd_set * alloc_fdset(int num)
 210 {
 211         fd_set *new_fdset;
 212         int size = num / 8;
 213
 214         if (size <= PAGE_SIZE)
 215                 new_fdset = (fd_set *) kmalloc(size, GFP_KERNEL);
 216         else
 217                 new_fdset = (fd_set *) vmalloc(size);
 218         return new_fdset;
 219 }
 220
 221 void free_fdset(fd_set *array, int num)
 222 {
 223         int size = num / 8;
 224
 225         if (num <= __FD_SETSIZE) /* Don't free an embedded fdset */
 226                 return;
 227         else if (size <= PAGE_SIZE)
 228                 kfree(array);
 229         else
 230                 vfree(array);
 231 }
 232
 233 static struct fdtable *alloc_fdtable(int nr)
 234 {
 235         struct fdtable *fdt = NULL;
 236         int nfds = 0;
 237         fd_set *new_openset = NULL, *new_execset = NULL;
 238         struct file **new_fds;
 239
 240         fdt = kmalloc(sizeof(*fdt), GFP_KERNEL);
 241         if (!fdt)
 242                 goto out;
 243         memset(fdt, 0, sizeof(*fdt));
 244
 245         nfds = __FD_SETSIZE;
 246         /* Expand to the max in easy steps */
 247         do {
 248                 if (nfds < (PAGE_SIZE * 8))
 249                         nfds = PAGE_SIZE * 8;
 250                 else {
 251                         nfds = nfds * 2;
 252                         if (nfds > NR_OPEN)
 253                                 nfds = NR_OPEN;
 254                 }
 255         } while (nfds <= nr);
 256
 257         new_openset = alloc_fdset(nfds);
 258         new_execset = alloc_fdset(nfds);
 259         if (!new_openset || !new_execset)
 260                 goto out;
 261         fdt->open_fds = new_openset;
 262         fdt->close_on_exec = new_execset;
 263         fdt->max_fdset = nfds;
 264
 265         nfds = NR_OPEN_DEFAULT;
 266         /*
 267          * Expand to the max in easy steps, and keep expanding it until
 268          * we have enough for the requested fd array size.
 269          */
 270         do {
 271 #if NR_OPEN_DEFAULT < 256
 272                 if (nfds < 256)
 273                         nfds = 256;
 274                 else
 275 #endif
 276                 if (nfds < (PAGE_SIZE / sizeof(struct file *)))
 277                         nfds = PAGE_SIZE / sizeof(struct file *);
 278                 else {
 279                         nfds = nfds * 2;
 280                         if (nfds > NR_OPEN)
 281                                 nfds = NR_OPEN;
 282                 }
 283         } while (nfds <= nr);
 284         new_fds = alloc_fd_array(nfds);
 285         if (!new_fds)
 286                 goto out;
 287         fdt->fd = new_fds;
 288         fdt->max_fds = nfds;
 289         fdt->free_files = NULL;
 290         return fdt;
 291 out:
 292         if (new_openset)
 293                 free_fdset(new_openset, nfds);
 294         if (new_execset)
 295                 free_fdset(new_execset, nfds);
 296         kfree(fdt);
 297         return NULL;
 298 }
 299
 300 /*
 301  * Expands the file descriptor table - it will allocate a new fdtable and
 302  * both fd array and fdset. It is expected to be called with the
 303  * files_lock held.
 304  */
 305 static int expand_fdtable(struct files_struct *files, int nr)
 306         __releases(files->file_lock)
 307         __acquires(files->file_lock)
 308 {
 309         int error = 0;
 310         struct fdtable *fdt;
 311         struct fdtable *nfdt = NULL;
 312
 313         spin_unlock(&files->file_lock);
 314         nfdt = alloc_fdtable(nr);
 315         if (!nfdt) {
 316                 error = -ENOMEM;
 317                 spin_lock(&files->file_lock);
 318                 goto out;
 319         }
 320
 321         spin_lock(&files->file_lock);
 322         fdt = files_fdtable(files);
 323         /*
 324          * Check again since another task may have expanded the
 325          * fd table while we dropped the lock
 326          */
 327         if (nr >= fdt->max_fds || nr >= fdt->max_fdset) {
 328                 copy_fdtable(nfdt, fdt);
 329         } else {
 330                 /* Somebody expanded while we dropped file_lock */
 331                 spin_unlock(&files->file_lock);
 332                 __free_fdtable(nfdt);
 333                 spin_lock(&files->file_lock);
 334                 goto out;
 335         }
 336         rcu_assign_pointer(files->fdt, nfdt);
 337         free_fdtable(fdt);
 338 out:
 339         return error;
 340 }
 341
 342 /*
 343  * Expand files.
 344  * Return <0 on error; 0 nothing done; 1 files expanded, we may have blocked.
 345  * Should be called with the files->file_lock spinlock held for write.
 346  */
 347 int expand_files(struct files_struct *files, int nr)
 348 {
 349         int err, expand = 0;
 350         struct fdtable *fdt;
 351
 352         fdt = files_fdtable(files);
 353         if (nr >= fdt->max_fdset || nr >= fdt->max_fds) {
 354                 if (fdt->max_fdset >= NR_OPEN ||
 355                         fdt->max_fds >= NR_OPEN || nr >= NR_OPEN) {
 356                         err = -EMFILE;
 357                         goto out;
 358                 }
 359                 expand = 1;
 360                 if ((err = expand_fdtable(files, nr)))
 361                         goto out;
 362         }
 363         err = expand;
 364 out:
 365         return err;
 366 }
 367
 368 static void __devinit fdtable_defer_list_init(int cpu)
 369 {
 370         struct fdtable_defer *fddef = &per_cpu(fdtable_defer_list, cpu);
 371         spin_lock_init(&fddef->lock);
 372         INIT_WORK(&fddef->wq, (void (*)(void *))free_fdtable_work, fddef);
 373         init_timer(&fddef->timer);
 374         fddef->timer.data = (unsigned long)fddef;
 375         fddef->timer.function = fdtable_timer;
 376         fddef->next = NULL;
 377 }
 378
 379 void __init files_defer_init(void)
 380 {
 381         int i;
 382         /* Really early - can't use for_each_cpu */
 383         for (i = 0; i < NR_CPUS; i++)
 384                 fdtable_defer_list_init(i);
 385 }