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 fdtable *next;
  25 };
  26
  27 /*
  28  * We use this list to defer free fdtables that have vmalloced
  29  * sets/arrays. By keeping a per-cpu list, we avoid having to embed
  30  * the work_struct in fdtable itself which avoids a 64 byte (i386) increase in
  31  * this per-task structure.
  32  */
  33 static DEFINE_PER_CPU(struct fdtable_defer, fdtable_defer_list);
  34
  35
  36 /*
  37  * Allocate an fd array, using kmalloc or vmalloc.
  38  * Note: the array isn't cleared at allocation time.
  39  */
  40 struct file ** alloc_fd_array(int num)
  41 {
  42         struct file **new_fds;
  43         int size = num * sizeof(struct file *);
  44
  45         if (size <= PAGE_SIZE)
  46                 new_fds = (struct file **) kmalloc(size, GFP_KERNEL);
  47         else
  48                 new_fds = (struct file **) vmalloc(size);
  49         return new_fds;
  50 }
  51
  52 void free_fd_array(struct file **array, int num)
  53 {
  54         int size = num * sizeof(struct file *);
  55
  56         if (!array) {
  57                 printk (KERN_ERR "free_fd_array: array = 0 (num = %d)\n", num);
  58                 return;
  59         }
  60
  61         if (num <= NR_OPEN_DEFAULT) /* Don't free the embedded fd array! */
  62                 return;
  63         else if (size <= PAGE_SIZE)
  64                 kfree(array);
  65         else
  66                 vfree(array);
  67 }
  68
  69 static void __free_fdtable(struct fdtable *fdt)
  70 {
  71         free_fdset(fdt->open_fds, fdt->max_fdset);
  72         free_fdset(fdt->close_on_exec, fdt->max_fdset);
  73         free_fd_array(fdt->fd, fdt->max_fds);
  74         kfree(fdt);
  75 }
  76
  77 static void free_fdtable_work(struct work_struct *work)
  78 {
  79         struct fdtable_defer *f =
  80                 container_of(work, struct fdtable_defer, wq);
  81         struct fdtable *fdt;
  82
  83         spin_lock_bh(&f->lock);
  84         fdt = f->next;
  85         f->next = NULL;
  86         spin_unlock_bh(&f->lock);
  87         while(fdt) {
  88                 struct fdtable *next = fdt->next;
  89                 __free_fdtable(fdt);
  90                 fdt = next;
  91         }
  92 }
  93
  94 static void free_fdtable_rcu(struct rcu_head *rcu)
  95 {
  96         struct fdtable *fdt = container_of(rcu, struct fdtable, rcu);
  97         int fdset_size, fdarray_size;
  98         struct fdtable_defer *fddef;
  99
 100         BUG_ON(!fdt);
 101         fdset_size = fdt->max_fdset / 8;
 102         fdarray_size = fdt->max_fds * sizeof(struct file *);
 103
 104         if (fdt->free_files) {
 105                 /*
 106                  * The this fdtable was embedded in the files structure
 107                  * and the files structure itself was getting destroyed.
 108                  * It is now safe to free the files structure.
 109                  */
 110                 kmem_cache_free(files_cachep, fdt->free_files);
 111                 return;
 112         }
 113         if (fdt->max_fdset <= EMBEDDED_FD_SET_SIZE &&
 114                 fdt->max_fds <= NR_OPEN_DEFAULT) {
 115                 /*
 116                  * The fdtable was embedded
 117                  */
 118                 return;
 119         }
 120         if (fdset_size <= PAGE_SIZE && fdarray_size <= PAGE_SIZE) {
 121                 kfree(fdt->open_fds);
 122                 kfree(fdt->close_on_exec);
 123                 kfree(fdt->fd);
 124                 kfree(fdt);
 125         } else {
 126                 fddef = &get_cpu_var(fdtable_defer_list);
 127                 spin_lock(&fddef->lock);
 128                 fdt->next = fddef->next;
 129                 fddef->next = fdt;
 130                 /* vmallocs are handled from the workqueue context */
 131                 schedule_work(&fddef->wq);
 132                 spin_unlock(&fddef->lock);
 133                 put_cpu_var(fdtable_defer_list);
 134         }
 135 }
 136
 137 void free_fdtable(struct fdtable *fdt)
 138 {
 139         if (fdt->free_files ||
 140                 fdt->max_fdset > EMBEDDED_FD_SET_SIZE ||
 141                 fdt->max_fds > NR_OPEN_DEFAULT)
 142                 call_rcu(&fdt->rcu, free_fdtable_rcu);
 143 }
 144
 145 /*
 146  * Expand the fdset in the files_struct.  Called with the files spinlock
 147  * held for write.
 148  */
 149 static void copy_fdtable(struct fdtable *nfdt, struct fdtable *fdt)
 150 {
 151         int i;
 152         int count;
 153
 154         BUG_ON(nfdt->max_fdset < fdt->max_fdset);
 155         BUG_ON(nfdt->max_fds < fdt->max_fds);
 156         /* Copy the existing tables and install the new pointers */
 157
 158         i = fdt->max_fdset / (sizeof(unsigned long) * 8);
 159         count = (nfdt->max_fdset - fdt->max_fdset) / 8;
 160
 161         /*
 162          * Don't copy the entire array if the current fdset is
 163          * not yet initialised.
 164          */
 165         if (i) {
 166                 memcpy (nfdt->open_fds, fdt->open_fds,
 167                                                 fdt->max_fdset/8);
 168                 memcpy (nfdt->close_on_exec, fdt->close_on_exec,
 169                                                 fdt->max_fdset/8);
 170                 memset (&nfdt->open_fds->fds_bits[i], 0, count);
 171                 memset (&nfdt->close_on_exec->fds_bits[i], 0, count);
 172         }
 173
 174         /* Don't copy/clear the array if we are creating a new
 175            fd array for fork() */
 176         if (fdt->max_fds) {
 177                 memcpy(nfdt->fd, fdt->fd,
 178                         fdt->max_fds * sizeof(struct file *));
 179                 /* clear the remainder of the array */
 180                 memset(&nfdt->fd[fdt->max_fds], 0,
 181                        (nfdt->max_fds - fdt->max_fds) *
 182                                         sizeof(struct file *));
 183         }
 184 }
 185
 186 /*
 187  * Allocate an fdset array, using kmalloc or vmalloc.
 188  * Note: the array isn't cleared at allocation time.
 189  */
 190 fd_set * alloc_fdset(int num)
 191 {
 192         fd_set *new_fdset;
 193         int size = num / 8;
 194
 195         if (size <= PAGE_SIZE)
 196                 new_fdset = (fd_set *) kmalloc(size, GFP_KERNEL);
 197         else
 198                 new_fdset = (fd_set *) vmalloc(size);
 199         return new_fdset;
 200 }
 201
 202 void free_fdset(fd_set *array, int num)
 203 {
 204         if (num <= EMBEDDED_FD_SET_SIZE) /* Don't free an embedded fdset */
 205                 return;
 206         else if (num <= 8 * PAGE_SIZE)
 207                 kfree(array);
 208         else
 209                 vfree(array);
 210 }
 211
 212 static struct fdtable *alloc_fdtable(int nr)
 213 {
 214         struct fdtable *fdt = NULL;
 215         int nfds = 0;
 216         fd_set *new_openset = NULL, *new_execset = NULL;
 217         struct file **new_fds;
 218
 219         fdt = kzalloc(sizeof(*fdt), GFP_KERNEL);
 220         if (!fdt)
 221                 goto out;
 222
 223         nfds = max_t(int, 8 * L1_CACHE_BYTES, roundup_pow_of_two(nr + 1));
 224         if (nfds > NR_OPEN)
 225                 nfds = NR_OPEN;
 226
 227         new_openset = alloc_fdset(nfds);
 228         new_execset = alloc_fdset(nfds);
 229         if (!new_openset || !new_execset)
 230                 goto out;
 231         fdt->open_fds = new_openset;
 232         fdt->close_on_exec = new_execset;
 233         fdt->max_fdset = nfds;
 234
 235         nfds = NR_OPEN_DEFAULT;
 236         /*
 237          * Expand to the max in easy steps, and keep expanding it until
 238          * we have enough for the requested fd array size.
 239          */
 240         do {
 241 #if NR_OPEN_DEFAULT < 256
 242                 if (nfds < 256)
 243                         nfds = 256;
 244                 else
 245 #endif
 246                 if (nfds < (PAGE_SIZE / sizeof(struct file *)))
 247                         nfds = PAGE_SIZE / sizeof(struct file *);
 248                 else {
 249                         nfds = nfds * 2;
 250                         if (nfds > NR_OPEN)
 251                                 nfds = NR_OPEN;
 252                 }
 253         } while (nfds <= nr);
 254         new_fds = alloc_fd_array(nfds);
 255         if (!new_fds)
 256                 goto out2;
 257         fdt->fd = new_fds;
 258         fdt->max_fds = nfds;
 259         fdt->free_files = NULL;
 260         return fdt;
 261 out2:
 262         nfds = fdt->max_fdset;
 263 out:
 264         free_fdset(new_openset, nfds);
 265         free_fdset(new_execset, nfds);
 266         kfree(fdt);
 267         return NULL;
 268 }
 269
 270 /*
 271  * Expand the file descriptor table.
 272  * This function will allocate a new fdtable and both fd array and fdset, of
 273  * the given size.
 274  * Return <0 error code on error; 1 on successful completion.
 275  * The files->file_lock should be held on entry, and will be held on exit.
 276  */
 277 static int expand_fdtable(struct files_struct *files, int nr)
 278         __releases(files->file_lock)
 279         __acquires(files->file_lock)
 280 {
 281         struct fdtable *new_fdt, *cur_fdt;
 282
 283         spin_unlock(&files->file_lock);
 284         new_fdt = alloc_fdtable(nr);
 285         spin_lock(&files->file_lock);
 286         if (!new_fdt)
 287                 return -ENOMEM;
 288         /*
 289          * Check again since another task may have expanded the fd table while
 290          * we dropped the lock
 291          */
 292         cur_fdt = files_fdtable(files);
 293         if (nr >= cur_fdt->max_fds || nr >= cur_fdt->max_fdset) {
 294                 /* Continue as planned */
 295                 copy_fdtable(new_fdt, cur_fdt);
 296                 rcu_assign_pointer(files->fdt, new_fdt);
 297                 free_fdtable(cur_fdt);
 298         } else {
 299                 /* Somebody else expanded, so undo our attempt */
 300                 __free_fdtable(new_fdt);
 301         }
 302         return 1;
 303 }
 304
 305 /*
 306  * Expand files.
 307  * This function will expand the file structures, if the requested size exceeds
 308  * the current capacity and there is room for expansion.
 309  * Return <0 error code on error; 0 when nothing done; 1 when files were
 310  * expanded and execution may have blocked.
 311  * The files->file_lock should be held on entry, and will be held on exit.
 312  */
 313 int expand_files(struct files_struct *files, int nr)
 314 {
 315         struct fdtable *fdt;
 316
 317         fdt = files_fdtable(files);
 318         /* Do we need to expand? */
 319         if (nr < fdt->max_fdset && nr < fdt->max_fds)
 320                 return 0;
 321         /* Can we expand? */
 322         if (fdt->max_fdset >= NR_OPEN || fdt->max_fds >= NR_OPEN ||
 323             nr >= NR_OPEN)
 324                 return -EMFILE;
 325
 326         /* All good, so we try */
 327         return expand_fdtable(files, nr);
 328 }
 329
 330 static void __devinit fdtable_defer_list_init(int cpu)
 331 {
 332         struct fdtable_defer *fddef = &per_cpu(fdtable_defer_list, cpu);
 333         spin_lock_init(&fddef->lock);
 334         INIT_WORK(&fddef->wq, free_fdtable_work);
 335         fddef->next = NULL;
 336 }
 337
 338 void __init files_defer_init(void)
 339 {
 340         int i;
 341         for_each_possible_cpu(i)
 342                 fdtable_defer_list_init(i);
 343 }