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 static inline void * alloc_fdmem(unsigned int size)
  36 {
  37         if (size <= PAGE_SIZE)
  38                 return kmalloc(size, GFP_KERNEL);
  39         else
  40                 return vmalloc(size);
  41 }
  42
  43 static inline void free_fdarr(struct fdtable *fdt)
  44 {
  45         if (fdt->max_fds <= (PAGE_SIZE / sizeof(struct file *)))
  46                 kfree(fdt->fd);
  47         else
  48                 vfree(fdt->fd);
  49 }
  50
  51 static inline void free_fdset(struct fdtable *fdt)
  52 {
  53         if (fdt->max_fds <= (PAGE_SIZE * BITS_PER_BYTE / 2))
  54                 kfree(fdt->open_fds);
  55         else
  56                 vfree(fdt->open_fds);
  57 }
  58
  59 static void free_fdtable_work(struct work_struct *work)
  60 {
  61         struct fdtable_defer *f =
  62                 container_of(work, struct fdtable_defer, wq);
  63         struct fdtable *fdt;
  64
  65         spin_lock_bh(&f->lock);
  66         fdt = f->next;
  67         f->next = NULL;
  68         spin_unlock_bh(&f->lock);
  69         while(fdt) {
  70                 struct fdtable *next = fdt->next;
  71                 vfree(fdt->fd);
  72                 free_fdset(fdt);
  73                 kfree(fdt);
  74                 fdt = next;
  75         }
  76 }
  77
  78 void free_fdtable_rcu(struct rcu_head *rcu)
  79 {
  80         struct fdtable *fdt = container_of(rcu, struct fdtable, rcu);
  81         struct fdtable_defer *fddef;
  82
  83         BUG_ON(!fdt);
  84
  85         if (fdt->max_fds <= NR_OPEN_DEFAULT) {
  86                 /*
  87                  * This fdtable is embedded in the files structure and that
  88                  * structure itself is getting destroyed.
  89                  */
  90                 kmem_cache_free(files_cachep,
  91                                 container_of(fdt, struct files_struct, fdtab));
  92                 return;
  93         }
  94         if (fdt->max_fds <= (PAGE_SIZE / sizeof(struct file *))) {
  95                 kfree(fdt->fd);
  96                 kfree(fdt->open_fds);
  97                 kfree(fdt);
  98         } else {
  99                 fddef = &get_cpu_var(fdtable_defer_list);
 100                 spin_lock(&fddef->lock);
 101                 fdt->next = fddef->next;
 102                 fddef->next = fdt;
 103                 /* vmallocs are handled from the workqueue context */
 104                 schedule_work(&fddef->wq);
 105                 spin_unlock(&fddef->lock);
 106                 put_cpu_var(fdtable_defer_list);
 107         }
 108 }
 109
 110 /*
 111  * Expand the fdset in the files_struct.  Called with the files spinlock
 112  * held for write.
 113  */
 114 static void copy_fdtable(struct fdtable *nfdt, struct fdtable *ofdt)
 115 {
 116         unsigned int cpy, set;
 117
 118         BUG_ON(nfdt->max_fds < ofdt->max_fds);
 119         if (ofdt->max_fds == 0)
 120                 return;
 121
 122         cpy = ofdt->max_fds * sizeof(struct file *);
 123         set = (nfdt->max_fds - ofdt->max_fds) * sizeof(struct file *);
 124         memcpy(nfdt->fd, ofdt->fd, cpy);
 125         memset((char *)(nfdt->fd) + cpy, 0, set);
 126
 127         cpy = ofdt->max_fds / BITS_PER_BYTE;
 128         set = (nfdt->max_fds - ofdt->max_fds) / BITS_PER_BYTE;
 129         memcpy(nfdt->open_fds, ofdt->open_fds, cpy);
 130         memset((char *)(nfdt->open_fds) + cpy, 0, set);
 131         memcpy(nfdt->close_on_exec, ofdt->close_on_exec, cpy);
 132         memset((char *)(nfdt->close_on_exec) + cpy, 0, set);
 133 }
 134
 135 static struct fdtable * alloc_fdtable(unsigned int nr)
 136 {
 137         struct fdtable *fdt;
 138         char *data;
 139
 140         /*
 141          * Figure out how many fds we actually want to support in this fdtable.
 142          * Allocation steps are keyed to the size of the fdarray, since it
 143          * grows far faster than any of the other dynamic data. We try to fit
 144          * the fdarray into comfortable page-tuned chunks: starting at 1024B
 145          * and growing in powers of two from there on.
 146          */
 147         nr /= (1024 / sizeof(struct file *));
 148         nr = roundup_pow_of_two(nr + 1);
 149         nr *= (1024 / sizeof(struct file *));
 150         if (nr > NR_OPEN)
 151                 nr = NR_OPEN;
 152
 153         fdt = kmalloc(sizeof(struct fdtable), GFP_KERNEL);
 154         if (!fdt)
 155                 goto out;
 156         fdt->max_fds = nr;
 157         data = alloc_fdmem(nr * sizeof(struct file *));
 158         if (!data)
 159                 goto out_fdt;
 160         fdt->fd = (struct file **)data;
 161         data = alloc_fdmem(max_t(unsigned int,
 162                                  2 * nr / BITS_PER_BYTE, L1_CACHE_BYTES));
 163         if (!data)
 164                 goto out_arr;
 165         fdt->open_fds = (fd_set *)data;
 166         data += nr / BITS_PER_BYTE;
 167         fdt->close_on_exec = (fd_set *)data;
 168         INIT_RCU_HEAD(&fdt->rcu);
 169         fdt->next = NULL;
 170
 171         return fdt;
 172
 173 out_arr:
 174         free_fdarr(fdt);
 175 out_fdt:
 176         kfree(fdt);
 177 out:
 178         return NULL;
 179 }
 180
 181 /*
 182  * Expand the file descriptor table.
 183  * This function will allocate a new fdtable and both fd array and fdset, of
 184  * the given size.
 185  * Return <0 error code on error; 1 on successful completion.
 186  * The files->file_lock should be held on entry, and will be held on exit.
 187  */
 188 static int expand_fdtable(struct files_struct *files, int nr)
 189         __releases(files->file_lock)
 190         __acquires(files->file_lock)
 191 {
 192         struct fdtable *new_fdt, *cur_fdt;
 193
 194         spin_unlock(&files->file_lock);
 195         new_fdt = alloc_fdtable(nr);
 196         spin_lock(&files->file_lock);
 197         if (!new_fdt)
 198                 return -ENOMEM;
 199         /*
 200          * Check again since another task may have expanded the fd table while
 201          * we dropped the lock
 202          */
 203         cur_fdt = files_fdtable(files);
 204         if (nr >= cur_fdt->max_fds) {
 205                 /* Continue as planned */
 206                 copy_fdtable(new_fdt, cur_fdt);
 207                 rcu_assign_pointer(files->fdt, new_fdt);
 208                 if (cur_fdt->max_fds > NR_OPEN_DEFAULT)
 209                         call_rcu(&cur_fdt->rcu, free_fdtable_rcu);
 210         } else {
 211                 /* Somebody else expanded, so undo our attempt */
 212                 free_fdarr(new_fdt);
 213                 free_fdset(new_fdt);
 214                 kfree(new_fdt);
 215         }
 216         return 1;
 217 }
 218
 219 /*
 220  * Expand files.
 221  * This function will expand the file structures, if the requested size exceeds
 222  * the current capacity and there is room for expansion.
 223  * Return <0 error code on error; 0 when nothing done; 1 when files were
 224  * expanded and execution may have blocked.
 225  * The files->file_lock should be held on entry, and will be held on exit.
 226  */
 227 int expand_files(struct files_struct *files, int nr)
 228 {
 229         struct fdtable *fdt;
 230
 231         fdt = files_fdtable(files);
 232         /* Do we need to expand? */
 233         if (nr < fdt->max_fds)
 234                 return 0;
 235         /* Can we expand? */
 236         if (nr >= NR_OPEN)
 237                 return -EMFILE;
 238
 239         /* All good, so we try */
 240         return expand_fdtable(files, nr);
 241 }
 242
 243 static void __devinit fdtable_defer_list_init(int cpu)
 244 {
 245         struct fdtable_defer *fddef = &per_cpu(fdtable_defer_list, cpu);
 246         spin_lock_init(&fddef->lock);
 247         INIT_WORK(&fddef->wq, free_fdtable_work);
 248         fddef->next = NULL;
 249 }
 250
 251 void __init files_defer_init(void)
 252 {
 253         int i;
 254         for_each_possible_cpu(i)
 255                 fdtable_defer_list_init(i);
 256 }