fs/file_table.c

   1 /*
   2  *  linux/fs/file_table.c
   3  *
   4  *  Copyright (C) 1991, 1992  Linus Torvalds
   5  *  Copyright (C) 1997 David S. Miller (davem@caip.rutgers.edu)
   6  */
   7
   8 #include <linux/string.h>
   9 #include <linux/slab.h>
  10 #include <linux/file.h>
  11 #include <linux/init.h>
  12 #include <linux/module.h>
  13 #include <linux/smp_lock.h>
  14 #include <linux/fs.h>
  15 #include <linux/security.h>
  16 #include <linux/eventpoll.h>
  17 #include <linux/rcupdate.h>
  18 #include <linux/mount.h>
  19 #include <linux/capability.h>
  20 #include <linux/cdev.h>
  21 #include <linux/fsnotify.h>
  22
  23 /* sysctl tunables... */
  24 struct files_stat_struct files_stat = {
  25         .max_files = NR_FILE
  26 };
  27
  28 EXPORT_SYMBOL(files_stat); /* Needed by unix.o */
  29
  30 /* public. Not pretty! */
  31  __cacheline_aligned_in_smp DEFINE_SPINLOCK(files_lock);
  32
  33 static DEFINE_SPINLOCK(filp_count_lock);
  34
  35 /* slab constructors and destructors are called from arbitrary
  36  * context and must be fully threaded - use a local spinlock
  37  * to protect files_stat.nr_files
  38  */
  39 void filp_ctor(void *objp, struct kmem_cache *cachep, unsigned long cflags)
  40 {
  41         if ((cflags & (SLAB_CTOR_VERIFY|SLAB_CTOR_CONSTRUCTOR)) ==
  42             SLAB_CTOR_CONSTRUCTOR) {
  43                 unsigned long flags;
  44                 spin_lock_irqsave(&filp_count_lock, flags);
  45                 files_stat.nr_files++;
  46                 spin_unlock_irqrestore(&filp_count_lock, flags);
  47         }
  48 }
  49
  50 void filp_dtor(void *objp, struct kmem_cache *cachep, unsigned long dflags)
  51 {
  52         unsigned long flags;
  53         spin_lock_irqsave(&filp_count_lock, flags);
  54         files_stat.nr_files--;
  55         spin_unlock_irqrestore(&filp_count_lock, flags);
  56 }
  57
  58 static inline void file_free_rcu(struct rcu_head *head)
  59 {
  60         struct file *f =  container_of(head, struct file, f_u.fu_rcuhead);
  61         kmem_cache_free(filp_cachep, f);
  62 }
  63
  64 static inline void file_free(struct file *f)
  65 {
  66         call_rcu(&f->f_u.fu_rcuhead, file_free_rcu);
  67 }
  68
  69 /* Find an unused file structure and return a pointer to it.
  70  * Returns NULL, if there are no more free file structures or
  71  * we run out of memory.
  72  */
  73 struct file *get_empty_filp(void)
  74 {
  75         static int old_max;
  76         struct file * f;
  77
  78         /*
  79          * Privileged users can go above max_files
  80          */
  81         if (files_stat.nr_files >= files_stat.max_files &&
  82                                 !capable(CAP_SYS_ADMIN))
  83                 goto over;
  84
  85         f = kmem_cache_alloc(filp_cachep, GFP_KERNEL);
  86         if (f == NULL)
  87                 goto fail;
  88
  89         memset(f, 0, sizeof(*f));
  90         if (security_file_alloc(f))
  91                 goto fail_sec;
  92
  93         eventpoll_init_file(f);
  94         atomic_set(&f->f_count, 1);
  95         f->f_uid = current->fsuid;
  96         f->f_gid = current->fsgid;
  97         rwlock_init(&f->f_owner.lock);
  98         /* f->f_version: 0 */
  99         INIT_LIST_HEAD(&f->f_u.fu_list);
 100         return f;
 101
 102 over:
 103         /* Ran out of filps - report that */
 104         if (files_stat.nr_files > old_max) {
 105                 printk(KERN_INFO "VFS: file-max limit %d reached\n",
 106                                         files_stat.max_files);
 107                 old_max = files_stat.nr_files;
 108         }
 109         goto fail;
 110
 111 fail_sec:
 112         file_free(f);
 113 fail:
 114         return NULL;
 115 }
 116
 117 EXPORT_SYMBOL(get_empty_filp);
 118
 119 void fastcall fput(struct file *file)
 120 {
 121         if (atomic_dec_and_test(&file->f_count))
 122                 __fput(file);
 123 }
 124
 125 EXPORT_SYMBOL(fput);
 126
 127 /* __fput is called from task context when aio completion releases the last
 128  * last use of a struct file *.  Do not use otherwise.
 129  */
 130 void fastcall __fput(struct file *file)
 131 {
 132         struct dentry *dentry = file->f_dentry;
 133         struct vfsmount *mnt = file->f_vfsmnt;
 134         struct inode *inode = dentry->d_inode;
 135
 136         might_sleep();
 137
 138         fsnotify_close(file);
 139         /*
 140          * The function eventpoll_release() should be the first called
 141          * in the file cleanup chain.
 142          */
 143         eventpoll_release(file);
 144         locks_remove_flock(file);
 145
 146         if (file->f_op && file->f_op->release)
 147                 file->f_op->release(inode, file);
 148         security_file_free(file);
 149         if (unlikely(inode->i_cdev != NULL))
 150                 cdev_put(inode->i_cdev);
 151         fops_put(file->f_op);
 152         if (file->f_mode & FMODE_WRITE)
 153                 put_write_access(inode);
 154         file_kill(file);
 155         file->f_dentry = NULL;
 156         file->f_vfsmnt = NULL;
 157         file_free(file);
 158         dput(dentry);
 159         mntput(mnt);
 160 }
 161
 162 struct file fastcall *fget(unsigned int fd)
 163 {
 164         struct file *file;
 165         struct files_struct *files = current->files;
 166
 167         rcu_read_lock();
 168         file = fcheck_files(files, fd);
 169         if (file) {
 170                 if (!atomic_inc_not_zero(&file->f_count)) {
 171                         /* File object ref couldn't be taken */
 172                         rcu_read_unlock();
 173                         return NULL;
 174                 }
 175         }
 176         rcu_read_unlock();
 177
 178         return file;
 179 }
 180
 181 EXPORT_SYMBOL(fget);
 182
 183 /*
 184  * Lightweight file lookup - no refcnt increment if fd table isn't shared.
 185  * You can use this only if it is guranteed that the current task already
 186  * holds a refcnt to that file. That check has to be done at fget() only
 187  * and a flag is returned to be passed to the corresponding fput_light().
 188  * There must not be a cloning between an fget_light/fput_light pair.
 189  */
 190 struct file fastcall *fget_light(unsigned int fd, int *fput_needed)
 191 {
 192         struct file *file;
 193         struct files_struct *files = current->files;
 194
 195         *fput_needed = 0;
 196         if (likely((atomic_read(&files->count) == 1))) {
 197                 file = fcheck_files(files, fd);
 198         } else {
 199                 rcu_read_lock();
 200                 file = fcheck_files(files, fd);
 201                 if (file) {
 202                         if (atomic_inc_not_zero(&file->f_count))
 203                                 *fput_needed = 1;
 204                         else
 205                                 /* Didn't get the reference, someone's freed */
 206                                 file = NULL;
 207                 }
 208                 rcu_read_unlock();
 209         }
 210
 211         return file;
 212 }
 213
 214
 215 void put_filp(struct file *file)
 216 {
 217         if (atomic_dec_and_test(&file->f_count)) {
 218                 security_file_free(file);
 219                 file_kill(file);
 220                 file_free(file);
 221         }
 222 }
 223
 224 void file_move(struct file *file, struct list_head *list)
 225 {
 226         if (!list)
 227                 return;
 228         file_list_lock();
 229         list_move(&file->f_u.fu_list, list);
 230         file_list_unlock();
 231 }
 232
 233 void file_kill(struct file *file)
 234 {
 235         if (!list_empty(&file->f_u.fu_list)) {
 236                 file_list_lock();
 237                 list_del_init(&file->f_u.fu_list);
 238                 file_list_unlock();
 239         }
 240 }
 241
 242 int fs_may_remount_ro(struct super_block *sb)
 243 {
 244         struct list_head *p;
 245
 246         /* Check that no files are currently opened for writing. */
 247         file_list_lock();
 248         list_for_each(p, &sb->s_files) {
 249                 struct file *file = list_entry(p, struct file, f_u.fu_list);
 250                 struct inode *inode = file->f_dentry->d_inode;
 251
 252                 /* File with pending delete? */
 253                 if (inode->i_nlink == 0)
 254                         goto too_bad;
 255
 256                 /* Writeable file? */
 257                 if (S_ISREG(inode->i_mode) && (file->f_mode & FMODE_WRITE))
 258                         goto too_bad;
 259         }
 260         file_list_unlock();
 261         return 1; /* Tis' cool bro. */
 262 too_bad:
 263         file_list_unlock();
 264         return 0;
 265 }
 266
 267 void __init files_init(unsigned long mempages)
 268 {
 269         int n;
 270         /* One file with associated inode and dcache is very roughly 1K.
 271          * Per default don't use more than 10% of our memory for files.
 272          */
 273
 274         n = (mempages * (PAGE_SIZE / 1024)) / 10;
 275         files_stat.max_files = n;
 276         if (files_stat.max_files < NR_FILE)
 277                 files_stat.max_files = NR_FILE;
 278         files_defer_init();
 279 }