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/fdtable.h>
  12 #include <linux/init.h>
  13 #include <linux/module.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 #include <linux/sysctl.h>
  23 #include <linux/percpu_counter.h>
  24
  25 #include <asm/atomic.h>
  26
  27 /* sysctl tunables... */
  28 struct files_stat_struct files_stat = {
  29         .max_files = NR_FILE
  30 };
  31
  32 /* public. Not pretty! */
  33 __cacheline_aligned_in_smp DEFINE_SPINLOCK(files_lock);
  34
  35 static struct percpu_counter nr_files __cacheline_aligned_in_smp;
  36
  37 static inline void file_free_rcu(struct rcu_head *head)
  38 {
  39         struct file *f = container_of(head, struct file, f_u.fu_rcuhead);
  40
  41         put_cred(f->f_cred);
  42         kmem_cache_free(filp_cachep, f);
  43 }
  44
  45 static inline void file_free(struct file *f)
  46 {
  47         percpu_counter_dec(&nr_files);
  48         file_check_state(f);
  49         call_rcu(&f->f_u.fu_rcuhead, file_free_rcu);
  50 }
  51
  52 /*
  53  * Return the total number of open files in the system
  54  */
  55 static int get_nr_files(void)
  56 {
  57         return percpu_counter_read_positive(&nr_files);
  58 }
  59
  60 /*
  61  * Return the maximum number of open files in the system
  62  */
  63 int get_max_files(void)
  64 {
  65         return files_stat.max_files;
  66 }
  67 EXPORT_SYMBOL_GPL(get_max_files);
  68
  69 /*
  70  * Handle nr_files sysctl
  71  */
  72 #if defined(CONFIG_SYSCTL) && defined(CONFIG_PROC_FS)
  73 int proc_nr_files(ctl_table *table, int write, struct file *filp,
  74                      void __user *buffer, size_t *lenp, loff_t *ppos)
  75 {
  76         files_stat.nr_files = get_nr_files();
  77         return proc_dointvec(table, write, filp, buffer, lenp, ppos);
  78 }
  79 #else
  80 int proc_nr_files(ctl_table *table, int write, struct file *filp,
  81                      void __user *buffer, size_t *lenp, loff_t *ppos)
  82 {
  83         return -ENOSYS;
  84 }
  85 #endif
  86
  87 /* Find an unused file structure and return a pointer to it.
  88  * Returns NULL, if there are no more free file structures or
  89  * we run out of memory.
  90  *
  91  * Be very careful using this.  You are responsible for
  92  * getting write access to any mount that you might assign
  93  * to this filp, if it is opened for write.  If this is not
  94  * done, you will imbalance int the mount's writer count
  95  * and a warning at __fput() time.
  96  */
  97 struct file *get_empty_filp(void)
  98 {
  99         const struct cred *cred = current_cred();
 100         static int old_max;
 101         struct file * f;
 102
 103         /*
 104          * Privileged users can go above max_files
 105          */
 106         if (get_nr_files() >= files_stat.max_files && !capable(CAP_SYS_ADMIN)) {
 107                 /*
 108                  * percpu_counters are inaccurate.  Do an expensive check before
 109                  * we go and fail.
 110                  */
 111                 if (percpu_counter_sum_positive(&nr_files) >= files_stat.max_files)
 112                         goto over;
 113         }
 114
 115         f = kmem_cache_zalloc(filp_cachep, GFP_KERNEL);
 116         if (f == NULL)
 117                 goto fail;
 118
 119         percpu_counter_inc(&nr_files);
 120         if (security_file_alloc(f))
 121                 goto fail_sec;
 122
 123         INIT_LIST_HEAD(&f->f_u.fu_list);
 124         atomic_long_set(&f->f_count, 1);
 125         rwlock_init(&f->f_owner.lock);
 126         f->f_cred = get_cred(cred);
 127         eventpoll_init_file(f);
 128         /* f->f_version: 0 */
 129         return f;
 130
 131 over:
 132         /* Ran out of filps - report that */
 133         if (get_nr_files() > old_max) {
 134                 printk(KERN_INFO "VFS: file-max limit %d reached\n",
 135                                         get_max_files());
 136                 old_max = get_nr_files();
 137         }
 138         goto fail;
 139
 140 fail_sec:
 141         file_free(f);
 142 fail:
 143         return NULL;
 144 }
 145
 146 EXPORT_SYMBOL(get_empty_filp);
 147
 148 /**
 149  * alloc_file - allocate and initialize a 'struct file'
 150  * @mnt: the vfsmount on which the file will reside
 151  * @dentry: the dentry representing the new file
 152  * @mode: the mode with which the new file will be opened
 153  * @fop: the 'struct file_operations' for the new file
 154  *
 155  * Use this instead of get_empty_filp() to get a new
 156  * 'struct file'.  Do so because of the same initialization
 157  * pitfalls reasons listed for init_file().  This is a
 158  * preferred interface to using init_file().
 159  *
 160  * If all the callers of init_file() are eliminated, its
 161  * code should be moved into this function.
 162  */
 163 struct file *alloc_file(struct vfsmount *mnt, struct dentry *dentry,
 164                 fmode_t mode, const struct file_operations *fop)
 165 {
 166         struct file *file;
 167         struct path;
 168
 169         file = get_empty_filp();
 170         if (!file)
 171                 return NULL;
 172
 173         init_file(file, mnt, dentry, mode, fop);
 174         return file;
 175 }
 176 EXPORT_SYMBOL(alloc_file);
 177
 178 /**
 179  * init_file - initialize a 'struct file'
 180  * @file: the already allocated 'struct file' to initialized
 181  * @mnt: the vfsmount on which the file resides
 182  * @dentry: the dentry representing this file
 183  * @mode: the mode the file is opened with
 184  * @fop: the 'struct file_operations' for this file
 185  *
 186  * Use this instead of setting the members directly.  Doing so
 187  * avoids making mistakes like forgetting the mntget() or
 188  * forgetting to take a write on the mnt.
 189  *
 190  * Note: This is a crappy interface.  It is here to make
 191  * merging with the existing users of get_empty_filp()
 192  * who have complex failure logic easier.  All users
 193  * of this should be moving to alloc_file().
 194  */
 195 int init_file(struct file *file, struct vfsmount *mnt, struct dentry *dentry,
 196            fmode_t mode, const struct file_operations *fop)
 197 {
 198         int error = 0;
 199         file->f_path.dentry = dentry;
 200         file->f_path.mnt = mntget(mnt);
 201         file->f_mapping = dentry->d_inode->i_mapping;
 202         file->f_mode = mode;
 203         file->f_op = fop;
 204
 205         /*
 206          * These mounts don't really matter in practice
 207          * for r/o bind mounts.  They aren't userspace-
 208          * visible.  We do this for consistency, and so
 209          * that we can do debugging checks at __fput()
 210          */
 211         if ((mode & FMODE_WRITE) && !special_file(dentry->d_inode->i_mode)) {
 212                 file_take_write(file);
 213                 error = mnt_want_write(mnt);
 214                 WARN_ON(error);
 215         }
 216         return error;
 217 }
 218 EXPORT_SYMBOL(init_file);
 219
 220 void fput(struct file *file)
 221 {
 222         if (atomic_long_dec_and_test(&file->f_count))
 223                 __fput(file);
 224 }
 225
 226 EXPORT_SYMBOL(fput);
 227
 228 /**
 229  * drop_file_write_access - give up ability to write to a file
 230  * @file: the file to which we will stop writing
 231  *
 232  * This is a central place which will give up the ability
 233  * to write to @file, along with access to write through
 234  * its vfsmount.
 235  */
 236 void drop_file_write_access(struct file *file)
 237 {
 238         struct vfsmount *mnt = file->f_path.mnt;
 239         struct dentry *dentry = file->f_path.dentry;
 240         struct inode *inode = dentry->d_inode;
 241
 242         put_write_access(inode);
 243
 244         if (special_file(inode->i_mode))
 245                 return;
 246         if (file_check_writeable(file) != 0)
 247                 return;
 248         mnt_drop_write(mnt);
 249         file_release_write(file);
 250 }
 251 EXPORT_SYMBOL_GPL(drop_file_write_access);
 252
 253 /* __fput is called from task context when aio completion releases the last
 254  * last use of a struct file *.  Do not use otherwise.
 255  */
 256 void __fput(struct file *file)
 257 {
 258         struct dentry *dentry = file->f_path.dentry;
 259         struct vfsmount *mnt = file->f_path.mnt;
 260         struct inode *inode = dentry->d_inode;
 261
 262         might_sleep();
 263
 264         fsnotify_close(file);
 265         /*
 266          * The function eventpoll_release() should be the first called
 267          * in the file cleanup chain.
 268          */
 269         eventpoll_release(file);
 270         locks_remove_flock(file);
 271
 272         if (unlikely(file->f_flags & FASYNC)) {
 273                 if (file->f_op && file->f_op->fasync)
 274                         file->f_op->fasync(-1, file, 0);
 275         }
 276         if (file->f_op && file->f_op->release)
 277                 file->f_op->release(inode, file);
 278         security_file_free(file);
 279         if (unlikely(S_ISCHR(inode->i_mode) && inode->i_cdev != NULL))
 280                 cdev_put(inode->i_cdev);
 281         fops_put(file->f_op);
 282         put_pid(file->f_owner.pid);
 283         file_kill(file);
 284         if (file->f_mode & FMODE_WRITE)
 285                 drop_file_write_access(file);
 286         file->f_path.dentry = NULL;
 287         file->f_path.mnt = NULL;
 288         file_free(file);
 289         dput(dentry);
 290         mntput(mnt);
 291 }
 292
 293 struct file *fget(unsigned int fd)
 294 {
 295         struct file *file;
 296         struct files_struct *files = current->files;
 297
 298         rcu_read_lock();
 299         file = fcheck_files(files, fd);
 300         if (file) {
 301                 if (!atomic_long_inc_not_zero(&file->f_count)) {
 302                         /* File object ref couldn't be taken */
 303                         rcu_read_unlock();
 304                         return NULL;
 305                 }
 306         }
 307         rcu_read_unlock();
 308
 309         return file;
 310 }
 311
 312 EXPORT_SYMBOL(fget);
 313
 314 /*
 315  * Lightweight file lookup - no refcnt increment if fd table isn't shared.
 316  * You can use this only if it is guranteed that the current task already
 317  * holds a refcnt to that file. That check has to be done at fget() only
 318  * and a flag is returned to be passed to the corresponding fput_light().
 319  * There must not be a cloning between an fget_light/fput_light pair.
 320  */
 321 struct file *fget_light(unsigned int fd, int *fput_needed)
 322 {
 323         struct file *file;
 324         struct files_struct *files = current->files;
 325
 326         *fput_needed = 0;
 327         if (likely((atomic_read(&files->count) == 1))) {
 328                 file = fcheck_files(files, fd);
 329         } else {
 330                 rcu_read_lock();
 331                 file = fcheck_files(files, fd);
 332                 if (file) {
 333                         if (atomic_long_inc_not_zero(&file->f_count))
 334                                 *fput_needed = 1;
 335                         else
 336                                 /* Didn't get the reference, someone's freed */
 337                                 file = NULL;
 338                 }
 339                 rcu_read_unlock();
 340         }
 341
 342         return file;
 343 }
 344
 345
 346 void put_filp(struct file *file)
 347 {
 348         if (atomic_long_dec_and_test(&file->f_count)) {
 349                 security_file_free(file);
 350                 file_kill(file);
 351                 file_free(file);
 352         }
 353 }
 354
 355 void file_move(struct file *file, struct list_head *list)
 356 {
 357         if (!list)
 358                 return;
 359         file_list_lock();
 360         list_move(&file->f_u.fu_list, list);
 361         file_list_unlock();
 362 }
 363
 364 void file_kill(struct file *file)
 365 {
 366         if (!list_empty(&file->f_u.fu_list)) {
 367                 file_list_lock();
 368                 list_del_init(&file->f_u.fu_list);
 369                 file_list_unlock();
 370         }
 371 }
 372
 373 int fs_may_remount_ro(struct super_block *sb)
 374 {
 375         struct file *file;
 376
 377         /* Check that no files are currently opened for writing. */
 378         file_list_lock();
 379         list_for_each_entry(file, &sb->s_files, f_u.fu_list) {
 380                 struct inode *inode = file->f_path.dentry->d_inode;
 381
 382                 /* File with pending delete? */
 383                 if (inode->i_nlink == 0)
 384                         goto too_bad;
 385
 386                 /* Writeable file? */
 387                 if (S_ISREG(inode->i_mode) && (file->f_mode & FMODE_WRITE))
 388                         goto too_bad;
 389         }
 390         file_list_unlock();
 391         return 1; /* Tis' cool bro. */
 392 too_bad:
 393         file_list_unlock();
 394         return 0;
 395 }
 396
 397 void __init files_init(unsigned long mempages)
 398 {
 399         int n;
 400         /* One file with associated inode and dcache is very roughly 1K.
 401          * Per default don't use more than 10% of our memory for files.
 402          */
 403
 404         n = (mempages * (PAGE_SIZE / 1024)) / 10;
 405         files_stat.max_files = n;
 406         if (files_stat.max_files < NR_FILE)
 407                 files_stat.max_files = NR_FILE;
 408         files_defer_init();
 409         percpu_counter_init(&nr_files, 0);
 410 }