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