linux/fs/file_table.c
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   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/lglock.h>
  24#include <linux/percpu_counter.h>
  25#include <linux/percpu.h>
  26#include <linux/ima.h>
  27
  28#include <linux/atomic.h>
  29
  30#include "internal.h"
  31
  32/* sysctl tunables... */
  33struct files_stat_struct files_stat = {
  34        .max_files = NR_FILE
  35};
  36
  37DEFINE_LGLOCK(files_lglock);
  38
  39/* SLAB cache for file structures */
  40static struct kmem_cache *filp_cachep __read_mostly;
  41
  42static struct percpu_counter nr_files __cacheline_aligned_in_smp;
  43
  44static inline void file_free_rcu(struct rcu_head *head)
  45{
  46        struct file *f = container_of(head, struct file, f_u.fu_rcuhead);
  47
  48        put_cred(f->f_cred);
  49        kmem_cache_free(filp_cachep, f);
  50}
  51
  52static inline void file_free(struct file *f)
  53{
  54        percpu_counter_dec(&nr_files);
  55        file_check_state(f);
  56        call_rcu(&f->f_u.fu_rcuhead, file_free_rcu);
  57}
  58
  59/*
  60 * Return the total number of open files in the system
  61 */
  62static long get_nr_files(void)
  63{
  64        return percpu_counter_read_positive(&nr_files);
  65}
  66
  67/*
  68 * Return the maximum number of open files in the system
  69 */
  70unsigned long get_max_files(void)
  71{
  72        return files_stat.max_files;
  73}
  74EXPORT_SYMBOL_GPL(get_max_files);
  75
  76/*
  77 * Handle nr_files sysctl
  78 */
  79#if defined(CONFIG_SYSCTL) && defined(CONFIG_PROC_FS)
  80int proc_nr_files(ctl_table *table, int write,
  81                     void __user *buffer, size_t *lenp, loff_t *ppos)
  82{
  83        files_stat.nr_files = get_nr_files();
  84        return proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
  85}
  86#else
  87int proc_nr_files(ctl_table *table, int write,
  88                     void __user *buffer, size_t *lenp, loff_t *ppos)
  89{
  90        return -ENOSYS;
  91}
  92#endif
  93
  94/* Find an unused file structure and return a pointer to it.
  95 * Returns NULL, if there are no more free file structures or
  96 * we run out of memory.
  97 *
  98 * Be very careful using this.  You are responsible for
  99 * getting write access to any mount that you might assign
 100 * to this filp, if it is opened for write.  If this is not
 101 * done, you will imbalance int the mount's writer count
 102 * and a warning at __fput() time.
 103 */
 104struct file *get_empty_filp(void)
 105{
 106        const struct cred *cred = current_cred();
 107        static long old_max;
 108        struct file * f;
 109
 110        /*
 111         * Privileged users can go above max_files
 112         */
 113        if (get_nr_files() >= files_stat.max_files && !capable(CAP_SYS_ADMIN)) {
 114                /*
 115                 * percpu_counters are inaccurate.  Do an expensive check before
 116                 * we go and fail.
 117                 */
 118                if (percpu_counter_sum_positive(&nr_files) >= files_stat.max_files)
 119                        goto over;
 120        }
 121
 122        f = kmem_cache_zalloc(filp_cachep, GFP_KERNEL);
 123        if (f == NULL)
 124                goto fail;
 125
 126        percpu_counter_inc(&nr_files);
 127        f->f_cred = get_cred(cred);
 128        if (security_file_alloc(f))
 129                goto fail_sec;
 130
 131        INIT_LIST_HEAD(&f->f_u.fu_list);
 132        atomic_long_set(&f->f_count, 1);
 133        rwlock_init(&f->f_owner.lock);
 134        spin_lock_init(&f->f_lock);
 135        eventpoll_init_file(f);
 136        /* f->f_version: 0 */
 137        return f;
 138
 139over:
 140        /* Ran out of filps - report that */
 141        if (get_nr_files() > old_max) {
 142                pr_info("VFS: file-max limit %lu reached\n", get_max_files());
 143                old_max = get_nr_files();
 144        }
 145        goto fail;
 146
 147fail_sec:
 148        file_free(f);
 149fail:
 150        return NULL;
 151}
 152
 153/**
 154 * alloc_file - allocate and initialize a 'struct file'
 155 * @mnt: the vfsmount on which the file will reside
 156 * @dentry: the dentry representing the new file
 157 * @mode: the mode with which the new file will be opened
 158 * @fop: the 'struct file_operations' for the new file
 159 *
 160 * Use this instead of get_empty_filp() to get a new
 161 * 'struct file'.  Do so because of the same initialization
 162 * pitfalls reasons listed for init_file().  This is a
 163 * preferred interface to using init_file().
 164 *
 165 * If all the callers of init_file() are eliminated, its
 166 * code should be moved into this function.
 167 */
 168struct file *alloc_file(struct path *path, fmode_t mode,
 169                const struct file_operations *fop)
 170{
 171        struct file *file;
 172
 173        file = get_empty_filp();
 174        if (!file)
 175                return NULL;
 176
 177        file->f_path = *path;
 178        file->f_mapping = path->dentry->d_inode->i_mapping;
 179        file->f_mode = mode;
 180        file->f_op = fop;
 181
 182        /*
 183         * These mounts don't really matter in practice
 184         * for r/o bind mounts.  They aren't userspace-
 185         * visible.  We do this for consistency, and so
 186         * that we can do debugging checks at __fput()
 187         */
 188        if ((mode & FMODE_WRITE) && !special_file(path->dentry->d_inode->i_mode)) {
 189                file_take_write(file);
 190                WARN_ON(mnt_clone_write(path->mnt));
 191        }
 192        if ((mode & (FMODE_READ | FMODE_WRITE)) == FMODE_READ)
 193                i_readcount_inc(path->dentry->d_inode);
 194        return file;
 195}
 196EXPORT_SYMBOL(alloc_file);
 197
 198/**
 199 * drop_file_write_access - give up ability to write to a file
 200 * @file: the file to which we will stop writing
 201 *
 202 * This is a central place which will give up the ability
 203 * to write to @file, along with access to write through
 204 * its vfsmount.
 205 */
 206static void drop_file_write_access(struct file *file)
 207{
 208        struct vfsmount *mnt = file->f_path.mnt;
 209        struct dentry *dentry = file->f_path.dentry;
 210        struct inode *inode = dentry->d_inode;
 211
 212        put_write_access(inode);
 213
 214        if (special_file(inode->i_mode))
 215                return;
 216        if (file_check_writeable(file) != 0)
 217                return;
 218        mnt_drop_write(mnt);
 219        file_release_write(file);
 220}
 221
 222/* the real guts of fput() - releasing the last reference to file
 223 */
 224static void __fput(struct file *file)
 225{
 226        struct dentry *dentry = file->f_path.dentry;
 227        struct vfsmount *mnt = file->f_path.mnt;
 228        struct inode *inode = dentry->d_inode;
 229
 230        might_sleep();
 231
 232        fsnotify_close(file);
 233        /*
 234         * The function eventpoll_release() should be the first called
 235         * in the file cleanup chain.
 236         */
 237        eventpoll_release(file);
 238        locks_remove_flock(file);
 239
 240        if (unlikely(file->f_flags & FASYNC)) {
 241                if (file->f_op && file->f_op->fasync)
 242                        file->f_op->fasync(-1, file, 0);
 243        }
 244        if (file->f_op && file->f_op->release)
 245                file->f_op->release(inode, file);
 246        security_file_free(file);
 247        ima_file_free(file);
 248        if (unlikely(S_ISCHR(inode->i_mode) && inode->i_cdev != NULL &&
 249                     !(file->f_mode & FMODE_PATH))) {
 250                cdev_put(inode->i_cdev);
 251        }
 252        fops_put(file->f_op);
 253        put_pid(file->f_owner.pid);
 254        file_sb_list_del(file);
 255        if ((file->f_mode & (FMODE_READ | FMODE_WRITE)) == FMODE_READ)
 256                i_readcount_dec(inode);
 257        if (file->f_mode & FMODE_WRITE)
 258                drop_file_write_access(file);
 259        file->f_path.dentry = NULL;
 260        file->f_path.mnt = NULL;
 261        file_free(file);
 262        dput(dentry);
 263        mntput(mnt);
 264}
 265
 266void fput(struct file *file)
 267{
 268        if (atomic_long_dec_and_test(&file->f_count))
 269                __fput(file);
 270}
 271
 272EXPORT_SYMBOL(fput);
 273
 274struct file *fget(unsigned int fd)
 275{
 276        struct file *file;
 277        struct files_struct *files = current->files;
 278
 279        rcu_read_lock();
 280        file = fcheck_files(files, fd);
 281        if (file) {
 282                /* File object ref couldn't be taken */
 283                if (file->f_mode & FMODE_PATH ||
 284                    !atomic_long_inc_not_zero(&file->f_count))
 285                        file = NULL;
 286        }
 287        rcu_read_unlock();
 288
 289        return file;
 290}
 291
 292EXPORT_SYMBOL(fget);
 293
 294struct file *fget_raw(unsigned int fd)
 295{
 296        struct file *file;
 297        struct files_struct *files = current->files;
 298
 299        rcu_read_lock();
 300        file = fcheck_files(files, fd);
 301        if (file) {
 302                /* File object ref couldn't be taken */
 303                if (!atomic_long_inc_not_zero(&file->f_count))
 304                        file = NULL;
 305        }
 306        rcu_read_unlock();
 307
 308        return file;
 309}
 310
 311EXPORT_SYMBOL(fget_raw);
 312
 313/*
 314 * Lightweight file lookup - no refcnt increment if fd table isn't shared.
 315 *
 316 * You can use this instead of fget if you satisfy all of the following
 317 * conditions:
 318 * 1) You must call fput_light before exiting the syscall and returning control
 319 *    to userspace (i.e. you cannot remember the returned struct file * after
 320 *    returning to userspace).
 321 * 2) You must not call filp_close on the returned struct file * in between
 322 *    calls to fget_light and fput_light.
 323 * 3) You must not clone the current task in between the calls to fget_light
 324 *    and fput_light.
 325 *
 326 * The fput_needed flag returned by fget_light should be passed to the
 327 * corresponding fput_light.
 328 */
 329struct file *fget_light(unsigned int fd, int *fput_needed)
 330{
 331        struct file *file;
 332        struct files_struct *files = current->files;
 333
 334        *fput_needed = 0;
 335        if (atomic_read(&files->count) == 1) {
 336                file = fcheck_files(files, fd);
 337                if (file && (file->f_mode & FMODE_PATH))
 338                        file = NULL;
 339        } else {
 340                rcu_read_lock();
 341                file = fcheck_files(files, fd);
 342                if (file) {
 343                        if (!(file->f_mode & FMODE_PATH) &&
 344                            atomic_long_inc_not_zero(&file->f_count))
 345                                *fput_needed = 1;
 346                        else
 347                                /* Didn't get the reference, someone's freed */
 348                                file = NULL;
 349                }
 350                rcu_read_unlock();
 351        }
 352
 353        return file;
 354}
 355
 356struct file *fget_raw_light(unsigned int fd, int *fput_needed)
 357{
 358        struct file *file;
 359        struct files_struct *files = current->files;
 360
 361        *fput_needed = 0;
 362        if (atomic_read(&files->count) == 1) {
 363                file = fcheck_files(files, fd);
 364        } else {
 365                rcu_read_lock();
 366                file = fcheck_files(files, fd);
 367                if (file) {
 368                        if (atomic_long_inc_not_zero(&file->f_count))
 369                                *fput_needed = 1;
 370                        else
 371                                /* Didn't get the reference, someone's freed */
 372                                file = NULL;
 373                }
 374                rcu_read_unlock();
 375        }
 376
 377        return file;
 378}
 379
 380void put_filp(struct file *file)
 381{
 382        if (atomic_long_dec_and_test(&file->f_count)) {
 383                security_file_free(file);
 384                file_sb_list_del(file);
 385                file_free(file);
 386        }
 387}
 388
 389static inline int file_list_cpu(struct file *file)
 390{
 391#ifdef CONFIG_SMP
 392        return file->f_sb_list_cpu;
 393#else
 394        return smp_processor_id();
 395#endif
 396}
 397
 398/* helper for file_sb_list_add to reduce ifdefs */
 399static inline void __file_sb_list_add(struct file *file, struct super_block *sb)
 400{
 401        struct list_head *list;
 402#ifdef CONFIG_SMP
 403        int cpu;
 404        cpu = smp_processor_id();
 405        file->f_sb_list_cpu = cpu;
 406        list = per_cpu_ptr(sb->s_files, cpu);
 407#else
 408        list = &sb->s_files;
 409#endif
 410        list_add(&file->f_u.fu_list, list);
 411}
 412
 413/**
 414 * file_sb_list_add - add a file to the sb's file list
 415 * @file: file to add
 416 * @sb: sb to add it to
 417 *
 418 * Use this function to associate a file with the superblock of the inode it
 419 * refers to.
 420 */
 421void file_sb_list_add(struct file *file, struct super_block *sb)
 422{
 423        lg_local_lock(&files_lglock);
 424        __file_sb_list_add(file, sb);
 425        lg_local_unlock(&files_lglock);
 426}
 427
 428/**
 429 * file_sb_list_del - remove a file from the sb's file list
 430 * @file: file to remove
 431 * @sb: sb to remove it from
 432 *
 433 * Use this function to remove a file from its superblock.
 434 */
 435void file_sb_list_del(struct file *file)
 436{
 437        if (!list_empty(&file->f_u.fu_list)) {
 438                lg_local_lock_cpu(&files_lglock, file_list_cpu(file));
 439                list_del_init(&file->f_u.fu_list);
 440                lg_local_unlock_cpu(&files_lglock, file_list_cpu(file));
 441        }
 442}
 443
 444#ifdef CONFIG_SMP
 445
 446/*
 447 * These macros iterate all files on all CPUs for a given superblock.
 448 * files_lglock must be held globally.
 449 */
 450#define do_file_list_for_each_entry(__sb, __file)               \
 451{                                                               \
 452        int i;                                                  \
 453        for_each_possible_cpu(i) {                              \
 454                struct list_head *list;                         \
 455                list = per_cpu_ptr((__sb)->s_files, i);         \
 456                list_for_each_entry((__file), list, f_u.fu_list)
 457
 458#define while_file_list_for_each_entry                          \
 459        }                                                       \
 460}
 461
 462#else
 463
 464#define do_file_list_for_each_entry(__sb, __file)               \
 465{                                                               \
 466        struct list_head *list;                                 \
 467        list = &(sb)->s_files;                                  \
 468        list_for_each_entry((__file), list, f_u.fu_list)
 469
 470#define while_file_list_for_each_entry                          \
 471}
 472
 473#endif
 474
 475/**
 476 *      mark_files_ro - mark all files read-only
 477 *      @sb: superblock in question
 478 *
 479 *      All files are marked read-only.  We don't care about pending
 480 *      delete files so this should be used in 'force' mode only.
 481 */
 482void mark_files_ro(struct super_block *sb)
 483{
 484        struct file *f;
 485
 486retry:
 487        lg_global_lock(&files_lglock);
 488        do_file_list_for_each_entry(sb, f) {
 489                struct vfsmount *mnt;
 490                if (!S_ISREG(f->f_path.dentry->d_inode->i_mode))
 491                       continue;
 492                if (!file_count(f))
 493                        continue;
 494                if (!(f->f_mode & FMODE_WRITE))
 495                        continue;
 496                spin_lock(&f->f_lock);
 497                f->f_mode &= ~FMODE_WRITE;
 498                spin_unlock(&f->f_lock);
 499                if (file_check_writeable(f) != 0)
 500                        continue;
 501                file_release_write(f);
 502                mnt = mntget(f->f_path.mnt);
 503                /* This can sleep, so we can't hold the spinlock. */
 504                lg_global_unlock(&files_lglock);
 505                mnt_drop_write(mnt);
 506                mntput(mnt);
 507                goto retry;
 508        } while_file_list_for_each_entry;
 509        lg_global_unlock(&files_lglock);
 510}
 511
 512void __init files_init(unsigned long mempages)
 513{ 
 514        unsigned long n;
 515
 516        filp_cachep = kmem_cache_create("filp", sizeof(struct file), 0,
 517                        SLAB_HWCACHE_ALIGN | SLAB_PANIC, NULL);
 518
 519        /*
 520         * One file with associated inode and dcache is very roughly 1K.
 521         * Per default don't use more than 10% of our memory for files. 
 522         */ 
 523
 524        n = (mempages * (PAGE_SIZE / 1024)) / 10;
 525        files_stat.max_files = max_t(unsigned long, n, NR_FILE);
 526        files_defer_init();
 527        lg_lock_init(&files_lglock, "files_lglock");
 528        percpu_counter_init(&nr_files, 0);
 529} 
 530
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