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