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/config.h>
   9 #include <linux/string.h>
  10 #include <linux/slab.h>
  11 #include <linux/file.h>
  12 #include <linux/init.h>
  13 #include <linux/module.h>
  14 #include <linux/smp_lock.h>
  15 #include <linux/fs.h>
  16 #include <linux/security.h>
  17 #include <linux/eventpoll.h>
  18 #include <linux/rcupdate.h>
  19 #include <linux/mount.h>
  20 #include <linux/capability.h>
  21 #include <linux/cdev.h>
  22 #include <linux/fsnotify.h>
  23 #include <linux/sysctl.h>
  24 #include <linux/percpu_counter.h>
  25
  26 #include <asm/atomic.h>
  27
  28 /* sysctl tunables... */
  29 struct files_stat_struct files_stat = {
  30         .max_files = NR_FILE
  31 };
  32
  33 /* public. Not pretty! */
  34 __cacheline_aligned_in_smp DEFINE_SPINLOCK(files_lock);
  35
  36 static struct percpu_counter nr_files __cacheline_aligned_in_smp;
  37
  38 static inline void file_free_rcu(struct rcu_head *head)
  39 {
  40         struct file *f =  container_of(head, struct file, f_u.fu_rcuhead);
  41         kmem_cache_free(filp_cachep, f);
  42 }
  43
  44 static inline void file_free(struct file *f)
  45 {
  46         percpu_counter_dec(&nr_files);
  47         call_rcu(&f->f_u.fu_rcuhead, file_free_rcu);
  48 }
  49
  50 /*
  51  * Return the total number of open files in the system
  52  */
  53 static int get_nr_files(void)
  54 {
  55         return percpu_counter_read_positive(&nr_files);
  56 }
  57
  58 /*
  59  * Return the maximum number of open files in the system
  60  */
  61 int get_max_files(void)
  62 {
  63         return files_stat.max_files;
  64 }
  65 EXPORT_SYMBOL_GPL(get_max_files);
  66
  67 /*
  68  * Handle nr_files sysctl
  69  */
  70 #if defined(CONFIG_SYSCTL) && defined(CONFIG_PROC_FS)
  71 int proc_nr_files(ctl_table *table, int write, struct file *filp,
  72                      void __user *buffer, size_t *lenp, loff_t *ppos)
  73 {
  74         files_stat.nr_files = get_nr_files();
  75         return proc_dointvec(table, write, filp, buffer, lenp, ppos);
  76 }
  77 #else
  78 int proc_nr_files(ctl_table *table, int write, struct file *filp,
  79                      void __user *buffer, size_t *lenp, loff_t *ppos)
  80 {
  81         return -ENOSYS;
  82 }
  83 #endif
  84
  85 /* Find an unused file structure and return a pointer to it.
  86  * Returns NULL, if there are no more free file structures or
  87  * we run out of memory.
  88  */
  89 struct file *get_empty_filp(void)
  90 {
  91         struct task_struct *tsk;
  92         static int old_max;
  93         struct file * f;
  94
  95         /*
  96          * Privileged users can go above max_files
  97          */
  98         if (get_nr_files() >= files_stat.max_files && !capable(CAP_SYS_ADMIN)) {
  99                 /*
 100                  * percpu_counters are inaccurate.  Do an expensive check before
 101                  * we go and fail.
 102                  */
 103                 if (percpu_counter_sum(&nr_files) >= files_stat.max_files)
 104                         goto over;
 105         }
 106
 107         f = kmem_cache_alloc(filp_cachep, GFP_KERNEL);
 108         if (f == NULL)
 109                 goto fail;
 110
 111         percpu_counter_inc(&nr_files);
 112         memset(f, 0, sizeof(*f));
 113         if (security_file_alloc(f))
 114                 goto fail_sec;
 115
 116         tsk = current;
 117         INIT_LIST_HEAD(&f->f_u.fu_list);
 118         atomic_set(&f->f_count, 1);
 119         rwlock_init(&f->f_owner.lock);
 120         f->f_uid = tsk->fsuid;
 121         f->f_gid = tsk->fsgid;
 122         eventpoll_init_file(f);
 123         /* f->f_version: 0 */
 124         return f;
 125
 126 over:
 127         /* Ran out of filps - report that */
 128         if (get_nr_files() > old_max) {
 129                 printk(KERN_INFO "VFS: file-max limit %d reached\n",
 130                                         get_max_files());
 131                 old_max = get_nr_files();
 132         }
 133         goto fail;
 134
 135 fail_sec:
 136         file_free(f);
 137 fail:
 138         return NULL;
 139 }
 140
 141 EXPORT_SYMBOL(get_empty_filp);
 142
 143 void fastcall fput(struct file *file)
 144 {
 145         if (atomic_dec_and_test(&file->f_count))
 146                 __fput(file);
 147 }
 148
 149 EXPORT_SYMBOL(fput);
 150
 151 /* __fput is called from task context when aio completion releases the last
 152  * last use of a struct file *.  Do not use otherwise.
 153  */
 154 void fastcall __fput(struct file *file)
 155 {
 156         struct dentry *dentry = file->f_dentry;
 157         struct vfsmount *mnt = file->f_vfsmnt;
 158         struct inode *inode = dentry->d_inode;
 159
 160         might_sleep();
 161
 162         fsnotify_close(file);
 163         /*
 164          * The function eventpoll_release() should be the first called
 165          * in the file cleanup chain.
 166          */
 167         eventpoll_release(file);
 168         locks_remove_flock(file);
 169
 170         if (file->f_op && file->f_op->release)
 171                 file->f_op->release(inode, file);
 172         security_file_free(file);
 173         if (unlikely(inode->i_cdev != NULL))
 174                 cdev_put(inode->i_cdev);
 175         fops_put(file->f_op);
 176         if (file->f_mode & FMODE_WRITE)
 177                 put_write_access(inode);
 178         file_kill(file);
 179         file->f_dentry = NULL;
 180         file->f_vfsmnt = NULL;
 181         file_free(file);
 182         dput(dentry);
 183         mntput(mnt);
 184 }
 185
 186 struct file fastcall *fget(unsigned int fd)
 187 {
 188         struct file *file;
 189         struct files_struct *files = current->files;
 190
 191         rcu_read_lock();
 192         file = fcheck_files(files, fd);
 193         if (file) {
 194                 if (!atomic_inc_not_zero(&file->f_count)) {
 195                         /* File object ref couldn't be taken */
 196                         rcu_read_unlock();
 197                         return NULL;
 198                 }
 199         }
 200         rcu_read_unlock();
 201
 202         return file;
 203 }
 204
 205 EXPORT_SYMBOL(fget);
 206
 207 /*
 208  * Lightweight file lookup - no refcnt increment if fd table isn't shared.
 209  * You can use this only if it is guranteed that the current task already
 210  * holds a refcnt to that file. That check has to be done at fget() only
 211  * and a flag is returned to be passed to the corresponding fput_light().
 212  * There must not be a cloning between an fget_light/fput_light pair.
 213  */
 214 struct file fastcall *fget_light(unsigned int fd, int *fput_needed)
 215 {
 216         struct file *file;
 217         struct files_struct *files = current->files;
 218
 219         *fput_needed = 0;
 220         if (likely((atomic_read(&files->count) == 1))) {
 221                 file = fcheck_files(files, fd);
 222         } else {
 223                 rcu_read_lock();
 224                 file = fcheck_files(files, fd);
 225                 if (file) {
 226                         if (atomic_inc_not_zero(&file->f_count))
 227                                 *fput_needed = 1;
 228                         else
 229                                 /* Didn't get the reference, someone's freed */
 230                                 file = NULL;
 231                 }
 232                 rcu_read_unlock();
 233         }
 234
 235         return file;
 236 }
 237
 238
 239 void put_filp(struct file *file)
 240 {
 241         if (atomic_dec_and_test(&file->f_count)) {
 242                 security_file_free(file);
 243                 file_kill(file);
 244                 file_free(file);
 245         }
 246 }
 247
 248 void file_move(struct file *file, struct list_head *list)
 249 {
 250         if (!list)
 251                 return;
 252         file_list_lock();
 253         list_move(&file->f_u.fu_list, list);
 254         file_list_unlock();
 255 }
 256
 257 void file_kill(struct file *file)
 258 {
 259         if (!list_empty(&file->f_u.fu_list)) {
 260                 file_list_lock();
 261                 list_del_init(&file->f_u.fu_list);
 262                 file_list_unlock();
 263         }
 264 }
 265
 266 int fs_may_remount_ro(struct super_block *sb)
 267 {
 268         struct list_head *p;
 269
 270         /* Check that no files are currently opened for writing. */
 271         file_list_lock();
 272         list_for_each(p, &sb->s_files) {
 273                 struct file *file = list_entry(p, struct file, f_u.fu_list);
 274                 struct inode *inode = file->f_dentry->d_inode;
 275
 276                 /* File with pending delete? */
 277                 if (inode->i_nlink == 0)
 278                         goto too_bad;
 279
 280                 /* Writeable file? */
 281                 if (S_ISREG(inode->i_mode) && (file->f_mode & FMODE_WRITE))
 282                         goto too_bad;
 283         }
 284         file_list_unlock();
 285         return 1; /* Tis' cool bro. */
 286 too_bad:
 287         file_list_unlock();
 288         return 0;
 289 }
 290
 291 void __init files_init(unsigned long mempages)
 292 {
 293         int n;
 294         /* One file with associated inode and dcache is very roughly 1K.
 295          * Per default don't use more than 10% of our memory for files.
 296          */
 297
 298         n = (mempages * (PAGE_SIZE / 1024)) / 10;
 299         files_stat.max_files = n;
 300         if (files_stat.max_files < NR_FILE)
 301                 files_stat.max_files = NR_FILE;
 302         files_defer_init();
 303         percpu_counter_init(&nr_files);
 304 }