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/mount.h>
  18 #include <linux/cdev.h>
  19
  20 /* sysctl tunables... */
  21 struct files_stat_struct files_stat = {
  22         .max_files = NR_FILE
  23 };
  24
  25 EXPORT_SYMBOL(files_stat); /* Needed by unix.o */
  26
  27 /* public. Not pretty! */
  28  __cacheline_aligned_in_smp DEFINE_SPINLOCK(files_lock);
  29
  30 static DEFINE_SPINLOCK(filp_count_lock);
  31
  32 /* slab constructors and destructors are called from arbitrary
  33  * context and must be fully threaded - use a local spinlock
  34  * to protect files_stat.nr_files
  35  */
  36 void filp_ctor(void * objp, struct kmem_cache_s *cachep, unsigned long cflags)
  37 {
  38         if ((cflags & (SLAB_CTOR_VERIFY|SLAB_CTOR_CONSTRUCTOR)) ==
  39             SLAB_CTOR_CONSTRUCTOR) {
  40                 unsigned long flags;
  41                 spin_lock_irqsave(&filp_count_lock, flags);
  42                 files_stat.nr_files++;
  43                 spin_unlock_irqrestore(&filp_count_lock, flags);
  44         }
  45 }
  46
  47 void filp_dtor(void * objp, struct kmem_cache_s *cachep, unsigned long dflags)
  48 {
  49         unsigned long flags;
  50         spin_lock_irqsave(&filp_count_lock, flags);
  51         files_stat.nr_files--;
  52         spin_unlock_irqrestore(&filp_count_lock, flags);
  53 }
  54
  55 static inline void file_free(struct file *f)
  56 {
  57         kmem_cache_free(filp_cachep, f);
  58 }
  59
  60 /* Find an unused file structure and return a pointer to it.
  61  * Returns NULL, if there are no more free file structures or
  62  * we run out of memory.
  63  */
  64 struct file *get_empty_filp(void)
  65 {
  66 static int old_max;
  67         struct file * f;
  68
  69         /*
  70          * Privileged users can go above max_files
  71          */
  72         if (files_stat.nr_files < files_stat.max_files ||
  73                                 capable(CAP_SYS_ADMIN)) {
  74                 f = kmem_cache_alloc(filp_cachep, GFP_KERNEL);
  75                 if (f) {
  76                         memset(f, 0, sizeof(*f));
  77                         if (security_file_alloc(f)) {
  78                                 file_free(f);
  79                                 goto fail;
  80                         }
  81                         eventpoll_init_file(f);
  82                         atomic_set(&f->f_count, 1);
  83                         f->f_uid = current->fsuid;
  84                         f->f_gid = current->fsgid;
  85                         rwlock_init(&f->f_owner.lock);
  86                         /* f->f_version: 0 */
  87                         INIT_LIST_HEAD(&f->f_list);
  88                         f->f_maxcount = INT_MAX;
  89                         return f;
  90                 }
  91         }
  92
  93         /* Ran out of filps - report that */
  94         if (files_stat.max_files >= old_max) {
  95                 printk(KERN_INFO "VFS: file-max limit %d reached\n",
  96                                         files_stat.max_files);
  97                 old_max = files_stat.max_files;
  98         } else {
  99                 /* Big problems... */
 100                 printk(KERN_WARNING "VFS: filp allocation failed\n");
 101         }
 102 fail:
 103         return NULL;
 104 }
 105
 106 EXPORT_SYMBOL(get_empty_filp);
 107
 108 void fastcall fput(struct file *file)
 109 {
 110         if (atomic_dec_and_test(&file->f_count))
 111                 __fput(file);
 112 }
 113
 114 EXPORT_SYMBOL(fput);
 115
 116 /* __fput is called from task context when aio completion releases the last
 117  * last use of a struct file *.  Do not use otherwise.
 118  */
 119 void fastcall __fput(struct file *file)
 120 {
 121         struct dentry *dentry = file->f_dentry;
 122         struct vfsmount *mnt = file->f_vfsmnt;
 123         struct inode *inode = dentry->d_inode;
 124
 125         might_sleep();
 126         /*
 127          * The function eventpoll_release() should be the first called
 128          * in the file cleanup chain.
 129          */
 130         eventpoll_release(file);
 131         locks_remove_flock(file);
 132
 133         if (file->f_op && file->f_op->release)
 134                 file->f_op->release(inode, file);
 135         security_file_free(file);
 136         if (unlikely(inode->i_cdev != NULL))
 137                 cdev_put(inode->i_cdev);
 138         fops_put(file->f_op);
 139         if (file->f_mode & FMODE_WRITE)
 140                 put_write_access(inode);
 141         file_kill(file);
 142         file->f_dentry = NULL;
 143         file->f_vfsmnt = NULL;
 144         file_free(file);
 145         dput(dentry);
 146         mntput(mnt);
 147 }
 148
 149 struct file fastcall *fget(unsigned int fd)
 150 {
 151         struct file *file;
 152         struct files_struct *files = current->files;
 153
 154         spin_lock(&files->file_lock);
 155         file = fcheck_files(files, fd);
 156         if (file)
 157                 get_file(file);
 158         spin_unlock(&files->file_lock);
 159         return file;
 160 }
 161
 162 EXPORT_SYMBOL(fget);
 163
 164 /*
 165  * Lightweight file lookup - no refcnt increment if fd table isn't shared.
 166  * You can use this only if it is guranteed that the current task already
 167  * holds a refcnt to that file. That check has to be done at fget() only
 168  * and a flag is returned to be passed to the corresponding fput_light().
 169  * There must not be a cloning between an fget_light/fput_light pair.
 170  */
 171 struct file fastcall *fget_light(unsigned int fd, int *fput_needed)
 172 {
 173         struct file *file;
 174         struct files_struct *files = current->files;
 175
 176         *fput_needed = 0;
 177         if (likely((atomic_read(&files->count) == 1))) {
 178                 file = fcheck_files(files, fd);
 179         } else {
 180                 spin_lock(&files->file_lock);
 181                 file = fcheck_files(files, fd);
 182                 if (file) {
 183                         get_file(file);
 184                         *fput_needed = 1;
 185                 }
 186                 spin_unlock(&files->file_lock);
 187         }
 188         return file;
 189 }
 190
 191
 192 void put_filp(struct file *file)
 193 {
 194         if (atomic_dec_and_test(&file->f_count)) {
 195                 security_file_free(file);
 196                 file_kill(file);
 197                 file_free(file);
 198         }
 199 }
 200
 201 void file_move(struct file *file, struct list_head *list)
 202 {
 203         if (!list)
 204                 return;
 205         file_list_lock();
 206         list_move(&file->f_list, list);
 207         file_list_unlock();
 208 }
 209
 210 void file_kill(struct file *file)
 211 {
 212         if (!list_empty(&file->f_list)) {
 213                 file_list_lock();
 214                 list_del_init(&file->f_list);
 215                 file_list_unlock();
 216         }
 217 }
 218
 219 int fs_may_remount_ro(struct super_block *sb)
 220 {
 221         struct list_head *p;
 222
 223         /* Check that no files are currently opened for writing. */
 224         file_list_lock();
 225         list_for_each(p, &sb->s_files) {
 226                 struct file *file = list_entry(p, struct file, f_list);
 227                 struct inode *inode = file->f_dentry->d_inode;
 228
 229                 /* File with pending delete? */
 230                 if (inode->i_nlink == 0)
 231                         goto too_bad;
 232
 233                 /* Writeable file? */
 234                 if (S_ISREG(inode->i_mode) && (file->f_mode & FMODE_WRITE))
 235                         goto too_bad;
 236         }
 237         file_list_unlock();
 238         return 1; /* Tis' cool bro. */
 239 too_bad:
 240         file_list_unlock();
 241         return 0;
 242 }
 243
 244 void __init files_init(unsigned long mempages)
 245 {
 246         int n;
 247         /* One file with associated inode and dcache is very roughly 1K.
 248          * Per default don't use more than 10% of our memory for files.
 249          */
 250
 251         n = (mempages * (PAGE_SIZE / 1024)) / 10;
 252         files_stat.max_files = n;
 253         if (files_stat.max_files < NR_FILE)
 254                 files_stat.max_files = NR_FILE;
 255 }