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 fastcall 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 fastcall __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 fastcall *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 fastcall *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 } 362