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 * Be very careful using this. You are responsible for 88 * getting write access to any mount that you might assign 89 * to this filp, if it is opened for write. If this is not 90 * done, you will imbalance int the mount's writer count 91 * and a warning at __fput() time. 92 */ 93 struct file *get_empty_filp(void) 94 { 95 struct task_struct *tsk; 96 static int old_max; 97 struct file * f; 98 99 /* 100 * Privileged users can go above max_files 101 */ 102 if (get_nr_files() >= files_stat.max_files && !capable(CAP_SYS_ADMIN)) { 103 /* 104 * percpu_counters are inaccurate. Do an expensive check before 105 * we go and fail. 106 */ 107 if (percpu_counter_sum_positive(&nr_files) >= files_stat.max_files) 108 goto over; 109 } 110 111 f = kmem_cache_zalloc(filp_cachep, GFP_KERNEL); 112 if (f == NULL) 113 goto fail; 114 115 percpu_counter_inc(&nr_files); 116 if (security_file_alloc(f)) 117 goto fail_sec; 118 119 tsk = current; 120 INIT_LIST_HEAD(&f->f_u.fu_list); 121 atomic_set(&f->f_count, 1); 122 rwlock_init(&f->f_owner.lock); 123 f->f_uid = tsk->fsuid; 124 f->f_gid = tsk->fsgid; 125 eventpoll_init_file(f); 126 /* f->f_version: 0 */ 127 return f; 128 129 over: 130 /* Ran out of filps - report that */ 131 if (get_nr_files() > old_max) { 132 printk(KERN_INFO "VFS: file-max limit %d reached\n", 133 get_max_files()); 134 old_max = get_nr_files(); 135 } 136 goto fail; 137 138 fail_sec: 139 file_free(f); 140 fail: 141 return NULL; 142 } 143 144 EXPORT_SYMBOL(get_empty_filp); 145 146 /** 147 * alloc_file - allocate and initialize a 'struct file' 148 * @mnt: the vfsmount on which the file will reside 149 * @dentry: the dentry representing the new file 150 * @mode: the mode with which the new file will be opened 151 * @fop: the 'struct file_operations' for the new file 152 * 153 * Use this instead of get_empty_filp() to get a new 154 * 'struct file'. Do so because of the same initialization 155 * pitfalls reasons listed for init_file(). This is a 156 * preferred interface to using init_file(). 157 * 158 * If all the callers of init_file() are eliminated, its 159 * code should be moved into this function. 160 */ 161 struct file *alloc_file(struct vfsmount *mnt, struct dentry *dentry, 162 mode_t mode, const struct file_operations *fop) 163 { 164 struct file *file; 165 struct path; 166 167 file = get_empty_filp(); 168 if (!file) 169 return NULL; 170 171 init_file(file, mnt, dentry, mode, fop); 172 return file; 173 } 174 EXPORT_SYMBOL(alloc_file); 175 176 /** 177 * init_file - initialize a 'struct file' 178 * @file: the already allocated 'struct file' to initialized 179 * @mnt: the vfsmount on which the file resides 180 * @dentry: the dentry representing this file 181 * @mode: the mode the file is opened with 182 * @fop: the 'struct file_operations' for this file 183 * 184 * Use this instead of setting the members directly. Doing so 185 * avoids making mistakes like forgetting the mntget() or 186 * forgetting to take a write on the mnt. 187 * 188 * Note: This is a crappy interface. It is here to make 189 * merging with the existing users of get_empty_filp() 190 * who have complex failure logic easier. All users 191 * of this should be moving to alloc_file(). 192 */ 193 int init_file(struct file *file, struct vfsmount *mnt, struct dentry *dentry, 194 mode_t mode, const struct file_operations *fop) 195 { 196 int error = 0; 197 file->f_path.dentry = dentry; 198 file->f_path.mnt = mntget(mnt); 199 file->f_mapping = dentry->d_inode->i_mapping; 200 file->f_mode = mode; 201 file->f_op = fop; 202 return error; 203 } 204 EXPORT_SYMBOL(init_file); 205 206 void fput(struct file *file) 207 { 208 if (atomic_dec_and_test(&file->f_count)) 209 __fput(file); 210 } 211 212 EXPORT_SYMBOL(fput); 213 214 /* __fput is called from task context when aio completion releases the last 215 * last use of a struct file *. Do not use otherwise. 216 */ 217 void __fput(struct file *file) 218 { 219 struct dentry *dentry = file->f_path.dentry; 220 struct vfsmount *mnt = file->f_path.mnt; 221 struct inode *inode = dentry->d_inode; 222 223 might_sleep(); 224 225 fsnotify_close(file); 226 /* 227 * The function eventpoll_release() should be the first called 228 * in the file cleanup chain. 229 */ 230 eventpoll_release(file); 231 locks_remove_flock(file); 232 233 if (file->f_op && file->f_op->release) 234 file->f_op->release(inode, file); 235 security_file_free(file); 236 if (unlikely(S_ISCHR(inode->i_mode) && inode->i_cdev != NULL)) 237 cdev_put(inode->i_cdev); 238 fops_put(file->f_op); 239 if (file->f_mode & FMODE_WRITE) 240 put_write_access(inode); 241 put_pid(file->f_owner.pid); 242 file_kill(file); 243 file->f_path.dentry = NULL; 244 file->f_path.mnt = NULL; 245 file_free(file); 246 dput(dentry); 247 mntput(mnt); 248 } 249 250 struct file *fget(unsigned int fd) 251 { 252 struct file *file; 253 struct files_struct *files = current->files; 254 255 rcu_read_lock(); 256 file = fcheck_files(files, fd); 257 if (file) { 258 if (!atomic_inc_not_zero(&file->f_count)) { 259 /* File object ref couldn't be taken */ 260 rcu_read_unlock(); 261 return NULL; 262 } 263 } 264 rcu_read_unlock(); 265 266 return file; 267 } 268 269 EXPORT_SYMBOL(fget); 270 271 /* 272 * Lightweight file lookup - no refcnt increment if fd table isn't shared. 273 * You can use this only if it is guranteed that the current task already 274 * holds a refcnt to that file. That check has to be done at fget() only 275 * and a flag is returned to be passed to the corresponding fput_light(). 276 * There must not be a cloning between an fget_light/fput_light pair. 277 */ 278 struct file *fget_light(unsigned int fd, int *fput_needed) 279 { 280 struct file *file; 281 struct files_struct *files = current->files; 282 283 *fput_needed = 0; 284 if (likely((atomic_read(&files->count) == 1))) { 285 file = fcheck_files(files, fd); 286 } else { 287 rcu_read_lock(); 288 file = fcheck_files(files, fd); 289 if (file) { 290 if (atomic_inc_not_zero(&file->f_count)) 291 *fput_needed = 1; 292 else 293 /* Didn't get the reference, someone's freed */ 294 file = NULL; 295 } 296 rcu_read_unlock(); 297 } 298 299 return file; 300 } 301 302 303 void put_filp(struct file *file) 304 { 305 if (atomic_dec_and_test(&file->f_count)) { 306 security_file_free(file); 307 file_kill(file); 308 file_free(file); 309 } 310 } 311 312 void file_move(struct file *file, struct list_head *list) 313 { 314 if (!list) 315 return; 316 file_list_lock(); 317 list_move(&file->f_u.fu_list, list); 318 file_list_unlock(); 319 } 320 321 void file_kill(struct file *file) 322 { 323 if (!list_empty(&file->f_u.fu_list)) { 324 file_list_lock(); 325 list_del_init(&file->f_u.fu_list); 326 file_list_unlock(); 327 } 328 } 329 330 int fs_may_remount_ro(struct super_block *sb) 331 { 332 struct file *file; 333 334 /* Check that no files are currently opened for writing. */ 335 file_list_lock(); 336 list_for_each_entry(file, &sb->s_files, f_u.fu_list) { 337 struct inode *inode = file->f_path.dentry->d_inode; 338 339 /* File with pending delete? */ 340 if (inode->i_nlink == 0) 341 goto too_bad; 342 343 /* Writeable file? */ 344 if (S_ISREG(inode->i_mode) && (file->f_mode & FMODE_WRITE)) 345 goto too_bad; 346 } 347 file_list_unlock(); 348 return 1; /* Tis' cool bro. */ 349 too_bad: 350 file_list_unlock(); 351 return 0; 352 } 353 354 void __init files_init(unsigned long mempages) 355 { 356 int n; 357 /* One file with associated inode and dcache is very roughly 1K. 358 * Per default don't use more than 10% of our memory for files. 359 */ 360 361 n = (mempages * (PAGE_SIZE / 1024)) / 10; 362 files_stat.max_files = n; 363 if (files_stat.max_files < NR_FILE) 364 files_stat.max_files = NR_FILE; 365 files_defer_init(); 366 percpu_counter_init(&nr_files, 0); 367 } 368