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 void fastcall fput(struct file *file) 141 { 142 if (atomic_dec_and_test(&file->f_count)) 143 __fput(file); 144 } 145 146 EXPORT_SYMBOL(fput); 147 148 /* __fput is called from task context when aio completion releases the last 149 * last use of a struct file *. Do not use otherwise. 150 */ 151 void fastcall __fput(struct file *file) 152 { 153 struct dentry *dentry = file->f_path.dentry; 154 struct vfsmount *mnt = file->f_path.mnt; 155 struct inode *inode = dentry->d_inode; 156 157 might_sleep(); 158 159 fsnotify_close(file); 160 /* 161 * The function eventpoll_release() should be the first called 162 * in the file cleanup chain. 163 */ 164 eventpoll_release(file); 165 locks_remove_flock(file); 166 167 if (file->f_op && file->f_op->release) 168 file->f_op->release(inode, file); 169 security_file_free(file); 170 if (unlikely(S_ISCHR(inode->i_mode) && inode->i_cdev != NULL)) 171 cdev_put(inode->i_cdev); 172 fops_put(file->f_op); 173 if (file->f_mode & FMODE_WRITE) 174 put_write_access(inode); 175 put_pid(file->f_owner.pid); 176 file_kill(file); 177 file->f_path.dentry = NULL; 178 file->f_path.mnt = NULL; 179 file_free(file); 180 dput(dentry); 181 mntput(mnt); 182 } 183 184 struct file fastcall *fget(unsigned int fd) 185 { 186 struct file *file; 187 struct files_struct *files = current->files; 188 189 rcu_read_lock(); 190 file = fcheck_files(files, fd); 191 if (file) { 192 if (!atomic_inc_not_zero(&file->f_count)) { 193 /* File object ref couldn't be taken */ 194 rcu_read_unlock(); 195 return NULL; 196 } 197 } 198 rcu_read_unlock(); 199 200 return file; 201 } 202 203 EXPORT_SYMBOL(fget); 204 205 /* 206 * Lightweight file lookup - no refcnt increment if fd table isn't shared. 207 * You can use this only if it is guranteed that the current task already 208 * holds a refcnt to that file. That check has to be done at fget() only 209 * and a flag is returned to be passed to the corresponding fput_light(). 210 * There must not be a cloning between an fget_light/fput_light pair. 211 */ 212 struct file fastcall *fget_light(unsigned int fd, int *fput_needed) 213 { 214 struct file *file; 215 struct files_struct *files = current->files; 216 217 *fput_needed = 0; 218 if (likely((atomic_read(&files->count) == 1))) { 219 file = fcheck_files(files, fd); 220 } else { 221 rcu_read_lock(); 222 file = fcheck_files(files, fd); 223 if (file) { 224 if (atomic_inc_not_zero(&file->f_count)) 225 *fput_needed = 1; 226 else 227 /* Didn't get the reference, someone's freed */ 228 file = NULL; 229 } 230 rcu_read_unlock(); 231 } 232 233 return file; 234 } 235 236 237 void put_filp(struct file *file) 238 { 239 if (atomic_dec_and_test(&file->f_count)) { 240 security_file_free(file); 241 file_kill(file); 242 file_free(file); 243 } 244 } 245 246 void file_move(struct file *file, struct list_head *list) 247 { 248 if (!list) 249 return; 250 file_list_lock(); 251 list_move(&file->f_u.fu_list, list); 252 file_list_unlock(); 253 } 254 255 void file_kill(struct file *file) 256 { 257 if (!list_empty(&file->f_u.fu_list)) { 258 file_list_lock(); 259 list_del_init(&file->f_u.fu_list); 260 file_list_unlock(); 261 } 262 } 263 264 int fs_may_remount_ro(struct super_block *sb) 265 { 266 struct list_head *p; 267 268 /* Check that no files are currently opened for writing. */ 269 file_list_lock(); 270 list_for_each(p, &sb->s_files) { 271 struct file *file = list_entry(p, struct file, f_u.fu_list); 272 struct inode *inode = file->f_path.dentry->d_inode; 273 274 /* File with pending delete? */ 275 if (inode->i_nlink == 0) 276 goto too_bad; 277 278 /* Writeable file? */ 279 if (S_ISREG(inode->i_mode) && (file->f_mode & FMODE_WRITE)) 280 goto too_bad; 281 } 282 file_list_unlock(); 283 return 1; /* Tis' cool bro. */ 284 too_bad: 285 file_list_unlock(); 286 return 0; 287 } 288 289 void __init files_init(unsigned long mempages) 290 { 291 int n; 292 /* One file with associated inode and dcache is very roughly 1K. 293 * Per default don't use more than 10% of our memory for files. 294 */ 295 296 n = (mempages * (PAGE_SIZE / 1024)) / 10; 297 files_stat.max_files = n; 298 if (files_stat.max_files < NR_FILE) 299 files_stat.max_files = NR_FILE; 300 files_defer_init(); 301 percpu_counter_init(&nr_files, 0); 302 } 303