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 } 305