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/rcupdate.h> 18 #include <linux/mount.h> 19 #include <linux/capability.h> 20 #include <linux/cdev.h> 21 #include <linux/fsnotify.h> 22 #include <linux/sysctl.h> 23 #include <linux/percpu_counter.h> 24 25 #include <asm/atomic.h> 26 27 /* sysctl tunables... */ 28 struct files_stat_struct files_stat = { 29 .max_files = NR_FILE 30 }; 31 32 /* public. Not pretty! */ 33 __cacheline_aligned_in_smp DEFINE_SPINLOCK(files_lock); 34 35 static struct percpu_counter nr_files __cacheline_aligned_in_smp; 36 37 static inline void file_free_rcu(struct rcu_head *head) 38 { 39 struct file *f = container_of(head, struct file, f_u.fu_rcuhead); 40 kmem_cache_free(filp_cachep, f); 41 } 42 43 static inline void file_free(struct file *f) 44 { 45 percpu_counter_dec(&nr_files); 46 call_rcu(&f->f_u.fu_rcuhead, file_free_rcu); 47 } 48 49 /* 50 * Return the total number of open files in the system 51 */ 52 static int get_nr_files(void) 53 { 54 return percpu_counter_read_positive(&nr_files); 55 } 56 57 /* 58 * Return the maximum number of open files in the system 59 */ 60 int get_max_files(void) 61 { 62 return files_stat.max_files; 63 } 64 EXPORT_SYMBOL_GPL(get_max_files); 65 66 /* 67 * Handle nr_files sysctl 68 */ 69 #if defined(CONFIG_SYSCTL) && defined(CONFIG_PROC_FS) 70 int proc_nr_files(ctl_table *table, int write, struct file *filp, 71 void __user *buffer, size_t *lenp, loff_t *ppos) 72 { 73 files_stat.nr_files = get_nr_files(); 74 return proc_dointvec(table, write, filp, buffer, lenp, ppos); 75 } 76 #else 77 int proc_nr_files(ctl_table *table, int write, struct file *filp, 78 void __user *buffer, size_t *lenp, loff_t *ppos) 79 { 80 return -ENOSYS; 81 } 82 #endif 83 84 /* Find an unused file structure and return a pointer to it. 85 * Returns NULL, if there are no more free file structures or 86 * we run out of memory. 87 */ 88 struct file *get_empty_filp(void) 89 { 90 struct task_struct *tsk; 91 static int old_max; 92 struct file * f; 93 94 /* 95 * Privileged users can go above max_files 96 */ 97 if (get_nr_files() >= files_stat.max_files && !capable(CAP_SYS_ADMIN)) { 98 /* 99 * percpu_counters are inaccurate. Do an expensive check before 100 * we go and fail. 101 */ 102 if (percpu_counter_sum(&nr_files) >= files_stat.max_files) 103 goto over; 104 } 105 106 f = kmem_cache_alloc(filp_cachep, GFP_KERNEL); 107 if (f == NULL) 108 goto fail; 109 110 percpu_counter_inc(&nr_files); 111 memset(f, 0, sizeof(*f)); 112 if (security_file_alloc(f)) 113 goto fail_sec; 114 115 tsk = current; 116 INIT_LIST_HEAD(&f->f_u.fu_list); 117 atomic_set(&f->f_count, 1); 118 rwlock_init(&f->f_owner.lock); 119 f->f_uid = tsk->fsuid; 120 f->f_gid = tsk->fsgid; 121 eventpoll_init_file(f); 122 /* f->f_version: 0 */ 123 return f; 124 125 over: 126 /* Ran out of filps - report that */ 127 if (get_nr_files() > old_max) { 128 printk(KERN_INFO "VFS: file-max limit %d reached\n", 129 get_max_files()); 130 old_max = get_nr_files(); 131 } 132 goto fail; 133 134 fail_sec: 135 file_free(f); 136 fail: 137 return NULL; 138 } 139 140 EXPORT_SYMBOL(get_empty_filp); 141 142 void fastcall fput(struct file *file) 143 { 144 if (atomic_dec_and_test(&file->f_count)) 145 __fput(file); 146 } 147 148 EXPORT_SYMBOL(fput); 149 150 /* __fput is called from task context when aio completion releases the last 151 * last use of a struct file *. Do not use otherwise. 152 */ 153 void fastcall __fput(struct file *file) 154 { 155 struct dentry *dentry = file->f_dentry; 156 struct vfsmount *mnt = file->f_vfsmnt; 157 struct inode *inode = dentry->d_inode; 158 159 might_sleep(); 160 161 fsnotify_close(file); 162 /* 163 * The function eventpoll_release() should be the first called 164 * in the file cleanup chain. 165 */ 166 eventpoll_release(file); 167 locks_remove_flock(file); 168 169 if (file->f_op && file->f_op->release) 170 file->f_op->release(inode, file); 171 security_file_free(file); 172 if (unlikely(inode->i_cdev != NULL)) 173 cdev_put(inode->i_cdev); 174 fops_put(file->f_op); 175 if (file->f_mode & FMODE_WRITE) 176 put_write_access(inode); 177 file_kill(file); 178 file->f_dentry = NULL; 179 file->f_vfsmnt = NULL; 180 file_free(file); 181 dput(dentry); 182 mntput(mnt); 183 } 184 185 struct file fastcall *fget(unsigned int fd) 186 { 187 struct file *file; 188 struct files_struct *files = current->files; 189 190 rcu_read_lock(); 191 file = fcheck_files(files, fd); 192 if (file) { 193 if (!atomic_inc_not_zero(&file->f_count)) { 194 /* File object ref couldn't be taken */ 195 rcu_read_unlock(); 196 return NULL; 197 } 198 } 199 rcu_read_unlock(); 200 201 return file; 202 } 203 204 EXPORT_SYMBOL(fget); 205 206 /* 207 * Lightweight file lookup - no refcnt increment if fd table isn't shared. 208 * You can use this only if it is guranteed that the current task already 209 * holds a refcnt to that file. That check has to be done at fget() only 210 * and a flag is returned to be passed to the corresponding fput_light(). 211 * There must not be a cloning between an fget_light/fput_light pair. 212 */ 213 struct file fastcall *fget_light(unsigned int fd, int *fput_needed) 214 { 215 struct file *file; 216 struct files_struct *files = current->files; 217 218 *fput_needed = 0; 219 if (likely((atomic_read(&files->count) == 1))) { 220 file = fcheck_files(files, fd); 221 } else { 222 rcu_read_lock(); 223 file = fcheck_files(files, fd); 224 if (file) { 225 if (atomic_inc_not_zero(&file->f_count)) 226 *fput_needed = 1; 227 else 228 /* Didn't get the reference, someone's freed */ 229 file = NULL; 230 } 231 rcu_read_unlock(); 232 } 233 234 return file; 235 } 236 237 238 void put_filp(struct file *file) 239 { 240 if (atomic_dec_and_test(&file->f_count)) { 241 security_file_free(file); 242 file_kill(file); 243 file_free(file); 244 } 245 } 246 247 void file_move(struct file *file, struct list_head *list) 248 { 249 if (!list) 250 return; 251 file_list_lock(); 252 list_move(&file->f_u.fu_list, list); 253 file_list_unlock(); 254 } 255 256 void file_kill(struct file *file) 257 { 258 if (!list_empty(&file->f_u.fu_list)) { 259 file_list_lock(); 260 list_del_init(&file->f_u.fu_list); 261 file_list_unlock(); 262 } 263 } 264 265 int fs_may_remount_ro(struct super_block *sb) 266 { 267 struct list_head *p; 268 269 /* Check that no files are currently opened for writing. */ 270 file_list_lock(); 271 list_for_each(p, &sb->s_files) { 272 struct file *file = list_entry(p, struct file, f_u.fu_list); 273 struct inode *inode = file->f_dentry->d_inode; 274 275 /* File with pending delete? */ 276 if (inode->i_nlink == 0) 277 goto too_bad; 278 279 /* Writeable file? */ 280 if (S_ISREG(inode->i_mode) && (file->f_mode & FMODE_WRITE)) 281 goto too_bad; 282 } 283 file_list_unlock(); 284 return 1; /* Tis' cool bro. */ 285 too_bad: 286 file_list_unlock(); 287 return 0; 288 } 289 290 void __init files_init(unsigned long mempages) 291 { 292 int n; 293 /* One file with associated inode and dcache is very roughly 1K. 294 * Per default don't use more than 10% of our memory for files. 295 */ 296 297 n = (mempages * (PAGE_SIZE / 1024)) / 10; 298 files_stat.max_files = n; 299 if (files_stat.max_files < NR_FILE) 300 files_stat.max_files = NR_FILE; 301 files_defer_init(); 302 percpu_counter_init(&nr_files, 0); 303 } 304