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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/fdtable.h> | |
12 | #include <linux/init.h> | |
13 | #include <linux/module.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 | file_check_state(f); | |
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 | * Be very careful using this. You are responsible for | |
90 | * getting write access to any mount that you might assign | |
91 | * to this filp, if it is opened for write. If this is not | |
92 | * done, you will imbalance int the mount's writer count | |
93 | * and a warning at __fput() time. | |
94 | */ | |
95 | struct file *get_empty_filp(void) | |
96 | { | |
97 | struct task_struct *tsk; | |
98 | static int old_max; | |
99 | struct file * f; | |
100 | ||
101 | /* | |
102 | * Privileged users can go above max_files | |
103 | */ | |
104 | if (get_nr_files() >= files_stat.max_files && !capable(CAP_SYS_ADMIN)) { | |
105 | /* | |
106 | * percpu_counters are inaccurate. Do an expensive check before | |
107 | * we go and fail. | |
108 | */ | |
109 | if (percpu_counter_sum_positive(&nr_files) >= files_stat.max_files) | |
110 | goto over; | |
111 | } | |
112 | ||
113 | f = kmem_cache_zalloc(filp_cachep, GFP_KERNEL); | |
114 | if (f == NULL) | |
115 | goto fail; | |
116 | ||
117 | percpu_counter_inc(&nr_files); | |
118 | if (security_file_alloc(f)) | |
119 | goto fail_sec; | |
120 | ||
121 | tsk = current; | |
122 | INIT_LIST_HEAD(&f->f_u.fu_list); | |
123 | atomic_long_set(&f->f_count, 1); | |
124 | rwlock_init(&f->f_owner.lock); | |
125 | f->f_uid = tsk->fsuid; | |
126 | f->f_gid = tsk->fsgid; | |
127 | eventpoll_init_file(f); | |
128 | /* f->f_version: 0 */ | |
129 | return f; | |
130 | ||
131 | over: | |
132 | /* Ran out of filps - report that */ | |
133 | if (get_nr_files() > old_max) { | |
134 | printk(KERN_INFO "VFS: file-max limit %d reached\n", | |
135 | get_max_files()); | |
136 | old_max = get_nr_files(); | |
137 | } | |
138 | goto fail; | |
139 | ||
140 | fail_sec: | |
141 | file_free(f); | |
142 | fail: | |
143 | return NULL; | |
144 | } | |
145 | ||
146 | EXPORT_SYMBOL(get_empty_filp); | |
147 | ||
148 | /** | |
149 | * alloc_file - allocate and initialize a 'struct file' | |
150 | * @mnt: the vfsmount on which the file will reside | |
151 | * @dentry: the dentry representing the new file | |
152 | * @mode: the mode with which the new file will be opened | |
153 | * @fop: the 'struct file_operations' for the new file | |
154 | * | |
155 | * Use this instead of get_empty_filp() to get a new | |
156 | * 'struct file'. Do so because of the same initialization | |
157 | * pitfalls reasons listed for init_file(). This is a | |
158 | * preferred interface to using init_file(). | |
159 | * | |
160 | * If all the callers of init_file() are eliminated, its | |
161 | * code should be moved into this function. | |
162 | */ | |
163 | struct file *alloc_file(struct vfsmount *mnt, struct dentry *dentry, | |
164 | mode_t mode, const struct file_operations *fop) | |
165 | { | |
166 | struct file *file; | |
167 | struct path; | |
168 | ||
169 | file = get_empty_filp(); | |
170 | if (!file) | |
171 | return NULL; | |
172 | ||
173 | init_file(file, mnt, dentry, mode, fop); | |
174 | return file; | |
175 | } | |
176 | EXPORT_SYMBOL(alloc_file); | |
177 | ||
178 | /** | |
179 | * init_file - initialize a 'struct file' | |
180 | * @file: the already allocated 'struct file' to initialized | |
181 | * @mnt: the vfsmount on which the file resides | |
182 | * @dentry: the dentry representing this file | |
183 | * @mode: the mode the file is opened with | |
184 | * @fop: the 'struct file_operations' for this file | |
185 | * | |
186 | * Use this instead of setting the members directly. Doing so | |
187 | * avoids making mistakes like forgetting the mntget() or | |
188 | * forgetting to take a write on the mnt. | |
189 | * | |
190 | * Note: This is a crappy interface. It is here to make | |
191 | * merging with the existing users of get_empty_filp() | |
192 | * who have complex failure logic easier. All users | |
193 | * of this should be moving to alloc_file(). | |
194 | */ | |
195 | int init_file(struct file *file, struct vfsmount *mnt, struct dentry *dentry, | |
196 | mode_t mode, const struct file_operations *fop) | |
197 | { | |
198 | int error = 0; | |
199 | file->f_path.dentry = dentry; | |
200 | file->f_path.mnt = mntget(mnt); | |
201 | file->f_mapping = dentry->d_inode->i_mapping; | |
202 | file->f_mode = mode; | |
203 | file->f_op = fop; | |
204 | ||
205 | /* | |
206 | * These mounts don't really matter in practice | |
207 | * for r/o bind mounts. They aren't userspace- | |
208 | * visible. We do this for consistency, and so | |
209 | * that we can do debugging checks at __fput() | |
210 | */ | |
211 | if ((mode & FMODE_WRITE) && !special_file(dentry->d_inode->i_mode)) { | |
212 | file_take_write(file); | |
213 | error = mnt_want_write(mnt); | |
214 | WARN_ON(error); | |
215 | } | |
216 | return error; | |
217 | } | |
218 | EXPORT_SYMBOL(init_file); | |
219 | ||
220 | void fput(struct file *file) | |
221 | { | |
222 | if (atomic_long_dec_and_test(&file->f_count)) | |
223 | __fput(file); | |
224 | } | |
225 | ||
226 | EXPORT_SYMBOL(fput); | |
227 | ||
228 | /** | |
229 | * drop_file_write_access - give up ability to write to a file | |
230 | * @file: the file to which we will stop writing | |
231 | * | |
232 | * This is a central place which will give up the ability | |
233 | * to write to @file, along with access to write through | |
234 | * its vfsmount. | |
235 | */ | |
236 | void drop_file_write_access(struct file *file) | |
237 | { | |
238 | struct vfsmount *mnt = file->f_path.mnt; | |
239 | struct dentry *dentry = file->f_path.dentry; | |
240 | struct inode *inode = dentry->d_inode; | |
241 | ||
242 | put_write_access(inode); | |
243 | ||
244 | if (special_file(inode->i_mode)) | |
245 | return; | |
246 | if (file_check_writeable(file) != 0) | |
247 | return; | |
248 | mnt_drop_write(mnt); | |
249 | file_release_write(file); | |
250 | } | |
251 | EXPORT_SYMBOL_GPL(drop_file_write_access); | |
252 | ||
253 | /* __fput is called from task context when aio completion releases the last | |
254 | * last use of a struct file *. Do not use otherwise. | |
255 | */ | |
256 | void __fput(struct file *file) | |
257 | { | |
258 | struct dentry *dentry = file->f_path.dentry; | |
259 | struct vfsmount *mnt = file->f_path.mnt; | |
260 | struct inode *inode = dentry->d_inode; | |
261 | ||
262 | might_sleep(); | |
263 | ||
264 | fsnotify_close(file); | |
265 | /* | |
266 | * The function eventpoll_release() should be the first called | |
267 | * in the file cleanup chain. | |
268 | */ | |
269 | eventpoll_release(file); | |
270 | locks_remove_flock(file); | |
271 | ||
272 | if (file->f_op && file->f_op->release) | |
273 | file->f_op->release(inode, file); | |
274 | security_file_free(file); | |
275 | if (unlikely(S_ISCHR(inode->i_mode) && inode->i_cdev != NULL)) | |
276 | cdev_put(inode->i_cdev); | |
277 | fops_put(file->f_op); | |
278 | put_pid(file->f_owner.pid); | |
279 | file_kill(file); | |
280 | if (file->f_mode & FMODE_WRITE) | |
281 | drop_file_write_access(file); | |
282 | file->f_path.dentry = NULL; | |
283 | file->f_path.mnt = NULL; | |
284 | file_free(file); | |
285 | dput(dentry); | |
286 | mntput(mnt); | |
287 | } | |
288 | ||
289 | struct file *fget(unsigned int fd) | |
290 | { | |
291 | struct file *file; | |
292 | struct files_struct *files = current->files; | |
293 | ||
294 | rcu_read_lock(); | |
295 | file = fcheck_files(files, fd); | |
296 | if (file) { | |
297 | if (!atomic_long_inc_not_zero(&file->f_count)) { | |
298 | /* File object ref couldn't be taken */ | |
299 | rcu_read_unlock(); | |
300 | return NULL; | |
301 | } | |
302 | } | |
303 | rcu_read_unlock(); | |
304 | ||
305 | return file; | |
306 | } | |
307 | ||
308 | EXPORT_SYMBOL(fget); | |
309 | ||
310 | /* | |
311 | * Lightweight file lookup - no refcnt increment if fd table isn't shared. | |
312 | * You can use this only if it is guranteed that the current task already | |
313 | * holds a refcnt to that file. That check has to be done at fget() only | |
314 | * and a flag is returned to be passed to the corresponding fput_light(). | |
315 | * There must not be a cloning between an fget_light/fput_light pair. | |
316 | */ | |
317 | struct file *fget_light(unsigned int fd, int *fput_needed) | |
318 | { | |
319 | struct file *file; | |
320 | struct files_struct *files = current->files; | |
321 | ||
322 | *fput_needed = 0; | |
323 | if (likely((atomic_read(&files->count) == 1))) { | |
324 | file = fcheck_files(files, fd); | |
325 | } else { | |
326 | rcu_read_lock(); | |
327 | file = fcheck_files(files, fd); | |
328 | if (file) { | |
329 | if (atomic_long_inc_not_zero(&file->f_count)) | |
330 | *fput_needed = 1; | |
331 | else | |
332 | /* Didn't get the reference, someone's freed */ | |
333 | file = NULL; | |
334 | } | |
335 | rcu_read_unlock(); | |
336 | } | |
337 | ||
338 | return file; | |
339 | } | |
340 | ||
341 | ||
342 | void put_filp(struct file *file) | |
343 | { | |
344 | if (atomic_long_dec_and_test(&file->f_count)) { | |
345 | security_file_free(file); | |
346 | file_kill(file); | |
347 | file_free(file); | |
348 | } | |
349 | } | |
350 | ||
351 | void file_move(struct file *file, struct list_head *list) | |
352 | { | |
353 | if (!list) | |
354 | return; | |
355 | file_list_lock(); | |
356 | list_move(&file->f_u.fu_list, list); | |
357 | file_list_unlock(); | |
358 | } | |
359 | ||
360 | void file_kill(struct file *file) | |
361 | { | |
362 | if (!list_empty(&file->f_u.fu_list)) { | |
363 | file_list_lock(); | |
364 | list_del_init(&file->f_u.fu_list); | |
365 | file_list_unlock(); | |
366 | } | |
367 | } | |
368 | ||
369 | int fs_may_remount_ro(struct super_block *sb) | |
370 | { | |
371 | struct file *file; | |
372 | ||
373 | /* Check that no files are currently opened for writing. */ | |
374 | file_list_lock(); | |
375 | list_for_each_entry(file, &sb->s_files, f_u.fu_list) { | |
376 | struct inode *inode = file->f_path.dentry->d_inode; | |
377 | ||
378 | /* File with pending delete? */ | |
379 | if (inode->i_nlink == 0) | |
380 | goto too_bad; | |
381 | ||
382 | /* Writeable file? */ | |
383 | if (S_ISREG(inode->i_mode) && (file->f_mode & FMODE_WRITE)) | |
384 | goto too_bad; | |
385 | } | |
386 | file_list_unlock(); | |
387 | return 1; /* Tis' cool bro. */ | |
388 | too_bad: | |
389 | file_list_unlock(); | |
390 | return 0; | |
391 | } | |
392 | ||
393 | void __init files_init(unsigned long mempages) | |
394 | { | |
395 | int n; | |
396 | /* One file with associated inode and dcache is very roughly 1K. | |
397 | * Per default don't use more than 10% of our memory for files. | |
398 | */ | |
399 | ||
400 | n = (mempages * (PAGE_SIZE / 1024)) / 10; | |
401 | files_stat.max_files = n; | |
402 | if (files_stat.max_files < NR_FILE) | |
403 | files_stat.max_files = NR_FILE; | |
404 | files_defer_init(); | |
405 | percpu_counter_init(&nr_files, 0); | |
406 | } |