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TOMOYO Linux Cross Reference
Linux/fs/file_table.c

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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/lglock.h>
 24 #include <linux/percpu_counter.h>
 25 #include <linux/percpu.h>
 26 #include <linux/ima.h>
 27 
 28 #include <linux/atomic.h>
 29 
 30 #include "internal.h"
 31 
 32 /* sysctl tunables... */
 33 struct files_stat_struct files_stat = {
 34         .max_files = NR_FILE
 35 };
 36 
 37 DEFINE_LGLOCK(files_lglock);
 38 
 39 /* SLAB cache for file structures */
 40 static struct kmem_cache *filp_cachep __read_mostly;
 41 
 42 static struct percpu_counter nr_files __cacheline_aligned_in_smp;
 43 
 44 static inline void file_free_rcu(struct rcu_head *head)
 45 {
 46         struct file *f = container_of(head, struct file, f_u.fu_rcuhead);
 47 
 48         put_cred(f->f_cred);
 49         kmem_cache_free(filp_cachep, f);
 50 }
 51 
 52 static inline void file_free(struct file *f)
 53 {
 54         percpu_counter_dec(&nr_files);
 55         file_check_state(f);
 56         call_rcu(&f->f_u.fu_rcuhead, file_free_rcu);
 57 }
 58 
 59 /*
 60  * Return the total number of open files in the system
 61  */
 62 static long get_nr_files(void)
 63 {
 64         return percpu_counter_read_positive(&nr_files);
 65 }
 66 
 67 /*
 68  * Return the maximum number of open files in the system
 69  */
 70 unsigned long get_max_files(void)
 71 {
 72         return files_stat.max_files;
 73 }
 74 EXPORT_SYMBOL_GPL(get_max_files);
 75 
 76 /*
 77  * Handle nr_files sysctl
 78  */
 79 #if defined(CONFIG_SYSCTL) && defined(CONFIG_PROC_FS)
 80 int proc_nr_files(ctl_table *table, int write,
 81                      void __user *buffer, size_t *lenp, loff_t *ppos)
 82 {
 83         files_stat.nr_files = get_nr_files();
 84         return proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
 85 }
 86 #else
 87 int proc_nr_files(ctl_table *table, int write,
 88                      void __user *buffer, size_t *lenp, loff_t *ppos)
 89 {
 90         return -ENOSYS;
 91 }
 92 #endif
 93 
 94 /* Find an unused file structure and return a pointer to it.
 95  * Returns NULL, if there are no more free file structures or
 96  * we run out of memory.
 97  *
 98  * Be very careful using this.  You are responsible for
 99  * getting write access to any mount that you might assign
100  * to this filp, if it is opened for write.  If this is not
101  * done, you will imbalance int the mount's writer count
102  * and a warning at __fput() time.
103  */
104 struct file *get_empty_filp(void)
105 {
106         const struct cred *cred = current_cred();
107         static long old_max;
108         struct file * f;
109 
110         /*
111          * Privileged users can go above max_files
112          */
113         if (get_nr_files() >= files_stat.max_files && !capable(CAP_SYS_ADMIN)) {
114                 /*
115                  * percpu_counters are inaccurate.  Do an expensive check before
116                  * we go and fail.
117                  */
118                 if (percpu_counter_sum_positive(&nr_files) >= files_stat.max_files)
119                         goto over;
120         }
121 
122         f = kmem_cache_zalloc(filp_cachep, GFP_KERNEL);
123         if (f == NULL)
124                 goto fail;
125 
126         percpu_counter_inc(&nr_files);
127         f->f_cred = get_cred(cred);
128         if (security_file_alloc(f))
129                 goto fail_sec;
130 
131         INIT_LIST_HEAD(&f->f_u.fu_list);
132         atomic_long_set(&f->f_count, 1);
133         rwlock_init(&f->f_owner.lock);
134         spin_lock_init(&f->f_lock);
135         eventpoll_init_file(f);
136         /* f->f_version: 0 */
137         return f;
138 
139 over:
140         /* Ran out of filps - report that */
141         if (get_nr_files() > old_max) {
142                 pr_info("VFS: file-max limit %lu reached\n", get_max_files());
143                 old_max = get_nr_files();
144         }
145         goto fail;
146 
147 fail_sec:
148         file_free(f);
149 fail:
150         return NULL;
151 }
152 
153 /**
154  * alloc_file - allocate and initialize a 'struct file'
155  * @mnt: the vfsmount on which the file will reside
156  * @dentry: the dentry representing the new file
157  * @mode: the mode with which the new file will be opened
158  * @fop: the 'struct file_operations' for the new file
159  *
160  * Use this instead of get_empty_filp() to get a new
161  * 'struct file'.  Do so because of the same initialization
162  * pitfalls reasons listed for init_file().  This is a
163  * preferred interface to using init_file().
164  *
165  * If all the callers of init_file() are eliminated, its
166  * code should be moved into this function.
167  */
168 struct file *alloc_file(struct path *path, fmode_t mode,
169                 const struct file_operations *fop)
170 {
171         struct file *file;
172 
173         file = get_empty_filp();
174         if (!file)
175                 return NULL;
176 
177         file->f_path = *path;
178         file->f_mapping = path->dentry->d_inode->i_mapping;
179         file->f_mode = mode;
180         file->f_op = fop;
181 
182         /*
183          * These mounts don't really matter in practice
184          * for r/o bind mounts.  They aren't userspace-
185          * visible.  We do this for consistency, and so
186          * that we can do debugging checks at __fput()
187          */
188         if ((mode & FMODE_WRITE) && !special_file(path->dentry->d_inode->i_mode)) {
189                 file_take_write(file);
190                 WARN_ON(mnt_clone_write(path->mnt));
191         }
192         if ((mode & (FMODE_READ | FMODE_WRITE)) == FMODE_READ)
193                 i_readcount_inc(path->dentry->d_inode);
194         return file;
195 }
196 EXPORT_SYMBOL(alloc_file);
197 
198 /**
199  * drop_file_write_access - give up ability to write to a file
200  * @file: the file to which we will stop writing
201  *
202  * This is a central place which will give up the ability
203  * to write to @file, along with access to write through
204  * its vfsmount.
205  */
206 static void drop_file_write_access(struct file *file)
207 {
208         struct vfsmount *mnt = file->f_path.mnt;
209         struct dentry *dentry = file->f_path.dentry;
210         struct inode *inode = dentry->d_inode;
211 
212         put_write_access(inode);
213 
214         if (special_file(inode->i_mode))
215                 return;
216         if (file_check_writeable(file) != 0)
217                 return;
218         mnt_drop_write(mnt);
219         file_release_write(file);
220 }
221 
222 /* the real guts of fput() - releasing the last reference to file
223  */
224 static void __fput(struct file *file)
225 {
226         struct dentry *dentry = file->f_path.dentry;
227         struct vfsmount *mnt = file->f_path.mnt;
228         struct inode *inode = dentry->d_inode;
229 
230         might_sleep();
231 
232         fsnotify_close(file);
233         /*
234          * The function eventpoll_release() should be the first called
235          * in the file cleanup chain.
236          */
237         eventpoll_release(file);
238         locks_remove_flock(file);
239 
240         if (unlikely(file->f_flags & FASYNC)) {
241                 if (file->f_op && file->f_op->fasync)
242                         file->f_op->fasync(-1, file, 0);
243         }
244         if (file->f_op && file->f_op->release)
245                 file->f_op->release(inode, file);
246         security_file_free(file);
247         ima_file_free(file);
248         if (unlikely(S_ISCHR(inode->i_mode) && inode->i_cdev != NULL &&
249                      !(file->f_mode & FMODE_PATH))) {
250                 cdev_put(inode->i_cdev);
251         }
252         fops_put(file->f_op);
253         put_pid(file->f_owner.pid);
254         file_sb_list_del(file);
255         if ((file->f_mode & (FMODE_READ | FMODE_WRITE)) == FMODE_READ)
256                 i_readcount_dec(inode);
257         if (file->f_mode & FMODE_WRITE)
258                 drop_file_write_access(file);
259         file->f_path.dentry = NULL;
260         file->f_path.mnt = NULL;
261         file_free(file);
262         dput(dentry);
263         mntput(mnt);
264 }
265 
266 void fput(struct file *file)
267 {
268         if (atomic_long_dec_and_test(&file->f_count))
269                 __fput(file);
270 }
271 
272 EXPORT_SYMBOL(fput);
273 
274 struct file *fget(unsigned int fd)
275 {
276         struct file *file;
277         struct files_struct *files = current->files;
278 
279         rcu_read_lock();
280         file = fcheck_files(files, fd);
281         if (file) {
282                 /* File object ref couldn't be taken */
283                 if (file->f_mode & FMODE_PATH ||
284                     !atomic_long_inc_not_zero(&file->f_count))
285                         file = NULL;
286         }
287         rcu_read_unlock();
288 
289         return file;
290 }
291 
292 EXPORT_SYMBOL(fget);
293 
294 struct file *fget_raw(unsigned int fd)
295 {
296         struct file *file;
297         struct files_struct *files = current->files;
298 
299         rcu_read_lock();
300         file = fcheck_files(files, fd);
301         if (file) {
302                 /* File object ref couldn't be taken */
303                 if (!atomic_long_inc_not_zero(&file->f_count))
304                         file = NULL;
305         }
306         rcu_read_unlock();
307 
308         return file;
309 }
310 
311 EXPORT_SYMBOL(fget_raw);
312 
313 /*
314  * Lightweight file lookup - no refcnt increment if fd table isn't shared.
315  *
316  * You can use this instead of fget if you satisfy all of the following
317  * conditions:
318  * 1) You must call fput_light before exiting the syscall and returning control
319  *    to userspace (i.e. you cannot remember the returned struct file * after
320  *    returning to userspace).
321  * 2) You must not call filp_close on the returned struct file * in between
322  *    calls to fget_light and fput_light.
323  * 3) You must not clone the current task in between the calls to fget_light
324  *    and fput_light.
325  *
326  * The fput_needed flag returned by fget_light should be passed to the
327  * corresponding fput_light.
328  */
329 struct file *fget_light(unsigned int fd, int *fput_needed)
330 {
331         struct file *file;
332         struct files_struct *files = current->files;
333 
334         *fput_needed = 0;
335         if (atomic_read(&files->count) == 1) {
336                 file = fcheck_files(files, fd);
337                 if (file && (file->f_mode & FMODE_PATH))
338                         file = NULL;
339         } else {
340                 rcu_read_lock();
341                 file = fcheck_files(files, fd);
342                 if (file) {
343                         if (!(file->f_mode & FMODE_PATH) &&
344                             atomic_long_inc_not_zero(&file->f_count))
345                                 *fput_needed = 1;
346                         else
347                                 /* Didn't get the reference, someone's freed */
348                                 file = NULL;
349                 }
350                 rcu_read_unlock();
351         }
352 
353         return file;
354 }
355 
356 struct file *fget_raw_light(unsigned int fd, int *fput_needed)
357 {
358         struct file *file;
359         struct files_struct *files = current->files;
360 
361         *fput_needed = 0;
362         if (atomic_read(&files->count) == 1) {
363                 file = fcheck_files(files, fd);
364         } else {
365                 rcu_read_lock();
366                 file = fcheck_files(files, fd);
367                 if (file) {
368                         if (atomic_long_inc_not_zero(&file->f_count))
369                                 *fput_needed = 1;
370                         else
371                                 /* Didn't get the reference, someone's freed */
372                                 file = NULL;
373                 }
374                 rcu_read_unlock();
375         }
376 
377         return file;
378 }
379 
380 void put_filp(struct file *file)
381 {
382         if (atomic_long_dec_and_test(&file->f_count)) {
383                 security_file_free(file);
384                 file_sb_list_del(file);
385                 file_free(file);
386         }
387 }
388 
389 static inline int file_list_cpu(struct file *file)
390 {
391 #ifdef CONFIG_SMP
392         return file->f_sb_list_cpu;
393 #else
394         return smp_processor_id();
395 #endif
396 }
397 
398 /* helper for file_sb_list_add to reduce ifdefs */
399 static inline void __file_sb_list_add(struct file *file, struct super_block *sb)
400 {
401         struct list_head *list;
402 #ifdef CONFIG_SMP
403         int cpu;
404         cpu = smp_processor_id();
405         file->f_sb_list_cpu = cpu;
406         list = per_cpu_ptr(sb->s_files, cpu);
407 #else
408         list = &sb->s_files;
409 #endif
410         list_add(&file->f_u.fu_list, list);
411 }
412 
413 /**
414  * file_sb_list_add - add a file to the sb's file list
415  * @file: file to add
416  * @sb: sb to add it to
417  *
418  * Use this function to associate a file with the superblock of the inode it
419  * refers to.
420  */
421 void file_sb_list_add(struct file *file, struct super_block *sb)
422 {
423         lg_local_lock(&files_lglock);
424         __file_sb_list_add(file, sb);
425         lg_local_unlock(&files_lglock);
426 }
427 
428 /**
429  * file_sb_list_del - remove a file from the sb's file list
430  * @file: file to remove
431  * @sb: sb to remove it from
432  *
433  * Use this function to remove a file from its superblock.
434  */
435 void file_sb_list_del(struct file *file)
436 {
437         if (!list_empty(&file->f_u.fu_list)) {
438                 lg_local_lock_cpu(&files_lglock, file_list_cpu(file));
439                 list_del_init(&file->f_u.fu_list);
440                 lg_local_unlock_cpu(&files_lglock, file_list_cpu(file));
441         }
442 }
443 
444 #ifdef CONFIG_SMP
445 
446 /*
447  * These macros iterate all files on all CPUs for a given superblock.
448  * files_lglock must be held globally.
449  */
450 #define do_file_list_for_each_entry(__sb, __file)               \
451 {                                                               \
452         int i;                                                  \
453         for_each_possible_cpu(i) {                              \
454                 struct list_head *list;                         \
455                 list = per_cpu_ptr((__sb)->s_files, i);         \
456                 list_for_each_entry((__file), list, f_u.fu_list)
457 
458 #define while_file_list_for_each_entry                          \
459         }                                                       \
460 }
461 
462 #else
463 
464 #define do_file_list_for_each_entry(__sb, __file)               \
465 {                                                               \
466         struct list_head *list;                                 \
467         list = &(sb)->s_files;                                  \
468         list_for_each_entry((__file), list, f_u.fu_list)
469 
470 #define while_file_list_for_each_entry                          \
471 }
472 
473 #endif
474 
475 /**
476  *      mark_files_ro - mark all files read-only
477  *      @sb: superblock in question
478  *
479  *      All files are marked read-only.  We don't care about pending
480  *      delete files so this should be used in 'force' mode only.
481  */
482 void mark_files_ro(struct super_block *sb)
483 {
484         struct file *f;
485 
486 retry:
487         lg_global_lock(&files_lglock);
488         do_file_list_for_each_entry(sb, f) {
489                 struct vfsmount *mnt;
490                 if (!S_ISREG(f->f_path.dentry->d_inode->i_mode))
491                        continue;
492                 if (!file_count(f))
493                         continue;
494                 if (!(f->f_mode & FMODE_WRITE))
495                         continue;
496                 spin_lock(&f->f_lock);
497                 f->f_mode &= ~FMODE_WRITE;
498                 spin_unlock(&f->f_lock);
499                 if (file_check_writeable(f) != 0)
500                         continue;
501                 file_release_write(f);
502                 mnt = mntget(f->f_path.mnt);
503                 /* This can sleep, so we can't hold the spinlock. */
504                 lg_global_unlock(&files_lglock);
505                 mnt_drop_write(mnt);
506                 mntput(mnt);
507                 goto retry;
508         } while_file_list_for_each_entry;
509         lg_global_unlock(&files_lglock);
510 }
511 
512 void __init files_init(unsigned long mempages)
513 { 
514         unsigned long n;
515 
516         filp_cachep = kmem_cache_create("filp", sizeof(struct file), 0,
517                         SLAB_HWCACHE_ALIGN | SLAB_PANIC, NULL);
518 
519         /*
520          * One file with associated inode and dcache is very roughly 1K.
521          * Per default don't use more than 10% of our memory for files. 
522          */ 
523 
524         n = (mempages * (PAGE_SIZE / 1024)) / 10;
525         files_stat.max_files = max_t(unsigned long, n, NR_FILE);
526         files_defer_init();
527         lg_lock_init(&files_lglock, "files_lglock");
528         percpu_counter_init(&nr_files, 0);
529 } 
530 

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