Free Electrons

Embedded Linux Experts

  1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
/*
 *  linux/fs/file_table.c
 *
 *  Copyright (C) 1991, 1992  Linus Torvalds
 *  Copyright (C) 1997 David S. Miller (davem@caip.rutgers.edu)
 */

#include <linux/string.h>
#include <linux/slab.h>
#include <linux/file.h>
#include <linux/fdtable.h>
#include <linux/init.h>
#include <linux/module.h>
#include <linux/fs.h>
#include <linux/security.h>
#include <linux/eventpoll.h>
#include <linux/rcupdate.h>
#include <linux/mount.h>
#include <linux/capability.h>
#include <linux/cdev.h>
#include <linux/fsnotify.h>
#include <linux/sysctl.h>
#include <linux/lglock.h>
#include <linux/percpu_counter.h>
#include <linux/percpu.h>
#include <linux/ima.h>

#include <asm/atomic.h>

#include "internal.h"

/* sysctl tunables... */
struct files_stat_struct files_stat = {
	.max_files = NR_FILE
};

DECLARE_LGLOCK(files_lglock);
DEFINE_LGLOCK(files_lglock);

/* SLAB cache for file structures */
static struct kmem_cache *filp_cachep __read_mostly;

static struct percpu_counter nr_files __cacheline_aligned_in_smp;

static inline void file_free_rcu(struct rcu_head *head)
{
	struct file *f = container_of(head, struct file, f_u.fu_rcuhead);

	put_cred(f->f_cred);
	kmem_cache_free(filp_cachep, f);
}

static inline void file_free(struct file *f)
{
	percpu_counter_dec(&nr_files);
	file_check_state(f);
	call_rcu(&f->f_u.fu_rcuhead, file_free_rcu);
}

/*
 * Return the total number of open files in the system
 */
static long get_nr_files(void)
{
	return percpu_counter_read_positive(&nr_files);
}

/*
 * Return the maximum number of open files in the system
 */
unsigned long get_max_files(void)
{
	return files_stat.max_files;
}
EXPORT_SYMBOL_GPL(get_max_files);

/*
 * Handle nr_files sysctl
 */
#if defined(CONFIG_SYSCTL) && defined(CONFIG_PROC_FS)
int proc_nr_files(ctl_table *table, int write,
                     void __user *buffer, size_t *lenp, loff_t *ppos)
{
	files_stat.nr_files = get_nr_files();
	return proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
}
#else
int proc_nr_files(ctl_table *table, int write,
                     void __user *buffer, size_t *lenp, loff_t *ppos)
{
	return -ENOSYS;
}
#endif

/* Find an unused file structure and return a pointer to it.
 * Returns NULL, if there are no more free file structures or
 * we run out of memory.
 *
 * Be very careful using this.  You are responsible for
 * getting write access to any mount that you might assign
 * to this filp, if it is opened for write.  If this is not
 * done, you will imbalance int the mount's writer count
 * and a warning at __fput() time.
 */
struct file *get_empty_filp(void)
{
	const struct cred *cred = current_cred();
	static long old_max;
	struct file * f;

	/*
	 * Privileged users can go above max_files
	 */
	if (get_nr_files() >= files_stat.max_files && !capable(CAP_SYS_ADMIN)) {
		/*
		 * percpu_counters are inaccurate.  Do an expensive check before
		 * we go and fail.
		 */
		if (percpu_counter_sum_positive(&nr_files) >= files_stat.max_files)
			goto over;
	}

	f = kmem_cache_zalloc(filp_cachep, GFP_KERNEL);
	if (f == NULL)
		goto fail;

	percpu_counter_inc(&nr_files);
	if (security_file_alloc(f))
		goto fail_sec;

	INIT_LIST_HEAD(&f->f_u.fu_list);
	atomic_long_set(&f->f_count, 1);
	rwlock_init(&f->f_owner.lock);
	f->f_cred = get_cred(cred);
	spin_lock_init(&f->f_lock);
	eventpoll_init_file(f);
	/* f->f_version: 0 */
	return f;

over:
	/* Ran out of filps - report that */
	if (get_nr_files() > old_max) {
		pr_info("VFS: file-max limit %lu reached\n", get_max_files());
		old_max = get_nr_files();
	}
	goto fail;

fail_sec:
	file_free(f);
fail:
	return NULL;
}

/**
 * alloc_file - allocate and initialize a 'struct file'
 * @mnt: the vfsmount on which the file will reside
 * @dentry: the dentry representing the new file
 * @mode: the mode with which the new file will be opened
 * @fop: the 'struct file_operations' for the new file
 *
 * Use this instead of get_empty_filp() to get a new
 * 'struct file'.  Do so because of the same initialization
 * pitfalls reasons listed for init_file().  This is a
 * preferred interface to using init_file().
 *
 * If all the callers of init_file() are eliminated, its
 * code should be moved into this function.
 */
struct file *alloc_file(struct path *path, fmode_t mode,
		const struct file_operations *fop)
{
	struct file *file;

	file = get_empty_filp();
	if (!file)
		return NULL;

	file->f_path = *path;
	file->f_mapping = path->dentry->d_inode->i_mapping;
	file->f_mode = mode;
	file->f_op = fop;

	/*
	 * These mounts don't really matter in practice
	 * for r/o bind mounts.  They aren't userspace-
	 * visible.  We do this for consistency, and so
	 * that we can do debugging checks at __fput()
	 */
	if ((mode & FMODE_WRITE) && !special_file(path->dentry->d_inode->i_mode)) {
		file_take_write(file);
		WARN_ON(mnt_clone_write(path->mnt));
	}
	ima_counts_get(file);
	return file;
}
EXPORT_SYMBOL(alloc_file);

/**
 * drop_file_write_access - give up ability to write to a file
 * @file: the file to which we will stop writing
 *
 * This is a central place which will give up the ability
 * to write to @file, along with access to write through
 * its vfsmount.
 */
void drop_file_write_access(struct file *file)
{
	struct vfsmount *mnt = file->f_path.mnt;
	struct dentry *dentry = file->f_path.dentry;
	struct inode *inode = dentry->d_inode;

	put_write_access(inode);

	if (special_file(inode->i_mode))
		return;
	if (file_check_writeable(file) != 0)
		return;
	mnt_drop_write(mnt);
	file_release_write(file);
}
EXPORT_SYMBOL_GPL(drop_file_write_access);

/* the real guts of fput() - releasing the last reference to file
 */
static void __fput(struct file *file)
{
	struct dentry *dentry = file->f_path.dentry;
	struct vfsmount *mnt = file->f_path.mnt;
	struct inode *inode = dentry->d_inode;

	might_sleep();

	fsnotify_close(file);
	/*
	 * The function eventpoll_release() should be the first called
	 * in the file cleanup chain.
	 */
	eventpoll_release(file);
	locks_remove_flock(file);

	if (unlikely(file->f_flags & FASYNC)) {
		if (file->f_op && file->f_op->fasync)
			file->f_op->fasync(-1, file, 0);
	}
	if (file->f_op && file->f_op->release)
		file->f_op->release(inode, file);
	security_file_free(file);
	ima_file_free(file);
	if (unlikely(S_ISCHR(inode->i_mode) && inode->i_cdev != NULL))
		cdev_put(inode->i_cdev);
	fops_put(file->f_op);
	put_pid(file->f_owner.pid);
	file_sb_list_del(file);
	if (file->f_mode & FMODE_WRITE)
		drop_file_write_access(file);
	file->f_path.dentry = NULL;
	file->f_path.mnt = NULL;
	file_free(file);
	dput(dentry);
	mntput(mnt);
}

void fput(struct file *file)
{
	if (atomic_long_dec_and_test(&file->f_count))
		__fput(file);
}

EXPORT_SYMBOL(fput);

struct file *fget(unsigned int fd)
{
	struct file *file;
	struct files_struct *files = current->files;

	rcu_read_lock();
	file = fcheck_files(files, fd);
	if (file) {
		if (!atomic_long_inc_not_zero(&file->f_count)) {
			/* File object ref couldn't be taken */
			rcu_read_unlock();
			return NULL;
		}
	}
	rcu_read_unlock();

	return file;
}

EXPORT_SYMBOL(fget);

/*
 * Lightweight file lookup - no refcnt increment if fd table isn't shared.
 *
 * You can use this instead of fget if you satisfy all of the following
 * conditions:
 * 1) You must call fput_light before exiting the syscall and returning control
 *    to userspace (i.e. you cannot remember the returned struct file * after
 *    returning to userspace).
 * 2) You must not call filp_close on the returned struct file * in between
 *    calls to fget_light and fput_light.
 * 3) You must not clone the current task in between the calls to fget_light
 *    and fput_light.
 *
 * The fput_needed flag returned by fget_light should be passed to the
 * corresponding fput_light.
 */
struct file *fget_light(unsigned int fd, int *fput_needed)
{
	struct file *file;
	struct files_struct *files = current->files;

	*fput_needed = 0;
	if (likely((atomic_read(&files->count) == 1))) {
		file = fcheck_files(files, fd);
	} else {
		rcu_read_lock();
		file = fcheck_files(files, fd);
		if (file) {
			if (atomic_long_inc_not_zero(&file->f_count))
				*fput_needed = 1;
			else
				/* Didn't get the reference, someone's freed */
				file = NULL;
		}
		rcu_read_unlock();
	}

	return file;
}

void put_filp(struct file *file)
{
	if (atomic_long_dec_and_test(&file->f_count)) {
		security_file_free(file);
		file_sb_list_del(file);
		file_free(file);
	}
}

static inline int file_list_cpu(struct file *file)
{
#ifdef CONFIG_SMP
	return file->f_sb_list_cpu;
#else
	return smp_processor_id();
#endif
}

/* helper for file_sb_list_add to reduce ifdefs */
static inline void __file_sb_list_add(struct file *file, struct super_block *sb)
{
	struct list_head *list;
#ifdef CONFIG_SMP
	int cpu;
	cpu = smp_processor_id();
	file->f_sb_list_cpu = cpu;
	list = per_cpu_ptr(sb->s_files, cpu);
#else
	list = &sb->s_files;
#endif
	list_add(&file->f_u.fu_list, list);
}

/**
 * file_sb_list_add - add a file to the sb's file list
 * @file: file to add
 * @sb: sb to add it to
 *
 * Use this function to associate a file with the superblock of the inode it
 * refers to.
 */
void file_sb_list_add(struct file *file, struct super_block *sb)
{
	lg_local_lock(files_lglock);
	__file_sb_list_add(file, sb);
	lg_local_unlock(files_lglock);
}

/**
 * file_sb_list_del - remove a file from the sb's file list
 * @file: file to remove
 * @sb: sb to remove it from
 *
 * Use this function to remove a file from its superblock.
 */
void file_sb_list_del(struct file *file)
{
	if (!list_empty(&file->f_u.fu_list)) {
		lg_local_lock_cpu(files_lglock, file_list_cpu(file));
		list_del_init(&file->f_u.fu_list);
		lg_local_unlock_cpu(files_lglock, file_list_cpu(file));
	}
}

#ifdef CONFIG_SMP

/*
 * These macros iterate all files on all CPUs for a given superblock.
 * files_lglock must be held globally.
 */
#define do_file_list_for_each_entry(__sb, __file)		\
{								\
	int i;							\
	for_each_possible_cpu(i) {				\
		struct list_head *list;				\
		list = per_cpu_ptr((__sb)->s_files, i);		\
		list_for_each_entry((__file), list, f_u.fu_list)

#define while_file_list_for_each_entry				\
	}							\
}

#else

#define do_file_list_for_each_entry(__sb, __file)		\
{								\
	struct list_head *list;					\
	list = &(sb)->s_files;					\
	list_for_each_entry((__file), list, f_u.fu_list)

#define while_file_list_for_each_entry				\
}

#endif

int fs_may_remount_ro(struct super_block *sb)
{
	struct file *file;
	/* Check that no files are currently opened for writing. */
	lg_global_lock(files_lglock);
	do_file_list_for_each_entry(sb, file) {
		struct inode *inode = file->f_path.dentry->d_inode;

		/* File with pending delete? */
		if (inode->i_nlink == 0)
			goto too_bad;

		/* Writeable file? */
		if (S_ISREG(inode->i_mode) && (file->f_mode & FMODE_WRITE))
			goto too_bad;
	} while_file_list_for_each_entry;
	lg_global_unlock(files_lglock);
	return 1; /* Tis' cool bro. */
too_bad:
	lg_global_unlock(files_lglock);
	return 0;
}

/**
 *	mark_files_ro - mark all files read-only
 *	@sb: superblock in question
 *
 *	All files are marked read-only.  We don't care about pending
 *	delete files so this should be used in 'force' mode only.
 */
void mark_files_ro(struct super_block *sb)
{
	struct file *f;

retry:
	lg_global_lock(files_lglock);
	do_file_list_for_each_entry(sb, f) {
		struct vfsmount *mnt;
		if (!S_ISREG(f->f_path.dentry->d_inode->i_mode))
		       continue;
		if (!file_count(f))
			continue;
		if (!(f->f_mode & FMODE_WRITE))
			continue;
		spin_lock(&f->f_lock);
		f->f_mode &= ~FMODE_WRITE;
		spin_unlock(&f->f_lock);
		if (file_check_writeable(f) != 0)
			continue;
		file_release_write(f);
		mnt = mntget(f->f_path.mnt);
		/* This can sleep, so we can't hold the spinlock. */
		lg_global_unlock(files_lglock);
		mnt_drop_write(mnt);
		mntput(mnt);
		goto retry;
	} while_file_list_for_each_entry;
	lg_global_unlock(files_lglock);
}

void __init files_init(unsigned long mempages)
{ 
	unsigned long n;

	filp_cachep = kmem_cache_create("filp", sizeof(struct file), 0,
			SLAB_HWCACHE_ALIGN | SLAB_PANIC, NULL);

	/*
	 * One file with associated inode and dcache is very roughly 1K.
	 * Per default don't use more than 10% of our memory for files. 
	 */ 

	n = (mempages * (PAGE_SIZE / 1024)) / 10;
	files_stat.max_files = max_t(unsigned long, n, NR_FILE);
	files_defer_init();
	lg_lock_init(files_lglock);
	percpu_counter_init(&nr_files, 0);
}