[mirror_ubuntu-artful-kernel.git] / fs / file_table.c

/*
 *  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/percpu_counter.h>

#include <asm/atomic.h>

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

/* public. Not pretty! */
__cacheline_aligned_in_smp DEFINE_SPINLOCK(files_lock);

/* 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 int get_nr_files(void)
{
	return percpu_counter_read_positive(&nr_files);
}

/*
 * Return the maximum number of open files in the system
 */
int 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_dointvec(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 int 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) {
		printk(KERN_INFO "VFS: file-max limit %d 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)) {
		int error = 0;
		file_take_write(file);
		error = mnt_clone_write(path->mnt);
		WARN_ON(error);
	}
	return file;
}

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

EXPORT_SYMBOL(fput);

/**
 * 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);

/* __fput is called from task context when aio completion releases the last
 * last use of a struct file *.  Do not use otherwise.
 */
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);
	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_kill(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);
}

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 only if it is guranteed that the current task already 
 * holds a refcnt to that file. That check has to be done at fget() only
 * and a flag is returned to be passed to the corresponding fput_light().
 * There must not be a cloning between an fget_light/fput_light pair.
 */
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_kill(file);
		file_free(file);
	}
}

void file_move(struct file *file, struct list_head *list)
{
	if (!list)
		return;
	file_list_lock();
	list_move(&file->f_u.fu_list, list);
	file_list_unlock();
}

void file_kill(struct file *file)
{
	if (!list_empty(&file->f_u.fu_list)) {
		file_list_lock();
		list_del_init(&file->f_u.fu_list);
		file_list_unlock();
	}
}

int fs_may_remount_ro(struct super_block *sb)
{
	struct file *file;

	/* Check that no files are currently opened for writing. */
	file_list_lock();
	list_for_each_entry(file, &sb->s_files, f_u.fu_list) {
		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;
	}
	file_list_unlock();
	return 1; /* Tis' cool bro. */
too_bad:
	file_list_unlock();
	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:
	file_list_lock();
	list_for_each_entry(f, &sb->s_files, f_u.fu_list) {
		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;
		f->f_mode &= ~FMODE_WRITE;
		if (file_check_writeable(f) != 0)
			continue;
		file_release_write(f);
		mnt = mntget(f->f_path.mnt);
		file_list_unlock();
		/*
		 * This can sleep, so we can't hold
		 * the file_list_lock() spinlock.
		 */
		mnt_drop_write(mnt);
		mntput(mnt);
		goto retry;
	}
	file_list_unlock();
}

void __init files_init(unsigned long mempages)
{ 
	int 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 = n; 
	if (files_stat.max_files < NR_FILE)
		files_stat.max_files = NR_FILE;
	files_defer_init();
	percpu_counter_init(&nr_files, 0);
}
Commit	Line	Data
	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	/* SLAB cache for file structures */
	36	static struct kmem_cache *filp_cachep __read_mostly;
	37
	38	static struct percpu_counter nr_files __cacheline_aligned_in_smp;
	39
	40	static inline void file_free_rcu(struct rcu_head *head)
	41	{
	42	struct file *f = container_of(head, struct file, f_u.fu_rcuhead);
	43
	44	put_cred(f->f_cred);
	45	kmem_cache_free(filp_cachep, f);
	46	}
	47
	48	static inline void file_free(struct file *f)
	49	{
	50	percpu_counter_dec(&nr_files);
	51	file_check_state(f);
	52	call_rcu(&f->f_u.fu_rcuhead, file_free_rcu);
	53	}
	54
	55	/*
	56	* Return the total number of open files in the system
	57	*/
	58	static int get_nr_files(void)
	59	{
	60	return percpu_counter_read_positive(&nr_files);
	61	}
	62
	63	/*
	64	* Return the maximum number of open files in the system
	65	*/
	66	int get_max_files(void)
	67	{
	68	return files_stat.max_files;
	69	}
	70	EXPORT_SYMBOL_GPL(get_max_files);
	71
	72	/*
	73	* Handle nr_files sysctl
	74	*/
	75	#if defined(CONFIG_SYSCTL) && defined(CONFIG_PROC_FS)
	76	int proc_nr_files(ctl_table *table, int write,
	77	void __user buffer, size_t lenp, loff_t *ppos)
	78	{
	79	files_stat.nr_files = get_nr_files();
	80	return proc_dointvec(table, write, buffer, lenp, ppos);
	81	}
	82	#else
	83	int proc_nr_files(ctl_table *table, int write,
	84	void __user buffer, size_t lenp, loff_t *ppos)
	85	{
	86	return -ENOSYS;
	87	}
	88	#endif
	89
	90	/* Find an unused file structure and return a pointer to it.
	91	* Returns NULL, if there are no more free file structures or
	92	* we run out of memory.
	93	*
	94	* Be very careful using this. You are responsible for
	95	* getting write access to any mount that you might assign
	96	* to this filp, if it is opened for write. If this is not
	97	* done, you will imbalance int the mount's writer count
	98	* and a warning at __fput() time.
	99	*/
	100	struct file *get_empty_filp(void)
	101	{
	102	const struct cred *cred = current_cred();
	103	static int old_max;
	104	struct file * f;
	105
	106	/*
	107	* Privileged users can go above max_files
	108	*/
	109	if (get_nr_files() >= files_stat.max_files && !capable(CAP_SYS_ADMIN)) {
	110	/*
	111	* percpu_counters are inaccurate. Do an expensive check before
	112	* we go and fail.
	113	*/
	114	if (percpu_counter_sum_positive(&nr_files) >= files_stat.max_files)
	115	goto over;
	116	}
	117
	118	f = kmem_cache_zalloc(filp_cachep, GFP_KERNEL);
	119	if (f == NULL)
	120	goto fail;
	121
	122	percpu_counter_inc(&nr_files);
	123	if (security_file_alloc(f))
	124	goto fail_sec;
	125
	126	INIT_LIST_HEAD(&f->f_u.fu_list);
	127	atomic_long_set(&f->f_count, 1);
	128	rwlock_init(&f->f_owner.lock);
	129	f->f_cred = get_cred(cred);
	130	spin_lock_init(&f->f_lock);
	131	eventpoll_init_file(f);
	132	/* f->f_version: 0 */
	133	return f;
	134
	135	over:
	136	/* Ran out of filps - report that */
	137	if (get_nr_files() > old_max) {
	138	printk(KERN_INFO "VFS: file-max limit %d reached\n",
	139	get_max_files());
	140	old_max = get_nr_files();
	141	}
	142	goto fail;
	143
	144	fail_sec:
	145	file_free(f);
	146	fail:
	147	return NULL;
	148	}
	149
	150	/**
	151	* alloc_file - allocate and initialize a 'struct file'
	152	* @mnt: the vfsmount on which the file will reside
	153	* @dentry: the dentry representing the new file
	154	* @mode: the mode with which the new file will be opened
	155	* @fop: the 'struct file_operations' for the new file
	156	*
	157	* Use this instead of get_empty_filp() to get a new
	158	* 'struct file'. Do so because of the same initialization
	159	* pitfalls reasons listed for init_file(). This is a
	160	* preferred interface to using init_file().
	161	*
	162	* If all the callers of init_file() are eliminated, its
	163	* code should be moved into this function.
	164	*/
	165	struct file alloc_file(struct path path, fmode_t mode,
	166	const struct file_operations *fop)
	167	{
	168	struct file *file;
	169
	170	file = get_empty_filp();
	171	if (!file)
	172	return NULL;
	173
	174	file->f_path = *path;
	175	file->f_mapping = path->dentry->d_inode->i_mapping;
	176	file->f_mode = mode;
	177	file->f_op = fop;
	178
	179	/*
	180	* These mounts don't really matter in practice
	181	* for r/o bind mounts. They aren't userspace-
	182	* visible. We do this for consistency, and so
	183	* that we can do debugging checks at __fput()
	184	*/
	185	if ((mode & FMODE_WRITE) && !special_file(path->dentry->d_inode->i_mode)) {
	186	int error = 0;
	187	file_take_write(file);
	188	error = mnt_clone_write(path->mnt);
	189	WARN_ON(error);
	190	}
	191	return file;
	192	}
	193
	194	void fput(struct file *file)
	195	{
	196	if (atomic_long_dec_and_test(&file->f_count))
	197	__fput(file);
	198	}
	199
	200	EXPORT_SYMBOL(fput);
	201
	202	/**
	203	* drop_file_write_access - give up ability to write to a file
	204	* @file: the file to which we will stop writing
	205	*
	206	* This is a central place which will give up the ability
	207	* to write to @file, along with access to write through
	208	* its vfsmount.
	209	*/
	210	void drop_file_write_access(struct file *file)
	211	{
	212	struct vfsmount *mnt = file->f_path.mnt;
	213	struct dentry *dentry = file->f_path.dentry;
	214	struct inode *inode = dentry->d_inode;
	215
	216	put_write_access(inode);
	217
	218	if (special_file(inode->i_mode))
	219	return;
	220	if (file_check_writeable(file) != 0)
	221	return;
	222	mnt_drop_write(mnt);
	223	file_release_write(file);
	224	}
	225	EXPORT_SYMBOL_GPL(drop_file_write_access);
	226
	227	/* __fput is called from task context when aio completion releases the last
	228	* last use of a struct file *. Do not use otherwise.
	229	*/
	230	void __fput(struct file *file)
	231	{
	232	struct dentry *dentry = file->f_path.dentry;
	233	struct vfsmount *mnt = file->f_path.mnt;
	234	struct inode *inode = dentry->d_inode;
	235
	236	might_sleep();
	237
	238	fsnotify_close(file);
	239	/*
	240	* The function eventpoll_release() should be the first called
	241	* in the file cleanup chain.
	242	*/
	243	eventpoll_release(file);
	244	locks_remove_flock(file);
	245
	246	if (unlikely(file->f_flags & FASYNC)) {
	247	if (file->f_op && file->f_op->fasync)
	248	file->f_op->fasync(-1, file, 0);
	249	}
	250	if (file->f_op && file->f_op->release)
	251	file->f_op->release(inode, file);
	252	security_file_free(file);
	253	if (unlikely(S_ISCHR(inode->i_mode) && inode->i_cdev != NULL))
	254	cdev_put(inode->i_cdev);
	255	fops_put(file->f_op);
	256	put_pid(file->f_owner.pid);
	257	file_kill(file);
	258	if (file->f_mode & FMODE_WRITE)
	259	drop_file_write_access(file);
	260	file->f_path.dentry = NULL;
	261	file->f_path.mnt = NULL;
	262	file_free(file);
	263	dput(dentry);
	264	mntput(mnt);
	265	}
	266
	267	struct file *fget(unsigned int fd)
	268	{
	269	struct file *file;
	270	struct files_struct *files = current->files;
	271
	272	rcu_read_lock();
	273	file = fcheck_files(files, fd);
	274	if (file) {
	275	if (!atomic_long_inc_not_zero(&file->f_count)) {
	276	/* File object ref couldn't be taken */
	277	rcu_read_unlock();
	278	return NULL;
	279	}
	280	}
	281	rcu_read_unlock();
	282
	283	return file;
	284	}
	285
	286	EXPORT_SYMBOL(fget);
	287
	288	/*
	289	* Lightweight file lookup - no refcnt increment if fd table isn't shared.
	290	* You can use this only if it is guranteed that the current task already
	291	* holds a refcnt to that file. That check has to be done at fget() only
	292	* and a flag is returned to be passed to the corresponding fput_light().
	293	* There must not be a cloning between an fget_light/fput_light pair.
	294	*/
	295	struct file fget_light(unsigned int fd, int fput_needed)
	296	{
	297	struct file *file;
	298	struct files_struct *files = current->files;
	299
	300	*fput_needed = 0;
	301	if (likely((atomic_read(&files->count) == 1))) {
	302	file = fcheck_files(files, fd);
	303	} else {
	304	rcu_read_lock();
	305	file = fcheck_files(files, fd);
	306	if (file) {
	307	if (atomic_long_inc_not_zero(&file->f_count))
	308	*fput_needed = 1;
	309	else
	310	/* Didn't get the reference, someone's freed */
	311	file = NULL;
	312	}
	313	rcu_read_unlock();
	314	}
	315
	316	return file;
	317	}
	318
	319
	320	void put_filp(struct file *file)
	321	{
	322	if (atomic_long_dec_and_test(&file->f_count)) {
	323	security_file_free(file);
	324	file_kill(file);
	325	file_free(file);
	326	}
	327	}
	328
	329	void file_move(struct file file, struct list_head list)
	330	{
	331	if (!list)
	332	return;
	333	file_list_lock();
	334	list_move(&file->f_u.fu_list, list);
	335	file_list_unlock();
	336	}
	337
	338	void file_kill(struct file *file)
	339	{
	340	if (!list_empty(&file->f_u.fu_list)) {
	341	file_list_lock();
	342	list_del_init(&file->f_u.fu_list);
	343	file_list_unlock();
	344	}
	345	}
	346
	347	int fs_may_remount_ro(struct super_block *sb)
	348	{
	349	struct file *file;
	350
	351	/* Check that no files are currently opened for writing. */
	352	file_list_lock();
	353	list_for_each_entry(file, &sb->s_files, f_u.fu_list) {
	354	struct inode *inode = file->f_path.dentry->d_inode;
	355
	356	/* File with pending delete? */
	357	if (inode->i_nlink == 0)
	358	goto too_bad;
	359
	360	/* Writeable file? */
	361	if (S_ISREG(inode->i_mode) && (file->f_mode & FMODE_WRITE))
	362	goto too_bad;
	363	}
	364	file_list_unlock();
	365	return 1; /* Tis' cool bro. */
	366	too_bad:
	367	file_list_unlock();
	368	return 0;
	369	}
	370
	371	/**
	372	* mark_files_ro - mark all files read-only
	373	* @sb: superblock in question
	374	*
	375	* All files are marked read-only. We don't care about pending
	376	* delete files so this should be used in 'force' mode only.
	377	*/
	378	void mark_files_ro(struct super_block *sb)
	379	{
	380	struct file *f;
	381
	382	retry:
	383	file_list_lock();
	384	list_for_each_entry(f, &sb->s_files, f_u.fu_list) {
	385	struct vfsmount *mnt;
	386	if (!S_ISREG(f->f_path.dentry->d_inode->i_mode))
	387	continue;
	388	if (!file_count(f))
	389	continue;
	390	if (!(f->f_mode & FMODE_WRITE))
	391	continue;
	392	f->f_mode &= ~FMODE_WRITE;
	393	if (file_check_writeable(f) != 0)
	394	continue;
	395	file_release_write(f);
	396	mnt = mntget(f->f_path.mnt);
	397	file_list_unlock();
	398	/*
	399	* This can sleep, so we can't hold
	400	* the file_list_lock() spinlock.
	401	*/
	402	mnt_drop_write(mnt);
	403	mntput(mnt);
	404	goto retry;
	405	}
	406	file_list_unlock();
	407	}
	408
	409	void __init files_init(unsigned long mempages)
	410	{
	411	int n;
	412
	413	filp_cachep = kmem_cache_create("filp", sizeof(struct file), 0,
	414	SLAB_HWCACHE_ALIGN \| SLAB_PANIC, NULL);
	415
	416	/*
	417	* One file with associated inode and dcache is very roughly 1K.
	418	* Per default don't use more than 10% of our memory for files.
	419	*/
	420
	421	n = (mempages * (PAGE_SIZE / 1024)) / 10;
	422	files_stat.max_files = n;
	423	if (files_stat.max_files < NR_FILE)
	424	files_stat.max_files = NR_FILE;
	425	files_defer_init();
	426	percpu_counter_init(&nr_files, 0);
	427	}