fs/file.c - linux - Git at Google

 /*
  *  linux/fs/file.c
  *
  *  Copyright (C) 1998-1999, Stephen Tweedie and Bill Hawes
  *
  *  Manage the dynamic fd arrays in the process files_struct.
  */

 #include <linux/module.h>
 #include <linux/fs.h>
 #include <linux/mm.h>
 #include <linux/mmzone.h>
 #include <linux/time.h>
 #include <linux/sched.h>
 #include <linux/slab.h>
 #include <linux/vmalloc.h>
 #include <linux/file.h>
 #include <linux/fdtable.h>
 #include <linux/bitops.h>
 #include <linux/interrupt.h>
 #include <linux/spinlock.h>
 #include <linux/rcupdate.h>
 #include <linux/workqueue.h>

 struct fdtable_defer {
 	spinlock_t lock;
 	struct work_struct wq;
 	struct fdtable *next;
 };

 int sysctl_nr_open __read_mostly = 1024*1024;
 int sysctl_nr_open_min = BITS_PER_LONG;
 int sysctl_nr_open_max = 1024 * 1024; /* raised later */

 /*
  * We use this list to defer free fdtables that have vmalloced
  * sets/arrays. By keeping a per-cpu list, we avoid having to embed
  * the work_struct in fdtable itself which avoids a 64 byte (i386) increase in
  * this per-task structure.
  */
 static DEFINE_PER_CPU(struct fdtable_defer, fdtable_defer_list);

 static void *alloc_fdmem(size_t size)
 {
 	/*
 	 * Very large allocations can stress page reclaim, so fall back to
 	 * vmalloc() if the allocation size will be considered "large" by the VM.
 	 */
 	if (size <= (PAGE_SIZE << PAGE_ALLOC_COSTLY_ORDER)) {
 		void *data = kmalloc(size, GFP_KERNEL|__GFP_NOWARN);
 		if (data != NULL)
 			return data;
 	}
 	return vmalloc(size);
 }

 static void free_fdmem(void *ptr)
 {
 	is_vmalloc_addr(ptr) ? vfree(ptr) : kfree(ptr);
 }

 static void __free_fdtable(struct fdtable *fdt)
 {
 	free_fdmem(fdt->fd);
 	free_fdmem(fdt->open_fds);
 	kfree(fdt);
 }

 static void free_fdtable_work(struct work_struct *work)
 {
 	struct fdtable_defer *f =
 		container_of(work, struct fdtable_defer, wq);
 	struct fdtable *fdt;

 	spin_lock_bh(&f->lock);
 	fdt = f->next;
 	f->next = NULL;
 	spin_unlock_bh(&f->lock);
 	while(fdt) {
 		struct fdtable *next = fdt->next;

 		__free_fdtable(fdt);
 		fdt = next;
 	}
 }

 void free_fdtable_rcu(struct rcu_head *rcu)
 {
 	struct fdtable *fdt = container_of(rcu, struct fdtable, rcu);
 	struct fdtable_defer *fddef;

 	BUG_ON(!fdt);

 	if (fdt->max_fds <= NR_OPEN_DEFAULT) {
 		/*
 		 * This fdtable is embedded in the files structure and that
 		 * structure itself is getting destroyed.
 		 */
 		kmem_cache_free(files_cachep,
 				container_of(fdt, struct files_struct, fdtab));
 		return;
 	}
 	if (!is_vmalloc_addr(fdt->fd) && !is_vmalloc_addr(fdt->open_fds)) {
 		kfree(fdt->fd);
 		kfree(fdt->open_fds);
 		kfree(fdt);
 	} else {
 		fddef = &get_cpu_var(fdtable_defer_list);
 		spin_lock(&fddef->lock);
 		fdt->next = fddef->next;
 		fddef->next = fdt;
 		/* vmallocs are handled from the workqueue context */
 		schedule_work(&fddef->wq);
 		spin_unlock(&fddef->lock);
 		put_cpu_var(fdtable_defer_list);
 	}
 }

 /*
  * Expand the fdset in the files_struct.  Called with the files spinlock
  * held for write.
  */
 static void copy_fdtable(struct fdtable *nfdt, struct fdtable *ofdt)
 {
 	unsigned int cpy, set;

 	BUG_ON(nfdt->max_fds < ofdt->max_fds);

 	cpy = ofdt->max_fds * sizeof(struct file *);
 	set = (nfdt->max_fds - ofdt->max_fds) * sizeof(struct file *);
 	memcpy(nfdt->fd, ofdt->fd, cpy);
 	memset((char *)(nfdt->fd) + cpy, 0, set);

 	cpy = ofdt->max_fds / BITS_PER_BYTE;
 	set = (nfdt->max_fds - ofdt->max_fds) / BITS_PER_BYTE;
 	memcpy(nfdt->open_fds, ofdt->open_fds, cpy);
 	memset((char *)(nfdt->open_fds) + cpy, 0, set);
 	memcpy(nfdt->close_on_exec, ofdt->close_on_exec, cpy);
 	memset((char *)(nfdt->close_on_exec) + cpy, 0, set);
 }

 static struct fdtable * alloc_fdtable(unsigned int nr)
 {
 	struct fdtable *fdt;
 	void *data;

 	/*
 	 * Figure out how many fds we actually want to support in this fdtable.
 	 * Allocation steps are keyed to the size of the fdarray, since it
 	 * grows far faster than any of the other dynamic data. We try to fit
 	 * the fdarray into comfortable page-tuned chunks: starting at 1024B
 	 * and growing in powers of two from there on.
 	 */
 	nr /= (1024 / sizeof(struct file *));
 	nr = roundup_pow_of_two(nr + 1);
 	nr *= (1024 / sizeof(struct file *));
 	/*
 	 * Note that this can drive nr *below* what we had passed if sysctl_nr_open
 	 * had been set lower between the check in expand_files() and here.  Deal
 	 * with that in caller, it's cheaper that way.
 	 *
 	 * We make sure that nr remains a multiple of BITS_PER_LONG - otherwise
 	 * bitmaps handling below becomes unpleasant, to put it mildly...
 	 */
 	if (unlikely(nr > sysctl_nr_open))
 		nr = ((sysctl_nr_open - 1) | (BITS_PER_LONG - 1)) + 1;

 	fdt = kmalloc(sizeof(struct fdtable), GFP_KERNEL);
 	if (!fdt)
 		goto out;
 	fdt->max_fds = nr;
 	data = alloc_fdmem(nr * sizeof(struct file *));
 	if (!data)
 		goto out_fdt;
 	fdt->fd = data;

 	data = alloc_fdmem(max_t(size_t,
 				 2 * nr / BITS_PER_BYTE, L1_CACHE_BYTES));
 	if (!data)
 		goto out_arr;
 	fdt->open_fds = data;
 	data += nr / BITS_PER_LONG;
 	fdt->close_on_exec = data;
 	fdt->next = NULL;

 	return fdt;

 out_arr:
 	free_fdmem(fdt->fd);
 out_fdt:
 	kfree(fdt);
 out:
 	return NULL;
 }

 /*
  * Expand the file descriptor table.
  * This function will allocate a new fdtable and both fd array and fdset, of
  * the given size.
  * Return <0 error code on error; 1 on successful completion.
  * The files->file_lock should be held on entry, and will be held on exit.
  */
 static int expand_fdtable(struct files_struct *files, int nr)
 	__releases(files->file_lock)
 	__acquires(files->file_lock)
 {
 	struct fdtable *new_fdt, *cur_fdt;

 	spin_unlock(&files->file_lock);
 	new_fdt = alloc_fdtable(nr);
 	spin_lock(&files->file_lock);
 	if (!new_fdt)
 		return -ENOMEM;
 	/*
 	 * extremely unlikely race - sysctl_nr_open decreased between the check in
 	 * caller and alloc_fdtable().  Cheaper to catch it here...
 	 */
 	if (unlikely(new_fdt->max_fds <= nr)) {
 		__free_fdtable(new_fdt);
 		return -EMFILE;
 	}
 	/*
 	 * Check again since another task may have expanded the fd table while
 	 * we dropped the lock
 	 */
 	cur_fdt = files_fdtable(files);
 	if (nr >= cur_fdt->max_fds) {
 		/* Continue as planned */
 		copy_fdtable(new_fdt, cur_fdt);
 		rcu_assign_pointer(files->fdt, new_fdt);
 		if (cur_fdt->max_fds > NR_OPEN_DEFAULT)
 			free_fdtable(cur_fdt);
 	} else {
 		/* Somebody else expanded, so undo our attempt */
 		__free_fdtable(new_fdt);
 	}
 	return 1;
 }

 /*
  * Expand files.
  * This function will expand the file structures, if the requested size exceeds
  * the current capacity and there is room for expansion.
  * Return <0 error code on error; 0 when nothing done; 1 when files were
  * expanded and execution may have blocked.
  * The files->file_lock should be held on entry, and will be held on exit.
  */
 int expand_files(struct files_struct *files, int nr)
 {
 	struct fdtable *fdt;

 	fdt = files_fdtable(files);

 	/*
 	 * N.B. For clone tasks sharing a files structure, this test
 	 * will limit the total number of files that can be opened.
 	 */
 	if (nr >= rlimit(RLIMIT_NOFILE))
 		return -EMFILE;

 	/* Do we need to expand? */
 	if (nr < fdt->max_fds)
 		return 0;

 	/* Can we expand? */
 	if (nr >= sysctl_nr_open)
 		return -EMFILE;

 	/* All good, so we try */
 	return expand_fdtable(files, nr);
 }

 static int count_open_files(struct fdtable *fdt)
 {
 	int size = fdt->max_fds;
 	int i;

 	/* Find the last open fd */
 	for (i = size / BITS_PER_LONG; i > 0; ) {
 		if (fdt->open_fds[--i])
 			break;
 	}
 	i = (i + 1) * BITS_PER_LONG;
 	return i;
 }

 /*
  * Allocate a new files structure and copy contents from the
  * passed in files structure.
  * errorp will be valid only when the returned files_struct is NULL.
  */
 struct files_struct *dup_fd(struct files_struct *oldf, int *errorp)
 {
 	struct files_struct *newf;
 	struct file **old_fds, **new_fds;
 	int open_files, size, i;
 	struct fdtable *old_fdt, *new_fdt;

 	*errorp = -ENOMEM;
 	newf = kmem_cache_alloc(files_cachep, GFP_KERNEL);
 	if (!newf)
 		goto out;

 	atomic_set(&newf->count, 1);

 	spin_lock_init(&newf->file_lock);
 	newf->next_fd = 0;
 	new_fdt = &newf->fdtab;
 	new_fdt->max_fds = NR_OPEN_DEFAULT;
 	new_fdt->close_on_exec = newf->close_on_exec_init;
 	new_fdt->open_fds = newf->open_fds_init;
 	new_fdt->fd = &newf->fd_array[0];
 	new_fdt->next = NULL;

 	spin_lock(&oldf->file_lock);
 	old_fdt = files_fdtable(oldf);
 	open_files = count_open_files(old_fdt);

 	/*
 	 * Check whether we need to allocate a larger fd array and fd set.
 	 */
 	while (unlikely(open_files > new_fdt->max_fds)) {
 		spin_unlock(&oldf->file_lock);

 		if (new_fdt != &newf->fdtab)
 			__free_fdtable(new_fdt);

 		new_fdt = alloc_fdtable(open_files - 1);
 		if (!new_fdt) {
 			*errorp = -ENOMEM;
 			goto out_release;
 		}

 		/* beyond sysctl_nr_open; nothing to do */
 		if (unlikely(new_fdt->max_fds < open_files)) {
 			__free_fdtable(new_fdt);
 			*errorp = -EMFILE;
 			goto out_release;
 		}

 		/*
 		 * Reacquire the oldf lock and a pointer to its fd table
 		 * who knows it may have a new bigger fd table. We need
 		 * the latest pointer.
 		 */
 		spin_lock(&oldf->file_lock);
 		old_fdt = files_fdtable(oldf);
 		open_files = count_open_files(old_fdt);
 	}

 	old_fds = old_fdt->fd;
 	new_fds = new_fdt->fd;

 	memcpy(new_fdt->open_fds, old_fdt->open_fds, open_files / 8);
 	memcpy(new_fdt->close_on_exec, old_fdt->close_on_exec, open_files / 8);

 	for (i = open_files; i != 0; i--) {
 		struct file *f = *old_fds++;
 		if (f) {
 			get_file(f);
 		} else {
 			/*
 			 * The fd may be claimed in the fd bitmap but not yet
 			 * instantiated in the files array if a sibling thread
 			 * is partway through open().  So make sure that this
 			 * fd is available to the new process.
 			 */
 			__clear_open_fd(open_files - i, new_fdt);
 		}
 		rcu_assign_pointer(*new_fds++, f);
 	}
 	spin_unlock(&oldf->file_lock);

 	/* compute the remainder to be cleared */
 	size = (new_fdt->max_fds - open_files) * sizeof(struct file *);

 	/* This is long word aligned thus could use a optimized version */
 	memset(new_fds, 0, size);

 	if (new_fdt->max_fds > open_files) {
 		int left = (new_fdt->max_fds - open_files) / 8;
 		int start = open_files / BITS_PER_LONG;

 		memset(&new_fdt->open_fds[start], 0, left);
 		memset(&new_fdt->close_on_exec[start], 0, left);
 	}

 	rcu_assign_pointer(newf->fdt, new_fdt);

 	return newf;

 out_release:
 	kmem_cache_free(files_cachep, newf);
 out:
 	return NULL;
 }

 static void __devinit fdtable_defer_list_init(int cpu)
 {
 	struct fdtable_defer *fddef = &per_cpu(fdtable_defer_list, cpu);
 	spin_lock_init(&fddef->lock);
 	INIT_WORK(&fddef->wq, free_fdtable_work);
 	fddef->next = NULL;
 }

 void __init files_defer_init(void)
 {
 	int i;
 	for_each_possible_cpu(i)
 		fdtable_defer_list_init(i);
 	sysctl_nr_open_max = min((size_t)INT_MAX, ~(size_t)0/sizeof(void *)) &
 			     -BITS_PER_LONG;
 }

 struct files_struct init_files = {
 	.count		= ATOMIC_INIT(1),
 	.fdt		= &init_files.fdtab,
 	.fdtab		= {
 		.max_fds	= NR_OPEN_DEFAULT,
 		.fd		= &init_files.fd_array[0],
 		.close_on_exec	= init_files.close_on_exec_init,
 		.open_fds	= init_files.open_fds_init,
 	},
 	.file_lock	= __SPIN_LOCK_UNLOCKED(init_task.file_lock),
 };

 /*
  * allocate a file descriptor, mark it busy.
  */
 int alloc_fd(unsigned start, unsigned flags)
 {
 	struct files_struct *files = current->files;
 	unsigned int fd;
 	int error;
 	struct fdtable *fdt;

 	spin_lock(&files->file_lock);
 repeat:
 	fdt = files_fdtable(files);
 	fd = start;
 	if (fd < files->next_fd)
 		fd = files->next_fd;

 	if (fd < fdt->max_fds)
 		fd = find_next_zero_bit(fdt->open_fds, fdt->max_fds, fd);

 	error = expand_files(files, fd);
 	if (error < 0)
 		goto out;

 	/*
 	 * If we needed to expand the fs array we
 	 * might have blocked - try again.
 	 */
 	if (error)
 		goto repeat;

 	if (start <= files->next_fd)
 		files->next_fd = fd + 1;

 	__set_open_fd(fd, fdt);
 	if (flags & O_CLOEXEC)
 		__set_close_on_exec(fd, fdt);
 	else
 		__clear_close_on_exec(fd, fdt);
 	error = fd;
 #if 1
 	/* Sanity check */
 	if (rcu_dereference_raw(fdt->fd[fd]) != NULL) {
 		printk(KERN_WARNING "alloc_fd: slot %d not NULL!\n", fd);
 		rcu_assign_pointer(fdt->fd[fd], NULL);
 	}
 #endif

 out:
 	spin_unlock(&files->file_lock);
 	return error;
 }

 int get_unused_fd(void)
 {
 	return alloc_fd(0, 0);
 }
 EXPORT_SYMBOL(get_unused_fd);
	/*
	* linux/fs/file.c
	*
	* Copyright (C) 1998-1999, Stephen Tweedie and Bill Hawes
	*
	* Manage the dynamic fd arrays in the process files_struct.
	*/

	#include <linux/module.h>
	#include <linux/fs.h>
	#include <linux/mm.h>
	#include <linux/mmzone.h>
	#include <linux/time.h>
	#include <linux/sched.h>
	#include <linux/slab.h>
	#include <linux/vmalloc.h>
	#include <linux/file.h>
	#include <linux/fdtable.h>
	#include <linux/bitops.h>
	#include <linux/interrupt.h>
	#include <linux/spinlock.h>
	#include <linux/rcupdate.h>
	#include <linux/workqueue.h>

	struct fdtable_defer {
	spinlock_t lock;
	struct work_struct wq;
	struct fdtable *next;
	};

	int sysctl_nr_open __read_mostly = 1024*1024;
	int sysctl_nr_open_min = BITS_PER_LONG;
	int sysctl_nr_open_max = 1024 * 1024; /* raised later */

	/*
	* We use this list to defer free fdtables that have vmalloced
	* sets/arrays. By keeping a per-cpu list, we avoid having to embed
	* the work_struct in fdtable itself which avoids a 64 byte (i386) increase in
	* this per-task structure.
	*/
	static DEFINE_PER_CPU(struct fdtable_defer, fdtable_defer_list);

	static void *alloc_fdmem(size_t size)
	{
	/*
	* Very large allocations can stress page reclaim, so fall back to
	* vmalloc() if the allocation size will be considered "large" by the VM.
	*/
	if (size <= (PAGE_SIZE << PAGE_ALLOC_COSTLY_ORDER)) {
	void *data = kmalloc(size, GFP_KERNEL\|__GFP_NOWARN);
	if (data != NULL)
	return data;
	}
	return vmalloc(size);
	}

	static void free_fdmem(void *ptr)
	{
	is_vmalloc_addr(ptr) ? vfree(ptr) : kfree(ptr);
	}

	static void __free_fdtable(struct fdtable *fdt)
	{
	free_fdmem(fdt->fd);
	free_fdmem(fdt->open_fds);
	kfree(fdt);
	}

	static void free_fdtable_work(struct work_struct *work)
	{
	struct fdtable_defer *f =
	container_of(work, struct fdtable_defer, wq);
	struct fdtable *fdt;

	spin_lock_bh(&f->lock);
	fdt = f->next;
	f->next = NULL;
	spin_unlock_bh(&f->lock);
	while(fdt) {
	struct fdtable *next = fdt->next;

	__free_fdtable(fdt);
	fdt = next;
	}
	}

	void free_fdtable_rcu(struct rcu_head *rcu)
	{
	struct fdtable *fdt = container_of(rcu, struct fdtable, rcu);
	struct fdtable_defer *fddef;

	BUG_ON(!fdt);

	if (fdt->max_fds <= NR_OPEN_DEFAULT) {
	/*
	* This fdtable is embedded in the files structure and that
	* structure itself is getting destroyed.
	*/
	kmem_cache_free(files_cachep,
	container_of(fdt, struct files_struct, fdtab));
	return;
	}
	if (!is_vmalloc_addr(fdt->fd) && !is_vmalloc_addr(fdt->open_fds)) {
	kfree(fdt->fd);
	kfree(fdt->open_fds);
	kfree(fdt);
	} else {
	fddef = &get_cpu_var(fdtable_defer_list);
	spin_lock(&fddef->lock);
	fdt->next = fddef->next;
	fddef->next = fdt;
	/* vmallocs are handled from the workqueue context */
	schedule_work(&fddef->wq);
	spin_unlock(&fddef->lock);
	put_cpu_var(fdtable_defer_list);
	}
	}

	/*
	* Expand the fdset in the files_struct. Called with the files spinlock
	* held for write.
	*/
	static void copy_fdtable(struct fdtable nfdt, struct fdtable ofdt)
	{
	unsigned int cpy, set;

	BUG_ON(nfdt->max_fds < ofdt->max_fds);

	cpy = ofdt->max_fds * sizeof(struct file *);
	set = (nfdt->max_fds - ofdt->max_fds) * sizeof(struct file *);
	memcpy(nfdt->fd, ofdt->fd, cpy);
	memset((char *)(nfdt->fd) + cpy, 0, set);

	cpy = ofdt->max_fds / BITS_PER_BYTE;
	set = (nfdt->max_fds - ofdt->max_fds) / BITS_PER_BYTE;
	memcpy(nfdt->open_fds, ofdt->open_fds, cpy);
	memset((char *)(nfdt->open_fds) + cpy, 0, set);
	memcpy(nfdt->close_on_exec, ofdt->close_on_exec, cpy);
	memset((char *)(nfdt->close_on_exec) + cpy, 0, set);
	}

	static struct fdtable * alloc_fdtable(unsigned int nr)
	{
	struct fdtable *fdt;
	void *data;

	/*
	* Figure out how many fds we actually want to support in this fdtable.
	* Allocation steps are keyed to the size of the fdarray, since it
	* grows far faster than any of the other dynamic data. We try to fit
	* the fdarray into comfortable page-tuned chunks: starting at 1024B
	* and growing in powers of two from there on.
	*/
	nr /= (1024 / sizeof(struct file *));
	nr = roundup_pow_of_two(nr + 1);
	nr = (1024 / sizeof(struct file ));
	/*
	* Note that this can drive nr below what we had passed if sysctl_nr_open
	* had been set lower between the check in expand_files() and here. Deal
	* with that in caller, it's cheaper that way.
	*
	* We make sure that nr remains a multiple of BITS_PER_LONG - otherwise
	* bitmaps handling below becomes unpleasant, to put it mildly...
	*/
	if (unlikely(nr > sysctl_nr_open))
	nr = ((sysctl_nr_open - 1) \| (BITS_PER_LONG - 1)) + 1;

	fdt = kmalloc(sizeof(struct fdtable), GFP_KERNEL);
	if (!fdt)
	goto out;
	fdt->max_fds = nr;
	data = alloc_fdmem(nr * sizeof(struct file *));
	if (!data)
	goto out_fdt;
	fdt->fd = data;

	data = alloc_fdmem(max_t(size_t,
	2 * nr / BITS_PER_BYTE, L1_CACHE_BYTES));
	if (!data)
	goto out_arr;
	fdt->open_fds = data;
	data += nr / BITS_PER_LONG;
	fdt->close_on_exec = data;
	fdt->next = NULL;

	return fdt;

	out_arr:
	free_fdmem(fdt->fd);
	out_fdt:
	kfree(fdt);
	out:
	return NULL;
	}

	/*
	* Expand the file descriptor table.
	* This function will allocate a new fdtable and both fd array and fdset, of
	* the given size.
	* Return <0 error code on error; 1 on successful completion.
	* The files->file_lock should be held on entry, and will be held on exit.
	*/
	static int expand_fdtable(struct files_struct *files, int nr)
	__releases(files->file_lock)
	__acquires(files->file_lock)
	{
	struct fdtable new_fdt, cur_fdt;

	spin_unlock(&files->file_lock);
	new_fdt = alloc_fdtable(nr);
	spin_lock(&files->file_lock);
	if (!new_fdt)
	return -ENOMEM;
	/*
	* extremely unlikely race - sysctl_nr_open decreased between the check in
	* caller and alloc_fdtable(). Cheaper to catch it here...
	*/
	if (unlikely(new_fdt->max_fds <= nr)) {
	__free_fdtable(new_fdt);
	return -EMFILE;
	}
	/*
	* Check again since another task may have expanded the fd table while
	* we dropped the lock
	*/
	cur_fdt = files_fdtable(files);
	if (nr >= cur_fdt->max_fds) {
	/* Continue as planned */
	copy_fdtable(new_fdt, cur_fdt);
	rcu_assign_pointer(files->fdt, new_fdt);
	if (cur_fdt->max_fds > NR_OPEN_DEFAULT)
	free_fdtable(cur_fdt);
	} else {
	/* Somebody else expanded, so undo our attempt */
	__free_fdtable(new_fdt);
	}
	return 1;
	}

	/*
	* Expand files.
	* This function will expand the file structures, if the requested size exceeds
	* the current capacity and there is room for expansion.
	* Return <0 error code on error; 0 when nothing done; 1 when files were
	* expanded and execution may have blocked.
	* The files->file_lock should be held on entry, and will be held on exit.
	*/
	int expand_files(struct files_struct *files, int nr)
	{
	struct fdtable *fdt;

	fdt = files_fdtable(files);

	/*
	* N.B. For clone tasks sharing a files structure, this test
	* will limit the total number of files that can be opened.
	*/
	if (nr >= rlimit(RLIMIT_NOFILE))
	return -EMFILE;

	/* Do we need to expand? */
	if (nr < fdt->max_fds)
	return 0;

	/* Can we expand? */
	if (nr >= sysctl_nr_open)
	return -EMFILE;

	/* All good, so we try */
	return expand_fdtable(files, nr);
	}

	static int count_open_files(struct fdtable *fdt)
	{
	int size = fdt->max_fds;
	int i;

	/* Find the last open fd */
	for (i = size / BITS_PER_LONG; i > 0; ) {
	if (fdt->open_fds[--i])
	break;
	}
	i = (i + 1) * BITS_PER_LONG;
	return i;
	}

	/*
	* Allocate a new files structure and copy contents from the
	* passed in files structure.
	* errorp will be valid only when the returned files_struct is NULL.
	*/
	struct files_struct dup_fd(struct files_struct oldf, int *errorp)
	{
	struct files_struct *newf;
	struct file old_fds, new_fds;
	int open_files, size, i;
	struct fdtable old_fdt, new_fdt;

	*errorp = -ENOMEM;
	newf = kmem_cache_alloc(files_cachep, GFP_KERNEL);
	if (!newf)
	goto out;

	atomic_set(&newf->count, 1);

	spin_lock_init(&newf->file_lock);
	newf->next_fd = 0;
	new_fdt = &newf->fdtab;
	new_fdt->max_fds = NR_OPEN_DEFAULT;
	new_fdt->close_on_exec = newf->close_on_exec_init;
	new_fdt->open_fds = newf->open_fds_init;
	new_fdt->fd = &newf->fd_array[0];
	new_fdt->next = NULL;

	spin_lock(&oldf->file_lock);
	old_fdt = files_fdtable(oldf);
	open_files = count_open_files(old_fdt);

	/*
	* Check whether we need to allocate a larger fd array and fd set.
	*/
	while (unlikely(open_files > new_fdt->max_fds)) {
	spin_unlock(&oldf->file_lock);

	if (new_fdt != &newf->fdtab)
	__free_fdtable(new_fdt);

	new_fdt = alloc_fdtable(open_files - 1);
	if (!new_fdt) {
	*errorp = -ENOMEM;
	goto out_release;
	}

	/* beyond sysctl_nr_open; nothing to do */
	if (unlikely(new_fdt->max_fds < open_files)) {
	__free_fdtable(new_fdt);
	*errorp = -EMFILE;
	goto out_release;
	}

	/*
	* Reacquire the oldf lock and a pointer to its fd table
	* who knows it may have a new bigger fd table. We need
	* the latest pointer.
	*/
	spin_lock(&oldf->file_lock);
	old_fdt = files_fdtable(oldf);
	open_files = count_open_files(old_fdt);
	}

	old_fds = old_fdt->fd;
	new_fds = new_fdt->fd;

	memcpy(new_fdt->open_fds, old_fdt->open_fds, open_files / 8);
	memcpy(new_fdt->close_on_exec, old_fdt->close_on_exec, open_files / 8);

	for (i = open_files; i != 0; i--) {
	struct file f = old_fds++;
	if (f) {
	get_file(f);
	} else {
	/*
	* The fd may be claimed in the fd bitmap but not yet
	* instantiated in the files array if a sibling thread
	* is partway through open(). So make sure that this
	* fd is available to the new process.
	*/
	__clear_open_fd(open_files - i, new_fdt);
	}
	rcu_assign_pointer(*new_fds++, f);
	}
	spin_unlock(&oldf->file_lock);

	/* compute the remainder to be cleared */
	size = (new_fdt->max_fds - open_files) * sizeof(struct file *);

	/* This is long word aligned thus could use a optimized version */
	memset(new_fds, 0, size);

	if (new_fdt->max_fds > open_files) {
	int left = (new_fdt->max_fds - open_files) / 8;
	int start = open_files / BITS_PER_LONG;

	memset(&new_fdt->open_fds[start], 0, left);
	memset(&new_fdt->close_on_exec[start], 0, left);
	}

	rcu_assign_pointer(newf->fdt, new_fdt);

	return newf;

	out_release:
	kmem_cache_free(files_cachep, newf);
	out:
	return NULL;
	}

	static void __devinit fdtable_defer_list_init(int cpu)
	{
	struct fdtable_defer *fddef = &per_cpu(fdtable_defer_list, cpu);
	spin_lock_init(&fddef->lock);
	INIT_WORK(&fddef->wq, free_fdtable_work);
	fddef->next = NULL;
	}

	void __init files_defer_init(void)
	{
	int i;
	for_each_possible_cpu(i)
	fdtable_defer_list_init(i);
	sysctl_nr_open_max = min((size_t)INT_MAX, ~(size_t)0/sizeof(void *)) &
	-BITS_PER_LONG;
	}

	struct files_struct init_files = {
	.count = ATOMIC_INIT(1),
	.fdt = &init_files.fdtab,
	.fdtab = {
	.max_fds = NR_OPEN_DEFAULT,
	.fd = &init_files.fd_array[0],
	.close_on_exec = init_files.close_on_exec_init,
	.open_fds = init_files.open_fds_init,
	},
	.file_lock = __SPIN_LOCK_UNLOCKED(init_task.file_lock),
	};

	/*
	* allocate a file descriptor, mark it busy.
	*/
	int alloc_fd(unsigned start, unsigned flags)
	{
	struct files_struct *files = current->files;
	unsigned int fd;
	int error;
	struct fdtable *fdt;

	spin_lock(&files->file_lock);
	repeat:
	fdt = files_fdtable(files);
	fd = start;
	if (fd < files->next_fd)
	fd = files->next_fd;

	if (fd < fdt->max_fds)
	fd = find_next_zero_bit(fdt->open_fds, fdt->max_fds, fd);

	error = expand_files(files, fd);
	if (error < 0)
	goto out;

	/*
	* If we needed to expand the fs array we
	* might have blocked - try again.
	*/
	if (error)
	goto repeat;

	if (start <= files->next_fd)
	files->next_fd = fd + 1;

	__set_open_fd(fd, fdt);
	if (flags & O_CLOEXEC)
	__set_close_on_exec(fd, fdt);
	else
	__clear_close_on_exec(fd, fdt);
	error = fd;
	#if 1
	/* Sanity check */
	if (rcu_dereference_raw(fdt->fd[fd]) != NULL) {
	printk(KERN_WARNING "alloc_fd: slot %d not NULL!\n", fd);
	rcu_assign_pointer(fdt->fd[fd], NULL);
	}
	#endif

	out:
	spin_unlock(&files->file_lock);
	return error;
	}

	int get_unused_fd(void)
	{
	return alloc_fd(0, 0);
	}
	EXPORT_SYMBOL(get_unused_fd);