/*
   *  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/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 inline void * alloc_fdmem(unsigned int size)

  {

  	if (size <= PAGE_SIZE)

  		return kmalloc(size, GFP_KERNEL);
  	else
  		return vmalloc(size);

  }

  static inline void free_fdarr(struct fdtable *fdt)

  {

  	if (fdt->max_fds <= (PAGE_SIZE / sizeof(struct file *)))
  		kfree(fdt->fd);

  	else

  		vfree(fdt->fd);

  }

  static inline void free_fdset(struct fdtable *fdt)

  {

  	if (fdt->max_fds <= (PAGE_SIZE * BITS_PER_BYTE / 2))
  		kfree(fdt->open_fds);
  	else
  		vfree(fdt->open_fds);

  }

  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;

  		vfree(fdt->fd);
  		free_fdset(fdt);
  		kfree(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 (fdt->max_fds <= (PAGE_SIZE / sizeof(struct file *))) {

  		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;
  	char *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 = (struct file **)data;
  	data = alloc_fdmem(max_t(unsigned int,
  				 2 * nr / BITS_PER_BYTE, L1_CACHE_BYTES));
  	if (!data)
  		goto out_arr;
  	fdt->open_fds = (fd_set *)data;
  	data += nr / BITS_PER_BYTE;
  	fdt->close_on_exec = (fd_set *)data;
  	INIT_RCU_HEAD(&fdt->rcu);
  	fdt->next = NULL;

  	return fdt;

  
  out_arr:
  	free_fdarr(fdt);
  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_fdarr(new_fdt);
  		free_fdset(new_fdt);
  		kfree(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_fdarr(new_fdt);
  		free_fdset(new_fdt);
  		kfree(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/(8*sizeof(long)); i > 0; ) {
  		if (fdt->open_fds->fds_bits[--i])
  			break;
  	}
  	i = (i+1) * 8 * sizeof(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 = (fd_set *)&newf->close_on_exec_init;
  	new_fdt->open_fds = (fd_set *)&newf->open_fds_init;
  	new_fdt->fd = &newf->fd_array[0];
  	INIT_RCU_HEAD(&new_fdt->rcu);
  	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_fdarr(new_fdt);
  			free_fdset(new_fdt);
  			kfree(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_fdarr(new_fdt);
  			free_fdset(new_fdt);
  			kfree(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->fds_bits,
  		old_fdt->open_fds->fds_bits, open_files/8);
  	memcpy(new_fdt->close_on_exec->fds_bits,
  		old_fdt->close_on_exec->fds_bits, 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.
  			 */
  			FD_CLR(open_files - i, new_fdt->open_fds);
  		}
  		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 / (8 * sizeof(unsigned long));
  
  		memset(&new_fdt->open_fds->fds_bits[start], 0, left);
  		memset(&new_fdt->close_on_exec->fds_bits[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	= (fd_set *)&init_files.close_on_exec_init,
  		.open_fds	= (fd_set *)&init_files.open_fds_init,
  		.rcu		= RCU_HEAD_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->fds_bits,
  					   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;
  
  	FD_SET(fd, fdt->open_fds);
  	if (flags & O_CLOEXEC)
  		FD_SET(fd, fdt->close_on_exec);
  	else
  		FD_CLR(fd, fdt->close_on_exec);
  	error = fd;
  #if 1
  	/* Sanity check */

  	if (rcu_dereference_raw(fdt->fd[fd]) != NULL) {

  		printk(KERN_WARNING "alloc_fd: slot %d not NULL!
  ", 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);