kernel_linux/fs/file.c

/*
 *  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/fs.h>
#include <linux/mm.h>
#include <linux/time.h>
#include <linux/slab.h>
#include <linux/vmalloc.h>
#include <linux/file.h>
#include <linux/bitops.h>


/*
 * Allocate an fd array, using kmalloc or vmalloc.
 * Note: the array isn't cleared at allocation time.
 */
struct file ** alloc_fd_array(int num)
{
	struct file **new_fds;
	int size = num * sizeof(struct file *);

	if (size <= PAGE_SIZE)
		new_fds = (struct file **) kmalloc(size, GFP_KERNEL);
	else 
		new_fds = (struct file **) vmalloc(size);
	return new_fds;
}

void free_fd_array(struct file **array, int num)
{
	int size = num * sizeof(struct file *);

	if (!array) {
		printk (KERN_ERR "free_fd_array: array = 0 (num = %d)\n", num);
		return;
	}

	if (num <= NR_OPEN_DEFAULT) /* Don't free the embedded fd array! */
		return;
	else if (size <= PAGE_SIZE)
		kfree(array);
	else
		vfree(array);
}

/*
 * Expand the fd array in the files_struct.  Called with the files
 * spinlock held for write.
 */

static int expand_fd_array(struct files_struct *files, int nr)
	__releases(files->file_lock)
	__acquires(files->file_lock)
{
	struct file **new_fds;
	int error, nfds;

	
	error = -EMFILE;
	if (files->max_fds >= NR_OPEN || nr >= NR_OPEN)
		goto out;

	nfds = files->max_fds;
	spin_unlock(&files->file_lock);

	/* 
	 * Expand to the max in easy steps, and keep expanding it until
	 * we have enough for the requested fd array size. 
	 */

	do {
#if NR_OPEN_DEFAULT < 256
		if (nfds < 256)
			nfds = 256;
		else 
#endif
		if (nfds < (PAGE_SIZE / sizeof(struct file *)))
			nfds = PAGE_SIZE / sizeof(struct file *);
		else {
			nfds = nfds * 2;
			if (nfds > NR_OPEN)
				nfds = NR_OPEN;
		}
	} while (nfds <= nr);

	error = -ENOMEM;
	new_fds = alloc_fd_array(nfds);
	spin_lock(&files->file_lock);
	if (!new_fds)
		goto out;

	/* Copy the existing array and install the new pointer */

	if (nfds > files->max_fds) {
		struct file **old_fds;
		int i;
		
		old_fds = xchg(&files->fd, new_fds);
		i = xchg(&files->max_fds, nfds);

		/* Don't copy/clear the array if we are creating a new
		   fd array for fork() */
		if (i) {
			memcpy(new_fds, old_fds, i * sizeof(struct file *));
			/* clear the remainder of the array */
			memset(&new_fds[i], 0,
			       (nfds-i) * sizeof(struct file *)); 

			spin_unlock(&files->file_lock);
			free_fd_array(old_fds, i);
			spin_lock(&files->file_lock);
		}
	} else {
		/* Somebody expanded the array while we slept ... */
		spin_unlock(&files->file_lock);
		free_fd_array(new_fds, nfds);
		spin_lock(&files->file_lock);
	}
	error = 0;
out:
	return error;
}

/*
 * Allocate an fdset array, using kmalloc or vmalloc.
 * Note: the array isn't cleared at allocation time.
 */
fd_set * alloc_fdset(int num)
{
	fd_set *new_fdset;
	int size = num / 8;

	if (size <= PAGE_SIZE)
		new_fdset = (fd_set *) kmalloc(size, GFP_KERNEL);
	else
		new_fdset = (fd_set *) vmalloc(size);
	return new_fdset;
}

void free_fdset(fd_set *array, int num)
{
	int size = num / 8;

	if (num <= __FD_SETSIZE) /* Don't free an embedded fdset */
		return;
	else if (size <= PAGE_SIZE)
		kfree(array);
	else
		vfree(array);
}

/*
 * Expand the fdset in the files_struct.  Called with the files spinlock
 * held for write.
 */
static int expand_fdset(struct files_struct *files, int nr)
	__releases(file->file_lock)
	__acquires(file->file_lock)
{
	fd_set *new_openset = NULL, *new_execset = NULL;
	int error, nfds = 0;

	error = -EMFILE;
	if (files->max_fdset >= NR_OPEN || nr >= NR_OPEN)
		goto out;

	nfds = files->max_fdset;
	spin_unlock(&files->file_lock);

	/* Expand to the max in easy steps */
	do {
		if (nfds < (PAGE_SIZE * 8))
			nfds = PAGE_SIZE * 8;
		else {
			nfds = nfds * 2;
			if (nfds > NR_OPEN)
				nfds = NR_OPEN;
		}
	} while (nfds <= nr);

	error = -ENOMEM;
	new_openset = alloc_fdset(nfds);
	new_execset = alloc_fdset(nfds);
	spin_lock(&files->file_lock);
	if (!new_openset || !new_execset)
		goto out;

	error = 0;
	
	/* Copy the existing tables and install the new pointers */
	if (nfds > files->max_fdset) {
		int i = files->max_fdset / (sizeof(unsigned long) * 8);
		int count = (nfds - files->max_fdset) / 8;
		
		/* 
		 * Don't copy the entire array if the current fdset is
		 * not yet initialised.  
		 */
		if (i) {
			memcpy (new_openset, files->open_fds, files->max_fdset/8);
			memcpy (new_execset, files->close_on_exec, files->max_fdset/8);
			memset (&new_openset->fds_bits[i], 0, count);
			memset (&new_execset->fds_bits[i], 0, count);
		}
		
		nfds = xchg(&files->max_fdset, nfds);
		new_openset = xchg(&files->open_fds, new_openset);
		new_execset = xchg(&files->close_on_exec, new_execset);
		spin_unlock(&files->file_lock);
		free_fdset (new_openset, nfds);
		free_fdset (new_execset, nfds);
		spin_lock(&files->file_lock);
		return 0;
	} 
	/* Somebody expanded the array while we slept ... */

out:
	spin_unlock(&files->file_lock);
	if (new_openset)
		free_fdset(new_openset, nfds);
	if (new_execset)
		free_fdset(new_execset, nfds);
	spin_lock(&files->file_lock);
	return error;
}

/*
 * Expand files.
 * Return <0 on error; 0 nothing done; 1 files expanded, we may have blocked.
 * Should be called with the files->file_lock spinlock held for write.
 */
int expand_files(struct files_struct *files, int nr)
{
	int err, expand = 0;

	if (nr >= files->max_fdset) {
		expand = 1;
		if ((err = expand_fdset(files, nr)))
			goto out;
	}
	if (nr >= files->max_fds) {
		expand = 1;
		if ((err = expand_fd_array(files, nr)))
			goto out;
	}
	err = expand;
out:
	return err;
}