/* $Id: ramfs.c 1824 2005-05-10 07:30:07Z hg $
 *
 * This file is subject to the terms and conditions of the GNU General Public
 * License.  See the file "COPYING" in the main directory of this archive
 * for more details.
 *
 * Copyright (C) 1992 - 1997, 2000-2003 Silicon Graphics, Inc. All rights reserved.
 */
#include <linux/module.h>
#include <linux/fs.h>
#include <linux/pagemap.h>
#include <linux/init.h>
#include <linux/string.h>
#include <asm/uaccess.h>
#include <asm/system.h>
#include <asm/machvec.h>

/* some random number */
#define HWGFS_MAGIC	0x12061983

static struct super_operations hwgfs_ops;
static struct address_space_operations hwgfs_aops;
static struct file_operations hwgfs_file_operations;
static struct inode_operations hwgfs_dir_inode_operations;

static int hwgfs_statfs(struct super_block *sb, struct statfs *buf)
{
	buf->f_type = HWGFS_MAGIC;
	buf->f_bsize = PAGE_CACHE_SIZE;
	buf->f_namelen = 255;
	return 0;
}

/*
 * Lookup the data. This is trivial - if the dentry didn't already
 * exist, we know it is negative.
 */
static struct dentry * hwgfs_lookup(struct inode *dir, struct dentry *dentry)
{
	d_add(dentry, NULL);
	return NULL;
}

/*
 * Read a page. Again trivial. If it didn't already exist
 * in the page cache, it is zero-filled.
 */
static int hwgfs_readpage(struct file *file, struct page * page)
{
	if (!Page_Uptodate(page)) {
		memset(kmap(page), 0, PAGE_CACHE_SIZE);
		kunmap(page);
		flush_dcache_page(page);
		SetPageUptodate(page);
	}
	UnlockPage(page);
	return 0;
}

static int hwgfs_prepare_write(struct file *file, struct page *page, unsigned offset, unsigned to)
{
	void *addr = kmap(page);
	if (!Page_Uptodate(page)) {
		memset(addr, 0, PAGE_CACHE_SIZE);
		flush_dcache_page(page);
		SetPageUptodate(page);
	}
	SetPageDirty(page);
	return 0;
}

static int hwgfs_commit_write(struct file *file, struct page *page, unsigned offset, unsigned to)
{
	struct inode *inode = page->mapping->host;
	loff_t pos = ((loff_t)page->index << PAGE_CACHE_SHIFT) + to;

	kunmap(page);
	if (pos > inode->i_size)
		inode->i_size = pos;
	return 0;
}

struct inode *hwgfs_get_inode(struct super_block *sb, int mode, int dev)
{
	struct inode * inode = new_inode(sb);

	if (inode) {
		inode->i_mode = mode;
		inode->i_uid = current->fsuid;
		inode->i_gid = current->fsgid;
		inode->i_blksize = PAGE_CACHE_SIZE;
		inode->i_blocks = 0;
		inode->i_rdev = NODEV;
		inode->i_mapping->a_ops = &hwgfs_aops;
		inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME;
		switch (mode & S_IFMT) {
		default:
			init_special_inode(inode, mode, dev);
			break;
		case S_IFREG:
			inode->i_fop = &hwgfs_file_operations;
			break;
		case S_IFDIR:
			inode->i_op = &hwgfs_dir_inode_operations;
			inode->i_fop = &dcache_dir_ops;
			break;
		case S_IFLNK:
			inode->i_op = &page_symlink_inode_operations;
			break;
		}
	}
	return inode;
}

/*
 * File creation. Allocate an inode, and we're done..
 */
static int hwgfs_mknod(struct inode *dir, struct dentry *dentry, int mode, int dev)
{
	struct inode * inode = hwgfs_get_inode(dir->i_sb, mode, dev);
	int error = -ENOSPC;

	if (inode) {
		d_instantiate(dentry, inode);
		dget(dentry);		/* Extra count - pin the dentry in core */
		error = 0;
	}
	return error;
}

static int hwgfs_mkdir(struct inode * dir, struct dentry * dentry, int mode)
{
	return hwgfs_mknod(dir, dentry, mode | S_IFDIR, 0);
}

static int hwgfs_create(struct inode *dir, struct dentry *dentry, int mode)
{
	return hwgfs_mknod(dir, dentry, mode | S_IFREG, 0);
}

/*
 * Link a file..
 */
static int hwgfs_link(struct dentry *old_dentry, struct inode * dir, struct dentry * dentry)
{
	struct inode *inode = old_dentry->d_inode;

	if (S_ISDIR(inode->i_mode))
		return -EPERM;

	inode->i_nlink++;
	atomic_inc(&inode->i_count);	/* New dentry reference */
	dget(dentry);		/* Extra pinning count for the created dentry */
	d_instantiate(dentry, inode);
	return 0;
}

static inline int hwgfs_positive(struct dentry *dentry)
{
	return dentry->d_inode && !d_unhashed(dentry);
}

/*
 * Check that a directory is empty (this works
 * for regular files too, they'll just always be
 * considered empty..).
 *
 * Note that an empty directory can still have
 * children, they just all have to be negative..
 */
static int hwgfs_empty(struct dentry *dentry)
{
	struct list_head *list;

	spin_lock(&dcache_lock);
	list = dentry->d_subdirs.next;

	while (list != &dentry->d_subdirs) {
		struct dentry *de = list_entry(list, struct dentry, d_child);

		if (hwgfs_positive(de)) {
			spin_unlock(&dcache_lock);
			return 0;
		}
		list = list->next;
	}
	spin_unlock(&dcache_lock);
	return 1;
}

/*
 * This works for both directories and regular files.
 * (non-directories will always have empty subdirs)
 */
static int hwgfs_unlink(struct inode * dir, struct dentry *dentry)
{
	int retval = -ENOTEMPTY;

	if (hwgfs_empty(dentry)) {
		struct inode *inode = dentry->d_inode;

		inode->i_nlink--;
		dput(dentry);			/* Undo the count from "create" - this does all the work */
		retval = 0;
	}
	return retval;
}

#define hwgfs_rmdir hwgfs_unlink

/*
 * The VFS layer already does all the dentry stuff for rename,
 * we just have to decrement the usage count for the target if
 * it exists so that the VFS layer correctly free's it when it
 * gets overwritten.
 */
static int hwgfs_rename(struct inode * old_dir, struct dentry *old_dentry, struct inode * new_dir,struct dentry *new_dentry)
{
	int error = -ENOTEMPTY;

	if (hwgfs_empty(new_dentry)) {
		struct inode *inode = new_dentry->d_inode;
		if (inode) {
			inode->i_nlink--;
			dput(new_dentry);
		}
		error = 0;
	}
	return error;
}

static int hwgfs_symlink(struct inode * dir, struct dentry *dentry, const char * symname)
{
	int error;

	error = hwgfs_mknod(dir, dentry, S_IFLNK | S_IRWXUGO, 0);
	if (!error) {
		int l = strlen(symname)+1;
		struct inode *inode = dentry->d_inode;
		error = block_symlink(inode, symname, l);
	}
	return error;
}

static int hwgfs_sync_file(struct file * file, struct dentry *dentry, int datasync)
{
	return 0;
}

static struct address_space_operations hwgfs_aops = {
	.readpage	= hwgfs_readpage,
	.writepage	= fail_writepage,
	.prepare_write	= hwgfs_prepare_write,
	.commit_write	= hwgfs_commit_write
};

static struct file_operations hwgfs_file_operations = {
	.read		= generic_file_read,
	.write		= generic_file_write,
	.mmap		= generic_file_mmap,
	.fsync		= hwgfs_sync_file,
};

static struct inode_operations hwgfs_dir_inode_operations = {
	.create		= hwgfs_create,
	.lookup		= hwgfs_lookup,
	.link		= hwgfs_link,
	.unlink		= hwgfs_unlink,
	.symlink	= hwgfs_symlink,
	.mkdir		= hwgfs_mkdir,
	.rmdir		= hwgfs_rmdir,
	.mknod		= hwgfs_mknod,
	.rename		= hwgfs_rename,
};

static struct super_operations hwgfs_ops = {
	.statfs		= hwgfs_statfs,
	.put_inode	= force_delete,
};

static struct super_block *hwgfs_read_super(struct super_block * sb, void * data, int silent)
{
	struct inode * inode;
	struct dentry * root;

	sb->s_blocksize = PAGE_CACHE_SIZE;
	sb->s_blocksize_bits = PAGE_CACHE_SHIFT;
	sb->s_magic = HWGFS_MAGIC;
	sb->s_op = &hwgfs_ops;
	inode = hwgfs_get_inode(sb, S_IFDIR | 0755, 0);
	if (!inode)
		return NULL;

	root = d_alloc_root(inode);
	if (!root) {
		iput(inode);
		return NULL;
	}
	sb->s_root = root;
	return sb;
}

static struct file_system_type hwgfs_fs_type = {
	.owner			= THIS_MODULE,
	.name			= "hwgfs",
	.read_super		= hwgfs_read_super,
	.fs_flags		= FS_SINGLE|FS_LITTER,
};

struct vfsmount *hwgfs_vfsmount;

int __init init_hwgfs_fs(void)
{
	int error;

	if (!ia64_platform_is("sn2"))
		return -ENODEV;

	error = register_filesystem(&hwgfs_fs_type);
	if (error)
		return error;

	hwgfs_vfsmount = kern_mount(&hwgfs_fs_type);
	if (IS_ERR(hwgfs_vfsmount))
		goto fail;
	return 0;

fail:
	unregister_filesystem(&hwgfs_fs_type);
	return PTR_ERR(hwgfs_vfsmount);
}

static void __exit exit_hwgfs_fs(void)
{
	unregister_filesystem(&hwgfs_fs_type);
}

MODULE_LICENSE("GPL");

module_init(init_hwgfs_fs)
module_exit(exit_hwgfs_fs)
