/*
   * ROMFS file system, Linux implementation
   *
   * Copyright (C) 1997-1999  Janos Farkas <chexum@shadow.banki.hu>
   *
   * Using parts of the minix filesystem
   * Copyright (C) 1991, 1992  Linus Torvalds
   *
   * and parts of the affs filesystem additionally
   * Copyright (C) 1993  Ray Burr
   * Copyright (C) 1996  Hans-Joachim Widmaier
   *
   * This program is free software; you can redistribute it and/or
   * modify it under the terms of the GNU General Public License
   * as published by the Free Software Foundation; either version
   * 2 of the License, or (at your option) any later version.
   *
   * Changes
   *					Changed for 2.1.19 modules
   *	Jan 1997			Initial release
   *	Jun 1997			2.1.43+ changes
   *					Proper page locking in readpage
   *					Changed to work with 2.1.45+ fs
   *	Jul 1997			Fixed follow_link
   *			2.1.47
   *					lookup shouldn't return -ENOENT
   *					from Horst von Brand:
   *					  fail on wrong checksum
   *					  double unlock_super was possible
   *					  correct namelen for statfs
   *					spotted by Bill Hawes:
   *					  readlink shouldn't iput()
   *	Jun 1998	2.1.106		from Avery Pennarun: glibc scandir()
   *					  exposed a problem in readdir
   *			2.1.107		code-freeze spellchecker run
   *	Aug 1998			2.1.118+ VFS changes
   *	Sep 1998	2.1.122		another VFS change (follow_link)
   *	Apr 1999	2.2.7		no more EBADF checking in
   *					  lookup/readdir, use ERR_PTR
   *	Jun 1999	2.3.6		d_alloc_root use changed
   *			2.3.9		clean up usage of ENOENT/negative
   *					  dentries in lookup
   *					clean up page flags setting
   *					  (error, uptodate, locking) in
   *					  in readpage
   *					use init_special_inode for
   *					  fifos/sockets (and streamline) in
   *					  read_inode, fix _ops table order
   *	Aug 1999	2.3.16		__initfunc() => __init change
   *	Oct 1999	2.3.24		page->owner hack obsoleted
   *	Nov 1999	2.3.27		2.3.25+ page->offset => index change
   */
  
  /* todo:
   *	- see Documentation/filesystems/romfs.txt
   *	- use allocated, not stack memory for file names?
   *	- considering write access...
   *	- network (tftp) files?
   *	- merge back some _op tables
   */
  
  /*
   * Sorry about some optimizations and for some goto's.  I just wanted
   * to squeeze some more bytes out of this code.. :)
   */
  
  #include <linux/module.h>
  #include <linux/types.h>
  #include <linux/errno.h>
  #include <linux/slab.h>
  #include <linux/romfs_fs.h>
  #include <linux/fs.h>
  #include <linux/init.h>
  #include <linux/pagemap.h>
  #include <linux/smp_lock.h>
  #include <linux/buffer_head.h>
  #include <linux/vfs.h>
  
  #include <asm/uaccess.h>
  
  struct romfs_inode_info {
  	unsigned long i_metasize;	/* size of non-data area */
  	unsigned long i_dataoffset;	/* from the start of fs */
  	struct inode vfs_inode;
  };
  
  /* instead of private superblock data */
  static inline unsigned long romfs_maxsize(struct super_block *sb)
  {
  	return (unsigned long)sb->s_fs_info;
  }
  
  static inline struct romfs_inode_info *ROMFS_I(struct inode *inode)
  {
  	return list_entry(inode, struct romfs_inode_info, vfs_inode);
  }
  
  static __u32
  romfs_checksum(void *data, int size)
  {
  	__u32 sum;
  	__be32 *ptr;
  
  	sum = 0; ptr = data;
  	size>>=2;
  	while (size>0) {
  		sum += be32_to_cpu(*ptr++);
  		size--;
  	}
  	return sum;
  }

  static const struct super_operations romfs_ops;

  
  static int romfs_fill_super(struct super_block *s, void *data, int silent)
  {
  	struct buffer_head *bh;
  	struct romfs_super_block *rsb;
  	struct inode *root;
  	int sz;
  
  	/* I would parse the options here, but there are none.. :) */
  
  	sb_set_blocksize(s, ROMBSIZE);
  	s->s_maxbytes = 0xFFFFFFFF;
  
  	bh = sb_bread(s, 0);
  	if (!bh) {
  		/* XXX merge with other printk? */
                  printk ("romfs: unable to read superblock
  ");
  		goto outnobh;
  	}
  
  	rsb = (struct romfs_super_block *)bh->b_data;
  	sz = be32_to_cpu(rsb->size);
  	if (rsb->word0 != ROMSB_WORD0 || rsb->word1 != ROMSB_WORD1
  	   || sz < ROMFH_SIZE) {
  		if (!silent)
  			printk ("VFS: Can't find a romfs filesystem on dev "
  				"%s.
  ", s->s_id);
  		goto out;
  	}
  	if (romfs_checksum(rsb, min_t(int, sz, 512))) {
  		printk ("romfs: bad initial checksum on dev "
  			"%s.
  ", s->s_id);
  		goto out;
  	}
  
  	s->s_magic = ROMFS_MAGIC;
  	s->s_fs_info = (void *)(long)sz;
  
  	s->s_flags |= MS_RDONLY;
  
  	/* Find the start of the fs */
  	sz = (ROMFH_SIZE +
  	      strnlen(rsb->name, ROMFS_MAXFN) + 1 + ROMFH_PAD)
  	     & ROMFH_MASK;
  
  	s->s_op	= &romfs_ops;
  	root = iget(s, sz);
  	if (!root)
  		goto out;
  
  	s->s_root = d_alloc_root(root);
  	if (!s->s_root)
  		goto outiput;
  
  	brelse(bh);
  	return 0;
  
  outiput:
  	iput(root);
  out:
  	brelse(bh);
  outnobh:
  	return -EINVAL;
  }
  
  /* That's simple too. */
  
  static int

  romfs_statfs(struct dentry *dentry, struct kstatfs *buf)

  {
  	buf->f_type = ROMFS_MAGIC;
  	buf->f_bsize = ROMBSIZE;
  	buf->f_bfree = buf->f_bavail = buf->f_ffree;

  	buf->f_blocks = (romfs_maxsize(dentry->d_sb)+ROMBSIZE-1)>>ROMBSBITS;

  	buf->f_namelen = ROMFS_MAXFN;
  	return 0;
  }
  
  /* some helper routines */
  
  static int
  romfs_strnlen(struct inode *i, unsigned long offset, unsigned long count)
  {
  	struct buffer_head *bh;
  	unsigned long avail, maxsize, res;
  
  	maxsize = romfs_maxsize(i->i_sb);
  	if (offset >= maxsize)
  		return -1;
  
  	/* strnlen is almost always valid */
  	if (count > maxsize || offset+count > maxsize)
  		count = maxsize-offset;
  
  	bh = sb_bread(i->i_sb, offset>>ROMBSBITS);
  	if (!bh)
  		return -1;		/* error */
  
  	avail = ROMBSIZE - (offset & ROMBMASK);
  	maxsize = min_t(unsigned long, count, avail);
  	res = strnlen(((char *)bh->b_data)+(offset&ROMBMASK), maxsize);
  	brelse(bh);
  
  	if (res < maxsize)
  		return res;		/* found all of it */
  
  	while (res < count) {
  		offset += maxsize;
  
  		bh = sb_bread(i->i_sb, offset>>ROMBSBITS);
  		if (!bh)
  			return -1;
  		maxsize = min_t(unsigned long, count - res, ROMBSIZE);
  		avail = strnlen(bh->b_data, maxsize);
  		res += avail;
  		brelse(bh);
  		if (avail < maxsize)
  			return res;
  	}
  	return res;
  }
  
  static int
  romfs_copyfrom(struct inode *i, void *dest, unsigned long offset, unsigned long count)
  {
  	struct buffer_head *bh;
  	unsigned long avail, maxsize, res;
  
  	maxsize = romfs_maxsize(i->i_sb);
  	if (offset >= maxsize || count > maxsize || offset+count>maxsize)
  		return -1;
  
  	bh = sb_bread(i->i_sb, offset>>ROMBSBITS);
  	if (!bh)
  		return -1;		/* error */
  
  	avail = ROMBSIZE - (offset & ROMBMASK);
  	maxsize = min_t(unsigned long, count, avail);
  	memcpy(dest, ((char *)bh->b_data) + (offset & ROMBMASK), maxsize);
  	brelse(bh);
  
  	res = maxsize;			/* all of it */
  
  	while (res < count) {
  		offset += maxsize;
  		dest += maxsize;
  
  		bh = sb_bread(i->i_sb, offset>>ROMBSBITS);
  		if (!bh)
  			return -1;
  		maxsize = min_t(unsigned long, count - res, ROMBSIZE);
  		memcpy(dest, bh->b_data, maxsize);
  		brelse(bh);
  		res += maxsize;
  	}
  	return res;
  }
  
  static unsigned char romfs_dtype_table[] = {
  	DT_UNKNOWN, DT_DIR, DT_REG, DT_LNK, DT_BLK, DT_CHR, DT_SOCK, DT_FIFO
  };
  
  static int
  romfs_readdir(struct file *filp, void *dirent, filldir_t filldir)
  {

  	struct inode *i = filp->f_path.dentry->d_inode;

  	struct romfs_inode ri;
  	unsigned long offset, maxoff;
  	int j, ino, nextfh;
  	int stored = 0;
  	char fsname[ROMFS_MAXFN];	/* XXX dynamic? */
  
  	lock_kernel();
  
  	maxoff = romfs_maxsize(i->i_sb);
  
  	offset = filp->f_pos;
  	if (!offset) {
  		offset = i->i_ino & ROMFH_MASK;
  		if (romfs_copyfrom(i, &ri, offset, ROMFH_SIZE) <= 0)
  			goto out;
  		offset = be32_to_cpu(ri.spec) & ROMFH_MASK;
  	}
  
  	/* Not really failsafe, but we are read-only... */
  	for(;;) {
  		if (!offset || offset >= maxoff) {
  			offset = maxoff;
  			filp->f_pos = offset;
  			goto out;
  		}
  		filp->f_pos = offset;
  
  		/* Fetch inode info */
  		if (romfs_copyfrom(i, &ri, offset, ROMFH_SIZE) <= 0)
  			goto out;
  
  		j = romfs_strnlen(i, offset+ROMFH_SIZE, sizeof(fsname)-1);
  		if (j < 0)
  			goto out;
  
  		fsname[j]=0;
  		romfs_copyfrom(i, fsname, offset+ROMFH_SIZE, j);
  
  		ino = offset;
  		nextfh = be32_to_cpu(ri.next);
  		if ((nextfh & ROMFH_TYPE) == ROMFH_HRD)
  			ino = be32_to_cpu(ri.spec);
  		if (filldir(dirent, fsname, j, offset, ino,
  			    romfs_dtype_table[nextfh & ROMFH_TYPE]) < 0) {
  			goto out;
  		}
  		stored++;
  		offset = nextfh & ROMFH_MASK;
  	}
  out:
  	unlock_kernel();
  	return stored;
  }
  
  static struct dentry *
  romfs_lookup(struct inode *dir, struct dentry *dentry, struct nameidata *nd)
  {
  	unsigned long offset, maxoff;
  	int fslen, res;
  	struct inode *inode;
  	char fsname[ROMFS_MAXFN];	/* XXX dynamic? */
  	struct romfs_inode ri;
  	const char *name;		/* got from dentry */
  	int len;
  
  	res = -EACCES;			/* placeholder for "no data here" */
  	offset = dir->i_ino & ROMFH_MASK;
  	lock_kernel();
  	if (romfs_copyfrom(dir, &ri, offset, ROMFH_SIZE) <= 0)
  		goto out;
  
  	maxoff = romfs_maxsize(dir->i_sb);
  	offset = be32_to_cpu(ri.spec) & ROMFH_MASK;
  
  	/* OK, now find the file whose name is in "dentry" in the
  	 * directory specified by "dir".  */
  
  	name = dentry->d_name.name;
  	len = dentry->d_name.len;
  
  	for(;;) {
  		if (!offset || offset >= maxoff)
  			goto out0;
  		if (romfs_copyfrom(dir, &ri, offset, ROMFH_SIZE) <= 0)
  			goto out;
  
  		/* try to match the first 16 bytes of name */
  		fslen = romfs_strnlen(dir, offset+ROMFH_SIZE, ROMFH_SIZE);
  		if (len < ROMFH_SIZE) {
  			if (len == fslen) {
  				/* both are shorter, and same size */
  				romfs_copyfrom(dir, fsname, offset+ROMFH_SIZE, len+1);
  				if (strncmp (name, fsname, len) == 0)
  					break;
  			}
  		} else if (fslen >= ROMFH_SIZE) {
  			/* both are longer; XXX optimize max size */
  			fslen = romfs_strnlen(dir, offset+ROMFH_SIZE, sizeof(fsname)-1);
  			if (len == fslen) {
  				romfs_copyfrom(dir, fsname, offset+ROMFH_SIZE, len+1);
  				if (strncmp(name, fsname, len) == 0)
  					break;
  			}
  		}
  		/* next entry */
  		offset = be32_to_cpu(ri.next) & ROMFH_MASK;
  	}
  
  	/* Hard link handling */
  	if ((be32_to_cpu(ri.next) & ROMFH_TYPE) == ROMFH_HRD)
  		offset = be32_to_cpu(ri.spec) & ROMFH_MASK;
  
  	if ((inode = iget(dir->i_sb, offset)))
  		goto outi;
  
  	/*
  	 * it's a bit funky, _lookup needs to return an error code
  	 * (negative) or a NULL, both as a dentry.  ENOENT should not
  	 * be returned, instead we need to create a negative dentry by
  	 * d_add(dentry, NULL); and return 0 as no error.
  	 * (Although as I see, it only matters on writable file
  	 * systems).
  	 */
  
  out0:	inode = NULL;
  outi:	res = 0;
  	d_add (dentry, inode);
  
  out:	unlock_kernel();
  	return ERR_PTR(res);
  }
  
  /*
   * Ok, we do readpage, to be able to execute programs.  Unfortunately,
   * we can't use bmap, since we may have looser alignments.
   */
  
  static int
  romfs_readpage(struct file *file, struct page * page)
  {
  	struct inode *inode = page->mapping->host;

  	loff_t offset, avail, readlen;

  	void *buf;
  	int result = -EIO;
  
  	page_cache_get(page);
  	lock_kernel();
  	buf = kmap(page);
  	if (!buf)
  		goto err_out;
  
  	/* 32 bit warning -- but not for us :) */

  	offset = page_offset(page);
  	if (offset < i_size_read(inode)) {

  		avail = inode->i_size-offset;
  		readlen = min_t(unsigned long, avail, PAGE_SIZE);
  		if (romfs_copyfrom(inode, buf, ROMFS_I(inode)->i_dataoffset+offset, readlen) == readlen) {
  			if (readlen < PAGE_SIZE) {
  				memset(buf + readlen,0,PAGE_SIZE-readlen);
  			}
  			SetPageUptodate(page);
  			result = 0;
  		}
  	}
  	if (result) {
  		memset(buf, 0, PAGE_SIZE);
  		SetPageError(page);
  	}
  	flush_dcache_page(page);
  
  	unlock_page(page);
  
  	kunmap(page);
  err_out:
  	page_cache_release(page);
  	unlock_kernel();
  
  	return result;
  }
  
  /* Mapping from our types to the kernel */

  static const struct address_space_operations romfs_aops = {

  	.readpage = romfs_readpage
  };

  static const struct file_operations romfs_dir_operations = {

  	.read		= generic_read_dir,
  	.readdir	= romfs_readdir,
  };

  static const struct inode_operations romfs_dir_inode_operations = {

  	.lookup		= romfs_lookup,
  };
  
  static mode_t romfs_modemap[] =
  {
  	0, S_IFDIR+0644, S_IFREG+0644, S_IFLNK+0777,
  	S_IFBLK+0600, S_IFCHR+0600, S_IFSOCK+0644, S_IFIFO+0644
  };
  
  static void
  romfs_read_inode(struct inode *i)
  {
  	int nextfh, ino;
  	struct romfs_inode ri;
  
  	ino = i->i_ino & ROMFH_MASK;
  	i->i_mode = 0;
  
  	/* Loop for finding the real hard link */
  	for(;;) {
  		if (romfs_copyfrom(i, &ri, ino, ROMFH_SIZE) <= 0) {
  			printk("romfs: read error for inode 0x%x
  ", ino);
  			return;
  		}
  		/* XXX: do romfs_checksum here too (with name) */
  
  		nextfh = be32_to_cpu(ri.next);
  		if ((nextfh & ROMFH_TYPE) != ROMFH_HRD)
  			break;
  
  		ino = be32_to_cpu(ri.spec) & ROMFH_MASK;
  	}
  
  	i->i_nlink = 1;		/* Hard to decide.. */
  	i->i_size = be32_to_cpu(ri.size);
  	i->i_mtime.tv_sec = i->i_atime.tv_sec = i->i_ctime.tv_sec = 0;
  	i->i_mtime.tv_nsec = i->i_atime.tv_nsec = i->i_ctime.tv_nsec = 0;
  	i->i_uid = i->i_gid = 0;
  
          /* Precalculate the data offset */
          ino = romfs_strnlen(i, ino+ROMFH_SIZE, ROMFS_MAXFN);
          if (ino >= 0)
                  ino = ((ROMFH_SIZE+ino+1+ROMFH_PAD)&ROMFH_MASK);
          else
                  ino = 0;
  
          ROMFS_I(i)->i_metasize = ino;
          ROMFS_I(i)->i_dataoffset = ino+(i->i_ino&ROMFH_MASK);
  
          /* Compute permissions */
          ino = romfs_modemap[nextfh & ROMFH_TYPE];
  	/* only "normal" files have ops */
  	switch (nextfh & ROMFH_TYPE) {
  		case 1:
  			i->i_size = ROMFS_I(i)->i_metasize;
  			i->i_op = &romfs_dir_inode_operations;
  			i->i_fop = &romfs_dir_operations;
  			if (nextfh & ROMFH_EXEC)
  				ino |= S_IXUGO;
  			i->i_mode = ino;
  			break;
  		case 2:
  			i->i_fop = &generic_ro_fops;
  			i->i_data.a_ops = &romfs_aops;
  			if (nextfh & ROMFH_EXEC)
  				ino |= S_IXUGO;
  			i->i_mode = ino;
  			break;
  		case 3:
  			i->i_op = &page_symlink_inode_operations;
  			i->i_data.a_ops = &romfs_aops;
  			i->i_mode = ino | S_IRWXUGO;
  			break;
  		default:
  			/* depending on MBZ for sock/fifos */
  			nextfh = be32_to_cpu(ri.spec);
  			init_special_inode(i, ino,
  					MKDEV(nextfh>>16,nextfh&0xffff));
  	}
  }

  static struct kmem_cache * romfs_inode_cachep;

  
  static struct inode *romfs_alloc_inode(struct super_block *sb)
  {
  	struct romfs_inode_info *ei;

  	ei = (struct romfs_inode_info *)kmem_cache_alloc(romfs_inode_cachep, GFP_KERNEL);

  	if (!ei)
  		return NULL;
  	return &ei->vfs_inode;
  }
  
  static void romfs_destroy_inode(struct inode *inode)
  {
  	kmem_cache_free(romfs_inode_cachep, ROMFS_I(inode));
  }

  static void init_once(void *foo, struct kmem_cache *cachep, unsigned long flags)

  {

  	struct romfs_inode_info *ei = foo;

  	inode_init_once(&ei->vfs_inode);

  }

  static int init_inodecache(void)
  {
  	romfs_inode_cachep = kmem_cache_create("romfs_inode_cache",
  					     sizeof(struct romfs_inode_info),

  					     0, (SLAB_RECLAIM_ACCOUNT|
  						SLAB_MEM_SPREAD),

  					     init_once);

  	if (romfs_inode_cachep == NULL)
  		return -ENOMEM;
  	return 0;
  }
  
  static void destroy_inodecache(void)
  {

  	kmem_cache_destroy(romfs_inode_cachep);

  }
  
  static int romfs_remount(struct super_block *sb, int *flags, char *data)
  {
  	*flags |= MS_RDONLY;
  	return 0;
  }

  static const struct super_operations romfs_ops = {

  	.alloc_inode	= romfs_alloc_inode,
  	.destroy_inode	= romfs_destroy_inode,
  	.read_inode	= romfs_read_inode,
  	.statfs		= romfs_statfs,
  	.remount_fs	= romfs_remount,
  };

  static int romfs_get_sb(struct file_system_type *fs_type,
  	int flags, const char *dev_name, void *data, struct vfsmount *mnt)

  {

  	return get_sb_bdev(fs_type, flags, dev_name, data, romfs_fill_super,
  			   mnt);

  }
  
  static struct file_system_type romfs_fs_type = {
  	.owner		= THIS_MODULE,
  	.name		= "romfs",
  	.get_sb		= romfs_get_sb,
  	.kill_sb	= kill_block_super,
  	.fs_flags	= FS_REQUIRES_DEV,
  };
  
  static int __init init_romfs_fs(void)
  {
  	int err = init_inodecache();
  	if (err)
  		goto out1;
          err = register_filesystem(&romfs_fs_type);
  	if (err)
  		goto out;
  	return 0;
  out:
  	destroy_inodecache();
  out1:
  	return err;
  }
  
  static void __exit exit_romfs_fs(void)
  {
  	unregister_filesystem(&romfs_fs_type);
  	destroy_inodecache();
  }
  
  /* Yes, works even as a module... :) */
  
  module_init(init_romfs_fs)
  module_exit(exit_romfs_fs)
  MODULE_LICENSE("GPL");