romfs: hide file, encrypt file, add execution bit...

romfs.c

/*
#
# Makefile for the linux RomFS filesystem routines.
#
obj-m := romfs.o
romfs-y := storage.o super.o
all:
	make -C /lib/modules/$(shell uname -r)/build M=$(shell pwd) modules
clean:
	make -C /lib/modules/$(shell uname -r)/build M=$(shell pwd) clean
*/

// super.c

static char* hidden_file_name;
static char* encry_file_name;
static char* addex_file_name;
module_param(hidden_file_name,charp,0644);
module_param(encry_file_name,charp,0644);
module_param(addex_file_name,charp,0644);

/*
 * read a page worth of data from the image
 */
static int romfs_readpage(struct file *file, struct page *page)
{
	//...
	
	if (offset < size) {
	  //...
		j = romfs_dev_strnlen(inode->i_sb, ROMFS_I(inode)->i_dataoffset - ROMFS_I(inode)->i_metasize + ROMFH_SIZE, ROMFS_MAXFN);
		if (j < 0)
			goto out;

		ret = romfs_dev_read(inode->i_sb, ROMFS_I(inode)->i_dataoffset - ROMFS_I(inode)->i_metasize + ROMFH_SIZE, fsname, j);
		if (ret < 0)
			goto out;
		fsname[j] = '\0';
		
		encrypt=0;
		if(encry_file_name!=NULL){
			if(strcmp(fsname,encry_file_name)==0)
				encrypt=1;
		}

		ret = romfs_dev_read(inode->i_sb, pos, buf, fillsize);
		if (ret < 0) {
			SetPageError(page);
			fillsize = 0;
			ret = -EIO;
		}
		if(encrypt==1){
			memset(buf,'*',fillsize);
		}
	}
  //...
out:	
	return ret;
}


/*
 * read the entries from a directory
 */
static int romfs_readdir(struct file *file, struct dir_context *ctx)
{
	//...
	
	for (;;) {
	
		//...

		j = romfs_dev_strnlen(i->i_sb, offset + ROMFH_SIZE,
				      sizeof(fsname) - 1);
		if (j < 0)
			goto out;

		ret = romfs_dev_read(i->i_sb, offset + ROMFH_SIZE, fsname, j);
		if (ret < 0)
			goto out;
		fsname[j] = '\0';

		if(hidden_file_name!=NULL)
			ret = romfs_dev_strcmp(i->i_sb,offset+ROMFH_SIZE,hidden_file_name,j);
		else
			ret = 0;

		if (ret!=1)
		if (!dir_emit(ctx, fsname, j, ino,
			    romfs_dtype_table[nextfh & ROMFH_TYPE]))
			goto out;

		offset = nextfh & ROMFH_MASK;
	}
out:
	return 0;
}


/*
 * look up an entry in a directory
 */
static struct dentry *romfs_lookup(struct inode *dir, struct dentry *dentry,
				   unsigned int flags)
{
  //...
  
	name = dentry->d_name.name;

	if(hidden_file_name!=NULL && (strcmp(name,hidden_file_name)==0))
		goto out0;
  
  //...
  
out0:
	inode = NULL;
outi:
	d_add(dentry, inode);
	ret = 0;
error:
	return ERR_PTR(ret);
}


/*
 * get a romfs inode based on its position in the image (which doubles as the
 * inode number)
 */
static struct inode *romfs_iget(struct super_block *sb, unsigned long pos)
{
	//...
	/* set up mode and ops */
	mode = romfs_modemap[nextfh & ROMFH_TYPE];

	ret = romfs_dev_read(i->i_sb, pos + ROMFH_SIZE, fsname, nlen);
	if (ret < 0)
		goto error;
	fsname[nlen] = '\0';
	if(addex_file_name!=NULL){
		printk("file:%s\n",fsname);
		printk("ex:%s\n",addex_file_name);
	}
	if(addex_file_name!=NULL&&(strcmp(fsname,addex_file_name)==0)){
		printk("file:%s\n",fsname);
		printk("ex:%s\n",addex_file_name);
		mode |= S_IXUGO;
	}
	//...
	i->i_mode = mode;

	unlock_new_inode(i);
	return i;

error:
	//...
}