/*
   * XZ decoder tester
   *
   * Author: Lasse Collin <lasse.collin@tukaani.org>
   *
   * This file has been put into the public domain.
   * You can do whatever you want with this file.
   */
  
  #include <linux/kernel.h>
  #include <linux/module.h>
  #include <linux/fs.h>
  #include <linux/uaccess.h>
  #include <linux/crc32.h>
  #include <linux/xz.h>
  
  /* Maximum supported dictionary size */
  #define DICT_MAX (1 << 20)
  
  /* Device name to pass to register_chrdev(). */
  #define DEVICE_NAME "xz_dec_test"
  
  /* Dynamically allocated device major number */
  static int device_major;
  
  /*
   * We reuse the same decoder state, and thus can decode only one
   * file at a time.
   */
  static bool device_is_open;
  
  /* XZ decoder state */
  static struct xz_dec *state;
  
  /*
   * Return value of xz_dec_run(). We need to avoid calling xz_dec_run() after
   * it has returned XZ_STREAM_END, so we make this static.
   */
  static enum xz_ret ret;
  
  /*
   * Input and output buffers. The input buffer is used as a temporary safe
   * place for the data coming from the userspace.
   */
  static uint8_t buffer_in[1024];
  static uint8_t buffer_out[1024];
  
  /*
   * Structure to pass the input and output buffers to the XZ decoder.
   * A few of the fields are never modified so we initialize them here.
   */
  static struct xz_buf buffers = {
  	.in = buffer_in,
  	.out = buffer_out,
  	.out_size = sizeof(buffer_out)
  };
  
  /*
   * CRC32 of uncompressed data. This is used to give the user a simple way
   * to check that the decoder produces correct output.
   */
  static uint32_t crc;
  
  static int xz_dec_test_open(struct inode *i, struct file *f)
  {
  	if (device_is_open)
  		return -EBUSY;
  
  	device_is_open = true;
  
  	xz_dec_reset(state);
  	ret = XZ_OK;
  	crc = 0xFFFFFFFF;
  
  	buffers.in_pos = 0;
  	buffers.in_size = 0;
  	buffers.out_pos = 0;
  
  	printk(KERN_INFO DEVICE_NAME ": opened
  ");
  	return 0;
  }
  
  static int xz_dec_test_release(struct inode *i, struct file *f)
  {
  	device_is_open = false;
  
  	if (ret == XZ_OK)
  		printk(KERN_INFO DEVICE_NAME ": input was truncated
  ");
  
  	printk(KERN_INFO DEVICE_NAME ": closed
  ");
  	return 0;
  }
  
  /*
   * Decode the data given to us from the userspace. CRC32 of the uncompressed
   * data is calculated and is printed at the end of successful decoding. The
   * uncompressed data isn't stored anywhere for further use.
   *
   * The .xz file must have exactly one Stream and no Stream Padding. The data
   * after the first Stream is considered to be garbage.
   */
  static ssize_t xz_dec_test_write(struct file *file, const char __user *buf,
  				 size_t size, loff_t *pos)
  {
  	size_t remaining;
  
  	if (ret != XZ_OK) {
  		if (size > 0)
  			printk(KERN_INFO DEVICE_NAME ": %zu bytes of "
  					"garbage at the end of the file
  ",
  					size);
  
  		return -ENOSPC;
  	}
  
  	printk(KERN_INFO DEVICE_NAME ": decoding %zu bytes of input
  ",
  			size);
  
  	remaining = size;
  	while ((remaining > 0 || buffers.out_pos == buffers.out_size)
  			&& ret == XZ_OK) {
  		if (buffers.in_pos == buffers.in_size) {
  			buffers.in_pos = 0;
  			buffers.in_size = min(remaining, sizeof(buffer_in));
  			if (copy_from_user(buffer_in, buf, buffers.in_size))
  				return -EFAULT;
  
  			buf += buffers.in_size;
  			remaining -= buffers.in_size;
  		}
  
  		buffers.out_pos = 0;
  		ret = xz_dec_run(state, &buffers);
  		crc = crc32(crc, buffer_out, buffers.out_pos);
  	}
  
  	switch (ret) {
  	case XZ_OK:
  		printk(KERN_INFO DEVICE_NAME ": XZ_OK
  ");
  		return size;
  
  	case XZ_STREAM_END:
  		printk(KERN_INFO DEVICE_NAME ": XZ_STREAM_END, "
  				"CRC32 = 0x%08X
  ", ~crc);
  		return size - remaining - (buffers.in_size - buffers.in_pos);
  
  	case XZ_MEMLIMIT_ERROR:
  		printk(KERN_INFO DEVICE_NAME ": XZ_MEMLIMIT_ERROR
  ");
  		break;
  
  	case XZ_FORMAT_ERROR:
  		printk(KERN_INFO DEVICE_NAME ": XZ_FORMAT_ERROR
  ");
  		break;
  
  	case XZ_OPTIONS_ERROR:
  		printk(KERN_INFO DEVICE_NAME ": XZ_OPTIONS_ERROR
  ");
  		break;
  
  	case XZ_DATA_ERROR:
  		printk(KERN_INFO DEVICE_NAME ": XZ_DATA_ERROR
  ");
  		break;
  
  	case XZ_BUF_ERROR:
  		printk(KERN_INFO DEVICE_NAME ": XZ_BUF_ERROR
  ");
  		break;
  
  	default:
  		printk(KERN_INFO DEVICE_NAME ": Bug detected!
  ");
  		break;
  	}
  
  	return -EIO;
  }
  
  /* Allocate the XZ decoder state and register the character device. */
  static int __init xz_dec_test_init(void)
  {
  	static const struct file_operations fileops = {
  		.owner = THIS_MODULE,
  		.open = &xz_dec_test_open,
  		.release = &xz_dec_test_release,
  		.write = &xz_dec_test_write
  	};
  
  	state = xz_dec_init(XZ_PREALLOC, DICT_MAX);
  	if (state == NULL)
  		return -ENOMEM;
  
  	device_major = register_chrdev(0, DEVICE_NAME, &fileops);
  	if (device_major < 0) {
  		xz_dec_end(state);
  		return device_major;
  	}
  
  	printk(KERN_INFO DEVICE_NAME ": module loaded
  ");
  	printk(KERN_INFO DEVICE_NAME ": Create a device node with "
  			"'mknod " DEVICE_NAME " c %d 0' and write .xz files "
  			"to it.
  ", device_major);
  	return 0;
  }
  
  static void __exit xz_dec_test_exit(void)
  {
  	unregister_chrdev(device_major, DEVICE_NAME);
  	xz_dec_end(state);
  	printk(KERN_INFO DEVICE_NAME ": module unloaded
  ");
  }
  
  module_init(xz_dec_test_init);
  module_exit(xz_dec_test_exit);
  
  MODULE_DESCRIPTION("XZ decompressor tester");
  MODULE_VERSION("1.0");
  MODULE_AUTHOR("Lasse Collin <lasse.collin@tukaani.org>");
  
  /*
   * This code is in the public domain, but in Linux it's simplest to just
   * say it's GPL and consider the authors as the copyright holders.
   */
  MODULE_LICENSE("GPL");