C snippets

/*
 * Copyright (C) 2009  Przemyslaw Pawelczyk <przemoc@gmail.com>
 *
 ***** Description ************************************************************
 *
 * Simple (and incomplete) syscalls interposition for accessing fixed-size Sun
 * xVM VirtualBox Virtual Disk Images (.vdi files), especially using sfdisk.
 *
 ***** License ****************************************************************
 *
 * GNU General Public License v2, v3
 *
 ***** Tested on **************************************************************
 *
 * - Debian 5.0.3 (x64)  w/ util-linux 2.13.1.1-1
 * - Slackware 12.1      w/ util-linux-ng 2.13.1
 * - Ubuntu 8.10 (x64)   w/ util-linux-ng 2.14
 * - Ubuntu 9.10 (x64)   w/ util-linux-ng 2.16
 *
 ***** Compilation ************************************************************
 *
 * $ gcc -fPIC -c               -o vdiwrap.o  vdiwrap.c &&
 *   gcc -nostdlib -shared -ldl -o vdiwrap.so vdiwrap.o
 *
 ***** Usage ******************************************************************
 *
 * # LD_PRELOAD="./vdiwrap.so" sfdisk -qluS image.vdi
 *
 ******************************************************************************
 *
 * vdiwrap.c  @ http://wiki.przemoc.net/snippets/c#vdiwrap.c  (version 0.2b)
 *
 */
 
#define _GNU_SOURCE
#define _LARGEFILE64_SOURCE
 
#include <dlfcn.h>
#include <stdarg.h>
#include <stdio.h>
#include <fcntl.h>
#include <unistd.h>
#include <string.h>
 
#define LOAD(name) orig_##name = dlsym(RTLD_NEXT, #name)
#if __LP64__
# define N(name) name
# define O(name) orig_##name
# define OFF_T off_t
# define STAT  stat
#else
# define N(name) name ## 64
# define O(name) orig_##name ## 64
# define OFF_T off64_t
# define STAT  stat64
#endif
 
#define OPEN_SIGNATURE   const char *__file, int __oflag, ...
#define LSEEK_SIGNATURE  int __fd, OFF_T __offset, int __whence
#define FXSTAT_SIGNATURE int __ver, int __fd, struct STAT *__stat_buf
 
 
static int vdi_fd = -1;
static int vdi_type = 0;
static int vdi_offset = 0;
 
static int   (*O(open))(OPEN_SIGNATURE);
static OFF_T (*O(lseek))(LSEEK_SIGNATURE);
static int   (*O(__fxstat))(FXSTAT_SIGNATURE);
 
/* Functions' prototypes */
 
int   N(open)(OPEN_SIGNATURE);
OFF_T N(lseek)(LSEEK_SIGNATURE);
int   N(__fxstat)(FXSTAT_SIGNATURE);
 
/* Initialization */
 
void _init()
{
	LOAD(open);
	LOAD(lseek);
	LOAD(__fxstat);
}
 
/* Functions' bodies */
 
int N(open)(OPEN_SIGNATURE)
{
	int result;
	int namelen;
	unsigned mode;
	va_list ap;
 
	if (__oflag & O_CREAT) {
		va_start(ap, __oflag);
		mode = va_arg(ap, unsigned);
		result = O(open)(__file, __oflag, mode);
		va_end(ap);
		return result;
	}
 
	result = O(open)(__file, __oflag);
 
	if (result > 0 && (namelen = strlen(__file)) && !strncasecmp(&__file[namelen - 4], ".vdi", 4)) {
		O(lseek)(result, 76, SEEK_SET);
		read(result, &vdi_type, 4);
		if (vdi_type == 2) {
			O(lseek)(result, 344, SEEK_SET);
			read(result, &vdi_offset, 4);
			O(lseek)(result, vdi_offset, SEEK_SET); 
			vdi_fd = result;
			dprintf(STDERR_FILENO, "--- VDI data offset == %d bytes ---\n", vdi_offset);
		} else
			vdi_fd = -1;
	}
 
	return result;
}
 
 
OFF_T N(lseek)(LSEEK_SIGNATURE)
{
	OFF_T result;
 
	if (__fd == vdi_fd && __whence == SEEK_SET)
		__offset += vdi_offset;
 
	result = O(lseek)(__fd, __offset, __whence);
 
	if (__fd == vdi_fd && result > 0)
		result -= vdi_offset;
 
	return result;
}
 
int N(__fxstat)(FXSTAT_SIGNATURE)
{
	int result = O(__fxstat)(__ver, __fd, __stat_buf);
 
	if (__fd == vdi_fd && result == 0)
		__stat_buf->st_size -= vdi_offset;
 
	return result;
}

/*
 * This work is hereby released into the Public Domain.
 *
 ******************************************************************************
 *
 * xor.c
 *
 */
 
#include <stdio.h>
#include <unistd.h>
#include <fcntl.h>
#include <stdlib.h>
#include <sys/stat.h>
 
#define XORBYTE	(0x8dUL)
#define XORINT	(XORBYTE | (XORBYTE << 8) | (XORBYTE << 16) | (XORBYTE << 24))
#ifdef __LP64__
	#define	XORLONG	((XORINT) | ((XORINT) << 32))
	#define LONG2	3
#else
	#define	XORLONG	XORINT
	#define	LONG2	2
#endif
#define	BUFSIZE	(2048 << 10)
 
#ifdef WIN32
	#define	MODE	(S_IRUSR | S_IWUSR)
#else   
	#define	MODE	(S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP | S_IROTH)
	#define	O_BINARY	0
#endif
 
int main(int argc, char *argv[])
{
	unsigned long *buf;
	int i, r, fin, fout;
	fin = open(argv[1], O_RDONLY | O_BINARY);
	fout = open(argv[2], O_CREAT | O_WRONLY | O_TRUNC | O_BINARY, MODE);
	buf = malloc((BUFSIZE >> LONG2) * sizeof(long));
	while ((r = read(fin, buf, BUFSIZE)) > 0) {
		for (i = 0; i < ((r + sizeof(long) - 1) >> LONG2); i++)
			buf[i] ^= XORLONG;
		write(fout, buf, r);
	}
	free(buf);
	close(fout);
	close(fin);
	return 0;
}