# lvresize -l 100%VG -r $LVM

#include <unistd.h>
#include <string.h>
#include <stdlib.h>
#include <stdio.h>
#include <fcntl.h>
#include <errno.h>

#define SIG		0x5452415020494645UL
#define HDR		0x5c
#define MBR		510
#define OS_EFI	0xEF
#define OS_GPT	0xEE
#define OS		450
#define LBA		0x200UL
#define ALL		0x400UL

struct part {
	long	t[2];		//type
	long	g[2];		//guid
	long	f;			//first LBA
	long	l;			//last  LBA
	long	a;			//attrs
	char	n[72];		//name;
} __attribute__ ((packed));

struct gpt {// NOTICE!: LBA's are zero based.
	long		s;		//sign
	int			r;		//rev
	int			h;		//headersize: 0x5c
	unsigned	hc;		//header crc32
	int			res;
	long		c;		//currentLBA
	long		b;		//backupLBA
	long		f;		//firstUsableLBA
	long		l;		//lastUsableLBA
	long		g[2];	//guid
	long		p;		//partition table LBA
	int			n;		//#part
	int			e;		//sizeof(struct part)
	unsigned	pc;		//part table crc32
	char	res2[420];
} __attribute__ ((packed));

static unsigned long	crc, crctab[256], poly = 0xEDB88320L;
static int				ii, jj;

unsigned crc32 (unsigned char *block, unsigned len){
   crc  = 0xFFFFFFFF;
   for (ii = 0; ii < len; ii++) crc = ((crc >> 8) & 0x00FFFFFF) ^ crctab[(crc ^ *block++) & 0xFF];
   return (crc ^ 0xFFFFFFFF);
}

void crc32tab(void){
	for (ii = 0; ii < 256; ii++){
		crc = ii;
		for (jj = 8; jj > 0; jj--){
			if(crc & 1)	crc = (crc >> 1) ^ poly;
			else		crc >>= 1;
		}
		crctab[ii] = crc;
	}
}

static struct gpt   *hd;
static struct part	*pr;
static char         buf[ALL];
static int          disk_fd, partindex, parttype;
static long         disksize, partstart, partsize;

static char
parttypes[5][16] = {
		{ 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00 }, //unused
		{ 0x28, 0x73, 0x2a, 0xc1, 0x1f, 0xf8, 0xd2, 0x11, 0xba, 0x4b, 0x00, 0xa0, 0xc9, 0x3e, 0xc9, 0x3b }, //efi
		{ 0xe3, 0xbc, 0x68, 0x4f, 0xcd, 0xe8, 0xb1, 0x4d, 0x96, 0xe7, 0xfb, 0xca, 0xf9, 0x84, 0xb7, 0x09 }, //lin64
		{ 0xaf, 0x3d, 0xc6, 0x0f, 0x83, 0x84, 0x72, 0x47, 0x8e, 0x79, 0x3d, 0x69, 0xd8, 0x47, 0x7d, 0xe4 }, //lin
		{ 0xb6, 0x7c, 0x6e, 0x51, 0xcf, 0x6e, 0xd6, 0x11, 0x8f, 0xf8, 0x00, 0x02, 0x2d, 0x09, 0x71, 0x2b }, //freebsd UFS
};

long time(long*);

int main(int ac, char* av[]){
	if(ac != 7){
		printf("Usage: %s  disk  disksize  parttype  partindex  partstart  partsize \n\t%s\n\t%s\n\t%s\n\t%s\n\t%s\n\t%s\n",
			av[0],
			"disk       : /dev/sdX",
			"disksize   : disk size (as LBA)",
			"parttype   : numeric type of partition",
			"partindex  : part index (0 based)",
			"partstart  : part start LBA (0 based)",
			"partsize   : part size (as LBA)"
		);
		printf("Supported part types:\n\t%s\n\t%s\n\t%s\n\t%s\n\t%s\n",
			"0 -> unused/free",
			"1 -> EFI",
			"2 -> linux x86_64 root",
			"3 -> linux fs",
			"4 -> freebsd ufs"
		);

		return 0;
	}

	time(NULL);

	disk_fd		= open(av[1], O_RDWR);
	disksize	= strtol(av[2], NULL, 10);
	parttype	= atoi(av[3]);
	partindex	= atoi(av[4]);
	partstart = strtol(av[5], NULL, 10);
	partsize	= strtol(av[6], NULL, 10);

	if(!disksize){
		read(disk_fd, buf, LBA);  //load pmbr
		read(disk_fd, buf, LBA);  //load gpt
		read(disk_fd, buf + LBA, LBA);  //load parts
		hd = (struct gpt*) buf;
		pr = (struct part*) (buf + LBA);
		printf("current  %ld  bakup  %ld  firstUsable  %ld lastUsable %ld  part %ld #parts %d entrysize %d hdrsize %d\n", hd->c, hd->b, hd->f, hd->l, hd->p, hd->n, hd->e, hd->h);

		for(ii=0; ii<4; ii++){
			printf("type  %lx %lx  firstUsable  %ld lastUsable %ld \n", pr[ii].t[0], pr[ii].t[1], pr[ii].f, pr[ii].l);
		}

		return 0;
	}

	crc32tab();

	buf[OS]		= OS_GPT;
	*(unsigned*)(buf + OS + 4)	= 1;
	*(unsigned*)(buf + OS + 8)	= 1;
	buf[MBR]	= 0x55;
	buf[MBR+1]	= 0xaa;
	crc = write(disk_fd, buf, LBA); //update pmbr
	printf("io1 %lu \n", crc);

	crc = read(disk_fd, buf, LBA);  //load gpt
	printf("io2 %lu \n", crc);
	crc = read(disk_fd, buf + LBA, LBA);  //load parts
	printf("io3 %lu \n", crc);

	memset(buf, 0, LBA);
	hd = (struct gpt*) buf;
	pr = (struct part*) (buf + LBA);

	hd->s = SIG;
	hd->r = 0x10000;
	hd->h = HDR;

	hd->c = 1;
	hd->b = hd->c; //disksize; backup disabled for simplicity

	hd->f = hd->c + 2;
	hd->l = disksize - 2; //son sektor bakup'a rezerve.

	hd->g[0] = time(NULL);
	hd->g[1] = time(NULL);

	hd->p = hd->c + 1;
	hd->n = 4;
	hd->e = 128;

	memcpy(pr[partindex].t, &parttypes[parttype], 16);
	pr[partindex].g[0] = time(NULL);
	pr[partindex].g[1] = time(NULL);
	pr[partindex].f = partstart;
	pr[partindex].l = partstart + partsize - 1;
	pr[partindex].a = 0;
/* once pc hesaplanmali! */
	hd->pc = crc32((unsigned char*)pr, hd->n * hd->e);
	hd->hc = crc32((unsigned char*)hd, hd->h);

	crc = lseek(disk_fd, LBA, SEEK_SET); //goto gpt
	printf("io4 %lu \n", crc);
	crc = write(disk_fd, buf, LBA); //update gpt
	printf("io4 %lu \n", crc);
	crc = write(disk_fd, buf+LBA, LBA); //update part table
	printf("io6 %lu \n", crc);
	sync();

	close(disk_fd);
	if(errno) perror("");

	return 0;
}