/* readboth --- read the md0 device and the disks that make it up, and** 	compare the blocks*/# include <fcntl.h># include <stdio.h># include <errno.h># include <string.h># include <stdlib.h># define BLOCK_SIZE				(32*1024)# define RAID5_ALGORITHM_LEFT_ASYMMETRIC 	(0)# define RAID5_ALGORITHM_RIGHT_ASYMMETRIC 	(1)# define RAID5_ALGORITHM_LEFT_SYMMETRIC 	(2)# define RAID5_ALGORITHM_RIGHT_SYMMETRIC 	(3)# define RAID_DISKS				(4)# define DATA_DISKS				(3)char *progname = "readboth";typedef struct {	char	*dev_name;	int	fd;} raid_tab_t;static raid_tab_t raid_tab[RAID_DISKS] = {	{ "/dev/hda12", 0 },	{ "/dev/hda13", 0 },	{ "/dev/hda14", 0 },	{ "/dev/hda15", 0 },};static void init_array (void);static void read_md (unsigned long blockno);static void read_array (unsigned long blockno);static unsigned long raid5_compute_block (unsigned long r_sector, 	unsigned int raid_disks, unsigned int data_disks, unsigned int *dd_idx,	unsigned int *pd_idx, int blocks_per_chunk);main (){	unsigned long block;	int dd_idx, pd_idx;	int blocks_per_chunk;	init_array ();	system ("/sbin/raidstart /dev/md0");	for (block = 0; block < 20; block++)		read_md (block);	system ("/sbin/raidstop /dev/md0");	for (block = 0; block < 20; block++)		read_array (block);	exit (0);}static voidinit_array (void){	int i;	raid_tab_t *rp;	for (rp = raid_tab; rp < raid_tab + RAID_DISKS; rp++) {		rp->fd = open (rp->dev_name, O_RDONLY);		if (rp->fd < 0) {			fprintf (stderr, "%s: can't open %s for reading (%s)\n",			    progname, rp->dev_name, strerror (errno));			exit (1);		}	}}static voidread_md (unsigned long blockno){	static int fd = -1;	long buf[BLOCK_SIZE / sizeof (long)];	if (fd == -1) {		fd = open ("/dev/md0", O_RDONLY);		if (fd < 0) {			fprintf (stderr, "%s: can't open %s for reading (%s)\n",			    progname, "/dev/md0", strerror (errno));			exit (2);		}	}	if (lseek (fd, (long) (blockno * BLOCK_SIZE), SEEK_SET) < 0) {		fprintf (stderr, "%s: lseek on /dev/md0 failed (%s)\n",		    progname, strerror (errno));		exit (3);	}	if (read (fd, (char *) buf, sizeof (buf)) < 0) {		fprintf (stderr, "%s: read on /dev/md0 failed (%s)\n",		    progname, strerror (errno));		exit (4);	}	printf ("   read_md: block %lu, *block = %d\n", blockno, *buf);}static voidread_array (unsigned long blockno){	long buf[BLOCK_SIZE / sizeof (long)];	unsigned long disk_blockno;	int dd_idx, pd_idx, fd;	disk_blockno = raid5_compute_block (blockno, RAID_DISKS, DATA_DISKS, 	    &dd_idx, &pd_idx, 1);	fd = raid_tab[dd_idx].fd;	if (lseek (fd, (long) (disk_blockno * BLOCK_SIZE), SEEK_SET) < 0) {		fprintf (stderr, "%s: lseek on %s failed (%s)\n",		    progname, raid_tab[dd_idx].dev_name, strerror (errno));		exit (3);	}	if (read (fd, (char *) buf, sizeof (buf)) < 0) {		fprintf (stderr, "%s: read on %s failed (%s)\n",		    progname, raid_tab[dd_idx].dev_name, strerror (errno));		exit (4);	}	printf ("read_array: block %lu, *block = %d\n", blockno, *buf);}static unsigned longraid5_compute_block (unsigned long r_sector, 	unsigned int raid_disks,	unsigned int data_disks, 	unsigned int *dd_idx,	unsigned int *pd_idx, int blocks_per_chunk){	unsigned long stripe;	unsigned long chunk_number;	unsigned int chunk_offset;	unsigned long new_sector;	int algorithm = RAID5_ALGORITHM_LEFT_SYMMETRIC;# ifdef TESTING# define PU(V)	printf ("%s = %6lu ", #V, V)# else# define PU(V)# endif /* TESTING */	PU (r_sector);	/* First compute the information on this sector */	/*	 * Compute the chunk number and the sector offset inside the chunk	 */	chunk_number = r_sector / blocks_per_chunk;	chunk_offset = r_sector % blocks_per_chunk;#if 0	PU (chunk_number);	PU (chunk_offset);#endif	/*	 * Compute the stripe number	 */	stripe = chunk_number / data_disks;#if 0	PU (stripe);#endif	/*	 * Compute the data disk and parity disk indexes inside the stripe	 */	*dd_idx = chunk_number % data_disks;	/*	 * Select the parity disk based on the user selected algorithm.	 */	switch (algorithm) {	case RAID5_ALGORITHM_LEFT_ASYMMETRIC:		*pd_idx = data_disks - stripe % raid_disks;		if (*dd_idx >= *pd_idx)			(*dd_idx)++;		break;	case RAID5_ALGORITHM_RIGHT_ASYMMETRIC:		*pd_idx = stripe % raid_disks;		if (*dd_idx >= *pd_idx)			(*dd_idx)++;		break;	case RAID5_ALGORITHM_LEFT_SYMMETRIC:		*pd_idx = data_disks - stripe % raid_disks;		*dd_idx = (*pd_idx + 1 + *dd_idx) % raid_disks;		break;	case RAID5_ALGORITHM_RIGHT_SYMMETRIC:		*pd_idx = stripe % raid_disks;		*dd_idx = (*pd_idx + 1 + *dd_idx) % raid_disks;		break;	default:		fprintf (stderr, "raid5: unsupported algorithm %d\n", 		    algorithm);	}	PU (*dd_idx);	PU (*pd_idx);	/*	 * Finally, compute the new sector number	 */	new_sector = stripe * blocks_per_chunk + chunk_offset;	PU (new_sector);	return new_sector;}