21.3.1 Reading the partition table

This shows how the partitioning information can be extracted in user-mode (running under Unix). In the kernel, it would likely be necessary to pass a driver_info structure to a device-specific read function. In this case, driver_info is simply a filename string.

/* This is the testing program for the partitioning code. */
#include <oskit/diskpart/diskpart.h>
#include <stdio.h>
#include <fcntl.h>

#define FILENAME "/dev/sd0c"

/* We pass in a fixed-size table; this defines how big we want it. */
#define MAX_PARTS 30
diskpart_t part_array[MAX_PARTS];

/*
 * In this case, we are defining the disk size to be 10000 sectors.
 * Normally, this would be the number of physical sectors on the
 * disk.  If the `disk' is a `file', it would be better to get the
 * equivalent number of sectors from the file size.
 * This is only used to fill in the whole-drive partition entry.
 */
#define DISK_SIZE 10000

/*
 * This is the function pointer I pass to the partition code
 * to read sectors on the drive.
 */
int my_read_fun(void *driver_info, int sector, char *buf);


int
main(int argc, char *argv[])
{
        int numparts;
        char *filename;

        if (argc == 2)
                filename = argv[1];
        else
                filename = FILENAME;

        /* call the partition code */
        numparts = diskpart_get_partition(filename, my_read_fun, part_array, 
                MAX_PARTS, DISK_SIZE);

        printf("%d partitions found\n",numparts);
        /* diskpart_dump(part_array, 0); */
}
 
static int
my_read_fun(void *driver_info, int sector, char *buf)
{
        char *filename = driver_info;

        int fd = open(filename, O_RDONLY, 0775);

        lseek(fd, SECTOR_SIZE * sector, SEEK_SET);
        read(fd, buf, SECTOR_SIZE);
        close(fd);

        /* Should bzero the result if read error occurs */
        return(0);
}