source: trunk/minix/commands/simple/loadramdisk.c@ 15

/*
loadramdisk.c

Copy a device or file specified as argument to /dev/ram
*/

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

#define RAM     "/dev/ram"

char buf[10240];

static unsigned long size_device(int fd);

int main(int argc, char *argv[])
{
        unsigned long off, size;
        int r, s, fd, ramfd;
        char *src;

        if (argc != 2)
        {
                fprintf(stderr, "Usage: loadramdisk <file>\n");
                exit(1);
        }
        src= argv[1];
        fd= open(src, O_RDONLY);
        if (fd < 0)
        {
                fprintf(stderr, "Unable to open '%s': %s\n",
                        src, strerror(errno));
                exit(1);
        }

        /* Get the size of the device */
        errno= 0;
        size= size_device(fd);
        if (errno != 0)
        {
                fprintf(stderr, "Lseek(end) failed on '%s': %s\n",
                        src, strerror(errno));
                exit(1);
        }
        if (lseek(fd, 0, SEEK_SET) != 0)
        {
                fprintf(stderr, "Lseek(0) failed on '%s': %s\n",
                        src, strerror(errno));
                exit(1);
        }

        ramfd= open(RAM, O_RDWR);
        if (ramfd < 0)
        {
                fprintf(stderr, "Unable to open '%s': %s\n",
                        RAM, strerror(errno));
                exit(1);
        }
        r= ioctl(ramfd, MIOCRAMSIZE, &size);
        if (r != 0)
        {
                fprintf(stderr, "MIOCRAMSIZE %lu failed on '%s': %s\n",
                        size, RAM, strerror(errno));
                exit(1);
        }

        off= 0;
        while (off < size)
        {
                r= read(fd, buf, sizeof(buf));
                if (r <= 0)
                {
                        fprintf(stderr, "error reading '%s': %s\n",
                                src, r == 0 ? "unexpected EOF" :
                                strerror(errno));
                        exit(1);
                }
                s= write(ramfd, buf, r);
                if (s != r)
                {
                        fprintf(stderr, "error writing to '%s': %s\n",
                                s >= 0 ? "short write" : strerror(errno));
                        exit(1);
                }
                off += r;
        }
        exit(0);
}

static unsigned long size_device(int fd)
{
        char b;
        int r;
        unsigned long low, mid, high;

        /* Try to find the size of a device using binary search */
        low= 0;
        high= -1;

        while (mid= low+(high-low)/2, mid > low)
        {
                if (lseek(fd, mid, SEEK_SET) != mid)
                {
                        fprintf(stderr, "lseek to %lu failed: %s\n",
                                mid, strerror(errno));
                        exit(1);
                }
                r= read(fd, &b, 1);
                if (r < 0)
                {
                        fprintf(stderr, "read failed at position %lu: %s\n",
                                mid, strerror(errno));
                        exit(1);
                }
                if (r > 0)
                        low= mid;
                else
                        high= mid;
        }
        return high;
}