create_image.c

一个用于学习的操作系统

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>

int main(int argc, char *argv[])
{
    /*FILE *fp;
    if (argc != 2) {
        printf("use: create_image filename\n");
        return 0;
    }

    fp = fopen(argv[1], "ab+");
    if (fp == NULL) {
        printf("open %s failed!\n", argv[1]);
        return 0;
    }

    fseek(fp, 1474560 - 1, SEEK_SET);
    fprintf(fp, "%d", 3);
    fclose(fp);
    */

    int fp;
    char *pbuf = NULL;
    int endpos = 0;
    if (argc != 2) {
        printf("use: create_image filename\n");
        return 0;
    }
    fp = open(argv[1], O_RDWR, O_CREAT | O_EXCL | O_SYNC);
    if (fp == -1) {
        perror("failed!\n");
        return 0;
    }

    endpos = lseek(fp, 0, SEEK_END);
    //printf("endpos:%d\n", endpos);
    pbuf = malloc(1474560 - endpos);
    memset(pbuf, 0, 1474560 - endpos);
    write(fp, pbuf, 1474560 - endpos);
    free(pbuf);
    close(fp);
    return 0;
}