第二次调用mmap失败，错误代码为22。我不知道第二次mmap调用有什么问题。请帮帮忙。

typedef int fd_t;

int 
main (int argc, char **argv) {

fd_t fd;
FILE *file;

const char *file_name = "db-sample.txt";

if (access(file_name, F_OK) == -1) {
    /* File do not exist or we dont have permissions, 
        then create the file*/
    file = fopen(file_name, "w+");
}
else {
    file = fopen(file_name, "r+");
}

if (!file) assert(0);

fd = fileno (file);

if (ftruncate(fd, 8192 * 64) == -1) {
    assert(0);
}

disk_io_write_to_file (fd, 0, "Hello World", strlen ("Hello World"));

lseek(fd,  0, SEEK_SET);

assert (write (fd, "Hello World",  strlen("Hello World") - 1) != -1 );

void *ptr1 = mmap (NULL, 8, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);

if (ptr1 == MAP_FAILED) {
    printf ("%d : Error : mmap failed with error %d\n", __LINE__, errno);
    exit(0);
}

void *ptr2 = mmap (NULL,  8192, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 8);

if (ptr2 == MAP_FAILED) {
    printf ("%d : Error : mmap failed with error %d\n", __LINE__, errno);
    exit(0;
}

munmap (ptr1, 8);
munmap (ptr2, 8192);

return 0;
}

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