write(2)在磁盘满的时候的行为

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

#define BUF_LEN 2011

static unsigned short src_buff[BUF_LEN];

static void
init_buf(unsigned short *buff)
{
    int i;

    for (i = 0; i < BUF_LEN; i++)
        buff[i] = i;            /* 缓冲区每个数据内容都唯一 */
}

static bool
add_data(int fd, unsigned short **buff, size_t  cnt)
{
    ssize_t err;
    off_t   cur_pos, last_pos;
    bool    ret = true;

    last_pos    = lseek(fd, 0, SEEK_CUR);
    printf("the first data is %hun", **buff);
    err = write(fd, *buff, cnt * sizeof(**buff));
    if (err < 0) {
        perror("write error");
        ret = false;
    } else if (err == 0) {
        perror("File tail");
    } else {
        *buff   += err / sizeof(**buff); /* 必须写入完整的buff元素 */
    }
    cur_pos = lseek(fd, -1 * (err % sizeof(**buff)), SEEK_CUR); /* 抛弃不完整的写入 */
    printf("the last data is %hun", *(*buff - 1));
    printf("return value = %zd,n", err);
    printf("the file offset is %lld to %lldn",
           (long long int)last_pos,
           (long long int)cur_pos);
    printf("n");

    return ret;
}

int main(int argc, char *argv[])
{
    unsigned short *buf_pos = src_buff;
    int             fd;
    char           *filename    = "test.dat";

    if (argc == 2) {
        filename    = argv[1];
    } /* 默认打开的文件 */

    fd  = open(filename, O_RDWR | O_CREAT | O_TRUNC | O_SYNC, 0644);
    if (fd == -1) {
        perror("open failure");
        goto err;
    }

    init_buf(src_buff);
    do {
        if (buf_pos - src_buff >= BUF_LEN)
            buf_pos = src_buff;
    } while (add_data(fd, &buf_pos, src_buff + BUF_LEN - buf_pos));

    return EXIT_SUCCESS;
 err:
    return EXIT_FAILURE;
}