/*
* linux/zBoot/piggyback.c
*
* (C) 1993 Hannu Savolainen
*/
/*
* This program reads the compressed system image from stdin and
* encapsulates it into an object file written to the stdout.
*/
//这个程序读取压缩的system映像文件从标准输入然后压缩后写入标准输出
#include <stdio.h>
#include <unistd.h>
#include <a.out.h>
//主函数
int main(int argc, char *argv[])
{
int c, n=0, len=0;
//定义缓冲区
char tmp_buf[512*1024];
//可执行文件头
struct exec obj = {0x00640107}; /* object header */
//输入的数据和输入的长度
char string_names[] = {"_input_data _input_len "};
//标号表，变量名
struct nlist var_names[2] = /* Symbol table */
{
{ /* _input_data */
(char *)4, 7, 0, 0, 0
},
{ /* _input_len */
(char *)16, 7, 0, 0, 0
}
};
len = 0;
//从标准输入中读取数据到缓冲区
while ((n = read(0, &tmp_buf[len], sizeof(tmp_buf)-len+1)) > 0)
len += n;
//校验读取的长度
if (n==-1)
{
perror("stdin");
exit(-1);
}
if (len >= sizeof(tmp_buf))
{
fprintf(stderr, "%s: Input too large
", argv[0]);
exit(-1);
}
//输出长度信息
fprintf(stderr, "Compressed size %d.
", len);
/*
* Output object header
*/
//输出对象头
obj.a_data = len + sizeof(long);
obj.a_syms = sizeof(var_names);
write(1, (char *)&obj, sizeof(obj));
/*
* Output data segment (compressed system & len)
*/
//输出数据段
write(1, tmp_buf, len);
write(1, (char *)&len, sizeof(len));
/*
* Output symbol table
*/
//输出符号表
var_names[1].n_value = len;
write(1, (char *)&var_names, sizeof(var_names));
/*
* Output string table
*/
//输出字符表
len = sizeof(string_names) + sizeof(len);
write(1, (char *)&len, sizeof(len));
write(1, string_names, sizeof(string_names));
exit(0);
}