d源码分析.doc

解压缩后进入busybox目录
make defconfig
make
make install
然后会生成_install 目录,里面就是编译好的可执行文件
源码位于./networking/

程序流程图:

程序中非常重要的就是2个buf,位于struct tsession结构体之后

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/*
This is how the buffers are used. The arrows indicate data flow.

+-------+ wridx1++ +------+ rdidx1++ +----------+
| | <-------------- | buf1 | <-------------- | |
| | size1-- +------+ size1++ | |
| pty | | socket |
| | rdidx2++ +------+ wridx2++ | |
| | --------------> | buf2 | --------------> | |
+-------+ size2++ +------+ size2-- +----------+

size1: "how many bytes are buffered for pty between rdidx1 and wridx1?"
size2: "how many bytes are buffered for socket between rdidx2 and wridx2?"

Each session has got two buffers. Buffers are circular. If sizeN == 0,
buffer is empty. If sizeN == BUFSIZE, buffer is full. In both these cases
rdidxN == wridxN.
*/
socket接收到远端的数据,写入count个字节到buf1中从rdidx1开始的空闲区域,然后size1 += count;rdidx1 += count;
pty可以写,从buf1中读取count个字节写入pty,然后size1 -= count;wridx1 += count;
pty可以读,写入count个字节到buf2中从rdidx2开始的空闲区域,然后size2 += count;rdidx2 += count;
socket可以发送数据到远端,从buf2中wridx2开始的位置读取count个字节,通过socket发送出去,然后size2 -= count;wridx2 += count;

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master_fd = create_and_bind_stream_or_die(opt_bindaddr, portnbr);
xlisten(master_fd, 1);

FD_ZERO(&rdfdset);
FD_ZERO(&wrfdset);