计算机 - Linux系统管理

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madfrogme

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第 11 楼

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gcc -std=c99 hello.c

启用gcc 的 1999 ISO C 扩展

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2012-09-01 10:05

madfrogme

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第 12 楼

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recv()， send() 函数和 read(), write() 函数很相似，

区别在于最后一个最后一个int flags

flags 有一个可选项是 MSG_WAITALL

它告诉内核只有达到了要求数量的字节之后才返回，所以说如果系统支持这个选项， readn() 就可以参照如下定义

#define    readn(fd, ptr, n)     recv(fd, ptr, n, MSG_WAITALL)

但是就算指定了MSG_WAITALL, 若果有信号产生，或是连接中断，或是socket发生错误，

也不能按要求返回

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2012-09-01 16:36

madfrogme

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第 13 楼

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SYN segment contains only TCP header and IP header.

SYN flooding 也就是在受到服务器的SYN-ACK之后发送RST

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2012-09-02 11:53

madfrogme

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第 14 楼

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A pending error cause a socket to be both readable and writable

connect() 返回0 则表示成功了

[ 本帖最后由 madfrogme 于 2012-9-5 17:11 编辑 ]

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2012-09-05 15:51

madfrogme

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第 15 楼

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EINPROGRESS :
The socket is non-blocking and the connection cannot be completed immediately.

It is possible to select() or poll() for completion by selecting socket for writing.

After select() indicates writablity, use getsockopt() to read the SO_ERROR option at

level SOL_SOCKET to determine whether connect() completed successfully( SO_ERROR is zero)

or unsuccessfully (SO_ERROR is one of the usual error codes explaining the reason for the failure).

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2012-09-05 16:57

madfrogme

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第 16 楼

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What happens if our call to connect on a normal blocking socket is interrupted, say, by a caught signal? Assuming the connect is not automatically restarted, it returns EINTR, But, we cannot call connect again to wait for the connection to complete. Doing so will return EADDRINUSE

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2012-09-06 09:32

madfrogme

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第 17 楼

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The Memory Management Unit (MMU) transforms a logical address into a linear address by means of a hardware circuit called a segmentation unit ;
subsequently, a second hardware circuit called a paging unit transforms the linear address into a physical address

[ 本帖最后由 madfrogme 于 2012-9-13 00:03 编辑 ]

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2012-09-12 22:30

madfrogme

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第 18 楼

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一个设备驱动器可以通过两种方法使用DMA,
synchronous DMA and asynchronous DMA.(同步与非同步）
同步DMA的情况下，数据的传输是通过进程的激发，
非同步DMA的情况下，数据的传输是通过硬件设备的激发
同步DMA的一个例子就是一个正在播放音频的声卡。
一个用户态程序将声音数据写入一个设备文件，
这个设备文件和声卡的digital signal processor(DSP)相关联。
声卡驱动器将这些声音数据积累在内核缓冲区里，
同时，声卡驱动器又指示声卡在一个很好的时机
将声音数据从内核缓冲区复制到DSP，它会激发一个中断，
并且设备驱动器检查内核缓冲区是否还有
声音数据，如果有，驱动器再一次激发DMA数据传输

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2012-09-12 22:53

madfrogme

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第 19 楼

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A logical address consists of two parts:
a segment identifier and an offset that specifies
the relative address within the segment.

The segment identifier is a 16-bit field called the Segment Selector
while the offset is a 32-bit field.

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2012-09-12 23:03

madfrogme

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第 20 楼

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Page cache一小例
when you first open a source file in a text editor,

data from the file is read into memory from disk.

As you edit the file, more and more pages are read in.

When you later compile the file,

the kernel can use the pages directly from the page cache;

it need not reread the file from disk.

Because users tend to read and manipulate the same files repeatedly,

the page cache reduces the need for a large number of disk operations.

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2012-09-12 23:41

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