reboot()系统调用的magic number

好吧，查阅reboot系统调用的时候发现，头两个参数是两个magic number，而且限定死了值，否则就是EINVAL

1

int reboot(int magic, int magic2, int cmd, void *arg);

manual这么写着：

This system call fail (with the error EINVAL) unless magic equals LINUX_REBOOT_MAGIC1 (that is, 0xfee1dead) and magic2 equals LINUX_REBOOT_MAGIC2 (that is, 672274793). However, since 2.1.17 also LINUX_REBOOT_MAGIC2A (that is, 85072278) and since 2.1.97 also LINUX_REBOOT_MAGIC2B (that is, 369367448) and since 2.5.71 also LINUX_REBOOT_MAGIC2C (that is, 537993216) are permitted as values for magic2. (The hexadecimal values of these constants are meaningful.)

好吧，那就转成十六进制看看：

672274793 = 0x28121969 85072278 = 0x05121996 369367448 = 0x16041998 537993216 = 0x20112000

em……是Linus Torvalds和三个女儿的生日

有啥用

好吧，搞清楚这些数字什么意思了，现在来想想这有什么用

其实也很简单，reboot系统调用是属于很危险的操作，如果寄存器内标识调用序号的值发生了改变，就可能启动reboot。为了预防万一，做了这层保护。除非参数的值也不小心改成这几个magicnumber（小概率事件），才会触发reboot。