“神奇”价值的设备驱动程序 [英] 'magic' value Device Driver

问题描述

tty_driver结构

struct tty_driver {
   int     magic;          /* magic number for this structure */
   struct kref kref;       /* Reference management */
   struct cdev cdev;
   struct module   *owner;
   const char      *driver_name;
   ....
   ....

我不明白为什么叫'magic'

I don't understand why is it called 'magic'

推荐答案

Magic数字通常指标识结构，文件类型或软件的特定常量。在这种情况下，tty_driver的魔术数显然总是这样定义：

Magic numbers often refer to specific constants that identify a structure, file type or software. In this case, the tty_driver's magic number is apparently always defined like this:

#define TTY_DRIVER_MAGIC        0x5402

在这种情况下，幻数的一种实际用法可能是检查第一个 sizeof（（ int）个字节，并确保它们 == 0x5402 ，然后将其余接收的字节转换为 tty_driver结构。在这方面，它还可以用于确定其余标头的适当字节顺序（小/大字节序）。

One practical use of the magic number in such a context might be to check the value of the first sizeof(int) bytes and make sure they == 0x5402 before casting the rest of the received bytes into a tty_driver struct. In this respect, it might also be used to determine the appropriate byte ordering (little/big endian) for the rest of the header.

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