What does the device number mean?

The equipment number is a string of numbers of the equipment. The manufacturer can identify the production batch, production place, date of manufacture and other information of the equipment based on this string of numbers. It has the same meaning as the person's ID number; in addition, the main The device number is used by the system to identify the driver, and the minor device number is used by the driver to identify the specific device.

The operating environment of this tutorial: Windows 7 system, Dell G3 computer.

What does the equipment number mean?

1. The equipment number is a string of numbers for the equipment. The manufacturer can identify the production batch and production location of the equipment based on this string of numbers. , information such as the date of manufacture, and the person’s ID number have the same meaning.

2. The major device number is used by the system to identify the driver, and the minor device number is used by the driver to identify the specific device. The special file of the character device driver can be indicated by "c" in the first column of the ls-l output. There are also block devices under dev, which are identified by "b". This chapter focuses only on character devices, although some of what is described below applies to block devices as well.

Related introduction:

View the major and minor device numbers

The special file of the character device driver can be indicated by the "c" in the first column output by ls-l . There are also block devices under /dev, which are identified by "b". This chapter focuses only on character devices, although some of what is described below applies to block devices as well.

If you execute the ls-l command, you will see two numbers (separated by commas) before the latest modification date in the device file entry. This position usually displays the file length. These two numbers are the major device number and minor device number of the corresponding device. The list below gives some of the devices on the system I use. Their major device numbers are 1,1 and their minor device numbers are 3,5.

crw-rw-rw- 1 root root 1, 3 Feb23 1999 null
crw-rw-rw- 1 root root 1, 5 Feb23 1999 zero

The major device number identifies the driver corresponding to the device. For example, /dev/null and /dev/zero are managed by driver 1, while all virtual consoles and serial terminals are managed by driver 4. Similarly, vcs1 and vcsa1 are managed by driver 7. When a device is opened, the kernel uses the major device number to dispatch and execute the corresponding driver.

The minor device number is used only by the corresponding device driver; other parts of the kernel do not use it and only pass it to the driver. So it's not surprising that a driver manages several devices (as shown in the example above), and the sequence number provides a way to distinguish them. Although the 2.4 version of the kernel introduces a new feature (optional): the device file system, devfs. If this file system is used, the device file will become simpler, but it will also be very different from the original. On the other hand, this new file system brings some user-visible incompatibilities.

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