Device files live in the system directory tree but are intrinsically different from regular files and directories. When a process accesses a regular file, it is accessing some data blocks in some disk partition through a filesystem; when a process accesses a device file, it is just driving a hardware device. For instance, a process might access a device file to read the room temperature from a digital thermometer connected to the computer. It is the VFS's responsibility to hide the differences between device files and regular files from application programs.
To do this, the VFS changes the default file operations of a device file when it is opened; as a result, each system call on the device file is translated to an invocation of a device-related function instead of the corresponding function of the hosting filesystem. The device-related function acts on the hardware device to perform the operation requested by the process. 14]
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