tailieunhanh - Linux Device Drivers-Chapter 14 :Network Drivers

Tham khảo tài liệu 'linux device drivers-chapter 14 :network drivers', công nghệ thông tin, hệ điều hành phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Chapter 14 Network Drivers We are now through discussing char and block drivers and are ready to move on to the fascinating world of networking. Network interfaces are the third standard class of Linux devices and this chapter describes how they interact with the rest of the kernel. The role of a network interface within the system is similar to that of a mounted block device. A block device registers its features in the blk_dev array and other kernel structures and it then transmits and receives blocks on request by means of its request function. Similarly a network interface must register itself in specific data structures in order to be invoked when packets are exchanged with the outside world. There are a few important differences between mounted disks and packetdelivery interfaces. To begin with a disk exists as a special file in the dev directory whereas a network interface has no such entry point. The normal file operations read write and so on do not make sense when applied to network interfaces so it is not possible to apply the Unix everything is a file approach to them. Thus network interfaces exist in their own namespace and export a different set of operations. Although you may object that applications use the read and write system calls when using sockets those calls act on a software object that is distinct from the interface. Several hundred sockets can be multiplexed on the same physical interface. But the most important difference between the two is that block drivers operate only in response to requests from the kernel whereas network drivers receive packets asynchronously from the outside. Thus while a block driver is asked to send a buffer toward the kernel the network device asksto push incoming packets toward the kernel. The kernel interface for network drivers is designed for this different mode of operation. Network drivers also have to be prepared to support a number of administrative tasks such as setting addresses modifying transmission