But if you add vines that entwine around branches randomly, you do not always have a unique path between the root and the other nodes anymore. He shows the purposes of major networking features and the trade-offs involved in choosing one solution over another. Because of the waste caused by looping, spin locks are used only on multiprocessor systems, and generally are used only when the developer expects the lock to be held for short intervals. A common example in the networking code is given by the routines that implement garbage collection. Part of the difficulty in understanding networks -- and implementing them -- is that the tasks are broken up and performed at many different times by different pieces of code.
When both the protocol and the local host are Big Endian, the conversion routines are simply no-ops because there is no need for any conversion. In the past few years he worked as a software engineer for Cisco Systems in the Silicon Valley, where he focused on Layer two switching, high availability, and network security. Cache lookup routines often take an input parameter that says whether a cache miss should or should not create a new element and add it to the cache. Any piece of code that uses goto can be rewritten without it. If all a function needs is to measure the passing of time, it can save the value of jiffies into a local variable and later compare the difference between jiffies and that timestamp against a time interval expressed in number of ticks to see how much time has passed since measurement started.
And if you already have a base knowledge of C, you can use the book's code walkthroughs to figure out exactly what this sophisticated part of the Linux kernel is doing. Vector Definitions In some cases, the definition of a data structure includes an optional block at the end. It is a simple yet powerful tool for searching, for example, where a function or variable is defined, where it is called, etc. Each mutual exclusion mechanism is the best choice for particular circumstances. Often, they request design changes to make a feature fit into the kernel the right way. A data unit is given different names, such as frame, packet, segment, and message, depending on the layer where it is used see for more details.
This is especially important in kernel code, even though the kernel supports kernel preemption. If you want to delve into the linux networking code of the kernel or if you are actually looking to modify a part of the networking code, this book is a must read. This leads to gradual memory exhaustion. Understanding Linux Network Internals is both a big-picture discussion and a no-nonsense guide to the details of Linux networking. If you are already using other source navigation tools, fine.
Garbage Collection Memory is a shared and limited resource and should not be wasted, particularly in the kernel because it does not use virtual memory. Unfortunately, you rarely see comments in the code that tell you this. If you also want to learn a bit more about networking in general then this book definitely is for you. This is done through notification chains. More than 150 witty poems. However, the compromise is often worth the gain: less redundant code means fewer bugs, easier code maintenance, simplified code paths, and other benefits.
But this still leaves the kernel developer with a problem: she must write code that can run on many different processors that support different endianness. This is used to reduce the damage of Denial of Service DoS attacks aimed at concentrating the elements of a hash table into a single bucket. Conversions Between Host and Network Order Data structures spanning more than one byte can be stored in memory with two different formats: Little Endian and Big Endian. Like the popular O'Reilly book, Understanding the Linux Kernel, this book clearly explains the underlying concepts and teaches you how to fol. This obviously makes Linux very attractive as an embedded operating system for network appliance products routers, switches, firewalls, load balancers, etc. The passing of time in kernel space is measured in ticks. You will see an example in.
Table of Contents Preface; The Audience for This Book; Background Information; Organization of the Material; Conventions Used in This Book; Using Code Examples; We'd Like to Hear from You; Safari Enabled; Acknowledgments; Part I: General Background; Chapter 1: Introduction; 1. However, because the C language does not provide explicit exceptions and they are often avoided in other languages as well because of the performance hit and coding complexity , carefully placed goto statements can make it easier to jump to code that handles undesired or peculiar events. This is pretty common, for example, with code that enforces sanity checks. Any piece of code that uses goto can be rewritten without it. When a Feature Is Offered as a Patch The kernel networking code is continuously evolving. Synopsis Christian Benvenuti received his masters degree in Computer Science at the University of Bologna in Italy.
Then it describes the interface between the kernel and the device drivers. Therefore, it is always important to minimize the number of inputs that hash to the same value. ! We see in the preceding examples how function pointers can be employed as interfaces between kernel components or as generic mechanisms to invoke the right function handler at the right time based on the result of something done by a different subsystem. They are usually called via wrappers, which manage the requests for allocation and deallocation at a higher level. This means that when abc is allocated with the optional block, placeholder points to the beginning of the block. A large number of flowcharts and other diagrams enhance the book's understandability.